3,061,412 United States Patent Office Patiented Oct. 30, 1962 2 The precipitation process, however, is undesirable in 3,061,452 that: multiple operations are involved, water soluble PREPARATION OF MERCURIC SULFDE compounds which are essential to the process are Anthony Giordano, 3838 E. 51st St., Cleveland, Ohio very expensive, handling the extremely poisonous and No Drawing. Filed Feb. 16, 1960, Ser. No. 8,901 corrosive water soluble mercury compounds is hazardous 1 Claim. (C. 23-134) and the washing out of by-product salts is necessitated. This invention relates to a method of manufacturing Another method which may be employed in the pro mercuric and mercuric sulfide dispersions and duction of solid solutions of cadmium-mercury is a method products obtained therefrom. which is set forth in U.S. Patent No. 2,850,402 and which Mercuric sulfide has long been prepared by various O may be defined as “the direct method of introducing processes, such as, for instance, by strongly compressing HgS.” The “direct method' is conveniently carried out mixtures of and mercury, by mixing sulfur and as follows. mercury in rotating cylinders and then heating the mix tures in retorts equipped with capitals to that mercuric DIRECT METHOD OF INTRODUCING HgS sulfide is collected in the capitals and by digesting mercury 5 (A) Reactants: with agitation in an aqueous solution of ammonium or (1) Elemental Hg and S, plus alkali polysulfide. alkali polysulfide in the presence of elemental sulfur. (2) CdSO4 solution. While all of the above methods will produce mercuric (3) BaS solution. sulfide, mercuric sulfide suitable for special applications (B) Procedure: often requires certain physical characteristics. Mercuric 20 (1) Hg and S are reacted in presence of alkali poly sulfide employed in the production of pigments, for in sulfide solution to form Hg.S. stance, and particularly in certain methods of production Nags of pigments of the class known as cadmium-mercury reds Hg-S-HO-HgS slurry necessitates a critical mercuric sulfide particle size. A prerequisite to the formation of a solid solution type 25 (2) CdSO is precipitated with BaS as follows: cadmium-mercury red pigment is that the mercury and CdSOA-BaS->CdS.BaSO4(Cd lithopone) cadmium components be combined with a certain degree (3) HgS slurry from step 1 and cadmium lithopone of intimacy prior to calcination. Such intimacy is de pendent upon the magnitude of attractive forces between precipitate of step 2 are mixed to form: individual particles of the various components. These 30 CdS.EIgS.BaS forces, in turn, depend upon particle size, that is, the -- smaller particles will result in greater attractive forces Intimate mixture required at this point than corresponding larger particles. If the particles are too small, the attractive forces will be such that (4) Mixture of step 3 is filtered-no washing nec hard, very tightly bound aggregates will be produced, 35 essary. which are undesirable in the formation of cadmium (5) Filter cake is dried. mercury red pigments. The more prevalent condition, (6) Subsequent steps are same as precipitation meth however, is that the particles are too large and the attrac od, starting from step 5. tive forces are therefore insufficient. The direct method while eliminating the undesirable Cadmium-mercury red pigments are commonly pro 40 features of the co-precipitation method has not been ex duced by preparing solid solutions of mercuric sulfide tensively employed due to the difficulty in obtaining Suit in . The solid solution, as has been ex able mercuric sulfide or more specifically mercuric Sul plained in the preceding paragraph, may only be obtained fide slurries of the proper particle size. from intimate admixtures of the cadmium and mercury It is, therefore, an object of this invention to provide components. At present mercury components of the de 45 an improved process for producing mercuric sulfide of sired particle size are obtained by precipitation, the pre a preselected particle size. cipitation process generally being combined in a manner It is another object of this invention to provide an in so as to co-precipitate both cadmium and mercury com proved process for producing an aqueous dispersion of ponents in the same operation. The co-precipitation mercuric sulfide of a preselected particle size. method of the prior art is generally carried out as 50 I have now discovered a method of preparing mercuric follows. sulfide having physical characteristics which lend then selves to the direct method of preparation of cadmium CO-PRECIPITATION METHOD mercury pigments. (A) Reactants: MERCURC SULFIDE PREPARATION (1) HgCl2--HO to form HgCl, solution. 55 (2) CdSO4 solution. The method of producing a finely divided dispersion (3) BaS solution. of mercury sulfide from elemental mercury and elemental (B) Procedure: sulfur may be stated broadly as being one wherein ele (1) HgCl2 and CdSO4 solutions are mixed together. mental mercury and at least stoichiometric proportions (2) HgCl2-CdSO mixture is precipitated with BaS 60 of elemental sulfur are reacted to form mercury sulfide as follows: by mixing in an aqueous solution of CdSO4--HgCl2-2BaS-> CdS.HgS.BaSO4--BaCl2 having a formula of Na2S, throughout the entire period of the reaction, wherein x is at least 3 and preferably (3) Precipitate of step 2 is filtered and washed free at least 4. It will be evident that the sodium polysulfide of by-product BaCl2. solution may also be described as a solu (4) Filter cake from step 3 is dried. 