Abstract: A metal is dissolved by a method which comprises establishing contact of the metal with a quaternary ammonium compound and a halogenated hydrocarbon or with a quaternary ammonium compound, a halogenated hydrocarbon, and a polar solvent.

Abstract: A method is disclosed for the quantitative removal and concentration of desired transition metal ions from a source solution which may contain larger concentrations of other metal and H.sup.+ ions. The method comprises bringing the source solution into contact with a compound comprising a pyridine containing ligand covalently bonded through an organic spacer silicon grouping to a solid inorganic support. The pyridine portion(s) of the compound has an affinity for the desired metal ions to form a complex thereby removing the desired metal ions from the source solution. The desired metal ions are removed from the compound by contacting the compound with a much smaller volume of a receiving solution having a greater affinity for the desired metal ions than does the pyridine ligand portion of the compound. The concentrated metal ions thus removed may be recovered by known methods.

Abstract: A process is disclosed to extract cobalt and optionally, at least one metal value selected from the group consisting of molybdenum, nickel, tungsten, and vanadium from metal-containing particles, such as spent hydroprocessing catalysts particles containing carbon residue. In this process, the spent catalyst particles are roasted in an oxygen-containing gas at a temperature of from 400.degree. C. to 600.degree. C., and then the roasted catalyst particles are contacted with an aqueous solution of ammonia, ammonium salt, and hydrogen peroxide. The aqueous solution has an initial pH of at least 9.5 and an initial hydrogen peroxide concentration of from 0.02 to 0.2 M. That aqueous solution is maintained at a pH of greater than 9.5.

Abstract: A method is disclosed for removing iron from iron-contaminated sulfuric acid to render the sulfuric acid suitable for ion membrane processing which comprises contacting the iron-contaminated sulfuric acid with an oxidizing agent to oxidize essentially all of the iron to the +3 oxidation state, contacting the resulting iron-contaminated sulfuric acid containing oxidized iron with a complexing agent which can be citric acid, oxalic acid, and tartaric acid, with the amount of the complexing agent being sufficient to complex essentially all of the oxidized iron, and contacting the resulting iron-contaminated sulfuric acid containing the complexed iron with activated carbon to remove essentially all of the iron and produce a purified sulfuric acid solution.

Abstract: A method is disclosed for removing organic and tungsten from sodium sulfate solutions to render the solutions suitable for ion membrane processing, which comprises contacting the solution wherein the pH of the solution is no greater than about 7, with activated carbon to remove essentially all of the organic and the tungsten therefrom and form a purified sodium sulfate solution.

Abstract: A process is provided for purifying phosphoric acid, such as wet process phosphoric acid by extracting the impure phosphoric acid with a nonaqueous solvent and contacting the nonaqueous solution of phosphoric acid with a strongly basic anion exchange resin and recovering the purified phosphoric acid by stripping the nonaqueous solution with an aqueous solution.

Abstract: A process is disclosed for purifying molybdenum containing arsenic and phosphorus which involves leaching molybdenum trioxide in an acid at a temperature of above about 70.degree. C.

Abstract: Described is a method of separating and recovering metal values from a waste stream containing metal hydroxides comprising the steps of providing an aqueous waste stream containing metal values including chromium; subjecting the waste stream to an oxidation process to convert the chromium to chromium (VI); precipitating the other metal values in the aqueous stream by adjusting the pH of the stream to cause the precipitations; and separately recovering the chromium (VI) from the remaining metal values. The process described pertains to separating and recovering metal values such as those from an electroplating process or an electroless process wherein the metals may be iron, cobalt, zinc, cadmium, nickel, copper, silver, aluminum and chromium. The chromium recovery step is performed by oxidizing chromium (III) to chromium (VI) preferably in the presence of a manganese catalyst and preferably utilizing ultrasound waves. The remaining metal values are separated by the use of a chelating ion exchange resin.

Abstract: A method of separating tungsten from molybdenum wherein impure acid leached molybdenum trioxide containing tungsten is combined with ammonium hydroxide to form an ammonium molybdate solution, the solution is contacted with tin (IV) oxide hydrate to cause sorption of essentially all of the tungsten contained therein without causing sorption of molybdenum, the tin (IV) oxide hydrate with the sorped tungsten is separated from the ammonium molybdate solution, and the ammonium molybdate solution is dried and fired to obtain purified molybdenum trioxide.

