Abstract: A method of removing sodium ions from an alkaline aqueous solution such as a leach solution which contains dissolved sodium tungstate. The method involves passing the solutions through the anode compartment of an electrolytic cell and passing an electrical direct current through the cell causing the sodium ions to pass through the cation selective membrane and tungstic acid to be produced in the anode compartment. Sodium-containing alkali is bled from the cathode compartment at a rate sufficient to prevent build-up of alkali in the cathode compartment. The tungstic acid is typically converted to ammonium tungstate by treatment with ammonia and then the ammonium tungstate further treated for recovery of the tungsten values.

Abstract: A process for the selective removal of arsenical material in the course of a process for the hot oxidizing attack on a uraniferous and/or molybdeniferous ore containing arsenical materials, comprising attacking said ore with an aqueous liquor of sodium or potassium carbonate and/or bicarbonate, said attack operation being carried out under conditions with respect to levels of concentration, temperatures and pressures which cause solubilization of the uranium and/or molybdenum and the arsenic present in the ore, then collecting a suspension of a solid phase in a liquid phase, and finally, separating said phases, wherein the arsenic which is solubilized in the attack operation is extracted in the form of magnesium arsenate by treating the material containing the arsenic with a magnesium compound.

Abstract: The present invention relates to a heteropoly acid containing carbon as a hetero atom. This heteropoly acid is useful as catalysts or starting materials for various reactions, color forming material or counter electrode material for electrochromic display element or the like.

Abstract: Process for the recovery of heavy metals from aqueous solution by reaction with soluble, functionally-substituted polymer upon which the heavy metal loads, and optionally crosslinks by interaction with the heavy metals present in solution. Metals including those having atomic numbers of 39-51, 57-84 and 89-117, inclusive, can be recovered by the practice of the present invention.

Abstract: A process is disclosed for recovering cobalt and chromium from a cobalt and chromium containing alloy. The process involves first digesting the alloy in concentrated hydrochloric acid at a sufficient temperature for a sufficient time to form a first solution containing the major portion of the cobalt, chromium, and any iron and nickel present in the alloy and a first solid and separating the first solution from the first solid. Oxalic acid is then added to the first solution in an amount sufficient to subsequently precipitate the major portion of the cobalt and any iron and nickel contained in the first solution followed by adjustment of the ph to from about 1 to about 2 with a base and maintaining the temperature below about 20.degree.

Abstract: A process is disclosed for producing pure molybdenum which involves contacting a molybdate solution with a true liquid alkaloid in an amount sufficient to form an alkaloid-molybdenum compound with essentially all of the molybdenum. The resulting alkaloid-treated solution is adjusted to a pH of from about 2 to 4 to form a precipitate consisting essentially of the compound and a mother liquor. The precipitate is then separated from the mother liquor and dissolved in ammonium hydroxide to form a two phase system consisting essentially of an alkaloid phase and a molybdenum phase followed by separation of the two phases. A pure ammonium molybdate compound is then crystallized from the molybdenum phase.

Abstract: The precipitation product of sodium tungstate dihydrate from a melt of sodium acetate-trihydrate is a nucleating agent for latent heat storage medium on the basis of sodium acetate-trihydrate, which produces a sure and from the first storage cycle on defect-free nucleation of the sodium acetate-trihydrate at the melting point or only a few degrees below the melting point.

Abstract: A process is disclosed for separating tungsten from a solution containing tungstate and perrhenate ions. The process involves reacting a sufficient amount of hydrochloric acid with the solution at a sufficient temperature to form a solid containing essentially all of the tungsten and a liquor containing essentially all of the rhenium, and separating the solid from the liquor.

Abstract: A process is disclosed for recovering tungsten and rhenium from a relatively impure tungsten and rhenium solution. The process involves adjusting the pH of the solution to from about 9.0 to about 10.0 to precipitate impurities, and removing the impurities. The purified solution is adjusted to a pH of from about 0.5 to about 7.0 with a mineral acid. To the purified solution is added a solution containing sufficient hexamine to subsequently form a first hexamine tungsten solid containing the major portion of the tungsten. The hexamine solution is at essentially at the same pH as that of the pH adjusted purified solution. The resulting hexamine-tungsten-rhenium mixture is agitated at a sufficiently low temperature for a sufficient time to form the first solid and a first mother liquor containing the major portion of the rhenium. The first solid is separated from the first mother liquor.

