Abstract: A method and system for removing toxic substances such as selenium from industrial and agricultural drain water, and particularly refinery effluent liquor, achieves very high removal of the toxic substance economically, by a chemical reduction process. Preferably, the effluent liquor is first filtered, which ordinarily is effective to remove selenium suspended in the liquor. Next the liquor is heated, preferably to about 150.degree. F., and a reducing agent such as finely powdered iron is added to bring, for example, the selenium down from a +6 valence to +4 and lower valences. Sulfur is added to the slurry to greatly improve the effectiveness of the iron in reducing the liquor. The slurry is constantly agitated. After a reaction time which may be about 15 minutes, an oxidizing agent is added, with the temperature of the slurry then raised to at least about 180.degree., with continued agitation.

Abstract: A method of removing Cr.sup.+6 from a solution is provided. In removing the Cr.sup.+6, an effective amount of an alkali metal dithionite is added to the solution to reduce substantially all of the Cr.sup.+6 to Cr.sup.+3. A soluble material is provided in the solution which will form a precipitate. Further, the soluble material is selected such that it will coprecipitate and tie up any dissolved or colloidal Cr.sup.+3 formed as a result of the reduction of the Cr.sup.+6. In one embodiment, the solution is alkaline and preferably, the pH of the solution is reduced sufficiently such that the soluble material will quickly precipitate and form the coprecipitate material with the Cr.sup.+3. Thereafter, the solution is filtered to remove the coprecipitated material from the solution and thereby form a supernatant solution suitable for waste discharge which has substantially lowered chromium values. The precipitate has the Cr.sup.+3 tied up in an insoluble non-leachable form.

Abstract: A process for treating a sludge comprises digesting the waste material with a mixture of sulfuric acid and hydrogen peroxide to form an acidic digestion solution and a digestion residue. The digestion residue containing the major portion of tungsten and other refractory metals is reacted with NaOH to solubilize the major portion of tungsten values to a liquid concentrate that is separated from the insoluble solid that contains the major portion of the other refractory metals such as tantalum and niobium. The digestion solution containing the major portion of the transition and rare metals is treated with a base to selectively recover iron as a solid iron hydroxide precipitate which is separated from the resulting liquor. The liquor is then treated again with a base to selectively recover the other metals such as Sc, Cr, rare earths, but not Mn, as a solid metal hydroxide precipitate that is separated from the solution.

Abstract: The present invention is directed to a method for treating a sludge containing substantial amounts of chromium, aluminum, calcium, iron, and phosphorous. The method comprises forming a slurry of the sludge; reacting the slurry with an acid to dissolve substantially all the aluminum and chromium and provide a solids residue comprising mostly calcium sulfate; separating the chromium/aluminum-containing solution from the solids residue; raising the pH of the chromium/aluminum solution to precipitate chromium as chromium hydroxide; and separating the chromium hydroxide from the remaining aluminum-containing solution. The chromium hydroxide is then enriched with an alkali or earth alkali compound and calcined in an oxidizing atmosphere to convert the chromium to a chromate. The calcine is leached in an aqueous medium at a controlled pH to yield a high concentration, high purity chromate solution suitable for producing metallic chromium or a variety of chromium chemicals.

Abstract: In the manufacture of ammonium paratungstate, sulfide is added to a tungsten-containing solution in order to precipitate molybdenum sulfide. Volatiles, including sulfides, evolved during this process are collected in a caustic scrubbing solution. The sulfide values in the caustic scrubbing solution may be reused to precipitate molybdenum sulfide by first treating the caustic scrubbing solution with alkaline earth chloride or sulfate to precipitate out alkaline earth carbonate.

Abstract: A process for removing at least a portion of any iron, copper, nickel and chromium ions that are chelated by a alkylenepolyamine polyacetic acid or salt in an aqueous liquid waste. The process comprises the steps of (a) adjusting the pH of the liquid to above about 10; (b) adding sufficient sodium sulfide to react with at least a portion of the copper ions; (c) separating precipitated iron and copper compounds; (d) adding nitric acid to adjust the pH to the range of about 6 to 8; (e) adding sufficient sodium nitrite to the liquid to react with at least a portion of the nickel and chromium present; (f) heating the liquid to above about 575.degree. F. for at least about 15 minutes to facilitate precipitation of nickel and chromium; and (g) separating precipitated solids to leave a non-hazardous filtrate.