Abstract: The present invention relates to a method for the selective extraction of the metals gold, silver, platinum or mercury ions or colloidal gold, from an aqueous solution containing at least one of these metal ions which comprises contacting the solution, at a pH of 2 or less, with cells or cell extracts of a microorganism capable of binding these metals for a period of time and under conditions sufficient to allow binding of the metals to the cells or cell extracts.

Abstract: According to a method and apparatus for inducing a photochemical reaction, a substrate is placed in a closed cell with a window for transmitting an ultraviolet beam therethrough and is located to oppose the window, a gas is filled to cause the phtoochemical reaction upon irradiation of the ultraviolet beam into the cell, ultraviolet pulses are repetitively controlled to emit at a predetermined intensity, an ultraviolet beam size and shape are adjusted in accordance with a size and a shape of an irradiation portion of the substrate, the repetition frequency of the ultraviolet beam is adjusted and set to effectively cause the photochemical reaction on the substrate in accordance with the adjusted ultraviolet beam size and shape, and the ultraviolet beam having the set beam size and shape at the repetition frequency is irradiated through the window of the cell.

Abstract: A process is described for recovering vanadium and zeolitic alumino-silicates from flyash and similar carbon-bearing heat treated materials. The process includes steps for the separation of carbon, followed by pressure leaching the carbon-depleted flyash in relatively dilute alkali metal hydroxide solutions at elevated temperatures. The leach liquor is separated from the residue and is subsequently treated in an amine containing solvent extraction process step for vanadium recovery, and optionally, for other metals present in the leach liquor. The vanadium in the strip liquor is precipitated to obtain vanadium containing compounds.The leach residue is treated separately to recover zeolitic alumino-silicates therefrom.In another variation of the process, the vanadium is recovered from the leach liquor by means of a strong base anoin exchange resin.

Abstract: Metal halides are ultrapurified by selective complexation with a complexing gent to form a charged first complex. A ligand forms an oppositely charged second complex with metallic impurities in the metal halide to be purified. A solution containing these complexes is then passed through an ion exchange column and the desired purified metal halide collected. The present method is particularly useful in the production of ultrapure metal halides, such as zirconium fluorinate, for metallic glasses.

Abstract: Aqueous effluent solutions containing metal cations may be treated with an extractant comprising an organophosphinic acid, a di-2-ethylhexyl phosphoric acid and/or an aliphatic amine to selectively separate chromium, nickel, cobalt, copper and lead cations from the aqueous solution. Typical extraction techniques include liquid-liquid extraction employing either mixer settlers or columns, liquid membrane extraction and selective supported membrane extraction.

Abstract: A process for removal and recovery of chromium ions (chromate, dichromate, or combinations thereof) from aqueous waste water of surface treatment phosphatizing solutions and for recycling of the treated waste water following replenishment wherein the aqueous waste water is initially partially clarified in a settling tank, with the effluent then being passed through an ion exchange column for removal of substantially all of the chromium ions therefrom. Following treatment in the ion exchange resin column, the chromium-free material is recharged with a supply of fresh chromium ions until the chrome ion content is at the desired level for metal surface treatment. The spent ion exchange resin columns are removed and replaced, as necessary, with the recharge of the resin columns making additional chromium available as a resource.

Abstract: There are disclosed method and apparatus for recovering chromium from chromium-containing wastes, using an electrolytic oxidation cell divided by an anion exchange membrane and a coupled transport module containing a membrane containing a chromium(VI) complexing agent.

Abstract: A process for the separation of molybdenum present in a sulfuric solution, in which the sulfuric solution is placed in contact with a stationary phase whose active group contains an oxime group, and the stationary phase is eluted using an alkaline solution.

Abstract: A process is disclosed for purifying molybdenum which involves adding to an acidic slurry of molybdenum trioxide, a source of magnesium ions in a solid form, with the amount of magnesium and the magnesium ion concentration in the subsequently formed ammonium molybdate solution being sufficient to subsequently form insoluble compounds containing greater than about 80% by weight of the arsenic and greater than about 80% by weight of the phosphorus, and ammonia in an amount sufficient to subsequently dissolve the molybdenum and subsequently form the insoluble compounds, digesting the resulting ammoniated slurry at a temperature sufficient to dissolve the molybdenum and form an ammonium molybdate solution while the pH is maintained at from about 9 to about 10 to form a solid containing the insoluble compounds, and separating the solid from the ammonium molybdate solution.