65 tion having at least 3 atoms of sulfur dissolved therein (5) Dried cake (green-cake) is calcined at about and that greater than 3 atoms of sulfur may be dissolved 500 C. in the sodium sulfide solution depending upon the amounts (6) Calcined product is quenched in water in order of sulfur present in excess of the stoichiometric amounts to cool and arrest calcination at correct point, required to form mercury sulfide. (7) Quenched product is ground, filtered, and dried, 70 The amount of sodium polysulfide employed and the (8) Dried finished cake is pulverized. degree of agitation determine the speed of the reaction 3,061,412 3. between the elemental mercury and sulfur. Very small tation is accompanied by a grinding, attritive, impact or amounts of sodium polysulfide appear to be effective in other shearing force. The shearing force has been found increasing the speed of the reaction. Optimum results, to be a necessary feature of the agitation to prevent the however, have been obtained when the amount of sodium formation of agglomerates or the formation of Substan polysulfide utilized ranges from about 0.015 to about 0.5 tial quantities of crystals in excess of 1 micron. While mole of sodium polysulfide per mole of elemental mer certain specific mechanical agitation means have been set cury. In general, an increase in the ratio of sodium forth for carrying out the process of this invention, it polysulfide to elemental mercury employed (Na2S/Hg) should be understood that any shearing type agitation increases the rate of the reaction. Above a molecular which will break up agglomerates and reduce crystal size ratio of about 0.5, however, the rate of increase in the 0 is within the scope of this invention. reaction rate does not appear to be as great as within Ball milling, other grinding action, shearing, any attri the indicated range. Similarly, the rate of the reaction tion, fracturing or like means of deagglomeration are is influenced by the degree of agitation, being faster with herein called "comminution' following Webster (New greater agitation and mixing action. When employed 20th Century Dictionary, second edition, p. 364). together, the two rate influencing factors enhance each 5 The following exemplify the process of the invention other and so various combinations of them can produce directed to the production of mercury sulfide and are a wide range of reaction periods. Consequently, the presented by way of illustration and are not to be con quantity of sodium polysulfide employed may be varied strued as limiting the scope of the invention thereto. to Suit various forms of mixing and agitation equipment. Example I For example, if the reaction is carried out in a ball or 20 pebble mill, which offers relatively slow agitation, the 188.5 grams of mercury, 31.8 grams of sulfur, and 110 Speed of reaction may be increased by employing a con grams of a 20% sodium sulfide solution (Na2S) were centration of catalyst approaching 0.5 mole of sodium placed in a laboratory Waring Blendor and it was found polysulfide per mole of mercury. On the other hand, if after 20 minutes that all of the mercury had been con the reaction is carried out in apparatus which produces 25 verted to black mercuric sulfide having a particle size violent agitation similar to a Waring Blendor, the speed suitable for use in the preparation of cadmium-mercury of reaction can be reduced by employing a sodium poly pigments. Sulfide amount approaching 0.015 mole of the polysulfide Example II per mole of mercury. As another method of preparing mercury sulfide, 401.2 In general, the concentration of the sodium polysulfide 30 grams of elemental mercury, 77 grams of elemental sul will be determined by the type of equipment in which fur amounting to 13 grams of excess sulfur, together the agitation and mixing of the mercury and the sulfur with 30 grams of a 15% solution of sodium sulfide and takes place. Concentrations of sodium polysulfide rang 180 grams of water were charged to a ball mill which ing from 0.005 to 1.5 (as Na2S) per mole of Hg may be was operated for 24 hours. At this point it was found Successfully employed. The concentration of sodium 35 that no residual mercury was remaining and that the polysulfide affects the chemical reaction, as is to be ex reaction had gone to completion. pected, according to the law of mass action. However, the ratio of sulfur in the sodium polysulfide is a critical Example III factor in determining the particle size of the resultant A sodium polysulfide solution was made by dissolving mercuric sulfide. 