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ATTORNEYS 3,732,094 United States Patent Office Patented May 8, 1973 2 Similarly, according to still another aspect of the inven 3,732,094 tion, if precious metals such as gold compounds are pres PROCESS FOR PREPARNG ELEMENTAL ent, they are selectively separated from the pregnant mer MERCURY Duane Brown, 104 E. Huntington Drive, Tempe, Ariz. cury leach liquor prior to the reduction steps for the same 85281, and Alton R. Carlson, 720 E. Dobbins Road, CaSO Phoenix, Ariz. 85040 In still another and more particular respect, the inven Filed June 29, 1970, Ser. No. 50,838 tion relates to a method for reducing the mercury con nt. C. C22b 3/00, 11/00, 43/00 tent of mercury-containing solutions to elemental mercury U.S. C. 75-101 R 1. Claims involving a preferred two-step reduction which includes 0 the formation of an intermediate, partially reduced, in soluble mercury compound which is physically separated ABSTRACT OF THE DISCLOSURE from the mother liquor before the second stage reduc This application discloses a process for recovering mer tion which completes the process of forming elemental cury from various mercury-containing materials such as mercury. ores, ore concentrates, alloys, amalgams and compounds. 5 Finally, the invention contemplates an overall inte According to one feature of the process, the mercury is ex grated process especially adapted for the production of ele tracted in the form of a soluble mercury complex by leach mental mercury from cinnabar ore or from cinnabar ore ing the mercury source with a novel leach liquid. The concentrates, the integrated process providing for the re novel leach liquid contains components which react during covery of virtually all of the reagents employed in the the leaching step to generate a hypohalite leach reagent in 20 reduction step, and the regeneration of the reducing agent situ. The hypohalite, in turn, oxidizes the mercury or mer for re-use. cury compound which is then solubilized in the leach liquid to form a strong pregnant liquor. DESCRIPTION OF THE PRIOR ART According to another feature of the process, arsenic, selenium and tellurium impurities are separated from the In the past, several methods have been employed to pregnant liquor by means of a novel technique involving 25 produce elemental mercury from its naturally occurring the formation of an insoluble metal hydroxide Suspen ore or by extracting it from its amalgams with other metals sion in the pregnant liquor, which suspension selectively and its compounds with other elements. Virtually all of adsorbs the soluble impurity metal compounds which are the virgin mercury is produced by winning the metal from in turn separated from the pregnant liquor. If gold com 30 its common mineral, cinnabar (HgS). The most common pounds are present in the purified pregnant liquor, they prior technique of producing elemental mercury from cin are selectively removed prior to the reduction step by con nabar involves roasting the naturally occurring ore under tacting the pregnant liquor with a combined reductant and highly oxidizing conditions and at elevated temperatures adsorbent for the gold. in the range of 500-1000° C. This process involves the According to another feature of the invention, preg 35 oxidation of the sulfur content of the cinnabar, forming nant leach liquors containing soluble mercury complexes, Sulfur dioxide gas and mercury vapor. The mercury vapor either prepared as described above or by any other suit is condensed by cooling with either air or water to approxi able process, are treated to reduce the mercury complex mately 40 C. or lower to form the liquid elemental to form elemental mercury in a single homogeneous liquid mercury. phase. The liquid phase reduction is preferably carried out 40 During the roasting step of the prior art method de in two stages, i.e., a first stage in which the mercury con scribed above, approximately 70-90% of the mercury tent of the leach liquor is only partially reduced to form content of the ore is separated and a substantial portion an insoluble mercury compound which is separated from of the separated mercury vapor is lost along with the the mother liquor. After separation of the partially re SOa byproduct. Aside from the very obvious air pollu duced insoluble mercury compound, it is treated with an 45 tion problems associated with the prior art roasting additional quantity of the reducing agent to complete the process, there are other important disadvantages such as reduction of the insoluble mercury compound to elemental the corrosion problems caused by the SO, and the fact mercury. that the mercury product contains substantial quantities of contaminants such as antimony oxides, arsenic oxides, 50 and the like. Furthermore, roasting is economically This invention relates to a process for preparing ele feasible only when very high-grade ore deposits are avail mental mercury. ble, e.g., containing above 5 lbs. Hg/ton. If such ores More particularly, the invention concerns a process are not available, then the ore must be concentrated by for winning mercury from various mercury-containing gravity, flotation or other beneficiation procedures. sources such as its naturally occurring ores (e.g., cinna 55 According to the Thornhill process developed in ap bar), ore concentrates, amalgams of mercury with other proximately 1917, cinnabar ore was leached with a dilute metals such as copper, silver, gold, the alkaline metals, solution of sodium hydroxide and sodium sulfide. This selenium, tellurium, arsenic, etc., and compounds of mer reaction could be conducted at ambient temperature but cury with other elements such as the halogens, OXygen, at elevated pH, i.e., at least above 9, to produce a very sulfur, etc. 60 dilute pregnant liquor containing sodium thiomercurate, In a further and still more particular aspect, the inven e.g., approximately 20 grams Hg/liter or less. It was tion concerns a method for separating mercury from such highly critical to maintain the pH at least above 9 in mercury-containing sources by means of leaching with a order to prevent reversal of the leach reaction, i.e., novel leach liquid, the components of the leach liquid re decomposition of the sodium thiomercurate into mer acting during the progress of the leaching step to form a 65 curic sulfide and sodium sulfite. The sodium thiomercu hypohalite leach reagent in situ. rate solution was then reacted with aluminum and an According to another aspect of the invention, impurities excess of sodium hydroxide in solution to produce ele such as soluble compounds of arsenic, selenium, and tel mental mercury and other reaction byproducts. Mercury lurium, if present, are separated from the pregnant mer thus produced was ordinarily contaminated with other cury leach liquor in order to improve the purity of the 70 ore-derived impurities such as arsenic, antimony, unre final mercury product as such compounds would other acted HgS, etc. Because of the contaminated mercury, wise be reduced in the following mercury reduction steps. the product of the Thornhill process required triple dis 3,732,094 3 4. tillation in order to render it sufficiently pure for com method of recovering the elemental mercury product mercial sale and use. The economics of the Thornhill from the purified pregnant liquor produced in Stage 2; process were also unfavorable because of the extremely FIG. 6 illustrates an alternate method for carrying out high aluminum consumption, i.e., approximately 0.30 the reduction step of Stage 3 for reduction and recovering 0.35 pound of aluminum per pound of mercury produced. the mercury product from the purified pregnant liquor According to still another proposed prior art tech from Stage 2; nique, the cinnabar ore was leached with a sodium thio FIG. 7 illustrates (Stage 4) the recovery of the reduc sulfate solution to produce a soluble mercury-thiosulfate tion reagent used to reduce the mercury complex in the complex. This complex was then contacted with copper preferred embodiment illustrated in FIG. 5; and powder and the ensuing reaction produced a mercury FIG. 8 illustrates (Stage 5) the regeneration of the copper amalgam. The amalgam was then briquetted and O reduction reagent recovered according to the process of the briquets were distilled, driving off mercury vapor, FIG. 7, for re-use in Stage 3. the remaining copper being recycled for use in the step of reducing the mercury-thiosulfate complex. Again, as GENERAL DESCRIPTION OF THE in the case of the other prior processes mentioned above, INVENTION the mercury product was grossly contaminated and re 5 The overall process of our invention involves three quired further extensive purification procedures such as general stages in one embodiment and another preferred redistillation before the product was suitable for commer embodiment involves an additional two general Stages. cial sale and use. Each stage will be discussed and described in detail below More recently, attempts have been made to win mer but, for the purpose of clarity, will be very briefly dis cury from its cinnabar ore by leaching the ore or concen 20 cussed at this point. trates of the ore with a solution of sodium or calcium Referring to the drawings, FIG. 1 is a simplified over hypochlorite. In solution, the hypochlorite salts dissociate all process flow sheet which generally illustrates the prac to form hypochlorite ion which is the active leach re tice of our invention and the two alternative embodiments agent. The hypochlorite ion oxidizes the mercuric sulfide thereof. For purposes of illustration, it will be assumed content of the cinnabar, forming soluble mercuric chlo 25 that the mercury-containing source is cinnabar ore. If the ride, calcium chloride, calcium sulfate and water. By this ore 10 is of sufficiently high mercury content, e.g., up technique, mercury concentrations in the pregnant leach wards of 30% Hg, it may be ground and transported liquor in the range 5-20 grams Hg/liter could be ob directly to the leaching step, Stage 1. On the other hand, tained. Again, as in the case of the Thornhill method, if the ore 1.0a is of somewhat lower mercury content, it this last-described technique produced such a very dilute 30 would be advantageous to subject the ore to conven pregnant liquor that the economics of the process were tional milling steps to produce a concentrate 10b before decidedly unfavorable. The reason that it was impossible performing the Stage 1 leaching operation. In Stage 1, to obtain higher mercury concentrations in the pregnant the pulverized ore 10 or the concentrate 10b is agitated liquor was the fact that it was only possible to obtain with a leach liquid formed by reacting an aqueous slurry a hypochlorite concentration in the leach liquid in the 35 of calcium carbonate or preferably calcium hydroxide range of 4% or less. Above this concentration, the hypo into which a halogen such as chlorine or bromine is chlorite undergoes degradation reactions, forming chlo continuously injected either as a gas or liquid. The HgS rate and chloride. content of the cinnabar ore is converted in the leaching In view of the very severe economic and technical 40 step to a soluble calcium tetrahalomercurate (II) com disadvantages of the prior processes, it would be highly plex. As will be apparent to those skilled in the art, the advantageous to provide a process for winning or recov halomercurate complex contains mercury in the +2 oxi ering mercury from various mercury-containing sources, dation state as indicated by the notation (II) following which process does not result in the production of dan the name of the compound, although Such notation will gerous and corrosive byproducts and pollutants, provides 45 be omitted in future references to this complex in this an intermediate pregnant liquor having a much higher application. Illustratively, the overall reaction which takes mercury content than was obtained in the prior art leach place during the leaching step if chlorine is employed as ing processes, a process in which the overall net con the halogen is: sumption of reagents is minimized and which produces (1) an elemental mercury product of very high purity-so 50 pure, in fact, that it is immediately saleable for commer cial use, without need for further purification steps. CaEIgCl. -- 2CaCl2 -- CaSO4.2H2O, J. -- 2 H2O BRIEF DESCRIPTION OF THE DRAWINGS (1a) We have now discovered an overall integrated process 55 which achieves these advantages. HgS + 4CaCO3 + 4Cl2 + 2H2O -? In the drawings, which depict for illustrative purposes CagCl4-2CaCl2 --CaSO4.2H2O --4CO the various embodiments of the invention and the pre As the chlorine is injected into the leach liquor, it reacts ferred embodiments thereof: with the calcium hydroxide or calcium carbonate to form FIG. 1 is a simplified overall process flow sheet illus 60 calcium hypochlorite and/or hypochlorous acid, depend trating the entire process embodying various features of ing upon the pH, as will be clear to those skilled in the the invention from the mining of the ore to the produc art. It will be noted that the hypochlorous acid or hypo tion of the final elemental mercury product and the chlorite is therefore generated in situ as required to oxi recovery and regeneration of certain of the reagents dize the mercuric sulfide content of the material being involved; 65 leached. Thus, as distinguished from the prior art hypo F.G. 2 is a more detailed flow sheet illustrating the chlorite leaching process, there will always be sufficient leaching step of Stage 1; hypochlorous acid or hypochlorite present in the leach FIG. 3 is a more detailed flow sheet illustrating the liquid to assure practically quantitative oxidation of the purification (Stage 2) of the pregnant liquor produced in mercuric sulfide, whereas in the prior art hypochlorite the leaching step of FIG. 2; 70 leach processes, the available hypochlorite content of the FIG. 4 illustrates an optional precious metal recovery each liquid was limited by the stability of calcium hypo step which may be included in the Stage 2 purification chlorite in the previously prepared leach liquid. Since the procedure; available hypochlorite content was low, the mercury con FIG. 5 is a more detailed flow sheet for the reduction tent of the prior art pregnant liquor was low. Further step of Stage 3 and illustrating the presently preferred 75 more, since the hypochlorite concentration of the leach 3,732,094 5 6 reagent was limited, no advantage was ever made of the a pregnant leach liquor containing the solubilized mer use of concentrates to increase the mercury value load cury in the form of mercuric chloride. In the prior proc in the pregnant liquor. By means of the process of the ess, the hypochlorite in the leach liquid was formed prior invention, however, one is able to obtain a pregnant liquor to the leaching step. The prior process also included the 11 from the leaching step containing from as low as 50 steps of reducing the solubilized mercury in the pregnant to as much as 190 grams or more of mercury per liter of liquor to form elemental mercury and the step of separat pregnant liquor. ing the elemental mercury from the leach liquor. Because the cinnabar ore is typically associated in na According to one embodiment of the process of the ture with other minerals, the pregnant liquor 11 from the present invention, the mercury is recovered from its leaching step (Stage 1) normally contains other soluble source with increasing efficiency and at higher production metals as impurities and is subjected to a purification step 0. rates by combining with the aforesaid reducing and sepa (Stage 2) for the removal of impurities such as arsenic, rating steps the step of forming the pregnant leach liquor selenium, tellurium, gold, and the like, which would be by leaching the mercury source with a novel leach liquid. reducible and troublesome in the reduction step (Stage 3). The novel leach liquid includes components which react In addition to the hypochlorous acid or hypochlorite during the leaching step to generate a hypohalite leach leach reagent