United States Patent (19) (11) 4,079,116 Ronzio et al. (45) Mar. 14, 1978

54 PROCESS FOR PRODUCING AMMONIUM Primary Examiner-Herbert T. Carter HEPTAMOLYBDATE AND/OR Attorney, Agent, or Firm-Harness, Dickey & Pierce AMMONUM DIMOLYBDATE (57 ABSTRACT (75) Inventors: Richard A. Ronzio, Golden; Phillip A process for producing a high purity ammonium hep K. Davis, Arvada; Robert C. Ziegler, tamolybdate and/or ammonium dimolybdate product Lakewood, all of Colo. by which a particulated molybdenum oxide concentrate 73) Assignee: AMAX Inc., New York, N.Y. is purified to remove contaminating metal cations, whereafter it is leached with an ammoniacal leach solu (21) Appl. No.: 754,593 tion to extract the molybdenum trioxide constituent 22 Filed: Dec. 27, 1976 therein as soluble ammonium molybdate compounds. The resultant ammoniacal leach solution is thereafter 51) Int. Cl...... C01G 39/00 concentrated at an elevated temperature, whereafter at 52 U.S. C...... 423/56; 423/54; least a portion thereof is adjusted to provide an am 423/58; 42.3/593; 23/297; 23/302 A monia-to-molybdenum trioxide mol ratio ranging from 58) Field of Search ...... 423/53, 56, 58,54, about 0.86:1 to about 1.25:1, and the adjusted solution 423/61, 593; 23/296,297, 302 A, 299, 305 R thereafter is cooled to effect a precipitation of ammo 56 References Cited nium heptamolybdate crystals which are separated and recovered, and the balance of the cooled solution is U.S. PATENT DOCUMENTS recirculated for admixture with additional ammoniacal 1,838,767 12/1931 Iredell ...... 423/56 leach solution. A portion of the concentrated ammonia 3,357,821 12/1967 Henrickson ...... 423/58 cal leach solution can be further concentrated by evapo 3,829,550 8/1974 Ronzio et al...... 42.3/55 ration to effect crystallization of ammonium dimolyb 3,848,049 11/1974 Ronzio et al...... , 423/56 3,932,580 1/1976 Vertes et al. ... 423/56 date which is separated and recovered. 3,957,946 5/1976 Ronzio et al. ... 423/54 3,963,823 6/1976 Kulkarni...... 423/56 9 Claims, 2 Drawing Figures

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4,079,116 1 2 and is heated to effect an evaporation of the water con PROCESS FOR PRODUCING AMMONUM stituent therein to a point approaching the saturation of HEPTAMOLYBDATE AND/ORAMMONUM the dissolved ammonium molybdate compounds DMOLYBDATE therein. In accordance with one embodiment of the process, at least a portion of the concentrated solution is BACKGROUND OF THE INVENTION withdrawn and the molar ratio of ammonia to molybde Ammonium heptamolybdate (NH)6Mo.O4.4H2O) num trioxide is adjusted by acidification or ion ex sometimes also referred to as ammonium paramolyb change to a range within about 0.86:1 to about 1.25:1 at date, comprises a valuable source of molybdate ions and an elevated temperature whereafter the adjusted solu is in extensive use as an analytical reagent, is employed 10 tion is cooled to a temperature of about 20° C or lower for synthesizing molybdenum-containing pigments and to effect a precipitation of ammonium heptamolybate catalysts for various liquid and gas phase hydrogenation crystals. The AHM crystals are separated from the and desulfurization reactions in petroleum refining op residual solution, such as by filtration or centrifugation, erations and coal technology, as well as for the produc and the residual solution is recycled for admixture with tion of a relatively pure grade of molybdenum metal. 15 additional ammoniacal leach solution which is recon A relatively high purity ammonium heptamolybdate centrated in the concentrator and again subjected to or AHM product has heretofore been produced on a adjustments followed by a cooling precipitation cycle. commercial scale by dissolving a high purity molybde By employing an evaporative crystallizer as a concen num trioxide in ammonium hydroxide to produce a trator, a controlled portion of the dissolved ammonium saturated solution having a pH of about 6 to about 6.6, 20 molybdate compounds can be recovered in the form of which thereafter is cooled from its saturation tempera ammonium dimolybdate. ture of about 55' C to temperatures as low as about 20 In accordance with an alternative embodiment of the C or lower. During the cooling cycle, a precipitation of process, a vacuum evaporator can be employed as the AHM crystals occurs which are removed such as by concentrator whereby a controlled adjustment in the centrifugation. The balance of the solution is employed 25 molar ratio of ammonia and molybdenum trioxide is for forming a fresh solution by the addition of further effected obviating the need for pH adjustment by acidi molybdenum trioxide and ammonia to provide the fication. proper pH at 55C, whereafter the cooling step is again The process can be operated