40 70 grams of elemental sulfur flour in 300 grams of 15% With respect to the temperature of the reaction, the sodium sulfide (Na2S) solution. To illustrate the effect reaction is preferably conducted at temperatures ranging of different proportions of sodium sulfide on the rate of from about room temperature (20° C.) to about 70° C. the reaction of elemental mercury and elemental sulfur, The reaction may be considered as moderately exothermic three runs were made wherein identical amounts of mer in that when the mixing of the elemental mercury and cury and sulfur, namely 100 grams of mercury and 17.6 sulfur is initiated at room temperature, the temperature grams of Sulfur (amounting to 1.62 g. excess sulfur) were of the mixture gradually rises. In general, it is best not placed into one-half pint glass jars half-full glass beads to permit the temperature to exceed about 90° C. since of /8' diameter and various proportions of sodium poly Sulfur is more soluble in the sodium polysulfide solution sulfide solution added thereto. These jars were subjected at higher temperatures and there is danger of depriving to agitation on a paint shaker as indicated in the table the mercury of sulfur so that the reaction will not be below. completed unless larger excesses of sulfur are present. Additionally, there is a tendency for the particles of mer Grams of Grains Tine to Run Poly- . Grams Total Complete cury Sulfide to increase in size at temperatures above No. sulfide Na2S/Fig of H2O Excess S/Na2S Reaction, about 90° C. in spite of agitation. Generally, however, Solution Used Sulfur Iours there is no difficulty in maintaining the temperature below Used Used about 70° C. without the need of cooling. 5 .0156 70 2.566 0.27 4.5 It is essential that sulfur be present in excess of the i5 0469 60 4.458 5.95 2.5 Stoichiometric amount necessary to combine with the ele 50 .56 15 1.08 4. 44 ... 5 mental mercury and in amounts sufficient to give a sodium polysulfide solution equivalent to a sodium sulfide solu The form of mercuric sulfide resulting from the herein tion (Na2S) having at least 3 atoms of sulfur dissolved described invention may be identified as being 100% less therein. Otherwise, the product formed will be contami than 20 microns, 90% less than 10 microns, 85% less nated with elemental mercury. Furthermore, the dis than 5 microns, and 75% less than 1 micron. Mercuric solved sulfur retards crystal growth. In this regard the 65 Sulfide of this type and aqueous dispersions thereof have dispersed form should be kept in the sodium polysulfide an affinity for certain precipitates, such as cadmium sul Solution until employed, for example, in the production fide (CdS) and cadmium sulfide lithopone (CdS.BaSO) of pigments. resulting in very intimate mixtures. As a result of these The agitation of the principal components in the so particular physical characteristics, the mercuric sulfide of dium polysulfide solution is preferably conducted until 70 this invention is suitable for the direct method of pro all of the mercury has been converted to black mercury duction of cadmium-mercury pigments as described in Sulfide although it may also be continued until red mer U.S. Patent No. 2,850,402. It has been found, however, cury Sulfide is produced. The latter form, however, has that the mercuric sulfide of this invention must be em a greater tendency to increase in particle size. The agi- 75 ployed in the form of a slurry. If the mercuric sulfide 3,061,412 5 6 is dried first and an attempt is then made to react, it will polysulfide being such that there will be present through be found that the mercuric sulfide particles have agglom out the reaction from 0.015 to 0.5 mole of the polysulfide erated and are no longer suitable for pigment purposes. for each mole of elemental mercury, there being at least The cadmium-mercury red pigments resultant from the three moles of sulfur in each mole of alkali metal poly use of the novel mercuric sulfide in the process of U.S. sulfide, the reaction being carried out in aqueous medium Patent No. 2,850,402 are superior to pigments produced at the above concentrations and in a temperature range by the co-precipitation process which had formerly been from room temperature to 90° C. and subjecting the the only extensively employed process in the art. reaction medium to simultaneous agitation and comminu Having thus described my invention, what I claim is: tion whereby to produce finer particles and to retard the A process for the preparation of mercuric sulfide of IO formation of aggregates of such particles once formed, particle size suitable for use in the manufacture of pig the resulting size of the particles being at least 75% of a ments comprising reacting elemental mercury and ele size finer than one micron and at least 90% of a size finer mental sulfur in the presence of an alkali metal polysulfide, than 10 microns. the quantities of elemental mercury and elemental sulfur being such that the sulfur is in excess of the stoichiometric 5 References Cited in the file of this patent amount required to produce HigS and the amount of said Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 4, page 948, paragraph 1. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, O6l 412 October 3O 1962 Anthony Giordano It is hereby certified that error appears in the above numbered pat correctedent requiring below. correction and that the said Letters Patent should read as

In the grant, lines l to 3 for "Anthony Giordano of Cleveland, Ohio," read -- Anthony Giordano, of Cleveland, Ohio, assignor to The Harshaw Chemical Company of Cleveland, Ohio, a corporation of Ohio -- ; line 12, for "Anthony Giordano, --;his inheirs" the headingread -- Theto theHarshaw printed Chemical specification Company, itsline successors3, for "Anthony Giordano, 3838 E. 151st St. Cleveland, Ohio read -- Anthony Giordano, Cleveland, Ohio, assignor to The OhioHarshaw -- Chemical Company Cleveland, Ohio, a corporation of Signed and sealed this 2nd day of April 1963.

(SEAL) At test :

ESTON G, JOHNSON DAVID L, LADD Attesting Officer Commissioner of Patent S