employed in the leaching step of Stage 1, 5 reagent in situ as consumed. The hypohalite generated one could employ any other hypohalite leach reagent. in situ in turn oxidizes the mercury or mercury com Thus, illustratively, one could employ a solution of disso pound in the mercury-containing source and solubilizes ciated metal hypochlorite, for example, a soluble alkali the oxidized mercury in the leach liquid in the form metal or alkaline earth metal hypochlorite such as sodi 20 of an extremely soluble and stable mercury complex. um, potassium, magnesium, or calcium hypochlorite in In accordance with another embodiment of the inven the dissociated state. Similarly, other hypohalites or hypo tion, impurities such as arsenic, selenium, and tellurium halous acids may be employed, such as hypobromous are separated from pregnant mercury leach liquors con acid or any suitable solution of a salt yielding the hypo taining solubilized mercury, according to a technique bromite ion, or hypoiodous acid. Of course, the halogen which includes the steps of forming an insoluble metal hy fluorine, does not form a hypofluorous acid and the hypo 25 droxide floc in the pregnant liquor, contacting the preg fluorite ion cannot exist. It will therefore be appreciated nant liquor with the insoluble floc for a length of time by those skilled in the art that the term "hypohalite leach to selectively adsorb the soluble impurity compounds reagent,' as used herein, means a solution containing upon the floc and separating the impurity-loaded floc any of the possible hypohalous acids, i.e., hypochlorous 30 from the pregnant liquor. acid, hypobromous acid or hypoiodous acid, either in the According to a further embodiment and feature of the dissociated or undissociated state, as well as solutions invention, the process provides a novel method for re containing any of the possible hypohalite ions such as ducing solubilized mercury compounds or complexes hypochlorite and hypobromite. from pregnant leach liquors. These pregnant leach liquors If the purified pregnant liquor 12 contains a sufficient 35 may be produced in accordance with the embodiment of quantity of precious metals such as gold, silver, platinum, our process described above or, alternatively, the preg etc., an optional precious metal recovery step is preferably nant leach liquor may be prepared according to any other included in Stage 2. suitable leaching process. According to this further em The purified pregnant liquor 12 containing the soluble bodiment of the invention, the solubilized mercury in calcium tetrachloromercurate complex is then subjected 40 the pregnant leach liquor is reduced to elemental mer to a reduction step (Stage 3) in which the tetrachloro cury with increased efficiency in a process involving a mercurate complex is reduced, yielding the desired ele two-stage reduction. In the first reduction stage, the mental mercury product 13. According to presently pre solubilized mercury is partially reduced by treatment with ferred embodiments of the invention, the reduction re a reducing agent, forming an insoluble mercury com agent can be one of two general types, either an acid 45 pound which is then separated from the mother liquor. aqueous solution of stannous chloride or an inorganic In the second reduction stage, the insoluble mercury acid or salt of phosphorus in which the phosphorus moiety compound, now separated from the mother liquor, is has an oxidation state of less than --5. These reductants treated with an additional quantity of reducing agent to may be used as reductants in homogeneous reducing solu complete the reduction, forming elemental mercury, tions when applied to the strong purified pregnant liquor 50 which is then separated from the spent reducing agent. containing the calcium tetrachloromercurate complex. According to still another preferred feature and em If the stannous chloride is employed as the reduction bodiment of the invention, the reduction of the solubil reagent, the spent liquor 14 from the reduction step (Stage ized mercury in the pregnant leach liquor is carried out in 3) is subjected to a reductant reagent recovery step a homogeneous liquid phase, i.e., the reduction reagent (Stage 4) in which the tin content of the spent liquor 55 is a liquid solution which is fully miscible and soluble in 14 is recovered as metallic tin 15 which, in turn, is sub the pregnant leach liquor. By carrying out the reduc jected to a reductant regeneration step (Stage 5) to re tion in a homogeneous liquid phase, the contact between convert the metallic tin into the desired stannous chloride the reduction reagent in the solution and the solubilized reduction reagent 16 which is recycled to the reduction mercury compound and/or complex is facilitated and the step (Stage 3). 60 reaction is thereby accelerated and substantially quantita On the other hand, if the reduction reagent employed tive recovery of the mercury in a high state of purity from in the reduction step (Stage 3) is the inorganic acid or the pregnant leach liquor is achieved. Furthermore, this salt of phosphorus described above, the spent liquor may eliminates mechanical occlusions of unused solid reagents, be merely discarded as the cost of the reagent is sufi protecting the purity of the mercury product from such ciently low to justify merely discarding the spent liquor. 65 occlusions. The homogeneous reducing solutions chosen are selective for reducing mercury under the conditions Detail Description-Stage 1 involved. As will be apparent from the above description of In the presently preferred embodiment of the inven FIG. 1, the process of the invention provides a method tion, the aforesaid leaching and reduction steps are com for winning mercury from mercury-containing sources 70 bined to produce an overall integrated process which is such as ores, ore concentrates, alloys, amalgams and com capable of practically quantitative recovery of the mer pounds of mercury. The process is an improvement in the cury from the mercury-containing source. According to prior art process, which includes the step of leaching the a further preferred embodiment, the reduction step of the mercury source with a leach liquid containing a hypo integrated process employs an aqueous solution of stan chiorite to oxidize and solubilize the mercury, forming 75 nous chloride as the reducing agent. When stannous chlo 3,732,094 7 8 ride is employed as the reducing agent, the mother liquor tively extract the mercury values from the mercury from the reduction step is treated with a reducing agent source and, assuming that stoichiometric portions of the to recover the tin values from the mother liquor by base have been provided, the reaction is substantially reducing the tin in the mother liquor to elemental tin complete by the time the pH of the leaching mixture has which is then reconverted into stannous chloride and reached approximately 6.4. The overall net reaction for recycled to the reduction step. the preferred embodiment of the leaching step is, there According to an alternate embodiment of the inven fore: tion, the reducing agent employed to recover the mercury values from the pregnant liquor is an inorganic acid or salt of phosphorus in which the phosphorus moiety has O an oxidation state of less than --5. According to still another embodiment of the inven Turning again to the drawings, FIG. 2 illustrates in tion, hypochlorous acid is generated in situ if the leach greater detail the steps forming Stage 1 of the process and reagent 21 is calcium carbonate rather than calcium hy the leaching steps which are employed to prepare the droxide as described above. According to this alternate impure pregnant liquor. As already noted above, the 5 embodiment, the stable soluble calcium tetrachloromer pulped ore 10 may be directly introduced into the leach curate complex is formed in the pregnant liquor by means ing tanks if it is of sufficiently high mercury content, for of the following overall equation: example, upwards of 30% mercury. On the other hand, if the ore 10a is of somewhat lower mercury content, for example as low as 0.025% mercury, it may optionally be subjected to a milling procedure to produce an ore con 20 Reaction 8 involves the intermediate reaction: centrate 10b which may, for example, contain from 5% (9) HgCl2--CaCl2 > CaHgCl to as high as 85% mercury. At any rate, the pulped ore For purposes of illustration, the preceding discussion has 10 or the ore concentrate 10b is introduced into a suit assumed that the mercury values were present as mer able leaching wat where, with agitation, it is contacted 25 curic sulfide such as would be present in cinnabar ores. with leach reagents in an aqueous medium formed of However, as will be apparent to those skilled in the art, recycled weak pregnant liquor 22 and makeup water 23. mercury values could be similarly extracted from free Chlorine 24 is injected into the leaching vat and the quicksilver, amalgams and alloys of mercury with other chlorine 24 reacts with the leach reagents 21 to form materials. In such cases, the mercury values would be con the hypochlorite leach reagent in situ. According to the 30 verted by the hypohalite leach reagent to mercuric chlo presently preferred embodiment of the invention, the ride and would then be converted to the extremely solu leach reagent 21 is a slurry of calcium hydroxide which ble and stable tetrachloromercurate complex according to reacts according to the following equation: Equation 9. Similarly, instead of chlorine, one could employ other The calcium hypochlorite formed according to Equation 35 halogens such as, for example, bromine, and one could 2 in turn reacts with the mercuric sulfide content of the employ other metal carbonates such as the alkali metal cinnabar ore or concentrate according to the following carbonates and the intermediate reaction would be: equation: (10) HgBra--2KBr->KHgBr 40 According to an even further embodiment of the in vention, one could employ sodium or other alkali metal forming an extremely soluble and stable calcium tetra bicarbonates as the leach reagent 21 since the pH of a chloromercurate complex (CaHgCl) and a calcium sul Saturated Sodium bicarbonate solution at room tempera fate (gypsum) precipitate. The tetrachloromercurate com ture is 8.0 and approximately 20% of the total hypo plex then reacts with additional quantities of calcium chlorite at this pH is in the form of free hypochlorous hydroxide according to the following equation: acid. The overall net equation for this embodiment is: (4) CaHgCl4--Ca(OH)2)2CaCl2--HgO--HO to form calcium chloride and a yellow precipitate of mer curic oxide. As the reaction proceeds with the addition 50 Assuming that stoichiometric portions of the base have of chlorine, the pH steadily drops from approximately been provided, this reaction goes practically to comple 11 to approximately 9. At approximately pH 9, the yel tion at approximately pH 6.5, with a mercury recovery low mercuric oxide precipitate reacts with the calcium efficiency in the order of 99.5%. The intermediate reac chloride formed in Equation 2, water, and additional tions are: chlorine according to the following equation: 5 5 (11a) 2NaHCO3--Cl2>NaCIO+NaCl+-2CO3--HO (5) HgO--HO--CaCl2-2Cl2 > CaFIgCl2.HCIO (11b) HgS-4NaClO->Na2HgCl4--NasO4 reforming the very soluble and stable calcium tetrachlo (11c) HigS-I-4HCIO--2NaCl->Na2HgCl4--HSO-2HC romercurate complex plus hydrochlorous acid generated in situ. The hypochlorous acid formed according to Equa 60 (11d) 2NaHCO3--HO->Na2SO4-4-2HO-I-2CO tion 5 then oxidizes additional quantities of mercuric sul (11e) NaHCO3--HCl->NaCl-+-H2O--CON fide from the ore or concentrate according to the fol Of the above-described embodiments of the leaching lowing equation: Step, the embodiment which employs calcium hydroxide (6) HgS-4HClO-CaCl->CaFIgCl4-HSO--2HCl 65 as the leach reagent 21 is preferred for several reasons: forming additional quantities of the very solube and stable (1) The solubility of calcium carbonate is reduced by the calcium tetrachloromercurate complex. The oxidation of buildup of the calcium chloride reaction by-product, a the mercuric sulfide according to Equation 6 is followed disadvantage not encountered when calcium hydroxide by the reactions: is used as a reagent, 70 (2) The embodiments described above involve the for (??) Ca(OH)--HSO >CaSO4.2H2O mation of carbon dioxide gas which leads to frothing (6b) Ca(OH)--2HCl->CaCl2.H2O in the leaching vessel causing practical difficulties; and (3) The use of calcium hydroxide as the leach reagent (6c) HgO--2HCl +-CaCl2 ? CaHgCl4--H2O permits one to carry out the leaching operation at a Equations 6-6(c) will proceed to substantially quantita 75 relatively high pH. In the other embodiments described 3,732,094. 9 O above, the pH during the leaching reaction is some as evidenced by a white milky appearance of the pregnant what lower, thereby temporarily solubilizing any iron liquor. When the pH of the pregnant liquor 33 has been oxide present in the ore or concentrate. This temporar adjusted to approximately pH 6.3, most of the zinc ion ily solubilized iron oxide would then precipitate as a present has been converted to the zinc hydroxide sus slime as the pH is increased during the progress of the pension. At that point, additional quantities of a zinc leaching reaction. hydroxide slurry 34 at pH 6.3 is added to the pregnant According to the preferred embodiment in which liquor. The zinc hydroxide forms according to the equa calcium hydroxide is employed as the leach reagent, the tions: reaction is conducted at substantially ambient tempera ture or slightly above, e.g., below 40 C. Since the leach reactions are exothermic and since the possibility of deg O radation of the hypochlorite leach reagent is increased The zinc hydroxide suspension formed in the pregnant with increasing temperature, it is desirable to provide liquor 33 and the added zinc hydroxide slurry 34 are auxiliary cooling coils in the leaching reactor such that allowed to remain in contact with the pregnant liquor the reaction mixture temperature does not substantially for approximately 15 minutes. exceed 40° C. The preferred technique is to suspend the 5 The purpose of the above-mentioned pH-adjustment ore or ore concentrate and the calcium hydroxide in the steps will now become apparent as it will be noticed that aqueous leach medium and inject chloride into the leach the zinc hydroxide slurry added in the adsorption and ing reaction mixture. Since calcium hydroxide is very Settling step will not, therefore, affect the pH of the much more soluble in the leaching reaction mixture, de pregnant liquor. As the zinc hydroxide slurry contacts spite the formation of calcium chloride, the hydroxyl ion 20 the impure pregnant liquor, the impurity materials such concentration is always sufficient to neutralize the acids as soluble arsenic, selenium, and tellurium compounds formed, thereby maintaining the pH at a sufficiently high are selectively adsorbed on the zinc hydroxide suspension. value, such that no iron oxide goes into solution. At the The adsorption mixture 35 is then subjected to a me beginning of the reaction, (i.e., at approximately pH 11), 25 chanical separation, for example, filtration, to prepare the leaching reaction mixture will have a rose-pink color a purified pregnant liquor 36. The solids 37 from the ation. As chlorination proceeds, a yellow precipitate of separation step are repulped and washed until the mercury mercuric oxide appears. The pH continues to drop and values are economically recovered. The wash liquid 23 for a time remains nearly constant between 9.0 and 9.5 is recycled as makeup water for the leaching step of during which time the leaching reaction mixtures takes 30 Stage 1. The adsorbed impurities and the mixture of on a yellowish coloration. As the pH continues to drop Zinc hydroxide calcium sulfate (gypsum) filter aid 38 may with further chlorine addition, the yellow mercuric oxide be discarded or may be further processed to recover goes back into the solution as the soluble tetrachloro metal values