Abstract: A method of removing undesired ions, such as chlorine, hypochlorite, chromium, cyanide and heavy metal ions, from an aqueous preparation containing one or more of said ions consists of adding to the aqueous preparation an effective amount of magnesium bisulfite to inactivate the undesired ions and then adjusting the pH of the mixture to an appropriate pH. Compositions containing magnesium bisulfite and divalent and trivalent ions are disclosed.

Abstract: Disclosed is a method of making particle which comprise hydrous trivalent chromium oxide having the empirical formula CrO.sub.2 H intimately associated with a pulverulent carbonaceous substrate. A composition is formed which comprises an aqueous solution of water-soluble hexavalent chromium compound and a reducing agent in an amount sufficient to reduce the hexavalent chromium compound to the hydrous trivalent chromium oxide and to reduce the hydrous trivalent chromium oxide to metallic chromium. The reducing agent comprises a water-insoluble pulverulent carbonaceous substrate. Chrome metal can be made by heating the particles at a temperature of about 1100.degree. to about 1400.degree. C.

Abstract: The chromic anhydride contained in soluble form (chromic acid) in exhausted, polluted chromium plating baths is recovered by alkalizing the exhausted chromium plating liquid to a pH comprised between 3 and 7 at a temperature of 70.degree. C. with a commercial sodium hydroxide solution, keeping the mass in reaction at this temperature for an hour and filtration separating the precipitate obtained. The filtered solution having a specific gravity of 1.25 kg/l, contains CrO.sub.3 (22% in weight) which is then reduced with sulphur dioxide to obtain a solution containing basic chromium sulphate and sodium sulphate, suitable for use as a tanning bath; in this manner pollution is avoided and the waste chromium is exploited. The solution containing CrO.sub.3 can also be introduced into a hexavalent chromium salt production cycle.

Abstract: An epoxidation reaction product formed by the molybdenum catalyzed reaction of propylene with tertiary butyl hydroperoxide to provide propylene oxide and tertiary butyl alcohol is separated by distillation into a propylene fraction, a propylene oxide fraction, a tertiary butyl alcohol fraction and a heavy liquid distillation fraction composed primarily of tertiary butyl hydroperoxide, tertiary butyl alcohol, dissolved molybdenum catalyst, and impurities including lower aliphatic C.sub.1 -C.sub.4 carboxylic acids, and the heavy liquid distillation fraction is saturated with ammonia to precipitate the molybdenum therefrom for recovery.

Abstract: An epoxidation reaction product formed by the molybdenum catalyzed reaction of propylene with tertiary butyl hydroperoxide to provide propylene oxide and tertiary butyl alcohol is separated by distillation into a propylene fraction, a propylene oxide fraction, a tertiary butyl alcohol fraction and a heavy liquid distillation fraction composed primarily of tertiary butyl hydroperoxide, tertiary butyl alcohol, dissolved molybdenum catalyst, and impurities including lower aliphatic C.sub.1 -C.sub.4 carboxylic acids, and the dissolved molybdenum content of the heavy distillation fraction is adjusted to about 300 to 500 ppm of dissolved molybdenum, if necessary, by treatment with a precipitating agent and contacted with a solid adsorbent consisting essentially of a synthetic, porous, high surface area amorphous magnesium silicate.

Abstract: Process for separating sulphate from a contaminating chromium component contained in an aqueous liquor by the crystallization of a sulphate compound. The sulphate may be separated substantially free of chromium component by adjustment of the pH to the range of from about 2.0 to about 6.5, followed by cooling of the liquor to precipitate the sulphate compound from solution which sulphate is subsequently removed. The process provides an effective method for the separation of sulphate from dichromate, and is particularly useful in the production of chlorate.

Abstract: Potassium impurity is removed from ammonium molybdate by dissolving the ammonium molybdate in hot acid, allowing the acid solution to cool whereby the ammonium molybdate precipitates out of the solution as molybdenum trioxide and then separating, washing and drying the molybdenum trioxide.

