Abstract: The process chemistry during the oxidation of molybdenite concentrates in an oxygen pressure leach can be controlled by regulating the amount of ferric iron and excess sulfuric acid recycled as autoclave discharge slurry or filtrate to the autoclave feed. A computer model capable of predicting the concentration of soluble molybdenum in the autoclave discharge and based on the concentrate and recycle analyses was developed.

Abstract: High purity ammonium dimolybdate or molybdenum oxide is produced by the pressure oxidation of low grade molybdenite concentrates or molybdenum intermediates. The process entails nearly complete oxidation of the sulfide minerals while optimizing the process chemistry and autoclave conditions to solubilize as little of the molybdenum values as possible. The autoclave discharge 12 is then subjected to a leaching step, either an alkaline leach 50, 400 or ammonium leach 250 process, before or after a liquid/solid separation step 20, 220, 410. The solution is then subjected to (a) filtration 60, 410, solvent extraction 70, 440, crystallization 90,450, and calcination 120, 480 or (b) filtration 260, 280, crystallization 290, and calcination 320 to produce a product suitable for chemical-grade molybdenum oxide 125, 325, 485.

Abstract: High purity ammonium dimolybdate or molybdenum oxide is produced by the pressure oxidation of low grade molybdenite concentrates or molybdenum intermediates. The process entails nearly complete oxidation of the sulfide minerals while optimizing the process chemistry and autoclave conditions to solubilize as little of the molybdenum values as possible. The autoclave discharge 12 is then subjected to a leaching step, either an alkaline leach 50, 400 or ammonium leach 250 process, before or after a liquid/solid separation step 20, 220, 410. The solution is then subjected to (a) filtration 60, 410, solvent extraction 70, 440, crystallization 90,450, and calcination 120, 480 or (b) filtration 260, 280, crystallization 290, and calcination 320 to produce a product suitable for chemical-grade molybdenum oxide 125, 325, 485.

Abstract: The process chemistry during the oxidation of molybdenite concentrates in an oxygen pressure leach can be controlled by regulating the amount of ferric iron and excess sulfuric acid recycled as autoclave discharge slurry or filtrate to the autoclave feed. A computer model capable of predicting the concentration of soluble molybdenum in the autoclave discharge and based on the concentrate and recycle analyses was developed.

Abstract: A copper alloy plumbing fixture containing interdispersed lead particles coated non-continuously on a water contact surface to resist the leaching of lead into potable water systems. The leach resistant fixture is prepared by immersing conventional copper alloys in a bismuth nitrate solution, selectively and non-continuously coating the lead dispersoid particles on the water contact surface with bismuth, tin or copper.

Abstract: A copper alloy plumbing fixture containing interdispersed lead particles coated noncontinuously on a water contact surface to resist the leaching of lead into potable water systems. The leach resistant fixture is prepared by immersing conventional copper alloys in a bismuth nitrate solution, selectively and noncontinuously coating the lead dispersoid particles on the water contact surface with bismuth. Tin may be substituted for bismuth to obtain similar results.

Abstract: A copper alloy plumbing fixture containing interdispersed lead particles coated noncontinuously on a water contact surface to resist the leaching of lead into potable water systems. The leach resistant fixture is prepared by immersing conventional copper alloys in a bismuth nitrate solution, selectively and noncontinuously coating the lead dispersoid particles on the water contact surface with bismuth. Tin may be substituted for bismuth to obtain similar results.

Abstract: A method for electrochemically minimizing sulfide scale buildup on a metal surface by connecting the surface as an anode and periodically reversing the current flow at predetermined intervals.

Abstract: A novel process for the recovery of alumina and potassium sulfate from alunite is provided comprising leaching the alunite with potassium hydroxide to which no sodium materials have been added, said leach solution being saturated with potassium sulfate. Aluminum values are solubilized into the leachate, and potassium and sulfur values are rendered soluble, but remain in the residue. The leachate is desilicated if necessary, preferably with lime, and aluminum trihydroxide is precipitated therefrom, followed by calcining to alumina product. The residue is leached to solubilize potassium sulfate in a secondary leach and the potassium sulfate product crystallized therefrom. Potassium hydroxide is regenerated from a portion of the potassium sulfate secondary leachate by several methods.Novel procedures for regenerating alkali metal hydroxides from the corresponding sulfates are also provided including routes involving formates and carbonates as intermediates and pyrohydrolysis.

Abstract: A process for stripping tungsten values from a tungsten-bearing acidic liquid organic phase into a basic aqueous ammoniacal stripping solution comprises mixing the organic phase and the stripping solution with a high-shear mixing device to maximize the pH gradient between the organic phase and the aqueous solution whereby growth of any precipitated ammonium paratungstate crystals is minimized and the dissolution thereof is maximized and to strip the tungsten values from the organic phase into the stripping solution.

Abstract: Vanadium and nickel values are selectively recovered from a petroleum coke residue by slurrying the coke in an aqueous solution of sodium carbonate providing an excess of the stoichiometric amount of sodium for formation of sodium vanadate and sodium sulfate, and then digesting the slurry at moderately elevated temperature in a pressurized autoclave under an oxygen overpressure supplying at least the stoichiometric amount of oxygen based on the vanadium and sulfur content of the slurry and advantageously sufficient additional oxygen to provide the thermal requirements of the digestion step by oxidation of carbon. In a continuous embodiment, the feed slurry temperature and feed solids content are adjusted according to a substantially inversely correlated relationship. The digestion temperature for a given total pressure and gas flow rate in the autoclave is adjusted to generate a pregnant liquor containing about 20 gpl to about 100 gpl of vanadate (V.sub.2 O.sub.