therefrom. mercurate complex, and at approximately pH 6.4, the As indicated on FIG. 3 by the dashed lines 39, the leaching reaction mixture takes on a grayish-white color 35 purified pregnant liquor 36 may optionally be subjected ation, and the mercuric sulfide is essentially quantitatively to further steps for the recovery of gold and other oxidized. precious metals. After completion of the leaching reaction as described OPTIONAL PRECIOUS METAL RECOVERY STEP above, the entire contents of the leaching reactor are subjected to an appropriate mechanical separation step, For the purpose of illustration, it will be assumed that e.g., filtration, The impure liquor 25 and the precipitated the purified pregnant liquor 36 contains sufficient gold calcium sulfate 26 gypsum) which acts as a filter aid, to economically justify inclusion of a precious metal re are separated, forming an impure pregnant liquor product covery step, i.e., approximately 20 milligrams of gold per 27 of the leaching step. Stage 1. This impure product liter in the form of a calcium tetrachloroaurate (III) pregnant liquor is then subjected to further purification 45 complex Ca(AuCl4)2. The gold can be selectively re procedures in Stage 2 as hereinafter described. The filter duced and adsorbed onto the surface of various insoluble cake 28 is repulped with wash water 29 and the repulped reducing agents, for example, mercurous chloride, ti cake 30 is again subjected to appropriate mechanical tanous hydroxide, and cuprous oxide. separation procedures, such as filtration, to produce a FIG. 4 illustrates in greater deiail the optional pre weak pregnant liquor 22 which is recycled for combina 50 ferred precious metal recovery step of Stage 2. The puri tion with makeup water 23 to the leaching step. The fied pregnant liquor 36 from the separation step of FIG. 3 tailings 31, mainly calcium sulfate plus gangue materials, is reacted with a stoichiometric excess of mercurous sul may be discarded. As indicated in FIG. 2 by the dashed fate, either in the form of a solution or powder, or a lines enclosing the repulping and separation steps, these mercurous perchlorate solution 4 in the presence of a procedures may optionally be repeated until the soluble 55 catalyst or promotor 42. The objective of this reaction is to add sufficient soluble mercurous ions (Hg2++) to mercury values remaining in the filter cake 28 have been the purified pregnant liquor to form freshly precipitated economically recovered. Curdy mercurous chloride, according to the equations: DETALED DESCRIPTION-STAGE 2 FIG. 3 illustrates in greater detail the operational 60 steps which are employed according to the preferred embodiment of the invention to purify the pregnant liquor In the freshly prepared curdy form, the mercurous chlo produced in the Stage 1 leaching operation. ride reacts with the gold complex according to the follow The impurities which are removed in Stage 2 are pri ing equation: marily compounds of arsenic, selenium, tellurium and 65 the like, which are normally associated with cinnabar (14) Promoter ores. The impure pregnant liquor 27 from Stage 2 is 3Hg2Ol2 -- Ca(AuCl4)2 -- 5CaCl2 -> 6CaFHgCl4 -- 2 Auº first treated with zinc chloride 28 (or zinc sulfate) and hydrochloric acid 29 to adjust the pH to a rather low The free gold produced according to the above reaction value, for example approximately pH 3. Calcium sul 70 is adsorbed on the excess mercurous chloride as the reac fate (gypsum) filter aid 32 is also added at this point. The tion proceeds. The reduction mixture 43 is then subjected low pH pregnant liquor 30 can then be very carefully to an appropriate mechanical separation step, for exam adjusted back to a higher pH value by controlled addi ple, filtration, to produce a gold-free purified pregnant tion of dilute sodium hydroxide 31. At pH of approxi leach liquor 36a. The solids 44 from the separation step mately 6.0, a zinc hydroxide suspension begins to form 75 may then be, illustratively, reacted with hypochlorous 3,732,094 1. 2 acid 45 which oxidizes the gold and mercurous chloride, required, but the mercury values as separated from the producing a solution containing a tetrachloroauric acid pregnant liquor in the first reduction step by reducing the 46 which can be then reduced by reaction with an appro soluble tetrachloromercurate complex to an insoluble mer priate selective reluctant 47 such as ferrous chloride or curous chloride solid, after separation from the relatively ferrous sulfate, yielding free gold metal 48 and a weak large volume of mother liquor, are more conveniently and pregnant liquor 22a containing soluble tetrachloromer rapidly reduced in the second reduction step in a much curic acid complex (HHgCl) which is recycled 22a to smaller vessel using smaller volumes of reduction reagent the Stage 1 leaching step. As mentioned above, a catalyst since the reduction reagent is not diluted in the second or promotor 42 is added to the reduction mixture al reduction step by the large volume of mother liquor with though the mechanism is not completely understood. The O which mercury values were formerly associated. The wash addition of this material greatly improves the rate of the waters 57 containing dilute SnCl4 and HCl are forwarded reduction of the gold complex as well as the efficiency of to the Stage 4 recovery step. the gold recovery. The promotor is prepared in the fol lowing proportions: Add one gram of Solid flaky Hg2Cl2 REDUCTION REAGENT RECOVERY-STAGE 4 to 8 ml. of the purified pregnant liquor. Then add two 15 FIG. 7 illustrates the recovery of the reduction reagent drops of a concentrated HAuCl4 solution (containing when the preferred reductant SnCl2 is used. The spent about 0.25 gram of gold per ml.), followed by the addi reducing solution 53, i.e., the calcium hexachlorostannate tion of three drops of 0.6 M Hg2 (ClO4)2 solution in 0.5 (IV) filtrate containing excess calcium chloride and hy M HClO4. A deep-blue slurry or suspension forms. drochloric acid from Stage 3 and the wash waters 57 are The promotor 42 is then added to the pregnant liquor 20 treated with a heterogenous reduction reagent 71 to re 36 in the proportion of approximately one milliliter of duce the tin values, forming metallic tin sponge. After the blue slurry per liter of pregnant liquor 36. After add formation of the tin sponge, the reduction mixture 72 ing the promotor, reduction reagent 41 (preferably a is subjected to appropriate mechanical separation pro 0.6 M mercurous perchlorate solution in 0.5 M HClO4) cedures such as filtration to separate the tin sponge 73 is added in an appreciable excess over that required to 25 from the filtrate 74. Optionally, if the filtrate 74 from the reduce the gold complex to free gold, for example, 2/2 separation step contains sufficient residual tin values to times the stoichiometric requirement. According to an economically justify recovery, the filtrate 74 may be sub alternative embodiment, one could optionally add mer jected to electrolysis to recover additional quantities of curous sulfate powder but this embodiment is not pres tin sponge 73a, after which the spent electrolyte is dis ently preferred because of the limited solubility of the 30 carded. The presently preferred reduction reagent 71 is mercurous sulfate powder in water. aluminum. The physical form of the aluminum is not Other alternative embodiments of the gold recovery highly critical and, for example, the aluminum may be in involves the use of Ti(OH)3 and Cu2O as insoluble re the form of scrap wire, scrap aluminum cuttings and even ductant-adsorbents. disposable aluminum food trays. Preferably, however, in STAGE 3 REDUCTION-PRESENTLY PREFERRED 35 order to avoid mechanical occlusion of aluminum in the METHOD tin sponge, one should employ aluminum bars or rods as The purified pregnant liquor 36 or the gold-stripped in this physical form the tin sponge forms a homogeneous purified liquor 36a from Stage 2 is treated in Stage 3 to coating on the outer surfaces of the bars or rods which reduce the calcium terachloromercurate complex to pro 40 is easily dislodged, exposing fresh aluminum surfaces for duce the desired elemental mercury product. FIG. 5 il further tin sponge formation. In addition to pure alumi lustrates the presently preferred mercury complex reduc num, one can employ practically any aluminum alloy ex tion technique. The pregnant liquor 36 or 36a is first cept those which contain appreciable quantities of copper, adjusted to 0.3 N HCl content and sufficient amount of i.e., about 0.5% Cu. In addition to aluminum, one can approximately 2.5 M stannous chloride in 3.5 NHCl 51 employ as the reduction reagent 71 various other metals is added to reduce the tetrachloromercurate complex in Such as zinc, magnesium and alloys thereof, again with the pregnant liquor to mercurous chloride (HgCl2) which the exception of such alloys containing appreciable quanti is insoluble in the mother liquor, according to the equa ties of copper. If the reduction reagent metal 71 contains tion: appreciable quantities of copper, the initial deposits of tin Sponge which form on the surface of the reduction reagent (15) 2CaHgCl-SnCl2->HgCl2--CaCl2--CaSnCls 50 metal is deposited in the form of a relatively impervious After this first partial reduction of the mercurate com coating which prevents further contact between the re plex, the reduction mixture is subjected to appropriate duction reagent metal and the spent solution 57. Alu mechanical separation procedures such as filtration to minum, zinc and magnesium and various low-copper separate the mercurous chloride solid 52 from the mother alloys of these metals with other metals are preferred liquor 53 which now contains calcium hexachlorostan 55 as the tin reductant in the Stage 4 recovery process. These nate (IV) (CaSnCls), excess calcium chloride, and HC1. metals are preferred because they have very high oxida The mercurous chloride solid 52 is then reacted with a tion potentials and are high above tin in the Electromotive stoichiometric excess 54 of the approximately 2.5 M Series. However, certain other elemental metals above tin SnCl2 in 3.5 N HCl to complete the reduction of the in the Electromotive Series cannot be employed as the tin mercurous chloride 52 to produce elemental mercury 55 60 reductant because the reaction will not proceed far enough which is so pure that it is only necessary to merely wash to reduce the stannic tin compound to elemental tin. the mercury product 55 of the second reduction step with For example, if iron is employed, the following reaction dilute HCl and then de-ionized water in order to produce takes place: the desired mercury product 56 of acceptable commercial (17) CaCl2 65 CaSm Cl6 -+- Fe ------>. Fe Cl3 + Sin Cl2 + CaCl2 purity. The equations for this second-stage reduction are: 0.3NHC1 and if nickel is employed, the following reaction takes place: (18) CaCl2 The importance of carrying out the reduction of the 70 CaSnCl6 -- Ni --> NiCl2 -- SnCl2 -- CaCl2 tetrachloromercurate complex in the pregnant liquor 36 0.3NHC or 36a in two steps, as illustrated in FIG. 5, will be ap preciated by those skilled in the art, as this technique The consumption of the reduction reagent metal 71 enables one to not only reduce the volumes of liquids is not excessive because the excess calcium chloride pres being handled and the quantities of reduction reagents ent in the spent solution 53 causes the reduction reaction 3,732,094 13 4 to go nearly quantitatively to completion at relatively low attemperatures ranging from 70° C. to boiling point. The acid concentrations. Thus, only a small quantity of the reaction in the first reduction step is: reduction reagent metal 71 is consumed by reaction (21a) with the acid in the spent solution 53 to form the corre (Equiv. HCl) sponding metal salt. The reaction which occurs in the pre -- CaCl2 ferred embodiment of the Stage 4 reduction step is: 5 NaH2PO3 + 4CaHgCly -- 2H2O --> 4CaCl2 + 2HgCl2 - (19) XSCaCl2 3CaSnCls - 4Al 3CaCl2 - 4AlCl3 + 3Sn. NaCl -- 3HCl -- H3PO3 0,3 IN HCl 0 (21b) HC--CaCl2 TIN-RECOVERY METHOD-ALTERNATE STAGE 4 HaPO2 - 4CaEdgCl4 -- 2H2O --> Instead of the preferred chemical reduction technique The reaction mixture 66 is then separated, e.g. by filtra described above, the tin values from the spent solution 53 tion, yielding a mercurous chloride solid 67, and the can be recovered by electrolysis. In this embodiment, the 5 spent reducing solution filtrate 68 which is discarded. The spent solution containing calcium hexachlorostannate (IV) mercurous chloride solid 67 is then reacted with a stoichi plus excess calcium chloride in 0.3 NHCl is fed into an ometric excess of the approximately 2.5 M HPO 69, electrolytic cell having graphite anodes, with cathodes prepared in the same manner as that employed in the formed of materials such as stainless steel or titanium first reducing step, to complete the reduction of the to which the tin sponge would not adhere. The tin sponge 20 mercurous chloride to elemental mercury 55a, in the pres 73a falls to the bottom of the electrolytic cell and is peri ence of approximately 50-100 grams of either calcium odically removed. chloride or sodium chloride per liter of reductant solu MURCURATE REDUCTANT REGENERATION tion. The reactions are as follows: STAGE 5 25 (22a) (Equiv. HC1) The tin sponge 73 from the Stage 4 tin recovery process HgCl2 - NahaPO -- 2EO --> is reconverted into a stannous chloride according to the CaCl2 or NaCl process illustrated in FIG. 8. The tin sponge 73 is re acted with the approximately 2.5 M SnCl4 in 3.5 NHCl 30 (22b) 81 (i.e., the spent reducing solution from the second (Equiv. HCl) reduction step of Stage 3). The tin sponge reduces the HgCl2 - 3PO2 -- 2H2O --> stannic chloride (or H2SnCls) in the spent reducing solu CaCl2 or NaCl tion 81 to stannous chloride and is, itself, oxidized to 4Hg -- 4HCl -- H3PO a the stannous state as per the equations: 35 The spent liquor 75 from the second reduction step (20a) SnCl4--Sn->2SnCla is also discarded. The elemental mercury product 55a (20b) HSnCls--Sn->2SnCl2.HCl of the second reduction step is washed with dilute HCl The reduction mixture 82 is then subjected to appropriate 76 and deionized water 77 to produce the final mercury physical separation techniques such as filtration and any 40 product 56a of acceptable commercial purity, the wash unreacted sponge 83 is recycled to the reduction step. waters 78 being discarded. The approximately 5.0 M stannous chloride solution 84 is Although in describing the alternate embodiment of then acidified with an equal volume of 3.5 NHCl, yield the Stage 3 mercurate reduction method reference was ing the desired approximately 2.5 M SnCl2 in 3.5 N HCl made to the preferred HPO2 reductant, one can employ 85, which is then recycled to Stage 3 for use as the re 45 as alternate reductants any other suitable reducing agent duction reagents 51 and 54. such as an inorganic acid or salt of phosphorus in which the phosphorus moiety is in an oxidation state of less ALTERNATE EMBODIMENT STAGE 3 than --5 (e.g. HPO or Na2HPO). Any of these acids or their acidified salts will reduce the tetrachloromercurate Instead of the presently preferred stannous chloride 50 complex and will themselves be oxidized to the --5 reduction of the tetrachloromercurate complex in the valence state. Of course, as will be apparent to those pregnant leach liquor 36 or 36a, one can employ the skilled in the art, the particular technique illustrated in process illustrated in FIG. 6. If this alternate mercurate FIG. 6 for preparing the mercurate reductant need not reduction process is employed. Stages 4 and 5 described be followed as many alternate methods could be em above can be eliminated because no particular economic 55 ployed to produce the mercurate reductant. In fact, in advantage can be gained by recovery of the reductant stead of the sodium hypophosphite monohydrate, one reagent. Therefore the spent reducing solutions are dis could employ any metallic phosphite or hypophosphite carded. Again, however, according to the preferred em such as, without limiting the generality thereof, the alkali bodiment of the invention, the tetrachloromercurate re metal and alkaline earth phosphites or hypophosphites, duction is accomplished in two steps, i.e., a reduction to 60 which are preferred because of their solubility in the insoluble mercurous chloride, which is then separated reductant reagent reaction mixture. However, even in from the mother liquor, and a second reduction step in soluble metal phosphites or hypophosphites can be used which the mercurous chloride is further reduced to form if they become soluble in the reductant reagent prepara elemental mercury. tion reaction mixture. Similarly, in addition to the hydro As shown in FIG. 6, the preferred mercurate reductant 65 chloric acid 63 component of the reductant preparation 61 is an approximately 2.5 M solution of HPO prepared reaction, one could use many other acids such as, without by reacting sodium hypophosphite monohydrate 62 with limiting the generality thereof, HBr, dilute HCIO, etc. an amount of hydrochloric acid 63 equimolar to the sodi Hydroiodic acid cannot be employed because it forms um hypophosphite 62, used or in slight excess. Sufficient an HgI2 complex which cannot be reduced. Highly oxi water 64 is added to the reaction mixture to produce O dizing acids such as nitric acids, HClO, HClO3, HClO3, the desired approximately 2.5 molar H3PO2. The mer concentrated HClO4, etc., would be similarly inoperable. curate reductant 61 is reacted with the purified leach The reader is cautioned that the use of concentrated liquor 36 or 36a in the presence of approximately 50-100 HClO4 would yield a potentially explosive mixture. grams of either calcium chloride or sodium chloride 65 Finally, of course, acids which form insoluble precipitates per liter of pregnant liquor. The reduction is carried out 75 with the reductant preparation reagents could not be used.