as a closed system to repeated. While the foregoing prior art process is emi which an impure molybdenum trioxide concentrate is nently satisfactory for producing an ammonium hep 30 fed in addition to make up ammonia and from which a tamolybdate product of the requisite purity, certain high purity ammonium heptamolybdate product, to economic disadvantages are inherent due to the neces gether with ammonium dimolybdate product, is recov sity of employing high purity starting materials, such as ered along with waste side streams comprising the ex molybdenum trioxide derived from sublimation or from tracted contaminating metal cations and the insoluble the calcination of ammonium dimolybdate (ADM) de 35 residue remaining at the completion of the ammoniacal rived from the evaporative crystallization of ammonia leaching step. In accordance with a preferred embodi cal solutions containing molybdate ions. ment of the present invention, carbon dioxide is em The present invention overcomes many of the disad ployed for effecting a pH adjustment of the solution vantages associated with prior art techniques for form prior to cooling crystallization to provide the requisite ing high purity ammonium heptamolybdate as well as mol ratio of ammonia to molybdenum trioxide which ammonium dimolybdate by directly utilizing impure subsequently is removed during reheating of the resid molybdenum oxide concentrates as a starting material, ual solution in the concentrator. achieving substantial cost savings over techniques here Additional advantages and benefits of the present tofore known. invention will become apparent upon a reading of the 45 description of the preferred embodiments taken in con SUMMARY OF THE INVENTION junction with the accompanying drawing. The benefits and advantages of the present invention are achieved by a process in which an impure particu BRIEF DESCRIPTION OF THE DRAWINGS lated molybdenum oxide concentrate, such as derived FIG. 1 comprises a schematic flow diagram of one from an air roasting of the molybdenite concentrate, is 50 embodiment of the process for producing a high purity first treated with a hot aqueous leach solution in order ammonium heptamolybdate or ammonium dimolybdate to solubilize and extract a substantial portion of the product; and contaminating metal cations present therein. The aque FIG. 2 of the drawings comprises a schematic flow ous leach solution is separated from the leached concen diagram of an alternative embodiment of the process in trate, such as by filtration, and preferably is further 55 which a high purity ammonium heptamolybdate prod processed to recover the solubilized molybdate ions uct is produced from an impure roasted molybdenum therein which are recirculated for further processing. oxide concentrate feed material. The aqueous leached concentrate thereafter is con tacted with an ammoniacal leach solution to form a DESCRIPTION OF THE PREFERRED slurry of a concentration ranging from about 20 to EMBODIMENTS about 50% solids containing an excess of ammonia. The The feed material to the process in accordance with ammoniacal leaching step is continued until substan the flow diagrams shown in FIGS. 1 and 2 of the draw tially all of the molybdenum trioxide constituent therein ings comprises a particulated impure or technical grade is converted to soluble ammonium molybdate com concentrate consisting predominantly of molybdenum pounds. 65 oxide and further containing various contaminating The ammoniacal leach solution thereafter is separated metal constituents and compounds thereof in percent from the remaining insoluble residue which is discarded ages varying in accordance with the particular charac and the leach solution is transferred to a concentrator teristics of the original ore body and the manner by 4,079,116 3 4. which the concentrate was produced. Most commonly, No. 535,671, filed Dec. 23, 1974, for "Molybdenum technical grade molybdenum oxide concentrates are Oxide. Purification Process', now U.S. Pat. No. produced from an air roasting of molybdenite (MoS) 3,957,946, the substance of which is incorporated herein concentrates produced such as by an oil flotation ex by reference. The further oxidation of contaminating traction beneficiation process, whereby the gangue metal compounds, such as compounds of potassium, constituents are reduced to a level less than about 40% copper, calcium, magnesium, iron, aluminum, lead, and preferably less than about 10% by weight. The oil zinc, bismuth, or the like, renders them more susceptible flotation beneficiation process is normally carried out in to extraction by water leaching, providing for increased a series of successive cycles, each including a grinding processing efficiency and providing a product