Abstract: A tungsten extraction process wherein tungsten values are extracted from an aqueous alkali metal tungstate solution by an organic solution containing an amine extractant wherein the organic solution consists essentially of from about 6% to about 10% by volume of said amine extractant, and the balance of said organic solution being an aromatic solvent consisting essentially of a mixture of alkyl benzenes wherein the alkyl benzenes have molecular weights of 120, 134, or 148 and the total number of carbon atoms in the alkyl chains attached to the benzene ring are either 3, 4, or 5, and thereafter the tungstate values are removed from the organic solution by stripping with aqueous ammonia, is improved by carrying out the stripping step in the aqueous continuous mode, and having as the stripping agent, an aqueous solution of ammonium metatungstate having a tungsten concentration which allows the strip solution to have a specific gravity of no greater than about 1.

Abstract: The compounds of the invention comprise the condensation product, as well as derivatives thereof, of two equivalents of a trimethyl cyclohexane-anhydride acid chloride derivative with one equivalent of an aromatic diamine. The scope of the invention includes the method of using the compounds of the invention as chelating agents for metals, metal ions or ions of metal complexes. In a preferred embodiment of the invention the binding moieties of the cyclohexane derivatives are rigidly held opposite each other, by restricting their rotation about the N-C aryl bonds, in order to more effectively bind the metals or the ions.

Abstract: Metal values including those of cobalt, vanadium, aluminum, molybdenum and tungsten are recovered from spent petroleum refining catalyst by acid leaching the metal values except those of molybdenum or tungsten, separating the resulting solution from the leach residue and selectively recovering the cobalt, vanadium and aluminum values from the solution and recovering the molybdenum and tungsten values from the leach residue.

Abstract: An improved process is disclosed for the purification of an impure aqueous solution containing heavy metal ions which comprises passing the impure solution through a bed of activated alumina adsorbent. The heavy metal ions are removed from the impure aqueous solution by adsorption onto the activated alumina adsorbent. The adsorbent may be regenerated for reuse and the adsorbed metals recovered by subsequently stripping the metal ions from the adsorbent and recycling the metal ions back to the process of origin. The pH of the effluent may be monitored to determine when the capacity of the adsorbent has been reached and regeneration of the adsorbent should be commenced. In a preferred embodiment, a portion of the activated alumina is pretreated with acid before passing the impure solution through the adsorbent to enhance the chromium ion adsorption of the acid-treated activated alumina and a portion of the regenerated activated alumina is again treated with acid after each regeneration cycle.

Abstract: The purpose of the process is to remove and to recover metals from their aqueous solution by the extraction process. As extractant is used monoesters of phosphonic acid wherein the alkyl group is a phenyl-vinyl group or straight-chained and the ester group is straight-chained. The particular advantage of the process is that the metals can be removed from aqueous solutions to be treated without neutralization of the acid quantity produced during extraction, and this acid solution produced can be circulated e.g. to the stage before the extraction. The process can be used to the removing of metals from the industrial waste waters.

Abstract: A process is disclosed for recovering tungsten, iron, and manganese from tungsten bearing material. The process involves digesting the material in a sufficient amount of sulfuric acid at a temperature of at least about 80.degree. C. for a sufficient time in the presence of coal as a reducing agent to form a digestion solution containing the major portion of the scandium, iron, and manganese and a digestion residue containing the major portion of the tungsten, followed by separating the solution from the residue. The major portion of the scandium can be extracted from the digestion solution with an organic solution consisting essentially of a mixture of tertiary alkyl primary amines which are present in an amount sufficient to extract the major portion of the scandium, and the balance an essentially aromatic solvent. The scandium is stripped from the organic with hydrochloric acid which is then separated from the stripped organic.

Abstract: A process is disclosed for recovering metals from chromium bearing material comprising one or more or the metals of cobalt, nickel, molybdenum, tungsten, iron, tin, aluminum. The process comprises atomizing the material to produce a flowable powder which is then fused in an oxidizing atmosphere with sufficient alkali metal hydroxide at a temperature sufficient to form a nonmagnetic fused material in which the chromium, tungsten and molybdenum are present as water soluble salts. The resulting fused material is then slurried with a sufficient amount of water to dissolve the water soluble compounds. The pH is adjusted to from about 9.2 to about 9.6 with an acid to allow insolubles to form which contain any cobalt, and nickel and the major portion of any iron, tin and aluminum followed by separating the insolubles from the resulting first liquor.