Abstract: A process is disclosed for recovering molybdenum from molybdenum disulfide. The process involves forming a slurry of the molybdenum disulfide in a solution of an alkali metal hydroxide, the amount of hydroxide being sufficient to react with at least a portion of the molybdenum disulfide to form an alkali metal molybdate and an alkali sulfate, heating the slurry in an oxidizing atmosphere at an elevated temperature and pressure and for a sufficient time to effect the conversion to the molybdate, and separating the pregnant liquor containing the molybdate from any residue. To the pregnant liquor is then added a sufficient amount of a hexamine to form a hexamine-molybdenum compound containing the major portion of the molybdenum, followed by adjusting the pH to from about 1.5 to about 3.8 to precipitate the major portion of the hexamine-molybdenum compound, and separating the compound from the resulting mother liquor.

Abstract: A process is disclosed for recovering cobalt in a relatively pure form from an impure cobalt bearing material. The process involves digesting the material in hydrochloric acid to form a solution essentially all of the cobalt and some impurities and insoluble material containing the remainder of the impurities, separating the solution from the insolubles, adding an oxalate producing compound in an amount sufficient to subsequently convert essentially all of the cobalt to cobalt oxalate to the solution, adjusting the pH of the oxalate treated solution to from about 1.5 to about 2.0 with a base to precipitate the cobalt, and finally separating the precipitate from the resulting mother liquor.

Abstract: A method for treating process waste consisting of uranium hexafluoride, UF.sub.6, molybdenum hexafluoride, MoF.sub.6 and molybdenum oxytetrafluoride, MoOF.sub.4 is provided wherein the foregoing mixture is hydrolyzed in an aqueous solution of ammonium carbonate and ammonium hydroxide. The resulting mother liquor is digested at 60.degree.-80.degree. C. to drive off carbon dioxide and convert the ammonium uranyl carbonate, (NH.sub.4).sub.4 UO.sub.2 (CO.sub.3).sub.3 to ammonium diuranate, (NH.sub.4).sub.2 U.sub.2 O.sub.7. The pH is maintained above 9 to prevent premature precipitation of the molybdenum values as molybdic acid or uranyl molybdate.The ammonium diuranate which forms as a yellow solid is filtered, slurried in aqueous ammonium hydroxide, filtered and dried. The yield is quantitative. Pyrolysis results in conversion of the diuranate salt to uranium oxide, U.sub.3 O.sub.8, of suitable purity to be recycled in the uranium hexafluoride production process.

Abstract: A process is disclosed for recovering tungsten and rhenium from a tungsten and rhenium bearing solution. The process involves adding sufficient hydrochloric acid to the solution to form a first precipitate containing essentially all of the tungsten and a first mother liquor having an acid concentration of at least about 1.25 normal, and containing the major portion the rhenium, followed by separating the first precipitate from the first mother liquor. A source of sulfide ions is then added to the first mother liquor with agitation for a sufficient time and with the amount of sulfide ions being sufficient to form a second precipitate containing essentially all of the rhenium which was in the first mother liquor, and a second mother liquor, followed by separation of the second precipitate from the second mother liquor.

Abstract: A process is disclosed for removing chromium from cobalt. The process involves first contacting an acidic cobalt chloride solution with an oxidizing agent, followed by adjusting the pH to from about 3.2 to about 5.5 with a base at a sufficient temperature to form a first solid containing essentially all of the chromium and a portion of the cobalt and a first liquor containing the balance of the cobalt, and then separating the first solid from the first liquor. The first solid is then heated at a sufficient temperature to remove essentially all of the water and form a second solid which is contacted with sufficient water and ammonium hydroxide to form a slurry which is at a pH of greater than about 3.8.

Abstract: The present invention refers to a method to recover trivalent chromium salts from reflux water originating from a hide tanning process, via the so-called "chromium" system, including the following steps in succession:flocculating all the trivalent chromium salts in the form of chromic hydroxide by treatment with an aqueous solution containing from 15 to 30%, by weight, of a salt made from a weak acid and a strong base, having a pH value lying between 6.9 and 7.2 and at a temperature lying betwen 22.degree. and 26.degree. C.;separating chromic hydrate, obtained in this way, from the aqueous dispersion by concentration in a clarifier-flocculating device and successive filtration of the concentrate until a precipitate, is obtained preferably containing approximately 20% dry residue, by weight and dissolving precipitate, thus obtained in sulphuric acid, at a pH value lying between 1.8 and 2 and at a temperature higher than 50.degree. C., preferably at 70.degree. C.