Abstract: A process for the heavy-metal decontamination of contaminated substances such as natural and industrial sludges, thermal residues and soils. The contaminated starting substance is treated with an acid and the dissolved metal salts are precipitated as metal hydroxides in the pH range of about 3.5-11. The exact control of the pH value makes it possible to isolate individual metal fractions which can be used as raw materials in the metallurgical industry.

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 process for eliminating an industrial waste sludge by converting its metal values into useful products involves the selective leaching of Mn, divalent Fe, and other valuable metals, such as Sc, Co, Cr, Ni, Th, rare earths, etc. with a mixture of dilute sulfuric acid and a reductant at ambient temperature. Scandium is recovered by passing the leachate through an ion exchange column which is packed with a weakly cationic resin. The retention of other metals on the resin column is negligible. The scandium is eluted from the resin column and converted to a solid product. The raffinate from the ion exchange column is titrated with an alkali solution to convert the metals, except divalent Mn and Fe, to a solid metal hydroxide. After the separation the filtrate is treated with an alkali and an oxidant to recover iron as a solid product of iron oxide which is separated from the solution.

Abstract: A process for the production of sodium dichromate comprising reacting sodium chromate with acids, the acids being sulfuric acid and NaHSO.sub.4 formed as a waste product in the production of CrO.sub.3 and thus being contaminated with chromium compounds, adding PO.sub.4 ions in excess to the NaHSO.sub.4 contaminated with chromium compounds and precipitating the Cr(III) present therein as CrPO.sub.4 at a temperature of 50.degree. to 100.degree. C. and at a pH value of 3 to 6.

Abstract: A method for recovering chromium from chromium-bearing material which comprises heating the material which can contain any one or combination of Co, Ni, Fe, Mo, and W with solid alkali metal hydroxide in an oxidizing atmosphere at 600.degree. C.-1000.degree. C. to form a fused material containing water soluble compounds of Cr, Mo, and W contained therein. The fused material is cooled and contacted with water to form a leach solution and a residue. The leach solution is adjusted to a pH of from about 5-8 with sulfuric acid, and a water soluble calcium salt is added. The chromium-rich liquor is then adjusted to a pH of 1-3 with sulfuric acid. Sodium metabisulfite is added to the chromium-rich liquor to reduce the chromium to the trivalent state after which the pH is adjusted to 5-8 with a base to form a precipitate of essentially all of the chromium.

Abstract: Directed to a process for producing a tungsten product of enhanced purity from ammonium paratungstate (APT) with a minimum number of processing steps which comprises mixing the APT with an ammonium solution, autoclaving the mixture at a temperature above the boiling point thereof to dissolve the APT and recrystallizing APT from the solution to yield an APT product of enhanced marketability.

Abstract: A method is provided for treating sludge containing substantial amounts of chromium, aluminum and iron and residuals of other elements. The method comprises forming a slurry of the sludge in water at a temperature ranging from ambient to 150.degree. F. with the specific gravity of the slurry ranging from about 1.05 to 1.25, and adding a mineral acid to the slurry to provide a pH ranging from about 0.1-3 to dissolve selectively the aluminum and the chromium and leave a solids residue containing gangue material comprising an oxidized iron compound, calcium sulfate, calcium fluoride, calcium silicate among other solids. The pH of the solution is controlled at range of about 2 to 3.5 to precipitate undesirable elements, including iron, without substantially adversely affecting the dissolved chromium and aluminum.

Abstract: A method and system for removing toxic substances such as selenium and molybdenum from agricultural irrigation water achieves nearly 100% removal of the toxic substance economically, by a chemical reduction process. The process is particulary efficacious for removing naturally occurring selenium and molybdenum from irrigation water which has seeped through the ground and taken compounds of these metals into solution. Preferably, the drain tile water solution is first concentrated, to about 30% dissolved solids. This may be economically accomplished by on site evaporation in an open pond which is impermeable to seepage. Next the concentrated brine solution is heated, preferably to about 150.degree. F., and a reducing agent such as finely powdered iron is added to bring, for example, the selenium down from a +6 valence to +4 and lower valences. Wettable sulfur is added to the slurry to greatly improve the effectiveness of the iron in reducing the solution. The slurry is constantly agitated.