of in step followed by a flotation step, in which the particle 10 creased purity. size of an ore comprised of a highly silicified and altered In accordance, with the flow diagram as shown in granite in which the molybdenite is distributed in the FIG. 1, the technical grade molybdenum oxide concen form of very fine-sized veinlets at a concentration usu trate is first subjected to a hot water leach treatment in ally ranging from about 0.3 to about 0.6% as mined is which the particulated feed material is pulped with progressively reduced to a particle size usually 35% + 15 water at a temperature generally ranging from about 70 100 mesh and the particles composed principally of up to about 95 C, and preferably around 80' C, at a molybdenite are separated from the silicious gangue solids concentration ranging from about 5 up to about materials employing hydrocarbon oils in combination 50% by weight, but below that at which difficulty is with various wetting agents. encountered in achieving good agitation and pumping The molybdenite concentrate thus produced is trans 20 of the pulped mass. Particularly satisfactory results are ferred to a roasting operation employing temperatures obtained employing solids concentrations of from about generally ranging from about 550' to about 700 Cin the 20 to about 50% and temperatures of about 80' C at presence of excess air to effect an oxidation of the pre which retention times of about 1 hour provide for a dominant portion of molybdenite to molybdenum ox substantially complete extraction of the contaminating ide. Roasting apparatuses commonly used for this pur 25 metals including contaminating metal molybdates along pose include a variety of well known multiple-hearth with some of the original molybdenum trioxide present. furnaces such as, for example, Herreshoff, McDougall, The resultant slurry is thereafter transferred from the Wedge, Nichols, etc., comprising a plurality of annular hot aqueous leaching tank to a filter A and the filtrate. shaped hearths disposed in vertically spaced relation containing the dissolved contaminating metal cations is ship on which the molybdenite concentrate is trans 30 transferred to a cation exchange resin column, while the ferred in a cascading fashion downwardly from the cake is transferred to an ammoniacal leaching tank. uppermost hearth while exposed to a countercurrent The filtrate from filter A is acidic, usually having a flow of hot flue gases to effect an oxidation thereof. pH of from about 2 to about 3 due to the presence of While the specific concentration of the molybdenum molybdic acid and is passed in contact with a suitable oxide constituent in the feed material is not critical, 35 cation exchange resin, whereby the contaminating technical grade concentrates containing at least about metal cations are selectively adsorbed and the effluent 80% and preferably at least about 90% molybdenum consisting predominantly of molybdic acid is returned oxide are preferred. to the ammoniacal leaching tank and is combined with The resultant roasted concentrate or technical grade the filter cake from filter A. Cation exchange resins oxide feed material, is usually of an average particle size suitable for this purpose include Amerlite IR 120, which less than about 100 mesh and any agglomerates pro is a sulfonic type cation exchange resin available from duced during the air roasting operation can be removed Rohm & Haas. Alternative satisfactory cation exchange by a supplemental grinding operation. Particle sizes less resins which are effective in adsorbing contaminating than about 100 mesh are preferred in accordance with metals such as potassium, copper, calcium, magnesium, the practice of the present invention in view of the 45 iron, etc., in an acid environment can also be employed. greater surface area of the feed material, facilitating a The cation exchange resin is preconditioned employing leaching of the feed and correspondingly reducing the an acid such as sulfuric acid to effect conversion thereof residence time required in the various leaching steps. to the hydrogen form, and after loading, the cations In accordance with a preferred practice of the pres adsorbed thereon are stripped with an acid such as ent invention, the conventional air roasted technical 50 sulfuric acid or hydrochloric acid at concentrations of grade concentrate is subjected to a supplemental re about 5 to about 10% acid. The eluate from the cation roasting operation in the presence of an oxygen exchange resin containing the contaminating cations is enriched atmosphere of substantially atmospheric pres transferred to an appropriate waste treatment process sure and at a temperature of from about 550 to about prior to discharge to waste. 