3,732,094 17 8 Two separate portions of cinnabar ore concentrate from Sulting tetrachloromercurate complex. The data obtained the Red Rock mine containing 39.7% mercury were placed are as follows: in each of two separate one-gallon wide-mouth glass fruit jars. Finely powdered calcite, calcium carbonate Leach step Run. No, Run No. 2 (CaCO3), was next added, followed by the addition of Wt. of concentrate, g------335 345 ASSay of conc., percent Hg.....---- a 39.7 39,7 slightly more than one liter of wash water from a pre Wit. Of contained mercury, g...... 4K « « 33.0 36, 9 vious run. Wt. of CaCO3 used, g------200 25 Chlorination time, hrs------a a 34 2% The slurry was vigorously agitated with the aid of an Upper temperature, C------44 49 electric stirrer and a slow stream of elemental chlorine First reduction: HCl (conc.) added, mil- 88 75 gas was conducted into the solution through a glass tube O SnCl2 (2M) added, ml. 73 78 running into the agitated mixed slurry of calcium car Second reduction: Time allowed, hrs. (in 2.5 M SnCl2, bonate and cinnabar ore concentrate, and reaching to strongly acidified with HCl)------2 () within an inch of the bottom of the leaching vessel. The Wt. Hg recovered, g.------132.4 134,1 Dry tailing residue, g------269.3 283.4 open end of the tube was attached to a fritted glass gas ASSay of tails, percent Eg- 06 .08 diffuser plug of coarse porosity, designed to diffuse the Percent reeovery, comtaimed Hg------99.5 98.5 chlorine gas into the agitated slurry as fine bubbles. The chlorine gas was delivered from a hundred-pound steel Left overnight. cylinder of commercial liquid chlorine under pressure. EXAMPLE 2. During chlorination, a gradual temperature rise of the This example illustrates the removal of arsenic and agitated slurry was noticed. A thick layer of large foamy 20 other impurities from the pregnant leach liquor of Ex bubbles of carbon dioxide (CO2) gradually gathered over ample 1. the liquid surface of the agitated aqueous slurry, about Exactly one liter of a pregnant mercury leach solution two to three inches or more in thickness. (measured out in a one-liter volumetric flask) prepared After chlorination had been completed, as observed by the Ca(OH)4-Cl2 leaching process on a Mexican by the escape of some free chlorine gas from the leaching 25 cinnabar ore concentrate containing over sixty percent vessel, the agitation was stopped and the reddish brown mercury containing 0.955 lb. Hg/gallon or 114.49 gms. slurry of insoluble residue (tails) was filtered with a large Hg/liter entirely as calcium tetrachloromercurate (II), Buchner funnel using Whatman cellulose filter paper, CaFIgCl4. The same leach solution also contained 126.8 under vacuum suction. The pregnant mercury leach solu gms. CaCl2/liter as free calcium chloride. tion filtrate was nearly clear and colorless. The reddish 30 The liter of mercury leach solution was placed in a brown filter cake in the Buchner funnel was washed with two-liter beaker and, with the aid of a magnetic stirring three quick portions of water, 100 milliliters each, and apparatus, the solution was vigorously agitated. To the the final filter cake had a thickness of about A6 inch. The agitated solution, 1.5 grams of dry zinc chloride (ZnCl2) filter cake was then given a more thorough Wash by re crystals were added, which rapidly dissolved. turning it to the leaching vessel containing 700 milliliters 35 Agitation was continued and a dilute solution of sodium of water and the slurry was again filtered under a vacuum hydroxide (e.g. 1.5%) was added a few milliliters at a Suction. time to the leach solution. After each small addition of Example la sodium hydroxide solution, very large quantities of an orange to yellow precipitate appeared, but very readily The following table contains a summary of results of 40 dissolved and completely disappeared within a few each of examples (Run 1 and Run 2), using calcium car seconds. bonate to form the leach reagent: Further quantities of sodium hydroxide solution were added until the mercury leach solution turned milky white and remained permanently in this condition. At this 45 point, the insoluble precipitate of zinc hydroxide Material or operation. Run Run2 (Zn(OH)2) was pure white and did not contain any ._. ——?????????-— (1) Weight of Red Rockore concentrate leached, trace of highly colored precipitates, and the pH of the LLS00LLSS SSS SSASq AA AAAAAAAAqAAAAAAA ASLAiAi iAASiLiLiSiiiiii MA qAAqA S qqi ii AA AA AAAA AAA 335 345 solution was between 6.3 and 6.5. (25trate, Mercury percent content mercury------of Red Rock ore concen 39.7 39.7 A thick slurry of zinc hydroxide (Zn(OH)2), formed (3) Weight of mercury in Red Rock ore concen 50 by mixing with agitation 50 milliliters of a zinc sulfate (4)trate Weight present, of dryinsoluble grams-:----:---:- residue (tails), - - grams- - - - - ??? 269.3183.0 283.4137.0 solution containing 100 gms. of ZnSO47H2O/liter with 5 Mercury contentofinsoluble residue (tails), 50 milliliters of sodium hydroxide solution containing 25 (6)peroetat------? Weight of finely powdered ? - - - - ??? - ????- -calcite, ?? ?????? ------calcium ?? ??? ? ?? ??? 0.06 0.08 gms. NaOH/liter was added rapidly to the mercury leach carbonate added to ore concentrate, grams---- 200 215 solution, pH of 6.3 for the slurry. (7)(8) MaximumChlorination temperature time, hours------reached during ???? 3% 2% 55 The solution at this point contained one gram of Zinc chlorination, degrees centigrade------44 4? as zinc hydroxide with a twenty-five percent or more (9) Time required to filter and separate reddish excess of the weight of zinc as zinc hydroxide, present as brown insoluble residue (tails) from pregnant zinc chloride. The total sulfate content from the zinc (10)mercury Mercury leach content solution, of pregnant minutes.------leach liquor: 6 5 (a) Gms. Hglliter------38.27 4.67 sulfate used for preparing the original zinc hydroxide (b) Libs. Hglgallon------0.32 0.4 60 slurry was precipitated from the mercury Solution as (1) Volume of water added to charge prior to CaSO-2HO which serves to advantage as an excellent chlorination, liters------19 filter aid when attempting to separate mercury leach solu (12)pregnant Total chloridemercury ion leach (Cl-) Solution, concentration gins. Cl-| of liter------? - - - ?? ? - - - - - ?? ? ? - - ?? 54.59 5.38 tions from zinc hydroxide precipitates by filtration. (13) Wolume of mercury leach solution obtained, The mercury leach solution containing a heavy milky (14)liters------Mercury recovered by chlorination - - ?? ???? leach- - ?? 3.48 2,70 65 white suspended slurry of zinc hydroxide and calcium ing, percent------5-5------98.8 98.3 sulfate was vigorously agitated for twenty minutes. At (5) Weight of mercury in insoluble residue 1.6 2.3 (tails), grams------the end of twenty minutes the agitation was stopped and ._.——????--— ~ " the solution was allowed to stand undisturbed for fifteen minutes. At the end of fifteen minutes the mixed precipi 70 tates of zinc hydroxide and calcium sulfate had rapidly Example 1b separated from the mercury solution, forming a layer of precipitate 34 inch thick at the bottom of the beaker. The This example illustrates the leaching of a cinnabar total height of the solution was 3% inches. concentrate using calcium carbonate to form the leach The mercury leach solution was filtered by vacuum reagent and the subsequent two-step reduction of the re 75 suction with a Buchner funnel of the appropriate size 3,732,094 19 20 using a double layer of Whatman i4 qualitative cellulose to 2 hours during which time the insoluble white precipi filter paper, 11.0 centimeters in diameter. Filtration was tate of zinc hydroxide settled out of the mercury solution very rapid and the mercury leach solution of 1.130 liters leaving a nearly clear and colorless Supernatant. in volume was completely filtered and separated from At the end of two hours, the settled zinc hydroxide the mixed precipitates of zinc hydroxide and calcium precipitate occupied a volume one quarter or less of the sulfate including wash water in 3/2 minutes, total volume of the solution. The filtrate obtained was perfectly clear and colorless The solution was decanted away from the settled zinc and completely free of sodiment. hydroxide precipitate and filtered through a large Buchner EXAMPLE 3 funnel of the appropriate size under vacuum suction using O a double layer of Whatman it 1 qualitative filter paper, This example illustrates the removal of arsenic and 15.0 centimeters in diameter. The rate of filtration was other impurities from sodium tetrachloromercurate preg extremely rapid at first, but as the last portion of solution nant liquors. Separate solutions prepared in accordance containing the zinc hydroxide precipitate ran into the with the technique described above using the sodium bi Buchner, it became increasingly more difficult to filter. carbonate leach reagent and containing 163.2 grams of Filtration of the entire volume of mercury solution in mercury per liter of pregnant liquors at a pH of about cluding the wash water took about two hours and the 1.0 and containing pentavalent arsenic impurities were filtrate was perfectly clear and colorless. treated according to the following procedure: Subsequent qualitative tests on the recovered zinc hy Two separate solutions at room temperature each droxide readily indicated the presence of appreciable approximately 2.85 liters in volume and containing 465 20 quantities of arsenic on the precipitate. Subsequent reduc grams of mercury entirely as sodium tetrachloromercurate tion of the mercurate complex to elemental mercury indi (II), Na2HgCl, with a ten percent excess of free sodium cated absence of arsenic in the pregnant solution since no chloride were contained in two separate four-liter beak interference with gathering of mercury droplets was ers. Each solution contained a few milligrams of penta observed. valent arsenic as H3AsO4. 25 EXAMPLE 4 The mercury solutions were agitated vigorously with the aid of an electric stirrer and concentrated sodium This example illustrates the removal of gold and other hydroxide solution (e.g. 35%) was slowly added to the precious metals from the purified pregnant leach liquor agitated solution at intervals of about a minute in order by means of curdy mercurous chloride. The pregnant to neutralize the free acidity of the solution and to raise 30 liquor containing 114.49 gms. of mercury per liter en and adjust the pH of the solution to about 6.3. tirely in the form of the tetrachloromercurate (II) com After the addition of a small quantity of sodium hy plex, also contains 126.8 gms. per liter of free calcium droxide to the mercury solution, very large quantities of chloride. The total gold content of the pregnant mercury an orange to yellow precipitate appeared, but very readily leach solution equaled 18.3 milligrams Au/liter as cal dissolved and completely disappeared within a few sec 35 cium tetrachloroaurate(III). The catalytic promoter used onds. Further small additions of concentrated sodium hy was approximately 0.75 ml. of a specially prepared Sus droxide solution likewise produced orange to yellow pre pension of flaky mercurous chloride impregnated with cipitates which completely dissolved within a few sec finely divided metallic gold prepared in the following way: onds. If too much sodium hydroxide solution was ac Add two drops of HAuCl4 or NaAuCl4 solution contain cidentally added, the orange to yellow precipitate re 40 ing 0.26 gm. Au/milliliter to an agitated slurry of one mained permanently suspended in the agitated solution, gram of flaky mercurous chloride (HgCl), in 8.0 milli So it was necessary to add a little concentrated hydro liters of mercury leach solution containing 120 gms. Hg/ chloric acid to lower the pH sufficiently until the highly liter as CaHgCl, and 133 gms. CaCl2/liter as free calcium colored precipitate had completely dissolved. More so chloride (CaCl2). The flaky HgCl is prepared by reduc dium hydroxide was carefully added to readjust the pH. ing acidic CaHgCl, solutions with sodium hypophosphite. The pH of the mercury solution was frequently deter Add three drops of mercurous perchlorate, Hg2(ClO4)2, mined by a strip of pHydrion test paper. Before the addi solution which is 0.6 M in mercurous perchlorate and 0.5 tion of any sodium hydroxide solution, the pH of the N in perchloric acid (HClO4). Shake vigorously at fre mercury solution was about one. Frequent additions of quent intervals over a period of five minutes. A deep blue sodium hydroxide readily raised the pH and the highly slurry forms. colored precipitate appeared to remain insoluble in the By reduction of the gold in solution to the metallic solution around the pH of seven to eight. state by an agitated slurry of curdy mercurous chloride, When the pH of the mercury solution was finally ad in the presence of a specially prepared catalytic promoter, and the simultaneous adsorption of the finely divided justed between 6.0 and 6.5 as indicated by pHydrion test metallic gold on to an excess of suspended curdy mercur paper, agitation was continued as a thick slurry of zinc ous chloride precipitate, the gold was removed from the hydroxide (Zn(OH)2) preformed by mixing and vigor mercury solution. ously agitating together 200 milliliters of a zinc sulfate The filtering media for the separation of the mercurous Solution containing 144.5 gms. ZnSO4·7H2O per liter with chloride precipitate containing the adsorbed gold, from 200 milliliters of sodium hydroxide solution containing 60 the concentrated mercury solution was a Buchner fun 31.5 gms. NaOH/liter was added to the mercury solution, nel of the appropriate size, using a double layer of What a little at first to assure that the pH of the solution was man #1 qualitative cellulose filter paper, 7.0 centimeters well adjusted to the point where a suspension of zinc in diameter. hydroxide remained insoluble in the mercury solution. The color of the final mercurous chloride precipitate This was indicated by a permanent milky white turbidity. containing the gold was deep blue. When the turbidity of the mercury solution remained The exact procedure was as follows: stable, the entire 400 milliliters of thick zinc hydroxide Exactly 1 liter of pregnant mercury leach solution slurry was added to the mercury solution. (measured in 1 liter volumetric flask) containing 0.955 The solution at this point contained five grams of zinc lb. Hg/gallon or 114.49 gms. Hg/liter entirely as calcium as zinc hydroxide with about thirty percent excess zinc O tetrachloromercurate (III), CaHgCl4, the same solution ion still unprecipitated present as zinc sulfate. also containing 126.8 gms. CaCl2/liter as free calcium The milky White mercury solution containing the sus chloride, previously treated with an agitated slurry of pended slurry of insoluble zinc hydroxide was vigorously Zinc hydroxide (Zn(OH)2) for the removal of arsenic agitated for five minutes, then agitation was stopped and had a final volume of 1.160 liters and was light yellow the solution was allowed to stand undisturbed for 1/2 75 in color due to the presence of gold in the solution. 