Abstract: Chelating agents on which metals such as uranium have been adsorbed are brought into contact with an eluent of aqueous solution containing reducing agents and basic compounds, until the metals are eluted. The elution is effected with large speed without degradation of the chelating agents. Preferred chelating agents are rather stable under basic conditions but not under acidic conditions, for example, those having .dbd.NOH group in their molecules. The reducing agents and basic compounds in the eluent are, for example, sulfurous acid or salts thereof and sodium hydroxide, respectively.

Abstract: Amine extractants useful in extracting metallic anions are modified with Lewis bases, having substantial organic solubility, such as tributyl phosphate, to improve the extraction capability of such amines. Generally, addition of Lewis bases to weakly basic amines increases the basicity of such amines.

Abstract: A process for the selective concentration of metal values in solution wherein said metal-containing solution is contacted with a multiple-phase system having a common solvent, thereby causing the preferential migration of metal values into one phase of said multiple-phase system. The phases of the system may then be isolated and the metal values recovered therefrom by conventional techniques.

Abstract: High-purity molybdenum or tungsten powder can be produced by a process comprising (a) decomposing a powder or an oxide powder of molybdenum or tungsten with hydrogen peroxide water; (b) bringing the resulting aqueous solution of molybdenum or tungsten into contact with a cation exchange resin; (c) concentrating the aqueous solution; and (d) reducing a concentrated solid material. By omitting reducing step (d), one can obtain high-purity molybdenum or tungsten oxide powders. Because the Mo and W powders and MoO.sub.3 and WO.sub.3 powders prepared by this invention are of an extremely high purity, they are useful as materials for targets of VLSI elements.

Abstract: Metal ions contained in trace in an aqueous solution are extracted, for quantitative analysis by an ICP emission spectrometer, with an organic solvent supplemented by chelate compounds in an extraction vessel having a thin cylindrical upper portion, to form an organic layer containing the extracted metal ions over an aqueous layer. After extraction, water is supplied from the bottom of the vessel in an amount so that the interface between the organic and aqueous layers is positioned at a predetermined position of the thin, upper portion where a liquid withdrawal port is provided. The organic layer is recovered from the withdrawal port.

Abstract: An improvement is disclosed in a process wherein tungsten values are extracted from an aqueous alkali metal tungstate solution by an organic extractant, and then stripped from the organic with an ammonia solution, the improvement being removing bromine from the major portion of the stripped organic and thereafter using at least a portion of the resulting bromine-free stripped organic to make up at least a portion of the organic extractant.

Abstract: Process for producing fluorides of Mo, W, Nb, Ta, V, Re, Ti, Zr, Hf, Co, Ni, Cr, Sb, Sn, Zn, Pb, Al and rare earth metals comprising heating fluorine-containing ammonium salts of corresponding metals in a stream of an inert or reducing gas to convert them into fluorides of the metals.

Abstract: Spent catalysts from hydrocarbon refining processes, comprising transition metal compounds on aluminum oxide-containing supports, are subjected to an oxidative roasting and are treated with sulfuric acid in a counter-current digester to dissolve metals. Following operations to separate compounds of the various transition metals, a solution containing approximately stoichiometric equivalents of aluminum and sulfate is obtained.

Abstract: A process is disclosed for recovering tungsten, scandium, iron, and manganese from tungsten bearing material. The process involves digesting the material in sufficient sulfuric acid at a sufficient temperature for a sufficient time in the presence of a reducing agent to form a digestion solution containing the major portion of the scandium, iron, and manganese, and a digestion residue containing the major portion of the tungsten, separating the digestion solution from the digestion residue and extracting essentially all of the scandium from the solution with an organic consisting essentially of an extracting agent which is a dialkyl phosphoric acid which is present in an amount sufficient to extract essentially all of the scandium without extracting appreciable amounts of iron and manganese, and the balance an essentially aromatic solvent.