650 Cfor a period of time sufficient to convert substan 55 In addition to the use of a cation exchange resin col tially all of the sub-oxides of lower oxides of molybde umn as depicted in FIG. 1, it is also contemplated that num to molybdenum trioxide and to further convert the alternative techniques can be employed to effect a sub contaminating metals and metal molybdite compounds stantially complete recovery of the molybdic acid con present to corresponding metal oxides and metal molyb stituents in the filtrate from filter A. For example, anion date compounds which are of increased solubility and solvent extraction or ion exchange resin systems can be can more readily be removed by the subsequent hot employed for extracting the dissolved molybdate anions aqueous leaching step. from the filtrate following the hot water leach treat The reroasting step is carried out in oxygen-enriched ment. Such an alternate arrangement is illustrated in the atmospheres containing upwards of 40% oxygen, and flow diagram depicted in FIG. 2 of the drawings in preferably atmospheres containing substantially 100% 65 which the filtrate from filter 1 is passed through an oxygen. A further description of the specific details and anion exchange resin to extract the dissolved molybdate benefits derived from the oxygen-enriched reroasting anions therein. Anion exchange resins that can be satis step is provided in United States patent application Ser. factorily employed include tertiary amine in styrene 4,079,116 5 6 divinyl benzene matrices, such as available under the covered as a solid crystalline ADM product. Conven designation IRA-93 from Rohm & Haas; type XE 270 tionally, at least a portion of the mother liquor from the and XE 299 resins which are also tertiary amine type evaporative crystallizer is bled to a pH adjustment tank resins available from Rohm & Haas; epichlorhydrine maintained at a temperature ranging from about 30 to polyamine condensation-type (aliphatic polyamine about 77°C and preferably at about 55°C and the pH of types) available in a granular state under the designation the ammoniacal solution bleed is adjusted by the addi A-305 from Ionic Chemical Co., as well as equivalent tion of an acidic agent, preferably carbon dioxide. The types which are effective to selectively adsorb the mo quantity of acid added to the pH adjustment tank is lybdate anion in a substantially neutral medium. controlled so as to effect a neutralization thereof and a When employing such anion exchange resins, it is O net pH within the range of from about 6.3 to about 7.0 necessary that the filtrate first be neutralized by the corresponding to an adjustment of the mol ratio of addition of a suitable base, such as sodium hydroxide, to ammonia to molybdenum trioxide within a range of a pH of about 3.0 to about 6.5 before entering the anion about 0.86:1 to about 1.25:1. For this purpose, acidic exchange column. The filtrate containing the contami substances that can be satisfactorily employed include nating metal cations passes through the anion exchange 15 H2SO, HCL, HNO3, and carbon dioxide, of which column and the effluent or raffinate, after appropriate carbon dioxide constitutes the preferred material. After treatment, is harmlessly discharged to waste. After pH adjustment, the adjusted solution maintained at a loading with molybdate anions, the resin in conve temperature of about 30 to about 77 C, preferably niently eluted employing an aqueous solution of ammo about 55C, is transferred to a cooling crystallizer in nium hydroxide and the resultant eluate containing which it is progressively cooled to a temperature of ammonium molybdate is transferred in accordance with about 20 C or below. In situations wherein the mother the arrangement shown in FIG. 2 to the evaporator in liquor withdrawn from the evaporative crystallizer is at admixture with the filtrate from filter 2. a pH of about 7.0 or below, no further pH adjustment is It is also contemplated that in lieu of employing ion required and the mother liquor can be directly trans exchange principles, the filtrate such as derived from 25 ferred to the cooling crystallizer as indicated by the filter A of FIG. 1 or filter 1 of FIG. 2 can be transferred dotted lines in FIG. 1. to a neutralizing tank to which an alkaline calcium com Under conditions wherein the mol ratio of ammonia pound is added for reaction with the dissolved molyb to molybdenum trioxide is about 1.25:1 and the solution date anions as well as some of the metal cation species is substantially saturated and at a temperature of 55' C, with the exception of potassium, forming thereby pre 30 a cooling thereof in the cooling crystallizer to a temper cipitates which are recovered by filtration, providing a ature of about 