3,732,094 21 22 The purified mercury liquor had a gold concentration Both solutions, light yellow in color, were gently of 18.3 mg. Au/liter but the total gold content of the agitated with the aid of an electric stirrer, and five grams solution was 21.2 milligrams of Au as calcium tetrachloro of freshly precipitated flaky mercurous chloride, HgCl, aurate(III), Ca (AuCl4)2. prepared by mixing 10 milliliters of sodium hypophos The light yellow mercury solution was vigorously agi phite solution containing 55 gms. NaH2POHO/liter tated in a two-liter beaker with the aid of a magnetic with 100 milliliters of 2.4 N hydrochloric acid (HC) stirring apparatus, and approximately 0.75 milliliter of containing 61 gms. HgCl2/liter at 100° C., was added to a suspension of a specially prepared catalytic promoter the clear, yellow concentrated sodium tetrachloromercu composed of flaky mercurous chloride impregnated with rate (III) solution containing the gold. finely divided metallic gold was added directly to the O Agitation was continued and 25 milliliters of approxi yellow colored mercury solution. mately 1.2 N sulfuric acid solution containing 30 gms. Agitation was continued and 0.82 milliliter of 0.5 Ti/liter as Ti(SO4)3 (titanous sulfate), was rapidly N perchloric acid (HClO4) containing 200 gms. Hgatt / added to the mercury solution. A light violet colored liter as mercurous perchlorate, Hg2(ClO4)2, equal to 2.5 solution was produced for about two seconds, and almost times the stoichiometric quantity required to quantita 5 immediately, in the presence of the suspended flaky tively reduce 21.2 milligrams of gold in solution to mercurous chloride precipitate, a very splendid deep blue metallic gold, was added to the yellow colored mercury insoluble precipitate was formed. The reaction is: solution drop by drop over a period of about one minute from a one milliliter graduated serological pipette. Each drop of mercurous perchlorate added to the mercury 20 leach solution, at once precipitated white, curdy mercur The gentle agitation of the solution was continued for ous chloride, HgCl2, which was readily held in suspension 10 minutes after the addition of the gold precipitation as small particles by the vigorous agitating action of the reagents in order to keep the blue precipitate in suspension. magnetic stirring bar. At the end of this time, five milliliters of one percent About two minutes after the last addition of mercurous 25 Dow Sepran NP-20 diluted to 100 milliliters was slowly perchlorate solution, the curdy insoluble slurry of mer added to the solution to rapidly coagulate the deep blue curous chloride precipitate turned from white to a sky precipitate. The agitation was stopped and the precipitate blue color. Vigorous agitation was continued for 20 was allowed to settle. minutes during which time the mercurous chloride pre The precipitate settled rapidly after standing 15 to 20 cipitate turned to progressively darker shades of blue. 30 minutes forming a colorless and very slightly turbid super At the end of 20 minutes the mercurous chloride pre natant Solution. The nearly clear solution could not be cipitate in suspension was a splendid deep blue color. filtered in any reasonable length of time, so as much of The agitation was stopped and the deep blue turbid the clear Solution as possible was decanted away from the mercury solution was filtered with a Buchner funnel Well-coagulated blue precipitate containing the gold. of the appropriate size by vacuum suction using a double The blue precipitate was readily filtered with a me layer of Whatman #1 qualitative cellulose filter paper, dium sized Buchner funnel using a thick Whatman 7.0 centimeters in diameter. #GF/C glass fiber filter paper, 9.0 centimeters in diam The filtration rate was fairly rapid taking 8/2 minutes eter, and the clear, colorless filtrate was combined with to filter 1.160 liters of mercury solution. The filtrate the decanted part of the solution containing the mercury. still had an appreciable blue turbidity so the filtrate ob 40 Subsequent recovery tests on the deep blue precipitate tained was refiltered over the residue on the filter paper readily produced a pure and yellow residue of metallic from the first filtration. The second filtration took 16 gold. minutes for 1.160 liters of mercury solution. The mercury EXAMPLE 6 solution filtrate after the second filtration was perfectly clear and colorless and free of all traces of blue turbidity This example illustrates the removal of gold and other and any yellow color due to gold in solution. Subsequent 45 precious metals from purified pregnant solutions prepared treatment of the blue precipitate produced a yellow resi by the sodium bicarbonate deach method. The sodium tet due of metallic gold. rachloroaurate complex is separated from the pregnant The catalytic promoter was prepared in the following liquor by means of reaction with ferrous sulfate in the way: add two drops of a solution of HAuCl4 or NaAuCl4 presence of a mercurous slurry according to the following containing 0.26 gm. Au/milliliter to an agitated suspension 50 overall equation: of one gram of flaky mercurous chloride in 8.0 milliliters of mercury leach solution containing 454 gms. Hg/gallon as free calcium chloride (the flaky HgCl is prepared by Duplicate solutions, each approximately four (4) liters reducing acidic CahgCl, solutions with sodium hypo in volume and each containing approximately 455 grams phosphite). 5 5 of mercury as sodium tetrachloromercurate, were con Add three drops of 0.5 N perchloric acid solution con tacted with five (5) grams of flaky mercurous chloride. taining 200 gms. Hg2+ /liter as Hg2(ClO4)2. Shake vig To each duplicate solution was added ten (10) ml. of so orously at frequent intervals over a period of five minutes. dium hypophosphite-liter and 100 ml. of 2.4 N hydro chloric acid at 100° C. Agitation was continued for twenty EXAMPLE 5 60 (20) minutes, after which the reaction mixture was fil tered to separate precipitated mercurous chloride and This example illustrates removal of gold and other metallic gold. The exact procedure followed is set forth precious metals from pregnant liquors by means of below. precipitation of titanous hydroxide by hydrolysis of Two separate mercury solutions approximately four titanous sulfate, and subsequent precipitation of gold by (4) liters in volume; each solution containing approxi the titanous hydroxide in the presence of mercurous mately 455 grams of mercury entirely as sodium tetra chloride. chloromercurate (III), Na2HgCl4, and a small quantity of Two separate mercury solutions previously treated with free sodium chloride, contained 107.3 and 114.0 milli a slurry of zinc hydroxide (Zn(OH)2) to remove arsenic, grams of gold respectively as sodium tetrachloroaurate and approximately four liters in volume, each solution O (III), NaAuCl4 containing approximately 445 grams of mercury entirely Both separate solutions were yellow in color and were as sodium tetrachloromercurate (II), Na2HgCl4, and a agitated with the aid of an electric stirrer. While the agi small quantity of free sodium chloride, contained 104.3 tation continued, five (5) grams of freshly precipitated and 112.3 milligrams of gold respectively as sodium flaky mercurous chloride, Hg2Cl2, prepared by mixing ten tetrachloroaurate (III), NaAuCl4 75 (10) milliliters of sodium hypophosphite solution contain 3,732,094 23 24 ing 55 grams NaH2PO2·H2O/liter with 100 milliliters solution. About 2 ml. of clear supernatant was treated of 2.4 N hydrochloric acid (HCl) containing 61 grams with a drop or two of stannous chloride solution to verify HgCl/liter at 100° C., was added to the clear yellow whether or not precipitation was complete. When the concentrated mercury solution containing the gold. addition of stannous chloride solution failed to produce Agitation was continued and 25 milliliters of approxi any trace of precipitate and the test solution remained mately 0.5 N sulfuric acid (H2SO) containing 204 grams perfectly clear, a stoichiometric volume of stannous chlo FeSO4·7H2O/liter was rapidly added to the mercury solu ride solution had been added to the 1.7 liters of mercury tion. After the addition of the ferrous sulfate solution (fer solution in the beaker to quantitatively reduce all of the rous chloride, FeC may be subsituted for FeSO4 if de sodium tetrachloromercuate (II) to an insoluble white sired) in the presence of the suspended slurry of flaky O precipitate of mercurous chloride. mercurous chloride, the concentrated mercury Solution The agitation was stopped and the very thick white within a short period of time turned from yellow to color slurry of mercurous chloride was very readily filtered less. with a large Buchner funnel using Whatman # 1 filter Within five (5) minutes after the addition of the gold paper under vacuum Suction. precipitation reagents with continued agitation, a dark 5 The entire process was carried out completely at room gray insoluble suspension with a slight tint of blue was temperature. formed. Agitation of the solution containing the gray Sus The mercurous chloride filter cake in the Buchner fun pension was continued for 20 minutes. nel was washed several times with small portions of 0.3 At the end of 20 minutes, the agitation was stopped N sulfuric acid in order to wash out as much stannic and the mercury solution was allowed to stand for at 20 chloride as possible from the filter cake, and these wash least one hour undisturbed, but after the first 20 min ings were combined with the major portion of the filtrate. utes of standing the dark gray insoluble suspension had Below is a summary of the data obtained from the re almost completely settled out of the mercury solution duction of sodium tetrachloromercurate (II) solutions forming a thin layer on the bottom of the beaker. The 0.3 N in Sulfuric acid, with a stannous chloride solution mercury solution at this point was very turbid with 25 entirely at room temperature: a finely divided brown suspension of metallic gold. After standing for at least an hour the brown gold Suspension began to settle out of the solution, leaving a clear and Rull umber (i) M.2 1.7 12 colorless mercury solution above the upper surface of 17 215 mercury solution still very turbid with the brown 30 7 200 suspension. 7 206 After standing for one hour, the solution was filtered 7 208 1 Volume of sodium tetrachloromercurate (I), Na2HgC used, in with a Buchner funnel of the appropriate size using What liters (i.7 liters colltaining 183 to 200 gums. of mercury). man iGF/C thick glass fiber filter paper, 9.0 centimeters 2 Stoichometric volumo of SnCl2 solution required to quantitatively in diameter. precipitate. HgCl2 from 1.7 liters of Na2HgCl, Solution. Approximately The filtration rate was extremely rapid and the turbid 482.6 gins. SnCl4/liter 3.5 N in HCl. brown suspension of gold was readily retained on the fil EXAMPLE 8 ter paper. The gray precipitate was likewise rapidly fil This example illustrates the precipitation of mercurous tered and the mercury solution filtrate was clear and color chloride from calcium tetrachloromercurate complex solu less, and completely free of all traces of brown turbidity. 40 tions by means of an alkali metal hypophosphite reduc EXAMPLE 7 ing agent. The overall equation is: This example illustrates the precipitation of mercurous HCl chloride from a solution of sodium tetrachloromercurate, NaH2PO -- 4CaHgCi - 2HO ---> employing a stannous chloride reducing agent. The overall 70°-80°C, equation is 4 CaCl2 -- 2EHg2Cl2 -- NaCl -- 3HCl -- EH3PO4 0.3NSO To a pregnant leach liquor prepared from a Mexican SnCl -- 2NaHgCls --> Ng Cl; -- Na2SnCls -- 2NaCl cinnabar concentrate, which was leached according to the Each of five separate solutions 1.7 liters in volume and process of Example 1 containing 114.49 grams Hg/liter each containing 183 to 200 grams of mercury entirely 50 was added 13.1 ml. of a reagent grade 38% hydrochloric as sodium tetrachloromercurate (II), Na2HgCl, in the acid in sufficient quantity to convert the sodium hypo presence of a small quantity of free sodium chloride were phosphite monohydrate to hypophosphorous acid each separately acidified to 0.3 N by the addition of 15 (HPO) ml. of 96 percent sulfuric acid. Each separate solution was contained in a three-liter 5 5 plus 10% stoichiometric excess of hydrochloric acid. 50 beaker and vigorously agitated with the aid of an elec ml. of 2.95 M sodium hypopohphite solution was added tric stirring apparatus. to the liter of pregnant leach liquor and the reduction was Supported above the three-liter beaker was a 250 ml. carried out at a temperature ranging from 68 C-83 C. burette clamped into position vertically above the beaker. A 5% stoichiometric excess of sodium hypophosphite was The burette was filled completely with stannous chloride 60 required to reduce the tetrochloromercurate complex to solution which was 3.5 N in hydrochloric acid and con mercurous chloride. Separation of the flaky mercurous taining approximately 482.6 gms. SnCl2/liter of Solution chloride precipitate was accomplished by means of filtra (approximately 2.5 M). tion through a Whatman it 1 filer paper. During vigorous agitation, the stannous chloride solu The exact details of the procedure are set forth below. tion was added rapidly from the burette at first, and a pure Exactly one liter (1000 ml.) of pregnant mercury white precipitate of mercurous chloride (HgCl2) was leach liquor containing 0.955 lb. Hg/gallon or 114.49 formed immediately, turning the solution a milky white. gms. Hg/liter as the very soluble calcium tetrachloro As the addition of stannous chloride solution from the mercurate (III) CaHgCl4 complex in the presence of a burette was continued, the mercurous chloride slurry considerable quantity of free calcium chloride, was pro thickened to such an extent that a considerably more wig duced by chlorinating a mercuric sulfide (cinnabar) con orous agitation with the electric stirrer was necessary. centrate in the presence of calcium hydroxide, and the After a considerable quantity of stannous chloride solu leach liquor formed was then treated to remove arsenic tion had been added, the vigorous agitation was stopped and gold. The slightly diluted pregnant liquor had a final and the slurry was allowed to settle forming a one-quarter volume of 1160 ml. (1.160 liters) after chemical treat inch layer of clear Supernatant at the top Surface of the IIlent. 3,732,094 25 26 The slightly diluted pregnant leach liquor was clear monohydrate was sufficient to precipitate 95% of the and colorless after chemical treatment, and 13.1 ml. of available mercury in solution as mercurous chloride concentrated analytical reagent 38% hydrochloric acid, (Hg2Cl2). 57.3 grams of sodium hypophosphite was a quantity of acid equivalent to 15.62 grams of sodium added to the vigorously agitated sodium tetrachloromer hypophosphite monohydrate as hypophosphorous acid curate (II) solution at 80 C. as follows: 23 ml. of dilute sodium hypophosphite solution containing 100 grams (H3PO) NaH2POHO/liter (actually added 2.3 grams of including a 10% excess of hydrochloric acid, was added NaH2POH2O). Within 30 seconds a snow-white precipi to the pregnant leach liquor, and was then heated to 70 tate of mercurous chloride (HgCl2) readily precipitated. with vigorous agitation. 