Abstract: A process is disclosed for recovering scandium from a tungsten bearing material containing tungsten, iron manganese and scandium. The process involves digesting the material in an aqueous solution selected from the group consisting of a saturated solution of sulfur dioxide and a sulfuric acid solution containing an additional reducing agent at a sufficient temperature for a sufficient time to form a digestion solution containing the major portion of the scandium, iron, and manganese, and a digestion solid containing the major portion of the tungsten which is separated from the digestion solution. The major portion of the scandium is extracted from the digestion solution with an organic consisting essentially of an extracting agent which is essentially a mixture of alkyl primary amines which are present in an amount sufficient to extract the major portion of the scandium without extracting appreciable amounts of iron and manganese, and the balance an essentially aromatic solvent.

Abstract: Soluble hexavalent chromium values are removed from aqueous chlorate solutions by employing a critical effective ratio of OH.sup.- :Cr.sub.2 O.sub.7.sup.= ions of at least 3:1 in the aqueous chlorate solution and by employing a dithionite to reduce the hexavalent chromium to trivalent chromium, preferably in the mole ratio of S.sub.2 O.sub.4.sup.= :Cr.sub.2 O.sub.7.sup.= of at least 3:1. The trivalent chromium forms chromic hydroxide (Cr(OH).sub.3) with the hydroxyl ions and precipitates from the aqueous chlorate solution. The process is rapid and effective in quantitative removal of hexavalent chromium from the aqueous chlorate solutions and is especially useful for the removal of sodium dichromate from cell liquor which is intended to be employed in chlorine dioxide production and which is produced by diaphragmless electrolysis of sodium chloride.

Abstract: A method is disclosed for purifying molybdenum which involves adding to an ammoniacal ammonium molybdate solution containing the impurities of phosphorus and arsenic with the phosphorus concentration being from about 0.01 to about 0.12 g/l, a soluble magnesium salt to form a precipitate comprising magnesium ammonium salts of the phosphorus and arsenic, and to form a purified ammonium molybdate solution. The amount of the magnesium salt is sufficient to result in a concentration of from about 0.005 to about 0.04 moles/l in the ammoniacal ammonium molybdate solution. The resulting purified ammonium molybdate contains no greater than about 0.01 g P/l. The precipitate is separated from the purified solution which is then contacted with a chelating cation exchange resin supplying a sufficient amount of a cation to result in removal of the major portion of the magnesium ions from the purified solution and form a further purified ammonium molybdate solution.

Abstract: This invention pertains to a new process for removing metals, especially contaminant metals, from spent catalysts. Also, this invention pertains to a catalyst composite with metals removed by the new process, and to several uses for the catalyst, including as a rejuvenated hydrotreating catalyst. The new process comprises (i) contacting the spent catalyst with a complexing agent with four or more coordinating groups, including at least two carboxylic acid type groups and at least one amino type group, and (ii) separating from the spent catalyst a mixture containing the complexing agent and the removed metals. By this process contaminant metals, like vanadium, are more selectively removed from the spent catalyst than are catalytic metals, like cobalt and molybdenum.

Abstract: A metal scavenger is composed of an addition product of a polyamine and an epihalohydrin. The addition product contains as substituent or substituents at least one carbodithio group and/or at least one carbodithioate salt group introduced therein by substituting the corresponding number of active hydrogen atom or atoms in the addition product. Metals can be scavenged from waste water by adding the metal scavenger together with at least one of sodium monosulfide, sodium polysulfides and sodium hydrogensulfide.

Abstract: A process for the purification by selective separation of uranium and/or molybdenum from zirconium and/or hafnium among other impurities contained in an amino organic phase by bringing them together with an aqueous sulphuric re-extraction solution, characterized in that, with a view to increasing the separation factor of the zirconium and/or hafnium on the one hand and the uranium and/or molbydenum on the other hand, the aqueous sulphuric re-extraction solution contains at least one alkali or equivalent sulphate.

Abstract: A process is disclosed for recovering tungsten, scandium, iron, and manganese from tungsten bearing material. The process involves digesting the material in sufficient sulfuric acid at a sufficient temperature for a sufficient time in the presence of a reducing agent to form a digestion solution containing the major portion of the scandium, iron, and manganese, and a digestion residue containing the major portion of the tungsten, separating the digestion solution from the digestion residue and extracting essentially all of the scandium from the solution with an organic consisting essentially of an extracting agent which is a dialkyl phosphoric acid which is present in an amount sufficient to extract essentially all of the scandium without extracting appreciable amounts of iron and manganese, and the balance an essentially aromatic solvent.