Abstract: A process for substantially completely removing a minor amount of molybdenum dissolved in a substantially anhydrous organic solution, such as a heavy distillation fraction resulting from the removal of unreacted propylene, propylene oxide and tertiary butyl alcohol from an epoxidation reaction mixture:wherein from about 1 to about 10 wt. % of an aqueous solution of sodium meta borate containing from about 1 to about 10 wt. % of dissolved sodium meta borate is added to an organic solution containing dissolved molybdenum catalyst in an amount sufficient to provide a molar excess of sodium meta borate, based on the gram atoms of dissolved molybdenum in said organic solution, to provide a mixture,wherein the mixture is maintained at a temperature ranging from about ambient temperature up to about 100.degree. C. at a pressure of about 0 to about 1,000 psig. for about 0.

Abstract: A process for the treatment of flue dust from copper and lead smelters includes the steps of subjecting a slurry (10) of water and flue dust to a first caustic leach (12) to form a first liquids soluble sulfate solution (14) and a first solids portion (15), subjecting the solids portion to a second caustic leach (16) to solubilize lead and arsenic in a second liquid portion (22) and, selectively extracting the arsenic from the second liquid portion by precipitation (23).

Abstract: According to the subject method of refining a ferrous ion-containing acid solution, a metal selected from a group including Al, Cr, V, B, and Zn or an acid solution of that metal is added to a ferrous ion-containing acid solution, such as an acid solution which remains after steel is washed with an acid. The pH value of the acid solution is controlled to be within the range of 3.5 to 6 by adding an alkali liquid to the acid solution, whereby a hydroxide salt of the added metal is produced in the acid solution and the impurities in the acid solution are captured by the produced hydroxide salt. As a result, the impurities can be eliminated from the acid solution such that the Si component (e.g., SiO.sub.2) content in the acid solution is within the range of 2 to 3 ppm or less. Since the content of the other impurities such as Al, Ti, and Cr can also be reduced, a high-purity iron oxide can be obtained from the resultant acid solution.

Abstract: An elastic bar member is coupled to an orbiting mass oscillator and the entire assembly is suspended from a cable or the like such that the bar member has freedom of lateral motion and is nakedly immersed in a slurry having particulate material contained therein such as a mineral ore reject from which metal has been extracted. The rotor of the orbiting mass oscillator is driven at a speed such as to generate cycloidal sonic energy in the bar preferably at a frequency such as to set up resonant standing wave vibration of the bar in a cycloidal quadrature pattern. The cycloidal vibrational energy tends to set the surrounding fluid material into a whirling rotation or rotary traveling wave which facilitates the agglomeration or coagulation of the particles in the material and enhances the settling operation to make for more complete separation of the particles from the liquid.

Abstract: A process for purifying an aqueous, hydrogen sulfide-scrubbing solution which contains a water-soluble transition metal component, such as a vanadium component or an iron component, in addition to at least one water-soluble organic compound, such as an aromatic sulfonate or an alkanolamine, in which the scrubbing solution is mixed with particles of a spent solid catalyst containing molybdenum and aluminum and a basic aqueous solution, preferably a solution comprising sodium aluminate, to form a slurry which is subsequently contacted with an oxygen-containing gas under conditions such that the molybdenum in the catalyst is solubilized. Thereafter, molybdenum is precipitated from the solution along with the water-soluble transition metal component and a wastewater substantially free of the transition metal component and the organic compound originally present in the scrubbing solution is recovered.

Abstract: An elastic bar member is clamped to an orbiting mass oscillator and the entire assembly is suspended from a cable or the like such that the bar member has freedom of lateral motion and is nakedly immersed in a leachant having a material contained therein such as a mineral ore from which metal is to be extracted. The rotor of the orbiting mass oscillator is driven at a speed such as to generate cycloidal sonic energy in the bar preferably at a frequency such as to set up resonant standing wave vibration of the bar in a cycloidal nutating pattern. The cycloidal vibrational energy tends to set the surrounding fluid material into a whirling rotation or rotary traveling wave which facilitates the mixing of the ore and leachant and enhances the leaching operation to make for more complete separation of the mineral from the ore.