Abstract: A chromium hydroxide precipitate obtained by a continuous process is described, wherein chromium containing waste waters are subjected to continuous hot treatment with acetic acid or with alkaline acetates and alkaline hydroxides at a temperature from 40.degree. C. to boiling point and at atmospheric pressure, at a pH higher than 6.5, preferably between 7 and 10, particularly about 7.5. Thus, a "sandy" type of chromium hydroxide is obtained, having a titer in Cr.sub.2 O.sub.3 of 20 to 40% by weight, which quickly filters, is easily soluble in acids, and thereby affords an easy valorization both as a tanning agent and as a raw material for preparing other chromium compound.

Abstract: A method is disclosed for removing tin from aqueous sodium tungstate solutions. The method involves adding ammonia to the sodium tungstate solution, adjusting the pH to above about 9.5 with an acid, adding magnesium chloride to form insoluble material containing the major portion of the tin, silicon, arsenic and phosphorus and a resulting sodium tungstate solution containing the major portion of the tungsten, and separating the insoluble material from the resulting solution.

Abstract: A selectively absorbent layer for solar collectors, comprising a mixture of chromium oxides resulting from thermal decomposition of chromium hexacarbonyl or substituted chromium carbonyl. The absorbent layer is deposited from a process gas containing the carbonyl gaseous phase, oxygen, and inert carrier gas. An intermediate reflective layer is provided between the absorbent layer and the substrate.

Abstract: Tungsten can be extracted into solution from tungsten carbide powder residues with aqueous hydrogen peroxide to a greater extent by employing in solution a catalytic quantity of hydrochloric acid, such as a mole ratio to the tungsten preferably in the range of at least 0.1:1 moles of HCl per mole tungsten, and often up to about 2.5 moles of HCl per mole of tungsten at 55.degree. to 85.degree. C. The selection of the mole ratio in practice usually takes into account the grade of tungsten carbide starting material. It is very preferable to use at least 7 moles hydrogen peroxide per mole of tungsten and an extraction temperature of 65.degree. to 75.degree. C.

Abstract: Metal chloride catalysts employed in liquid phase chlorination reactions are recovered by treating the reaction mass with oxygen or air to form solid metal oxychloride compounds which can be separated and reused.

Abstract: A method of recovering molybdenum oxide as in U.S. Pat. No. 4,379,127 wherein, however, the temperature in the autoclave and the pressure therein are controlled within narrow ranges by increasing the suspension density of the molybdenum sulfide suspension fed to the autoclave upon a fall in temperature and by adding water to the slurry of molybdenum sulfide concentrate formed before introduction into the autoclave upon an increase in temperature.

Abstract: A process for the selective recovery of cadmium, molybdenum, zinc, nickel and other metal values from wet process phosphoric acid and other acidic to slightly basic carrier solutions, wherein the metal-bearing solution is contacted with an organophosphene extractant to precipitate the metal values for subsequent separation from the solution. Separation may be effected by mechanical means or by scrubbing with a water-immiscible organic solvent such as kerosene for subsequent recovery of the metal values. The metal specie recovered is determined by the concentration of the organophosphene, which may be selectively adjusted to recover a series of metal values in a sequence of stages.

Abstract: A process for recovering the metal values from spent hydroprocessing catalyst particles. The metal values will include at least one metal of Group VIII of the Periodic Table and at least one metal of Group Vb or Group VIb of the Periodic Table. The spent catalyst particles are first roasted at between 400.degree. C. and 600.degree. C. and then contacted with a first aqueous solution of ammonia and an ammonium salt forming a first pregnant liquor. The once-leached spent hydroprocessing catalysts are contacted with a second aqueous solution of sulfur dioxide forming a second pregnant liquor. The metal values are precipitated from the second pregnant liquor with hydrogen sulfide and the precipitate is roasted with unroasted spent hydroprocessing catalysts. The metal values of Group Vb and Group VIb in the first pregnant liquor are transferred into a first organic solution by liquid ion exchange.