10 Next, 220 milliliters of sodium hypophosphite solution To the hot, acidic, vigorously agitated and slightly containing 250 grams NaH2POHO/liter was added to diluted leach liquor, 50 milliliters of a concentrated solu the vigorously agitated hot solution slowly over a period tion of sodium hypophosphite containing 312.4 gms. of about 5 minutes. NaH2PO HO/liter The temperature was raised to a maximum of 90° C. 5 after the addition of the last of the concentrated sodium was added slowly to the liquor over a period of about hypophosphite solution, and the very thick mercurous five minutes. The sodium hypophosphite solution added chloride slurry was vigorously agitated for an additional contained a sufficient quantity of sodium hypophosphite 15 minutes before being allowed to cool. monohydrate (15.62 grams) to quantitatively reduce and The resulting precipitate of mercurous chloride precipitate 114.49 grams of mercury as calcium tetra 20 (Hg2Cl2) was a very bright snow-white precipitate con chloromercurate (II) to an insoluble precipitate of mer sisting entirely of very small flaky particles, began im curous chloride, HgCl2, including a 5% excess of Sodi mediately to settle from the supernatant solution after um hypophosphite over the stoichiometric quantity re the vigorous agitation was stopped. quired for quantitative reduction. The supernatant above the settled mercurous chloride After the sodium hypophosphite solution had been 25 was a turbid white suspension consisting of finely di completely added, vigorous agitation was continued for vided mercurous chloride. 20 minutes, during which time the temperature rose to Each of the two separate batches of precipitated mer a maximum of 83 C. and after 20 minutes of agitation, curous chloride were allowed to stand for about 12 hours the solution and slurry hit a low of 68 C. before filtering. Filtration was carried out under vacuum During the reduction and precipitation process, the 30 suction, using a Buchner funnel and Whatman regular mercurous chloride separated from the hot solution as a cellulose filter paper. thick almost snow-white slurry in the form of small flakes Both separate batches of flaky mercurous chloride fil which, toward the end of 20 minutes of agitation, darkened tered at an extremely rapid rate, requiring no more than slightly. 5 minutes to filter to a “dry” filter cake. Each of the two The hot solution containing the flaky mercurous chlo 35 batches of mercurous chloride filter cakes were washed ride precipitate was filtered completely in five minutes by free of excess soluble salts with 800 milliliters of tap vacuum filtration through a small Buchner funnel using Water. Whatman it 1 qualitative cellulose filter paper, 7.0 cen The filtrate resulting from the filtration was prefectly timeters in diameter. The mercurous chloride filter cake clear and colorless. was washed with about 100 ml. of deionized water to re 40 EXAMPLE 10 move most of the soluble impurities in the filter cake such as chlorides and phosphates. This example illustrates the leaching of cinnabar ore The filtrate obtained was clear and colorless at first concentrates using sodium bicarbonate to form the leach but soon acquired a milky white turbidity and an ap reagent. The fundamental equation is: 45 preciable quantity of white mercurous chloride precipitate 10% excess of NaHCO3 settled to the bottom of the filtering flask, which was HgS + 8 NaHCO3 + 4 Clº allowed to stand undisturbed until it was certain that all Na2HgCl4 -- 4 NaCl -- Na2SO4 + 4 H2O -- 8 CO2 f of the soluble mercury in solution had been quantitatively reduced to mercurous chloride. The exact prodecure is described below: After approximately 20 hours of standing a consider (1) Used a Mexican cinnabar ore concentrate contain able quantity of mercurous chloride had precipitated out ing mercury as red mercuric sulfide. of the solution and was recovered by filtration through a (2) Weight of concentrate leached=96 grams. small Buchner funnel in the usual manner. (3) Mercury content of Mexican cinnabar ore concen trate = 64,4% mercury. EXAMPLE 9 5 5 (4) Weight of mercury contained in 96 grams of con This example illustrates the precipitation of HgCl2 centrates--61.82 grams. from sodium tetrachloromercurate solutions by means (5) Volume of water added to mixture of ore concen of a sodium hypophosphite reduction reagent. The fun trate and sodium bicarbonate prior to chlorination=400 damental equation involved is: milliliters. 80°C 60 (6) Highest recorded temperature during the leaching NaH2PO -- 4 Na2HgCl4 - 2H2O Hic process=63 C. (7) Lower temperature recorded prior to leach 2 Hg2Cl2 J -- 9 NaCl -- 3 HCl -- H3PO4 ing-21 C. Two separate solutions approximately 4 liters in volume (8) Color of Mexican concentrate residue after leach each, and each separate solution containing 465 grams of ing: brown. mercury entirely as sodium tetrachloromercurate (II) (9) Color of Mexican ore concentrate prior to leach (Na2HgCl) and a 10% excess of free sodium chloride ing: red. was heated to 80° C. with vigorous agitation. Fifty mil (10) Leaching time: liliters of concentrated analytical reagent grade 38% hy (a) First chlorination leaching of cinnabar ore concen drochloric acid was added to the vigorously agitated solu 70 trate using a quantity of sodium bicarbonate exactly tion, a quantity of acid equivalent to 57.3 grams of so stoichiometric to the mercury contained in the ore con dium hypophosphite monohydrate, (NaH2PO2H2O) as centrate=65 minutes. hypophosphorous acid, HPO, with an overall 10% ex (b) Second chlorination leaching of cinnabar ore con cess of hydrochloric acid also present. centrate after the addition of 10% excess of powdered The quantity of 57.3 grams of sodium hypophosphite 75 sodium bicarbonate=10 minutes. 3,732,094 27 28 A quantity of a red Mexican cinnabar ore concentrate tion leaching using sodium bicarbonate is given in the weighing exactly 96 grams and containing 64.4% mer following table: cury as mercuric sulfide, HgS, was placed in a one Material or Operation liter glass beaker, and 207.5 grams of powdered U.S.P. Weight of Mexican cinnabar ore concentrate sodium bicarbonate, NaHCO3, a quantity stoichiometric 5 to the weight of mercury contained in the concentrate, Was eached, grams ------96.0 added to the beaker. Mexican cinnabar ore concentrate, percent A volume of 400 milliliters of tap water was added to CrCly ------64.4 the mixture and, with the aid of an electric stirrer, the Weight of mercury contained in 96 grams of liquid contents were vigorously agitated, forming a mixed O cinnabar ore concentrate, grams ------61.82 slurry of ore concentrate and sodium bicarbonate. A cen Volume of pregnant mercury leach solution tigrade thermometer was placed in the beaker to record recovered, milliliters ------569 the temperature at regular intervals. Volume of wash liquid, milliters ------579.5 Chlorine gas, supplied under pressure from a 15-pound Time required to separate pregnant mercury tank of commercial grade liquid chlorine was continuous 5 leach solution from insoluble residue (tails), ly added at a rapid rate to the agitated slurry through a by filtration, minutes ------45 glass tube running into the slurry and reaching to within Time required for wash water to pass through an inch of the bottom of the leaching vessel, the open end the brown, insoluble filter cake (tails), by of the tube attached to a fritted glass gas diffuser plug of filtration, minutes ------17 coarse porosity, designed to diffuse the chlorine gas into 20 Mercury concentration in pregnant leach solu the agitated slurry as fine bubbles. Prior to chlorination, 1On: the agitated slurry was reddish pink in color, but as chlo (a) Gms. Hg/liter ------106.6 rination continued, the reddish-pink color of the slurry (b) Lbs. Hg/gallon ------0.89 rapidly faded and became brown. During chlorination, Mercury concentration in wash liquid: large red foamy bubbles of carbon dioxide, CO2, rapidly 25 (a) Gms. Hg/liter ------0.615 gathered above the aqueous slurry in a layer of about (b) Lbs. Hg/gallon ------0.0051 three inches in thickness and it was necessary at first to Insoluble brown residue (tails) remaining after break the bubbles to prevent them from spilling over the leaching: top of the beaker. After about 20 minutes of chlorination, (a) Weight of insoluble residue (tails), the height of the red bubble layer was about two inches; 30 Sans ------23.839 and, after this period of time, the height of the layer of (b) Lbs. Hg/ton in insoluble residue ---- 30.1 foamy bubbles readily declined. The color of the foamy (c) Percent mercury in insoluble brown layer rapidly faded, turning from a deep red to pale pink residue (tails) ------1.5 after about 35 minutes of chlorination. The bubble layer Highest temperature reached during chlorina was only about 14 inches thick and nearly white after 40 tion leaching, degrees centigrade ------63 minutes of chlorination (or leaching). Lowest temperature of slurry prior to leaching, The highest temperature reached during the chlorina degrees centigrade ------21 tion leaching process was 63 C. but after 40 minutes of pH of leaching solution: chlorination, the temperature began to steadily decline. (a) Agitated slurry prior to chlorina The escape of free chlorine gas from the leaching ves 40 tion ------8.0 sel was checked at regular intervals by discharging a (b) After chlorination leaching, final stream of ammonia from a plastic squirt bottle containing pregnant mercury leach solution ----- 5.0 a little concentrated ammonium hydroxide solution. When Weight of mercury in pregnant leach solution, ever free chlorine was present, a white smoke was pro TaII1S ------? - ?? ?? ------60.66 duced in relatively large quantities. Weight of mercury in wash water, grams ---- 0.36 Chlorination was allowed to continue for a total of 65 Total weight of mercury recovered by leach minutes. ?ing gramS ------6.02 After this period of time, ammonia vapor gave very Weight of mercury in 23.839 grams of brown considerable quantities of white smoke, so the leaching insoluble residue (tails), grams ------0.36 was stopped, and the brown slurry in the beaker was Percent mercury recovered from Mexican ore allowed to cool to room temperature. concentrate by chlorination leaching ------98.7-99.4 When cooled to room temperature, the brown slurry Weight of sodium bicarbonate (NaHCO) was vigorously agitated and a 10% excess of powdered used in chlorination leaching of mercury ore sodium bicarbonate (20.8 grams) was added to the aque COIlCeiltrate: ous slurry. A rapid and steady stream of chlorine gas was (a) Weight stoichiometric to total mer conducted into the agitated slurry for 10 minutes before 5 5 cury content of ore concentrate, ammonia vapor revealed the presence of large quantities SS ------207.5 of free chlorine gas escaping from the leaching vessel. (b) 10% excess of sodium bicarbonate, SS ------20.8 Chlorination was stopped, but the brown slurry was agi Leaching time: tated for an extra ten minutes to assure that the oxidation 60 (a) First chlorination leach, with 207.5 of the mercuric sulfide content of the ore concentrate was grams of Sodium bicarbonate, min reasonably complete. "* ------65 The brown slurry was filtered into a Buchner funnel of (b) Second chlorination leach, with 20.8 the appropriate size using a double layer of Whatman grams of Sodium bicarbonate (10% ex #GF/A glass fiber filter paper, 7.0 centimeters in diam cess), minutes ------O eter under vacuum suction. A clear, but deep yellow filtrate was obtained which, after standing for a few hours, EXAMPLE 11 became turbid with a yellow suspension. The yellow sus pension Settled out, forming a yellowish-red rust-colored The example illustrates leaching of cinnabar ore con sediment, and leaving a clear and colorless pregnant 70 Centrates employing calcium hydroxide to form the leach mercury leach solution behind. The brown filter cake of reagent. The fundamental equation is: insoluble residue (tails) was then washed with several portions of pure water. Hgs + 4Ca(OH). + 4C, F**Excess ***):of Ca(OH A complete Summary of results obtained by chlorina 75 CaHgCl + 2CaCl2 -- CaSO4·2H2O 2H2O 3,732,094 29 30 The exact procedure followed is described below: various shades of pink and orange-ish yellow, then grew A Mexican cinnabar ore concentrate was chlorinated paler in color, as leaching continued, until finally after and leached in an especially designed piece of equipment 1/2 hours of leaching, all noticeable color had disappeared consisting of a 250-gallon capacity all fiberglass vat Sur completely, leaving a suspended slurry which was a light rounded by an all stainless steel cooling jacket containing gray in color. a coil of titanium tubing about 400 feet in length placed After chlorination was stopped, the contents of the within the cooling jacket and a centrifugal pump attached leaching apparatus was allowed to agitate for a few min to the bottom outlet of the vat by a plastic pipe, designed utes extra, and the slurry was then pumped from the to draw in agitated liquid slurry and pump it under pres leacher into a large pan filter of 50-gallon capacity with sure through the 400-foot length of titanium tubing while O a filtering area of 1,090 square inches (7.57 square feet), introducing a very rapid, steady and continuous stream under vacuum suction. The pan filter was filled to ca of elemental chlorine gas through an especially designed pacity. inlet located just a few inches past the discharge outlet Filtration was rapid, and after each 50-gallons of slurry of the pump and attached to the lower end of the coiled filtered, the gray filter cake was removed from the pan titanium tubing. The upper end of the coiled tubing was 5 filter before further filtering was attempted to greatly attached to a plastic pipe, the open end reaching to within decrease the total time required to separate the pregnant six inches of the bottom of the leaching vat. mercury leach solution from the insoluble residue. Under An electrically driven paddle agitator provides the these conditions, filtering of 200 gallons of slurry took necessary agitation required to maintain a suspended, only about 1% hours to complete. The pregnant mercury mixed slurry of calcium hydroxide and cinnabar ore con 20 leach solution filtrate was colorless and only very slightly centrate turbild. The ore concentrate, weighing approximately 155 The pregnant mercury leach solution contained approxi pounds and containing 64.4% mercury as red mercuric mately 68.9 grams CaCl2/liter as free calcium chloride sulfide, HgS (with about 100 pounds of contained mer and 0.52 lb. Hg/gallon or 62.3 grams Hg/liter, and the cury), was dumped into the leach vat containing 150 to final portions of wash water contained 0.0022 lb. Hg/ 200 gallons of tap water. Two 50-pound sacks of com gallon. The light gray tails residue remaining after leach mercial hydrated lime (calcium hydroxide) were emptied ing and washing contained 15.5 lbs. Hg/ton, with an over into the leaching vat as a dry powder containing the agi all recovery of 99.2% of the total mercury contained in tated slurry of cinnabar ore concentrate, and when well the original concentrate. mixed, a very rapid, steady and continuous stream of ele 30 mental chlorine gas under pressure was added to the EXAMPLE 12 mixed slurry of calcium hydroxide (Ca(OH)) and cin This example illustrates the reduction of the solid nabar ore concentrate through the chlorine inlet of the mercurous chloride produced in Step 1 of the reduction leaching apparatus. The chlorine gas used for leaching process (Stage 3) to elemental mercury employing the was the regular commercial grade chlorine supplied as a 35 Stannous chloride reducing agent solution. The funda liquid in one-ton cylinders of steel. mental equation involved is: The pH of the mixed slurry prior to chlorination was 11.0. 