20°C or below effects a precipitation of cake consisting predominantly of calcium molybdate. up to about 40% of the molybdenum content therein in The calcium molybdate containing cake may suitably be the form of ammonium heptamolybdate crystals. recycled for admixture with the original concentrate At the conclusion of the cooling cycle, the AHM introduced to the air roasting operation or can be fur 35 crystals are removed from the mother liquor such as by ther utilized in alternative processes for producing mo filtration or centrifugation, and the residual ammonium lybdenum containing compounds. molybdate solution is recycled back to the evaporative In either event, the filter cake from filter A, as shown crystallizer in accordance with the arrangement illus in FIG. 1, is subjected to an ammoniacal leach treat trated in FIG. 1 of the drawings. The recycled solution ment in which the cake is again pulped at a concentra is again reheated and concentrated in the evaporative tion ranging from about 5 up to about 50% solids by crystallizer whereby the carbon dioxide constituent weight, and preferably from about 20 to about 50% therein is vaporized, the water is recycled to the hot solids in an aqueous solution containing from about 10 aqueous leach tank, while the volatilized ammonia is up to about 29% ammonia and at a temperature ranging returned to the ammoniacal leaching tank. from about 20 to about 30° C. A retention time ranging 45 In accordance with one practice of the present inven from about two to about five hours, and preferably from tion, the evaporative crystallizer can operate on a sub about three hours to about four hours, is effective to stantially continuous basis producing a crystalline extract substantially all of the molybdenum trioxide ADM product while the cooling crystallizer can oper constituents in the filter cake and oxidize and precipitate ate on an intermittent basis by the extraction of con all the iron as ferric hydroxide. The resultant slurry is 50 trolled bleed quantities of the saturated solution from thereafter transferred to filter B in which the residual the evaporative crystallizer for adjustment and subse aqueous and ammoniacal insoluble constituents com quent crystallization to recover a high purity AHM prising predominantly gangue minerals and Fe(OH)3 are product, removed and the cake discarded to waste. The process depicted in FIG. 2 of the drawings is The filtrate from filter B is transferred to a concentra 55 similar to that hereinabove described in connection tor, such as an evaporative crystallizer as shown in with FIG. 1 but as previously mentioned, the filtrate FIG. 1, in which it is heated to effect a removal of water from filter 1 is transferred through an anion exchange accompanied by an evolution of ammonia so as to effect column to effect an extraction of the dissolved molyb a concentration of the ammonium molybdate com date anions which are subsequently recovered by elu pounds therein to a concentration approaching satura tion and the resultant eluate containing ammonium mo tion. A heating of the ammoniacal leach solution in the lybdate is transferred to the ammoniacal leaching step evaporative crystallizer is performed at a temperature or preferably directly to the vacuum evaporator. The ranging from about 90 to above 98 C and may be hot water leaching step and the ammoniacal leaching carried out to an extent wherein all or a controlled step, including the intervening filtration steps, are per lesser amount of the dissolved ammonium molybdate 65 formed in the same manner employing the same condi compounds precipitate out in the form of ammonium tions as previously described in connection with FIG. 1. dimolybdate or ADM, (NH4)MoO), which are ex Following filtration in filter 2, the filtrate is concen tracted from the remaining mother liquor and are re trated in a vacuum evaporator, whereby appropriate 4,079,116 7 8 proportions of ammonia and water are extracted by 9.5. At the conclusion of the ammoniacal leaching step, evaporation and are subsequently recovered in a con the slurry is filtered and the filtrate containing 200-250 denser and transferred to a surge tank for recirculation grams per liter of molybdenum is concentrated by distil back to the ammoniacal leaching tank. The vacuum lation under a vacuum of 20 inches mercury at a temper evaporator is operated in a controlled manner, whereby ature not exceeding 75 C. The concentration is contin the mol ratio of ammonia to molybdenum trioxide is ued until the first crystals of AHM appear in the solu adjusted to within a range of about 0.86:1 to about tion. The condensate from the distillation is recovered 1.25:1, and the concentration of dissolved AHM is in and is of a pH ranging from 10-11 