Abstract: An improved process is disclosed for the treatment of molybdenite concentrate to remove impurities, such as copper and lead therefrom. According to this process, ferrous chloride liquor is introduced into a reactor which is made of a material that can withstand leaching with the use of ferric chloride at elevated temperatures and pressures. Sodium or calcium chloride may also be added to the reactor which is then sealed and subjected to chlorination until the rise in temperature, due to the exothermicity of the reaction, produces the desired concentration of the ferric ion to leach the impurities present in the concentrate to a desired level. Upon completion of the chlorination, the molybdenite concentrate is introduced into the reactor and is leached therein. Finally, the resulting pulp is filtered and washed to obtain the desired purified product.

Abstract: A process for extracting arsenic from aqueous solution to be purified, in accordance with claim 1 of U.S. Pat. No. 2,404,601, which also contains alkali metal carbonate, sulphate, hydroxide or hydrogen carbonate, and which may also contain at least one of the metals vanadium, uranium and molybdenum, comprising caustification of said solutions by means of lime to convert the carbonates into alkali metal hydroxides, followed by separation of an alkali metal hydroxide-enriched liquor and a first precipitate essentially containing calcium carbonate which is subjected to a washing operation, concentration by evaporation of the mixture of the washing liquor of the first precipitate to produce a second precipitate which essentially comprises alkali metal sulphate, which is characterized in that, before the aqueous solution is caustified, the aqueous solution is treated by a magnesium compound in an amount at least equal to the stoichiometric amount required to cause precipitation of magnesium arsenate.

Abstract: A process is provided for recovering metal values from spent hydrodesulfurization catalyst, the process comprising forming in a pressure reactor an aqueous slurry of finely divided spent catalyst and sodium carbonate, the spent catalyst containing by weight about 2 to 10% Mo, up to about 12% V (e.g., about 2 to 10%), about 0.5 to 4% Co, up to about 10% Ni (e.g., about 0.5 to 5%), occluded oil, coke, sulfide sulfur and the balance essentially alumina. The amount of sodium carbonate employed is at least sufficient under oxidizing conditions to convert molybdenum and any vanadium present to soluble Na.sub.2 MoO.sub.4 and NaVO.sub.3 and to neutralize SO.sub.3 produced during oxidation, the amount of sodium carbonate being at least that required stoichiometrically. The slurry is heated to a temperature of about 200.degree. C. to 350.degree. C. (e.g., 275.degree. C. to 325.degree. C.) and a pressure of about 800 psig to 2500 psig (e.g.

Abstract: A process is provided for recovering molybdenum and tungsten separately from a sulfide cake containing the same along with arsenic as an impurity. The process comprises dissolving essentially all of the tungsten and molybdenum values contained in the cake in a caustic solution containing at least about 5 but not more than about 6 moles of sodium hydroxide per mole of tungsten plus molybdenum contained in the cake, separating insoluble material from the resulting leach solution and then precipitating one metal value from the group consisting of molybdenum and tungsten preferentially from the other.

Abstract: Process for the recovery of molybdenum from an organic solution, such as a spent catalyst solution obtained from the molybdenum catalyzed epoxidation of an olefinically unsaturated organic compound with an organic hydroperoxide as oxidizing agent and removal from the crude epoxidation mixture of product epoxide and the alcohol corresponding to the hydroperoxide, said process comprising:(a) admixing the organic solution with water in an amount between about 0.5 and 10 percent, based on the weight of the organic solution;(b) heating the resultant admixture to a temperature in the range of between about 150.degree. C. and 250.degree. C. under pressure sufficient to maintain the admixture in the liquid phase and for a time sufficient to precipitate at least a portion of the molybdenum contained in the organic solution as a solid; and (c) separating the precipitated molybdenum containing solid from the organic solution.