Abstract: Processes are described for preparing pure ammonium molybdate from impure roasted molybdenum concentrates. An aqueous solution of nitric acid and ammonium nitrate is contacted with impure molybdenum concentrate to solubilize a major portion of the impurities. The resulting molybdenum concentrate is digested in ammonium hydroxide under conditions that maximize iron precipitation and removal. The resulting ammonium molybdate solution is separated from the sludge and further purified by chelating cation exchange resin in the ammonium form.

Abstract: Processes are described for preparing pure ammonium molybdate from impure roasted molybdenum concentrates. An aqueous solution of nitric acid, ammonium sulfate, and ammonium nitrate is contacted with impure molybdenum concentrate to solubilize a major portion of the impurities. The resulting molybdenum concentrate is digested in ammonium hydroxide under conditions that maximize iron precipitation and removal. The resulting ammonium molybdate solution is separated from the sludge and further purified by chelating cation exchange resin in the ammonium form.

Abstract: A process for the recovery of a heavy metal which comprises:bringing a polymer having pendant groups of the formula:--CO--NH--NH--CO--COOMin which M is hydrogen, sodium or potassium, into contact with an aqueous solution containing a heavy metal to have the heavy metal adsorbed by said polymer;andhaving said heavy metal desorbed from the said polymer.

Abstract: Processes are described for preparing pure ammonium molybdate from impure roasted molybdenum concentrates. An aqueous solution of hydrochloric acid and ammonium nitrate is contacted with impure molybdenum concentrate to solubilize a major portion of the impurities. The resulting molybdenum concentrate is digested in ammonium hydroxide under conditions that maximize iron precipitation and removal. The resulting ammonium molybdate solution is separated from the sludge and further purified by chelating cation exchange resin in the ammonium form.

Abstract: Processes are described for preparing pure ammonium molybdate from impure roasted molybdenum concentrates. An aqueous solution of sulfuric acid, ammonium sulfate, and ammonium persulfate is contacted with impure molybdenum concentrate to solubilize a major portion of the impurities. The resulting molybdenum concentrate is digested in ammonium hydroxide under conditions that maximize iron precipitation and removal. The resulting ammonium molybdate solution is separated from the sludge and further purified by chelating cation exchange resin in the ammonium form.

Abstract: New compounds have been prepared from dicyclopentadiene bis(methylamine) which have the following formula ##STR1## wherein substituents A, B, X and Y each are independently selected from radicals including hydrogen, hydroxyalkyl (wherein the alkyl group contains 2-6 carbon atoms) phosphonic, sulfonic, hydroxyethyl- and hydroxypropylsulfonic, methylenephosphonic methylene-, ethylene- and propylenesulfonic, alkylcarboxylic acid radicals (having 2-4 carbon atoms) and the alkali or alkaline earth metal, ammonia and amine salts of any of the phosphonic, sulfonic or carboxylic acid derivatives. At least one of the substituents must be other than a hydrogen. These compounds are useful chelating agents and those containing the methylenephosphonic substituents are good threshold agents.

Abstract: A method of continuous ion exchange for waste water treatment and metal recovery employs two membranes, each disposed in its own fluid-tight chamber. A feed solution containing metal ions is passed in contact with one membrane, the opposite side of which is in contact with a recirculating flow of liquid ion exchange material which receives selected dissolved mineral ions. The liquid ion exchange material is then passed over a second membrane, the other side of which is supplied with an eluant solution for further selective recovery of the desired mineral ion or ions. During recirculation the liquid ion exchange material is preferably passed through an aqueous separator. An apparatus for the practice of the present invention is also disclosed.

Abstract: In a process for recovering rhenium, a starting material containing tungsten and rhenium is reacted with sodium hydroxide and an oxidizing reactant to form a fused solid. The fused solid is dissolved in water to solubilize the tungsten and rhenium values and then pass through an anion exchange resin to remove the rhenium values and form a solution containing the tungsten values. The resin is stripped to obtain the rhenium values from the resin.

Abstract: Processes are described for preparing pure ammonium molybdate from impure roasted molybdenum concentrates. An aqueous solution of nitric acid, ammmonium sulfate, and ammonium nitrate is contacted with impure molybdenum concentrate to solubilize a major portion of the impurities. The resulting molybdenum concentrate is digested in ammonium hydroxide under conditions that maximize iron precipitation and removal. The resulting ammonium molybdate solution is separated from the sludge and further purified by chelating cation exchange resin in the ammonium form.