and contains from creased within a range of about 300 up to about 500 60-62% of the water in the original ammoniacal leach grams per liter approaching saturation of AHM in the 10 ing step filtrate. Upon reaching this point of concentra aqueous solution at about 55C. The concentrated solu tion, the vacuum is removed and the concentrated fil tion thereafter is directly transferred to a cooling crys trate is immediately cooled to 20 C and held at that tallizer without any need for a pH adjustment, where temperature for 1 hour while being subjected to occa upon a progressive cooling to a temperature of about sional stirring. The high purity crystals of AHM pro 20° C or below effects a precipitation of upwards of 15 duced during the cooling crystallization step are ex about 40% of the ammonium molybdate content in the tracted by filtration and dried at room temperature solution in a manner as previously described. The crys under vacuum. A total of 40-45% of the molybdenum tals of AHM are extracted employing a filter or centri present in the original molybdic oxide feed material is fuge, and the resultant crystalline cake is dried at a recovered in the form of an AHM product. The resul temperature of less than 55' C to avoid decomposition 20 tant filtrate from the AHM crystals has a pH of 7.8-7.9 of AHM such as by employing a vacuum dryer produc and contains 280-285 grams per liter of molybdenum. ing a high purity crystalline ammonium heptamolyb The AHM filtrate is subjected to further concentration date product. The filtrate from the filter or centrifuge is under vacuum in accordance with aforementioned pro conveniently recirculated to the surge tank is returned cedure and additional crystals of AHM are recovered. to the ammoniacal leaching tank in accordance with the 25 Alternatively, the AHM filtrate and the condensate flow diagram shown in FIG. 2. from the evaporative concentrator are recycled to the In order to further illustrate the process comprising ammonium hydroxide leaching step for use in leaching the present invention, the following examples are pro additional aqueous leached molybdic oxide concentrate vided. It will be understood that the examples are pro feed material. vided for illustrative purposes and are not intended to 30 EXAMPLE 3 be limiting of the scope of the present invention as A 150-gram sample of a reroasted molybdic oxide herein described and as set forth in the subjoined claims. feed material containing 90-98% molybdenum oxide is EXAMPLE 1. leached with 150 ml of deionized water to form a slurry A 150-gram sample of a reroasted molybdic oxide 35 having a 50% solids content. The hot aqueous leaching concentrate feed material containing 90-98% molybde step is carried out at 85°C for a period of 1 hour. The num trioxide is subjected to a hot aqueous leaching step hot aqueous leached feed material is recovered by filtra employing 150 ml of deionized water at 85 C for a tion and is washed with hot deionized water. The resul period of 1 hour. The resultant leached concentrate is tant washed filter cake is mixed with 250 ml of deion filtered and the cake is washed with hot deionized wa 40 ized water and 250 ml of a 29% solution of ammonia to ter. The washed filter cake is mixed with 250 ml of effect an ammoniacal leaching at room temperature for deionized water and 250 ml of a 29% solution of ammo a period of 4 hours. The slurry contains 16-18% molyb nia forming a slurry at room temperature containing denum oxide and is of a pH of 9.5. The resultant slurry 16-18% molybdenum trioxide having a pH of 9.5. The is filtered and the filtrate containing ammonium molyb ammoniacal leaching step is carried out for a period of 45 date compounds dissolved therein is evaporated at 98 four hours, whereafter the resultant slurry is filtered C to a concentration at which the first crystal formation and the filtrate containing the dissolved ammonium appears. The resultant liquor is cooled to 20 C in a molybdate compounds is saturated with carbon dioxide cooling crystallizer, whereupon the bulk of the AHM gas at 55' C corresponding to a use of 0.05 to 0.1 pounds crystals are formed and recovered. of carbon dioxide for each pound of molybdenum triox 50 While it will be apparent that the invention herein ide. The carbon dioxide treated filtrate is thereafter described is well calculated to achieve the advantages placed in a cooling crystallizer and cooled to a tempera and benefits set forth above, it will be appreciated that ture below 20' C. A yield of AHM crystals is recovered the invention is susceptible to modification, variation corresponding to approximately 45% of the molybde and change without departing from the spirit thereof, 55 What is claimed is: num content originally present in the feed material. 