Abstract: A process for extracting arsenic from aqueous solutions containing alkali metal carbonate, sulfate and hydroxide or hydrogen carbonate, at least one metal selected from the group consisting of vanadium, uranium and molybdenum in the form of an alkali metal salt, and inorganic and/or organic impurities, comprising the steps of caustifying the solution with lime to convert the alkali metal carbonates into hydroxides to precipitate the insoluble calcium salts formed, concentrating the solution by evaporation of the effluent liquids originating from the caustification step to obtain a precipitate substantially comprising alkali metal sulfate wherein the caustification is performed in two steps, consisting of (a) treating the solutions with an amount of lime approximately equal to but less than the stoichiometric amount necessary to convert the alkali metal carbonates into hydroxides as a first precipitate, and (b) after separating and washing the first precipitate, treating the resulting liquor with at least the

Abstract: Waste products from the chrome-tanning of hides are washed and then chopped in water, with subsequent hydrolyzation at a pH of at least 10.5 and at boiling or near-boiling temperature. The resulting suspension is filtered to yield a polypeptide solution and a cake of solids consisting essentially of chromium hydroxide. The solution is neutralized, dehydrated, cooled and filtered to provide a virtually chromium-free proteinaceous substance usable as plant or animal feed; the solids are washed, filtered and acidified to provide chromium sulfate suitable for reutilization in tanning.

Abstract: A process is disclosed wherein tungsten is recovered from hazardous waste material containing said tungsten, arsenic, and other impurities which can consist of magnesium, phosphorus, and silicon and the resulting waste is treated to render it nonhazardous according to EPA standards for arsenic. Said process involves digesting said hazardous waste material in an aqueous solution of an alkali metal hydroxide, adjusting the pH of the resulting solution to about 11.0 to about 13.0 with NaOH to precipitate essentially all of the magnesium and silicon species, filtering the digestion mix to remove the solids from said resulting solution which contains about 80 to about 100% of said tungsten and essentially none of said magnesium and said silicon, slurrying the hazardous solids in hot water, and adding to the slurry a ferric salt solution to precipitate ferric hydroxide, filtering this mixture to give a solid which passes the EPA standard test for solids with respect to arsenic.

Abstract: A process for the purification of solutions containing sodium or potassium carbonate, sulphate, hydroxide or hydrogen carbonate, and mainly at least one of the metals belonging to the group formed by vanadium, uranium or molybdenum, in the form of sodium or potassium salts, and inorganic and/or organic impurities, wherein the above-mentioned solutions are completely or partially caustified by the addition of an adequate amount of lime, whereby a first precipitate essentially containing calcium carbonate is separated, and the separated liquor is concentrated by evaporation until the hydroxide content is at most equal to 50%, to cause the production of a second precipitate which essentially comprises sodium or potassium sulphate, then, after separation thereof, a hydroxide-rich liquor is collected.This process is more particularly adapted for treatments of liquors resulting from the alkaline attach of vanadiferous and uraniferous ores.

Abstract: A method for recovering superalloy scrap is disclosed. The method involves oxidizing superalloy scrap in an aqueous acidic medium. The aqueous acidic medium has an oxidation potential sufficient to oxidize nonferrous additive superalloy elements to insoluble oxides thereof and to oxidize major superalloy constituents to aqueously soluble species. The insoluble solids from the aqueous solution are separated when the aqueous solution is extracted with an aqueously substantially insoluble tertiary amine to form an organic phase and an aqueous phase. The aqueous phase contains essentially nickel and chromium values. The organic phase is sequentially extracted with aqueous solutions which selectively solubilize individual metal value species to form individual aqueous solutions having substantially single metal value species therein. The metal value species solutions are processed to obtain substantially pure metals.

Abstract: The invention is directed to a process and apparatus for dissolving a molybdenum core wire in a tungsten filament coil which comprises reacting the filament coil in a sealed reaction vessel fitted with at least one liquid trap with an acid mixture containing nitric acid, sulfuric acid and water in the presence of an oxygen containing gas wherein the amount of the oxygen containing gas is controlled by a liquid level sensing device attached to the liquid trap. The invention enables efficient conversion of nitrogen oxide gases to nitric acid and recovery of molybdenum from the reaction vessel.

Abstract: A process for obtaining molybdenum as a useful product from aqueous solutions to be purified, according to claim 1 of French patent No.

Abstract: A process for enhancing recovery of cobalt from spent hydroprocessing catalysts when the spent catalyst particles are first roasted at between 400.degree. C. and 600.degree. C. and then contacted with a first aqueous solution of ammonia and an ammonium salt to recover nickel, cobalt, molybdenum and vanadium. The once-leached spent hydroprocessing catalysts are contacted with a second aqueous solution of sulfur dioxide. The metal values are precipitated with hydrogen sulfide and the precipitate is roasted with unroasted spent hydroprocessing catalysts.