Abstract: A method of processing manganese ore by adding the ore to an aqueous solution of acid and H.sub.2 O.sub.2 to form a leach pulp. The leach pulp is agitated for a predetermined time period at predetermined temperatures. The leach pulp is then separated into a solid fraction and a liquid fraction containing solubilized metals. The solubilized metals are then recovered from the liquid fraction.

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: A process for preparing a tungsten-188/rhenium-188 generator having a tungstate matrix containing W-188 produced by irradiating tungsten-186 in the tungstate compound. High activity, carrier-free rhenium-188 may be obtained by elution. Substrates for further purifying the rhenium-188 eluate are also described.

Abstract: There is disclosed a process and an apparatus for beneficiating a mineral ore, such as phosphate-containing ore, in a substantially vertical column. The feed subjected to the benefication preferably has a particle size of less than 20 mesh. The feed is introduced into the column, containing at least one baffle, into which there is also introduced a gas at the bottom portion thereof and a liquid through at least one column inlet at the top of the column. The baffle and the rates of introduction of the feed, the gas, and the liquid are such as to create relatively high turbulence conditions within the column. The enriched, beneficiated product is removed at the top of the column, while the waste products, such as silica-containing material, in the case of a phosphate ore, are recovered at the bottom of the column.

Abstract: A process for the removal of cyanide and other impurities from an aqueous solution is disclosed. The process comprises adding copper ion and ferrous ion as reagents to the solution at a pH of about 4 to 8 with a ratio of copper to cyanide in the range of 3:1 to 10:1 by weight and with a ratio of iron to copper of at least 0.3:1 by weight.

Abstract: Modified starch compositions and their use for flocculating mineral waste residues, particularly the red mud containing alumina liquors from bauxite residues, comprising the addition to an alumina liquor of a flocculating amount of a methylated starch which, optionally, may be hydrolyzed, or a methylated starch which is also sulfonated and, optionally, may be hydrolyzed. Preferably, the methylated starch compositions are potato and dasheen starch derivatives prepared at temperatures of about 50.degree. to about 85.degree. C.

Abstract: A method is disclosed for purifying ammonium dimolybdate which comprises dissolving ammonium dimolybdate containing arsenic as an impurity in water to form an ammonium molybdate solution and insolubles containing essentially all of the arsenic, filtering off the insolubles from the solution, adjusting the pH of the solution to at least about 9.0 and then crystallizing pure ammonium dimolybdate from the solution wherein the arsenic content is less than about 8 weight ppm.

Abstract: The present invention is a process for selectively precipitating molybdenum in a form that is substantially free from vanadium impurities. The molybdenum is precipitated in the form of ammonium octamolybdate which has a molybdenum to vanadium ratio of about 400:1 in an initial crystallization and a ratio of about 1300:1 in a subsequent recrystallization.

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: A process for the recovery of a spent molybdenum catalyst from a hydroprocess for the upgrading of a nickel and vanadium containing hydrocarbonaceous mineral oil. The nickel and vanadium contaminated molybdenum catalyst is oxidized to convert the metals to oxides. Aqueous ammonia is added to preferentially dissolve molybdenum from nickel and vanadium. An amount of ammonia is used in excess of the amount required to produce an active catalyst for recycle and the excess ammonia is removed prior to recycle of the catalyst. The selectively of the separation of molybdenum from nickel and vanadium is improved by adding a reducing agent before or during the ammonia dissolving step. Hydrazine is a suitable reducing agent. The recovered molybdenum is sulfided and recycled.

Abstract: A process is disclosed for recovering tungsten from tungsten bearing material containing arsenic. The process involves adjusting a water slurry of the material to a pH of less than about 4 with an acid to solubilize the major portion of the tungsten, adding an insoluble ferric compound to the slurry to form a two phase system in which the solid phase contains the major portion of the arsenic and of any phosphorus which may be present, and a solution phase containing the major portion of the tungsten. After separation of the solid from the solution, the solution is adjusted to a pH of less than about 2 with an acid and a suffficient amount of hexamethylenetetramine is added to the solution to precipitate the major portion of the tungsten, followed by separating the precipitate from the resulting liquor. The solid phase containing the arsenic and phosphorus, if any, can be contacted with water and a soluble ferric salt to produce a treated solid which passes the EP toxicity test.