Abstract: The scaling of autoclave and leaching-equipment surfaces during the high pressure leaching of nickeliferous oxide and silicate ores is controlled during leaching to favor the formation of scale containing substantial amounts of magnesium sulfate that is more easily removed by chemical dissolution using water or dilute sulfuric acid at temperatures ranging from about 50.degree. C. to 250.degree. C. than scale containing substantial amounts of alunite.

Abstract: A method is provided for inhibiting the formation of silica scale on flash-pot surfaces during the multi-stage flashing of sulfuric acid pressure-leach slurry obtained following the continuous autoclave leaching of nickel lateritic ore at elevated temperature and pressure during which silica is dissolved, wherein the leach slurry is subjected to a high-temperature flash stage such that the slurry at the flash temperature is supersaturated in soluble silica, and wherein the slurry is thereafter subjected to at least one additional flash at an intermediate-temperature flash stage at which silica precipitates and tends to form a scale accompanied by a decrease in said supersaturation.

Abstract: Synthetic scheelite (calcium tungstate) having a low sulfur content is produced in high yield from an aqueous solution of sodium tungstate, that can be contaminated with sulfate ion dissolved therein, by digesting the solution with solid calcium sulfate whereby low-sulfur calcium tungstate precipitates. The solution remaining after filtration of the calcium tungstate product can be treated with calcium sulfate to precipitate additional purified calcium tungstate or to generate a calcium tungstate-calcium sulfate mixture that can be recycled for digestion with additional sulfate-contaminated sodium tungstate solution.

Abstract: A process for the soda ash digestion of scheelite concentrates is provided, the process comprising forming a slurry of a scheelite concentrate in an aqueous sodium carbonate solution and then digesting the slurry in an autoclave at an elevated temperature of at least about 180.degree. C. The concentration of the Na.sub.2 CO.sub.3 solution is substantially inversely correlated to the digestion temperature and substantially directly correlated to the Na.sub.2 CO.sub.3 /WO.sub.3 weight ratio such as to effect the selective dissolution of at least about 95% of the WO.sub.3 in the concentrate and provide a pregnant liquor containing WO.sub.3 while inhibiting substantial dissolution of gangue minerals.

Abstract: Oxide ores or ore concentrates containing organic matter are slurried with water and heated to a temperature of at least about 230.degree. C. under an oxygen partial pressure of at least about 25 psi to oxidize the organic matter. Advantageously, the process in accordance with the present invention can be used in the treatment of tungsten concentrates and can be employed while the tungsten concentrates are being digested with sodium carbonate or sodium hydroxide solutions.

Abstract: A continuous process with feedback control is disclosed for the soda ash digestion of tungsten concentrates in which a slurry of the concentrate in an aqueous sodium carbonate solution is digested in an autoclave at a temperature of at least about 180.degree. C. to provide a pregnant solution of WO.sub.3. High dissolution efficiency is maintained during digestion by continuously monitoring the pregnant solution which includes determining the specific gravity and the Na.sub.2 CO.sub.3 concentration of the pregnant liquor from which feedback signals are produced which are used to control the amount of Na.sub.2 CO.sub.3 and H.sub.2 O fed to the slurry in accordance with the digestion conditions predetermined to provide the desired dissolution efficiency.

Abstract: A process for the soda ash digestion of refractory tungsten concentrates is provided, the process comprising forming a slurry of the concentrate in an aqueous solution to which sodium carbonate is added in stages while digesting the slurry in an autoclave at a selected elevated temperature of at least about 180.degree. C. to control the concentration of the sodium carbonate during digestion to provide high extraction yields of the contained WO.sub.3. The total amount of the Na.sub.2 CO.sub.3 added stage-wise to complete the digestion is substantially inversely correlated to the digestion temperature and substantially directly correlated to the Na.sub.2 CO.sub.3 /WO.sub.3 weight ratio such as to effect dissolution of at least about 97%, and generally at least about 98%, of the WO.sub.3 in the concentrate and provide a pregnant liquor containing WO.sub.3, the stage-wise addition of the sodium carbonate being such as to inhibit the dissolution of gangue minerals, such as silica, contained in the concentrate.

Abstract: A process for the soda digestion of mixed wolframite and scheelite concentrates is provided, the process comprising forming a slurry of the mixed wolframite and scheelite concentrates in an aqueous sodium carbonate solution and then digesting the slurry in an autoclave at a temperature of at least about 180.degree. C. During digestion a predetermined amount of sodium hydroxide is added calculated stoichiometrically to react with NaHCO.sub.3 formed as a result of the hydrolysis of FeCO.sub.3 or FeCO.sub.3 and MnCO.sub.3 produced during the digestion of the wolframite and convert it to Na.sub.2 CO.sub.3. The concentration of the Na.sub.2 CO.sub.3 solution is substantially inversely correlated to the digestion temperature and substantially directly correlated to the Na.sub.2 CO.sub.3 /WO.sub.3 weight ratio ranging from about 0.9 to 2 such as to effect dissolution of at least about 95% of the WO.sub.3 in the concentrate and provide a pregnant liquor containing said WO.sub.3.

Abstract: A calcium tungstate concentrate is produced by slurrying an aqueous sodium tungstate liquor with calcium carbonate at about 130.degree. C. to about 200.degree. C. while providing sufficient carbon dioxide overpressure to convert sodium carbonate in the slurry to sodium bicarbonate, wherein the conversion of sodium tungstate to solid calcium tungstate in the slurry is promoted. The carbon dioxide is then stripped from the slurry, causing the sodium bicarbonate to convert to sodium carbonate, and a calcium tungstate concentrate is filtered from the slurry. The invention is useful in upgrading impure calcium tungstate concentrates.