Abstract: Process for extracting molybdenum from aqueous solutions containing alkali metal carbonate, sulphate, hydroxide or hydrogen carbonate and, primarily, one at least of the metals belonging to the group formed by vanadium, uranium and molybdenum, in the form of alkali metal salts, and mineral and/or organic impurities, said solutions resulting from an ore attack cycle and being taken off after extraction of the metal being sought, in the form of a concentrate, wherein said solutions are caustified by the addition of a suitable amount of lime, converting the carbonate present into alkali metal hydroxide, a first precipitate is separated from the alkali metal hydroxide-rich liquor, said liquor is concentrated until the alkali metal hydroxide content is at most equal to 50%, to cause the production of a second precipitate formed by alkali metal sulphate and molybdate, which is solubilized in an aqueous recycle liquor, said re-dissolution liquor then being treated with sulphide ions and then acidified to give a pH-v

Abstract: Process for the purification of an aqueous solution containing alkali metal carbonate, sulphate, and hydroxide or hydrogen carbonate and primarily one at least of the metals belonging to the group formed by vanadium, uranium and molybdenum, in the form of alkali metal salts, and mineral and/or organic impurities, said solutions resulting from an ore attack cycle and being taken off after extraction of the metal being sought, which comprises treating said solutions by means of lime at a temperature which is at most equal to the boiling temperature, to convert the carbonate and hydrogen carbonate present into alkali metal hydroxide, then effecting separation and washing of a first precipitate of calcium carbonate and a liquor which is enriched in respect of alkali metal hydroxide, concentrating it by evaporation to cause production of a second precipitate which essentially comprises alkali metal sulphate, separating it from the hydroxide-rich liquid phase, re-dissolving it in an aqueous medium and treating the

Abstract: A direct precipitation method based on the insolubility of uranyl phosphate in carbonate containing solutions at pH 6-6.5 and its insolubility at pH 8 is described. The method eliminates the use of ion exchange columns for removing uranium values from uranium leachates and can be readily applied to an integrated field operation.

Abstract: A process for recovering uranium values from a sulphate solution containing dissolved uranium and molybdenum and with a pH not exceeding about 5.5, includes reacting the solution with ammonia at a pH in the range of from about 8 to about 10, without the solution existing for any significant time at a pH of around 7, with resultant precipitation of uranium values relatively uncontaminated by molybdenum. The uranium containing precipitate is separated from the remaining solution while maintaining the pH of the remaining solution within the same range.

Abstract: Molybdenum catalyst employed in the epoxidation of an olefin with an organic hydroperoxide preferably the epoxidation of propylene, is recovered from the bottoms fraction by adding aqueous alkaline material to the bottoms fraction and separating the aqueous phase. The molybdenum can be recovered from the aqueous phase by acidification and precipitating it as an insoluble compound.

Abstract: A continuous process is described, wherein chromium-containing waste waters are subjected to continuous hot treatment with acetic acid or with alkaline acetates and alkaline hydroxides at a temperature from 40.degree. C. to boiling point and at atmospheric pressure, at a pH higher than 6.5, preferably between 7 and 10, particularly about 7.5. Thus, a "sandy" type of chromium hydroxide is obtained, having a titer in Cr.sub.2 O.sub.3 of 20 to 40% by weight, which quickly filters, is easily soluble in acids, and thereby affords an easy valorization both as a tanning agent and as a raw material for preparing other chromium compound.

Abstract: An iron-free chromium(III) compound is precipitated at an elevated temperature and pressure from an acidic aqueous solution which contains iron and chromium. In order to prevent coprecipitation of iron, an additive is added to the precipitation stage in an amount sufficient to provide in the precipitation conditions at least 2 g/l of bivalent chromium in the solution.

Abstract: A method of recovering molybdenum oxide by oxidation of a molybdenum sulfide concentrate contaminated with impurities wherein the concentrate in an average particle size in the range of 20 to 90 microns is suspended to form an aqueous suspension which is oxidized at elevated temperature and an elevated oxygen partial pressure in an autoclave. The suspension withdrawn from the autoclave is subjected to filtration to remove the molybdenum oxide from the primary filtrate containing sulfuric acid and this filtrate is neutralized with lime to form calcium sulfate which is then removed from the suspension to provide a second filtrate. According to the invention, only this second filtrate is recirculated at a rate such that the suspension density in the oxidation stage is between 100 to 150 g of solids per liter and this suspension density is maintained in the oxidation stage by the recirculation.