Abstract: Carrier supported catalysts are prepared, comprising metal ions which in their most stable state occur as anions or as higher-valency cations which exhibit a poor interaction with the support material by deposition-precipitation through increasing the hydroxyl ion concentration in homogeneous solution. According to the invention, prior to deposition-precipitation the metal ions are electrochemically reduced to soluble metal ions having a lower valency. Preferably, the pH value of a suspension of the support to be loaded in a solution of the electrochemically reduced metal ions is homogeneously increased by hydrolysis of compounds such as urea or isocyanate, or by the controlled injection of an alkaline solution below the surface of the suspension.

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: The present invention involves a treatment technique for drastically reducing the volume of hazardous sludge generated by the chemical reduction of chromium contaminants and the precipitation of heavy metal contaminants from contaminated electroplating wastewater. The wastewater is first adjusted to a pH of from about 8 to 10 and then treated with sodium sulfide to provide sulfide ions to effect precipitation of heavy metal contaminants followed by treatment with ferrous sulfate or ferrous chloride to provide ferrous ions to chemically reduce the hexavalent chromium to its trivalent state. This method produces approximately one-fourth the sludge generated by the previously known acidic reaction treatment using only ferrous sulfide.

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 provided for the removal of lead contaminants from ores and mineral concentrates, comprising leaching the concentrates, at elevated temperatures, with an aqueous solution containing an aminopolycarboxylic acid. After separating the solution from the concentrates, lead can be precipitated by treating the solution with a sulfide; the solution can be recycled for use as a leachant.

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: A process for producing a non-hazardous sludge from an aqueous solution which contains heavy metals comprising the steps of: (a) adding phosphoric acid or an acid phosphate salt to the aqueous solution to precipitate the heavy metals; (b) lowering the pH of the solution to less than about 5.0; (c) adding a coagulant to the solution; (d) raising the pH of the solution to above about 7.0 by the addition of a calcium source; and (e) dewatering the resulting non-hazardous sludge.

Abstract: Metal values and alumina are recovered from spent, usually oily, catalysts by oxygen pressure leaching with sodium hydroxide and/or sodium aluminate to dissolve molybdenum, vanadium and/or tungsten and provide a solid, filterable residue containing alumina and cobalt and/or nickel, the residue is digested with sodium hydroxide to give a sodium aluminate solution and a residue enriched in nickel and/or cobalt, alumina is recovered from the sodium aluminate solution as a solid and the remaining supernatant solution is recycled to the oxygen pressure leaching step wherein the alumina content of the aluminate solution is precipitated and a bleed for metals in the aluminate solution is provided.

Abstract: A process is disclosed for recovering chromium from a chromium bearing material containing cobalt, molybdenum, and tungsten. The process involves roasting the material and alkali metal compound at a temperature of at least about 400.degree. C. for a sufficient time to react the alkali metal compound with the material and form a reacted mixture containing essentially all of the chromium, molybdenum, and tungsten as alkali salts. The reacted mixture is water leached to dissolve the alkali salts and form a leach solution containing essentially all of the chromium, molybdenum, and tungsten, and a leach solid containing essentially all of the cobalt. After separation of the leach solution from the leach solid, the pH of the leach solution is adjusted to from about 0.5 to about 3.0 with an acid and a sufficient amount of a reducing agent is added to reduce essentially all of the chromium to the trivalent state.

Abstract: Spent hydrodesulfurization catalysts containing alumina, at least one metal from the group consisting of molybdenum, tungsten and vanadium and at least one metal from the group consisting of nickel and cobalt, sulfur, and, usually, residual oil are oxygen pressure leached at a temperature of at least about 400.degree. F. with a base from the group consisting of sodium hydroxide and sodium aluminte in at least stoichimetric amount to yield a solution having a pH between about 7 and 9 containing dissolved molybdenum, vanadium and any tungsten which may be recovered and a readily filterable residue containing aluminum, nickel and cobalt which may be worked up to recover the valuable constituents, with overall processing being accomplished in an environmentally acceptable manner.