3.5N HCl Hg2Cl2 + SnCl2 - --> 2 Hgº! -- SnCl During the first few minutes of very rapid chlorina -- 2.5M SnCl2 or greater gº tion, there was a gradual drop in pH over a ten-minute 40 period to a level pH of between 9.0 and 9.5. Rapid chlori The exact procedure followed is described below: nation was continued for about 20 to 30 minutes, after Five separate, but equal, quantities of mercurous chlo which time the pH began to rapidly drop below 9.0, and ride were each reduced and precipitated from sodium a third 50-pound sack of hydrated lime was added. The tetrachloromercurate (II) solutions with stannous chlo pH was once again restored to between 9.0 and 9.5 and ride (SnCl2) and obtained as a filter cake as in the pre chlorination was continued. 45 vious examples and were reduced in sequence to metallic The pH of the agitated slurry during leaching held mercury as the final product of the process. steady for about one hour between 9.0 and 9.5, but after Each separate quantity of mercurous chloride was about 45 minutes of leaching, it was necessary to cut the placed in a 1-liter glass beaker, and 250 milliliters of 3.5 chlorination rate down appreciably because some free N hydrochloric acid (HCl) containing approximately chlorine gas was escaping from the surface of the agitated 50 482.6 grams SnCl2/liter was added at room temperature slurry in the leaching vat. Free chlorine was detected by to the white mercurous chloride in the beaker. The quan discharging a stream of ammonia from a plastic squirt tity of stannous chloride contained in 250 milliliters of bottle containing a little concentrated ammonium hy Solution (approximately 120.7 grams) was such that at droxide solution. Whenever free chlorine was present, a least a 25% excess of stannous chloride (SnCl) was White Smoke was produced in relatively large quantities. 55 always present over the stoichiometric quantity required At this point the rate of chlorination was always cut down to reduce the mercurous chloride quantitatively to metallic until no white smoke could be produced. mercury. After one hour of chlorination, the pH dropped below When the stannous chloride solution was added, the 9.0 for a second time, and about 30 pounds of additional beaker was placed on a hot plate under vigorous agitation hydrated lime was added to the vatto bring the pH up 60 With the aid of an electric stirrer. At first, a thick black again to between 9.0 and 9.5. The chlorination rate was slurry was formed in the beaker. relatively low for the last 30 minutes of leaching. The As soon as the stannous chloride was added at room slow chlorination rate was continued, and during this temperature, and under the influence of vigorous agitation, period of leaching, the pH gradually but steadily began to the slurry was rapidly raised to a temperature of 950 to decline to below 9.0. After 30 minutes the pH was down 65 100 C. and remained there until the mercurous chloride to 6.4 and the chlorination was stopped. had been quantitatively reduced to metallic mercury. During the entire leaching operation, the temperature At near boiling temperatures, the bulk of the mercurous of the agitated slurry was never allowed to exceed 400 C. chloride, HgCl2, was rapidly reduced to metallic mercury within the first 15 to 30 minutes, with the formation of a Whenever this temperature was exceeded, cold water was 70 heavy pool of tarnished metallig mercury on the bottom circulated through the cooling jacket as required to keep of the beaker and the solution was very turbid with a the temperature down. Suspended light gray material. During the chlorination procedure the agitated slurry As agitation continued at a high temperature, the light was reddish-pink at first, but as time went on, and chlori. gray turbidity gradually disappeared from the solution nation continued, the color of the slurry changed through 75 and, after 1/2 hours, the solution was Very nearly clear 3,732,094 3. 32 but yellow in color. The large pool of metallic mercury tratively, by the techniques of Examples 7-9, was added at the bottom of the beaker was very fluid and had a very in small pieces to the hot solution. After about 1 hour and bright silvery appearance. Agitation was stopped at this 20 minutes under agitation and between 95 to 100 C, point. the mercurous chloride was reduced almost quantitative The clear, yellow solution was decanted from the pure, ly to metallic mercury. liquid metallic mercury as much as possible and the re 5 mainder of the solution was separated completely from EXAMPLE 1.4 the mercury with the aid of a 30-milliliter separatory This example further illustrates the reduction of the funnel with a Teflon stopcock. The mercury was washed solid mercurous chloride produced in Step 1 of the re and then filtered to remove slight traces of surface impuri O duction process (Stage 3) to elemental mercury em ties. The final weight of metallic mercury obtained in all ploying Solutions of sodium hypophosphite as the reduc 5 cycles combined was 917.1 grams. ing agent. The fundamental equation involved is: HCl equivalent to EXAMPLE 13 NaH2PO as H3PO a This example illustrates the reduction of the solid 5 A959 to 110°C mercurous chloride produced in Step 1 of the reduction process (Stage 3) to elemental mercury employing solu 4Hgº -- NaCl -- 3HCl -- HIP O tions of sodium hypophosphite as the reducing agent. The Two separate portions of mercurous chloride (HgCl) filter cake, each containing approximately 114 grams fundamental equation involved is: of mercury, were reduced and precipitated from a preg HCl equivalent to 20 NaHPO as HPO. nant calcium tetrachloromercurate (II) leach solution as NaH2PO -- EIgCl2 + 2HO ------??? described above. Each separate portion was then reduced to metallic mercury as the final end product of the process. In the first test, a volume of 250 milliliters of 2.5 4Hgº -- NaCl -- 3HCl -- HIP O molar hydrochloric acid and 2.5 molar in sodium hypo The exact procedure followed is described below. 25 phosphite (NaH2PO2) containing 265 gms. Two separate but equal quantities of mercurous chlo ride (HgCl), each containing approximately 442 grams NaH2PO HO/liter of mercury, were reduced and precipitated from sodium and 125 gms. CaCl/liter as free calcium chloride tetrachloromercurate (II) solutions with sodium hypo (CaCl2) was introduced into a 600 milliliter beaker. phosphite (NaH2PO) and obtained as a filter cake in the 30 The beaker containing the reducing solution was placed previous examples and were reduced in sequence to metal on a hot plate and the temperature was rapidly raised lic mercury as the final product of the process. to near boiling, under vigorous agitation with the aid A volume of 345 milliliters of sodium hypophosphite of an electric stirrer. The mercurous chloride was added solution containing 50 gms. NaH2POHO/liter, together 35 to the hot solution by a spatula over a period of 5 to 10 with 72 milliliters of concentrated hydrochloric acid minutes and the temperature was maintained between (HCl), and 26.8 grams of sodium chloride (NaCl) were 100 and 105 C. A thick, black slurry was formed im mixed and diluted to a final volume of 1 liter in a 2-liter mediately, and after the first 15 minutes of agitation, a beaker. The solution contained a 50% excess of sodium pool of metallic mercury had collected on the bottom hypophosphite (NaH2PO2) over the stoichiometric quan 40 of the beaker. tity required to quantitatively reduce a sufficient quantity The agitated slurry turned from black through various of mercurous chloride to produce 442 grams of metallic shades of gray and, after 45 minutes, the temperature mercury. The solution contained a 10% excess of hydro was dropped to 95 C. A light gray slurry remained chloric acid (HCI) over the quantity equivalent to sodium Suspended in the hot solution. Gentle agitation was main hypophosphite as hypophorous acid (H3PO2). 45 tained at a temperature of 95° C. to 100° C. for the The beaker containing the reducing solution was placed time remaining-25 minutes. on a hot plate and vigorously agitated. The temperature of After 1 hour and 10 minutes, the agitation was stopped the solution was rapidly raised to near boiling and the and the solution was decanted away as much as possible mercurous chloride filter cake, broken up into many small from the liquid metallic mercury and the light gray pieces, was added directly to the hot solution. Vigorous crystalline solid salts accompanying the mercury. Pure agitation was continued and the slurry was maintained at water was added to the metallic mercury in the beaker a temperature from 95 to 100° C. during the reduction, and dissolved completely the solid salt residue almost and formation of metallic mercury. When the mercurous immediately. chloride was first added to the hot solution, a thick black The pure mercury was washed thoroughly and dried. slurry was formed in the beaker. Within 20 to 30 minutes, 5 5. The weight of mercury obtained was 110.73 grams. large pools of metallic mercury gathered at the bottom of In the second test, the mercury was placed back in the the beaker and the hot solution was very turbid with a reducing Solution and, with gentle agitation, the tempera suspended gray material. ture was rapidly raised to 105 C. and the small quantity Agitation at a high temperature was continued for 1. of mercurous chloride residue recovered after 20 hours hour, after which time the hot solution was nearly clear 60 from the leach solution was added to the hot reducing and colorless. A bright silvery white pool of metallic Solution. Agitation was allowed to continue for 15 mercury remained on the bottom of the beaker. minutes at 105 C., during which time the additional The solution, after cooling, was separated from the mercurous chloride was very rapidly reduced to metallic metallic mercury as much as possible by decantation and mercury, leaving a clear, colorless solution. the mercury was washed with pure water, then dried, and 65 The metallic mercury was washed and passed through filtered to remove slight traces of surface impurities. a 30 milliliter separatory funnel to free it from surface The decanted solution from the first reduction was impurities. adjusted in composition by adding 305 milliliters of sodi The final weight of pure, metallic mercury obtained um hypophosphite containing 50 gms. NaH2PO2-H2O/liter was 111.94 grams, corresponding to 97.8% of the total and 50 milliliters of concentrated hydrochloric acid. The mercury content of the original leach solution, recovered solution was diluted with deionized water to a final volume as metal. of at least 1 liter or slightly more. The solution was now EXAMPLE 1.5 ready for the second reduction. This example illustrates the recovery of tin as a tin The solution was agitated and heated to near boiling metal sponge from the barren mother liquor from the and the mercurous chloride filter cake, prepared, illus reduction steps of Stage 3 in which the preferred stan 3,732,094 33 34 nous chloride reduction reagent was employed. The EXAMPLE 16 fundamental equations involved are: This example further illustrates the recovery of tin as a tin metal sponge from the barren mother liquor from Ni 3Na2SnCls -- 4Al --> 6NaCl - 4ACls -- 3Sn the reduction steps of Stage 3 in which the preferred stan ExceSS NaCl 5 nous chloride reduction reagent was employed. The funda mental equations involved are: 0.3 NinC 3CaSin Cls + 4Alº -> 3CaCl2 + 4Al Cl3 -- 3Snº large excess of free The exact procedure employed is described below: O CaCl2 Each of five separate filtrates containing tin entirely as sodium hexachlorostannate (IV), Na2SnCls, obtained as the result of the precipitation of mercurous chloride The exact procedure employed is described below: from acidic and concentrated solutions of sodium tetra A typical filtrate, 0.3 N in hydrochloric acid (HCl), chloromercurate (II), Na2HgCl, by reduction with 15 and containing tin equivalent to 114 gms. Hg/liter after the stannous chloride, SnCl2, in sequence as in the previous reduction of the calcium tetrachloromercurate (III) con examples were placed in 3-liter beakers. tent to mercurous chloride, Hg2Cl2, contained 33.7 gms. The filtrate was clear and colorless and 0.3 N in Sul Sn/liter entirely as calcium hexachlorostannate (IV), furic acid (H2SO4). Each separate filtrate had a volume CaSnCls, and 157.7 gms. CaCl2/liter as free calcium chlo between 2.5 and 3 liters. Thirty (30) milliliters of con 20 ride, CaCl2. centrated 96% technical sulfuric acid was added to each A 60 milliliter portion of the calcium hexachlorostan separate solution in order to raise the acidity level to nate (IV) solution was contained in a 100-milliliter approximately 0.6 N sulfuric acid. In addition, each beaker. A rod of metallic aluminum 4% inches long and solution was about 0.2 N in hydrochloric acid (originat /2 inch in diameter was placed in the solution. A total ing from the addition of approximately 200 milliliters 25 area of 17.3 square centimeters of rod surface was exposed of stannous chloride solution, 3.5 N in hydrochloric acid to the solution. to accomplish the reduction of Na2HgCl4 to HgCl2). A vigorous reaction occurred almost immediately after Four (4) etched metallic aluminum rods, each about the rod was dipped into the solution and the entire ex 10 inches long and 2 inch in diameter, Were placed in posed rod surface was very rapidly covered with a very each of the five separate solutions with the rods be 30 loose, porous, and spongy layer of metallic tin. The for tween each other in such a fashion that every other rod mation of needle-like deposits of tin and deposits in the pointed in the same direction (X pattern). The same shape of bird feathers also accompanied the spongy four aluminum rods were used in all five separate solu variety. Considerable quantities of hydrogen gas were tions. liberated during the first few minutes of the reduction When the rods were first placed in each solution there 35 and the solution darkened considerably. A considerable was a vigorous reaction almost at once and large de quantity of heat was liberated during the reaction, and posits of very porous, spongy metallic tin Soon formed the temperature of the solution steadily increased from a coating several centimeters thick over the entire sub 24.0° C. to a maximum of 59.5° C. in a period of about 6 merged area of each rod. There was a vigorous evolution minutes. of hydrogen gas at the same time and a considerable 40 Frequent agitation and stirring readily separated the quantity of heat was liberated during the reaction. thick layer of spongy tin from the rod, with the immediate Occasionally, during the reduction, it was necessary formation of a new layer of metallic tin on the rod. After to remove the thick, spongy deposit of tin from the 10 minutes, with frequent agitation, almost all of the tin. aluminum rod. To do this, each rod was rapidly pulled in the solution had been reduced to the metallic state. out of the spongy tin, leaving a rod-shaped deposit of 45 Only small quantities of tin were deposited on the rod tin behind with a nearly perfect cylindrical hole in the after 10 minutes, and the solution was clear and colorless. middle of the tin deposit. The rate of evolution of hydrogen steadily decreased The rods were again placed in the solution and a new after 10 minutes, and after 1 hour and 15 minutes only a deposit of metallic tin at once began to cover the sur faint trace of hydrogen gas was liberated. After this face of each rod. 50 period of time the pH of the solution was approximately Frequently, needle-like and bird feather-shaped de 1, and the rod was removed. posits of tin accompanied the porous, spongy deposits. The spongy tin was separated from the solution by de Vigorous evolution of hydrogen gas continued each time cantation, and filtration of the solution through a 30 milli the rods were replaced in the tin solutions for the first liter Gooch crucible using Whatman, it GF/B glass fiber 20 to 45 minutes, during which time most of the sodium filter paper, 2.1 centimeters in diameter under vacuum hexachlorostannate (IV) in solution had been reduced Suction. and precipitated as metallic tin. Analysis of the solution revealed a residual tin content After about 45 minutes, the evolution of hydrogen gas of 0.36 gm. Sn/liter. After 1 hour and 15 minutes, 98.9% was considerably reduced and the aluminum rods were of the total tin content of the original solution was re allowed to stay in contact with the solution for 10 to 15 60 covered as metallic sponge tin. The consumption of metal hours. At the end of this time, tests indicated that only lic aluminum from the rod was 0.821 gram corresponding faint traces of tin were still present in the Solution, and to 0.12 lb. Al/lb. Hg for every pound of metallic mer that all of the tin originally present had been reduced to cury produced as a final product of the process. the metallic state by the rods. The spongy metallic tin was separated from the barren EXAMPLE 17 waste solution by decantation as much as possible and then readily dewatered by placing all of the tin in a This example illustrates the Stage 5 regeneration of Buchner funnel of the appropriate size using Whatman the preferred stannous chloride reducing agent by reaction #1 cellulose filter paper, 9.0 centimeters in diameter, between the spent stannic chloride solution from the Stage under vacuum suction. 