Abstract: Disclosed is a process for reducing hexavalent chromium [Cr(VI)] in aqueous solutions to trivalent chromium [Cr(III)] by reacting a catalyzed hydrazine composition with the hexavalent chromium at a pH in the range from about 6.0 to about 8.0 to form an aqueous slurry of trivalent chromium compound, said catalyzed hydrazine composition comprising(a) a hydrazine compound,(b) at least 0.0005 parts by weight of a quinone compound per one part of hydrazine compound; and, preferably;(c) at least about 0.0005 parts by weight of an organometallic complex per part of hydrazine compound, said organometallic complex being the reaction product of:(i) a hydroxide selected from the group consisting of cobaltous hydroxide and manganous hydroxide; and(ii) at least one organic ligand selected from the group consisting of unsubstituted and substituted amino derivatives of carboxylic acids and salts thereof.The solid particles of trivalent chromium may then be separated from the aqueous solution by conventional means (e.g.

Abstract: Tungsten is recovered from tungsten ore concentrates in the form of sodium tungstate by a basic process in which ground ore is first digested in a sodium hydroxide solution followed by diluting the solution to dissolve sodium tungstate separating the solution from the caustic insoluble sludge and crystallizing soluble sodium tungstate, wherein the present invention permits improved recovery of tungsten from difficult to process ores by the process steps of comminuting said tungsten ore concentrate to a particle size less than about 200 mesh, dispersing the comminuted ore to separate agglomerated particles, adding the dispersed ore to aqueous sodium hydroxide at a concentration of at least 10 molar and digesting at a temperature of from about 75.degree. C. to 150.degree. C. for a sufficient period of time to convert substantially all of the tungsten values to soluble sodium tungstate, and diluting the mixture to reduce the sodium hydroxide concentration to between about 4.5 and 5.

Abstract: Tungsten is recovered from tungsten ore concentrates in the form of sodium tungstate by a basic process in which ground ore is first digested in a sodium hydroxide solution followed by diluting the solution to dissolve sodium tungstate separating the solution from the caustic insoluble sludge and crystallizing soluble sodium tungstate, wherein the present invention permits improved recovery of tungsten from difficult to process ores by the process steps of drying the insoluble sludge portion, comminuting the dried sludge to a particle size less than about 200 mesh, and dissolving said comminuted sludge in 4.5-5.5 molar NaOH to recover substantially all of the tungsten values.

Abstract: Tungsten is recovered from tungsten ore concentrates in the form of sodium tungstate by a basic process in which ground ore is first digested in a sodium hydroxide solution followed by diluting the solution to dissolve sodium tungstate separating the solution from the caustic insoluble sludge and crystallizing soluble sodium tungstate, wherein the present invention permits improved recovery of tungsten from difficult to process ores by the process steps of comminuting said tungsten ore concentrate to a particle size less than 325 mesh, adding said comminuted ore to aqueous sodium hydroxide at a concentration of at least 10 molar and digesting at a temperature of from about 75.degree. C. to 150.degree. C. for a sufficient period of time to convert substantially all of the tungsten values to soluble sodium tungstate, and diluting the mixture to reduce the sodium hydroxide concentration to between about 4.5 and 5.5 molar at a temperature below about 90.degree. C.

Abstract: The process is principally based upon an electrochemical technique due to which the binding material for tungsten and cobalt is dissolved and from the solution under certain conditions cobalt or its composition is regained. From the undissolved material after electrolysis tungsten is disposed. By this improved method a very fast decomposition of the hard metal is obtained. Tungsten carbide scrap--a waste material from hard metal tools--can be a decomposed preferably by electrolysis as shown in FIGURE attached.

Abstract: Selected portions of metal carbide are recovered from scrap material containing pieces of cemented metal carbide having various compositions of metal carbide distributed in a matrix material. The scrap material is treated with a suitable liquid for a sufficient period of time to dissolve the matrix material and form a piece of matrix depleted metal carbide which is introduced as a feed into a ferrofluid material. A magnetic field is passed through the ferrofluid for positioning pieces of metal carbide of the type having a heavier density spaced from pieces of metal carbide of a lighter density. The separated portions of matrix depleted metal carbide are collected to produce metal carbide powder which may be further reprocessed to produce a desired cemented metal carbide.