1. A process for producing an ammonium molybdate EXAMPLE 2 product which comprises the steps of leaching a partic A 150-gram sample of a reroasted molybdic oxide ulated impure molybdenum oxide concentrate com concentrated feed material containing from 90-98% prised predominantly of molybdenum trioxide with molybdic oxide is leached for a period of one hour with 60 water at a temperature of from about 70 to about 95°C 150 ml of deionized water at a temperature of 85 C in at a solids concentration of from about 5 to about 50% the form of a slurry of 50% solid content. The hot water for a period of time sufficient to extract at least a portion leached molybdenum trioxide feed material is thereafter of the aqueous soluble contaminating metal cations filtered and washed with hot deionized water. The present in said feed material, extracting the water washed filter cake is mixed with 250 ml of deionized 65 leached said concentrate from the water leach solution, water and 250 ml of a 29% ammonia solution and the recovering the molybdate values dissolved in said water ammoniacal leaching step is carried out for a period of leach solution, leaching the water leached said concen four hours at room temperature. The slurry has a pH of trate with an ammoniacal leach solution to solubilize 4,079,116 9 10 and extract the molybdenum trioxide constituent form ammonium molybdate compounds and recovering therein as ammonium molybdate compounds, separat said eluted ammonium molybdate compounds. ing said ammoniacal leach solution from the remaining 4. The process as defined in claim 3 in which said insoluble residue, transferring the separated said ammo eluted ammonium molybdate compounds are recycled 5 to said concentrator. niacal leach solution to a concentrator and heating and 5. The process as defined in claim 1 wherein the ad concentrating said ammoniacal leach solution to a point justment of the mol ratio of NH:MoO, is performed by up to saturation of the dissolved said ammonium molyb neutralizing the concentrated said leach solution with date compounds therein, withdrawing at least a portion acid to provide a pH within the range of about 6.3 to of the concentrated said leach solution and adjusting the 10 about 7.0. NH: MoC) mol ratio thereof to within a range of about 6. The process as defined in claim 5 wherein the neu 0.86:1 to about 1.25:1, cooling the adjusted said leach tralization of the concentrated said leach solution is solution to effect a precipitation of ammonium hep achieved by the addition of carbon dioxide to said leach tamolybdate crystals, separating and recovering said solution. crystals from the cooled said leach solution, and recy 15 7. The process as defined in claim 1 in which the step of cooling the adjusted said leach solution is performed cling the cooled said leach solution for admixture with to produce a temperature of from about 20 to about 10 additional said separated said ammoniacal leach solu C. tion for concentration in said concentrator. 8. The process as defined in claim 1 wherein said 2. The process as defined in claim 1 in which the step 20 concentrator comprises an evaporative crystallizer and of recovering the molybdate values in said water leach the step of concentrating said ammoniacal leach solu solution is performed by contacting the separated said tion is performed to effect crystallization of at least water leach solution with a cation exchange resin to some of the ammonium molybdate compounds therein adsorb the solubilized contaminating cations therein as ammonium dimolybdate crystals in said evaporative and recycling the balance of said water leach solution in 25 crystallizer, and including the further step of separating admixture with the molybdenum oxide concentrate and said ammonium dimolybdate crystals from the mother ammoniacal leach solution in the ammoniacal leaching liquor, withdrawing at least a portion of the mother step. liquor from said evaporative crystallizer, adjusting the 3. The process as defined in claim 1 in which the step ammonia to molybdenum oxide mol ratio thereof and 30 cooling the adjusted mother liquor to effect precipita of recovering the molybdate values in said water leach tion of said ammonium heptamolybdate crystals. solution is performed by contacting the separated said 9. The process as defined in claim 1 including the water leach solution with anion exchange resin to ad further step of drying said ammonium heptamolybdate sorb the solubilized molybdate anions therein, discard crystals under vacuum at a temperature below about 55 ing the balance of said water leach solution, and eluting 35 C. the adsorbed said molybdate anions with ammonia to k is a sk

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