70 3 reduction steps with the tin sponge produced in accord The total consumption of metallic rods during the re ance with the preceding examples. The fundamental equa duction of the five separate batches combined was 157.9 tion involved is: grams of metallic aluminum, or 0.17 lb. Al/b. Hg, for 3.5 NEC every pound of metallic mercury produced as a final prod Sin Cla -- Snº -- — 2ShC) uct of the process. (room temperature or heated) 3,732,094 35 36 The exact procedure employed is described below: ated at the anode, from coming into contact with the At the end of each individual reduction cycle, the clear, calcium chloride solution containing stannous chloride yellow solution of stannic chloride (SnCl4) (containing (SnCl2) or with the metallic tin deposited at the cathode, such impurities as soluble chlorides of copper and iron), thereby preventing excessive losses of tin by oxidation. obtained as a result of the reduction of mercurous chloride The electrolyte was agitated at all times with the aid to metallic mercury was placed in a 400 milliliter beaker of a magnetic stirrer, and the liquid level of a Solution and the dewatered spongy metallic tin recovered from of pure calcium chloride inside the glass tube containing highly acidic solutions of sodium hexachlorostannate the graphite anode was always about /8 inch below the (IV) by aluminum reduction in the previous examples outside liquid level of the calcium chloride solution con was added to the yellow acidic stannic chloride (SnCl4) O taining the residual tin. The electrolysis was carried out solution in the beaker. at 4 volts using a current of 0.32 to 0.39 ampere Supplied The beaker was placed on a hot plate and the tempera from a 6-volt storage battery. ture was rapidly raised to between 70 and 85 C. The During electrolysis, bubbles of chlorine gas formed at heated contents of the beaker was stirred occasionally the anode and collected in the top portion of the inside of with a glass stirring rod by hand. The high temperature the glass tube as a greenish yellow gas. The tin readily was maintained for a period of about 20 minutes before collected as a porous, spongy, gray deposit over the entire cooling to room temperature. exposed roughly etched surface area of the aluminum During the reduction of the stannic chloride in solution cathode, and was easily dislodged from the cathode by to stannous chloride, the spongy metallic tin rapidly dis gentle shaking by hand. integrated and dissolved in the solution. The yellow color Electrolysis was continued for 3/2 hours. At the end of the solution rapidly disappeared and bright salmon 20 of this time, a considerable quantity of hydrogen gas was pink deposits of metallic copper were frequently noticed. liberated at the cathode, so the electrolysis was stopped A considerable quantity of brown insoluble sediment and the Small deposit of spongy residual tin was separated readily settled to the bottom of the beaker. After 20 min from the calcium chloride solution by filtering the solution utes, the hot solution was colorless and slightly turbid. 25 through a Buchner funnel of the appropriate size using The cooled solution was filtered rapidly through a Whatman it GF/A glass fiber filter paper 7.0 centimeters Buchner funnel of the appropriate size using Whatman in diameter under vacuum suction. The spongy tin was iGF/C thick glass fiber filter paper, 9.0 centimeters in Washed thoroughly with water to remove soluble chlorides. diameter, under vacuum suction. Generally, a second A complete summary of results obtained from the filtration was required to prepare a stannous chloride 30 electrolytic recovery of residual tin from concentrated solution which was not turbid. calcium chloride solutions containing stannous chloride A quantity of 75 milliliters of concentrated hydro and aluminum chloride is illustrated in the following chloric acid was added to the clear filtrate and the solu table. tion was then diluted to a final volume of 500 milliliters. The diluted solution of stannous chloride contained ap proximately 482.6 gms. SnCl2/liter and was approximate ly 3.5 N in hydrochloric acid. The solution was now ready for use in the next cycle as a reducing agent in the Material or operation Rum 1 R 2 reduction, precipitation, and recovery of metallic mercury. (1) Concentration of residualtin in calcium chloride 40 g!m$..Sr]{}}ter?tiopl?"S0 - - - - ? ? -----????????????? ? ? ? ? ? ? ? 0.39 .0.39 EXAMPLE 1.8 (2)tion, Total grams------weight of tin contained in 2 liters of solu 0.782 0,782 (3) Concentration of calcium chloride, g CaCl2.2H2O/liter------250 250 This example illustrates the optional electrolytic recov (4). 9oncentration of aluminum chloride, gms. ery of residual tin from the spent liquors from the tin AlCl36H2Ofliter------24 24 (5) Potential difference across electrodes of cloc reduction step (Stage 4). The fundamental equation lytic cell, volts------4. 4. involved is: (6) Concentration of stannous chloride in solution, (7)gns. Current SnCl2.2H2O/liter------requirement of electrolytic cell: 0.744 0.744. Concentrated (a) Highest current through cell, amperes------0.37 0.39 CaC solution (b) Lowest current through cell, amperes------0.32 0.36 SnCl 8) Total time of electrolysis, hrs...... 3-g 3% -electrolysis ---» Snº(-) - Claº (+) (9)Area of cathode, square centimeters.------200 200 50 (10) Corrosion of aluminum cathode, percent alumi um consumed------0.035 0,43 (1) Concentration of tin in calcuim chloride solu The exact procedures followed are described below: tion after electrolysis, gms. Sinfilter------0.06 0.0022 (2) Total weight of tin in 2 liters of solution after Two separate quantities of concentrated calcium chlo electrolysis, grams------0.0333 0.004 ride solutions, each 2 liters in volume and containing (13) Total tin recovered from the solution by elec tTOlySiSper00nt ??????????????????????? ? ? ? ? ? ? ? ? ? ? ? ?? 95.7 90,4 0.391 gm. Sn/liter as stannous chloride, 250 gms. (14) Consumption of electrical energy per pound of CaCl22H2O/liter, and 124 gms. AlCl36HO/liter was residual tin recovered, kilowatt hours|lb. Sun--- 2.93 3.06 electrolyzed in order to recover the residual tin content remaining in the solution after reduction of the calcium hexachlorostannate (IV) content of the original solution to tin sponge by metallic aluminum, as described above. 60 Each of the two solutions were placed in a 2-liter We claim: beaker and a 24-gauge metallic aluminum sheet 20 cen 1. A process for winning mercury from a mercury timeters long and 10 centimeters wide with a roughly containing Source, including ores, ore concentrates, alloys, etched surface on one side and curved in such a manner amalgams and compounds, which process comprises, in as to fit the curvature of the inside walls of the beaker combination, the steps of was used as a cathode (negative electrode) on which the (a) leaching said mercury-containing source to form stannous ion (Snt) could be reduced and collected as a pregnant liquor by contacting said source with a metallic tin. leach liquid comprising a solution of a hypohalite The anode (positive electrode) was a graphite rod leach reagent formed in situ by continuously injecting % inch in diameter and 12 inches long placed within a 70 chlorine or bromine into an aqueous slurry of said glass tube 3.5 centimeters in diameter and 23 centimeters Source containing an alkali metal compound or an long, the end of the tube of which was attached to a alkaline earth metal compound, as required, to oxi fritted disc 3 centimeters in diameter of medium porosity. dize and solubilize the mercury values of said source; The purpose of the fritted disc diaphragm was to allow (b) reducing said solubilized mercury values in said ions to migrate freely but prevent the chlorine gas, liber 75 pregnant liquor to elemental mercury with a reducing 3,732,094 37 38 agent comprising stannous chloride or an inorganic metal compound, as required, to oxidize and solubi acid or salt of phosphorous in which the phosphorous lize the mercury values of said source; moiety has an oxidation state of less than --5; and (b) forming a suspension of an insoluble metal hy (c) separating said elemental mercury from the mother droxide floc capable of selectively adsorbing said liquor. Soluble metallic impurities in said pregnant liquor; 2. Process of claim 1 in which said reduction step is (c) contacting said pregnant liquor with said metal carried out in a homogeneous liquid phase. hydroxide floc for a length of time sufficient to selec 3. Process of claim 1 wherein during said leaching gold tively adsorb said soluble metallic impurities upon values present are solubilized in the form of a gold-halide said fioc to form an impurity-loaded floc; complex or a gold-cyanide complex, the step of selec O (d) separating said impurity-loaded floc from said tively gold values from said pregnant liquor which com pregnant liquor; prises: (e) reducing said solubilized mercury values in said (a) selectively reducing said gold complex by con pregnant liquor to elemental mercury; and tacting said pregnant liquor with a pregnant liquor (f) separating said elemental mercury from the mother insoluble reducing agent for said gold complex, to 5 liquor. reduce said gold complex to finely divided metallic 9. Process of claim 8 in which said metal hydroxide gold; foc is zinc hydroxide. (b) simultaneously with said reduction of said gold 10. A process for winning mercury from a mercury complex to metallic gold, adsorbing said finely di containing source containing metallic impurities, including vided metallic gold upon the surface of an excess 20 Ores, ore concentrates, alloys, amalgams and compounds, quantity of said insoluble reducing agent, to form which process comprises, in combination, the steps of a gold-loaded insoluble floc; and (a) leaching said mercury-containing source to form a (c) separating said gold-loaded floc from said preg pregnant liquor containing soluble metallic impurities nant liquor. by contacting said source with a leach liquid com 4. A process for winning mercury from a mercury 25 prising a solution of a hypohalite leach reagent containing source, including ores, ore concentrates, alloys, formed in situ by continuously injecting chlorine or amalgams and compounds, which process comprises, in bromine into an aqueous slurry of said source con combination, the steps of taining an alkali metal compound or an alkaline earth (a) leaching said mercury-containing source to form a metal compound, as required, to oxidize and solubi pregnant liquor by contacting said source with a 30 lize the mercury values of said source; leach liquid comprising a solution of a hypohalite (b) separating soluble metallic impurities selected from leach reagent formed in situ by continuously injecting the class consisting of soluble compounds of arsenic, chlorine or bromine into an aqueous slurry of said Selenium and tellurium from said pregnant leach source containing an alkali metal compound or an liquor by alkaline earth metal compound, as required, to oxi (i) forming in said pregnant liquor a suspension dize and solubilize the mercury values of said source; of an insoluble metal hydroxide floc capable of (b) partially reducing said mercury values by treatment Selectively adsorbing said soluble metallic im with a reducing agent comprising stannous chloride purities, or an inorganic acid or salt of phosphorous in which (ii) contacting said pregnant leach liquor with said the phosphorous moiety has an oxidation state of 40 metal hydroxide floc for a length of time suf less than --5 to form a solid mercury compound; ficient to selectively adsorb said soluble impurity (c) next separating said solid mercury compound from compounds upon said floc to form an impurity the mother liquor; loaded floc, (d) next treating said solid mercury compound with (iii) separating said impurity-loaded floc from said an additional quantity of said reducing agent to 45 pregnant liquor; complete the reduction, forming elemental mercury; (c) reducing the purified pregnant leach liquor from and step (b) by (e) separating said elemental mercury from said re (i) a first reduction stage in which said solubilized ducing agent. mercury is partially reduced by treatment with 5. Process of claim 4 in which a reducing agent comprising stannous chlo (a) said reducing agent is an aqueous solution of ride or an inorganic acid or salt of phosphorous stannous chloride, in which the phosphorous moiety has an oxida (b) in which the mother liquor from the reduction tion state of less than --5, forming a solid mer steps is treated with a reducing agent to reduce the Cury compound and separating said solid mer tin content of said mother liquor to elemental tin, and cury compound from the mother liquor, and (c) said elemental tin is reconverted into stannous (ii) a Second reduction step in which said solid chloride and recycled to said reduction steps. mercury compound is treated with an additional 6. Process of claim 4 in which said reducing agent is quantity of Said reducing agent to complete the an inorganic acid or salt of phosphorous in which the reduction, forming elemental mercury; and phosphorous moiety has an oxidation state of less (d) separating said elemental mercury from said sec than --5. ond stage reduction step mixture. 7. Process of claim 4 in which said reduction step is 11. Process of claim 10 wherein during said leaching carried out in a homogeneous liquid phase. gold values present are solubilized in the form of a gold 8. A process for winning mercury from a mercury halide complex which is selectively separated from the containing source containing metallic impurities, including 65 purified pregnant leach liquor of step (b) by ores, ore concentrates, alloys, amalgams and compounds, (i) selectively reducing said gold complex by con which process comprises, in combination, the steps of tacting said pregnant liquor with an insoluble re (a) eaching said mercury-containing source to form ducing agent for said gold complex to reduce said a pregnant liquid containing soluble metallic impuri gold complex to finely divided metallic gold, ties by contacting said source with a leach liquid 70 (ii) simultaneously with said reduction of said gold comprising a solution of a hypohalite leach reagent complex to metallic gold, adsorbing said finely di formed in situ by continuously injecting chlorine or vided metallic gold upon the surface of an excess bromine into an aqueous slurry of said source con quantity of said insoluble reducing agent, to form taining an alkali metal compound or an alkaline earth 5 a gold-loaded insoluble floc, and 3,732,094 39 40 (iii) separating said gold-loaded floc from said preg- 1,637,481 8/1927 Glaeser ------75-121 nant liquor. 3,627,482 12/1971 Olson et al. ------75-121 X References Cited s UNITED STATES PATENTS HERBERT T. CARTER, Primary Examiner 3,476,552 11/1969 Parks et al. ------75-101 R 5 U.S. Cl. X.R. 3,574,600 4/1971 Scheiner et al. -- 75-101 R X 3,039,865 6/1962 Gilbert et al. ??? 75—118,121,108423—101