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: The iron content of Bayer process streams is reduced by contacting said stream with a tertiary hydroxyl-containing polyamine.

Abstract: The following inorganic compounds of iron, when added to Bayer process liquors, form a precipitate of the finely divided iron present in:A. Ferric oxide;B. Ferrous salts; orC. Ferrous salts in combination with ferric oxide.The precipitate is removed using a polymeric flocculating agent. This treatment reduces iron levels below those obtained using other iron removal treatments.

Abstract: The present invention is directed to a method for removing organic substances from aluminate liquors of the Bayer process. The method comprises the steps of contacting the liquor with an oxygen containing gas under elevated pressure in the presence of metallic ions acting as a catalyst to oxidize the organic substances, precipitating the metallic ions jointly with aluminum hydroxide, separating the precipitate from the oxidized liquor and recycling the precipitated aluminum hydroxide containing the metallic ions into the oxidation step as a catalyst carrier.

Abstract: The method of the present invention is a novel comprehensive process for maximizing the recovery of valuable mineral values from coal ash. Options may also be included for the production of saleable inorganic chemical by-products. The process employs both physical and chemical extraction techniques that maximize the yield of products while reducing the quantity of waste produced. Valuable minerals and chemicals such as cenospheres (hollow microspheres), carbon, magnetite (Fe.sub.3 O.sub.4), alumina (Al.sub.2 O.sub.3), iron oxide (Fe.sub.2 O.sub.3) and iron chloride (FeCl.sub.3) may be produced. Due to removal of carbon, magnetite, and iron oxide from the coal ash, the processed ash comprises a quality pozzolan.

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: The invention concerns a process for the precipitation of aluminium hydroxide by seeding in two phases, which is intended to produce at a high level of productivity alumina with large grains, referred to as `sandy coarse`, by precipitation in a succession of tanks in cascade relationship of a supersaturated solution of sodium aluminate coming from alkaline attack on bauxite in accordance with the BAYER process. The process comprises three stages:in the first agglomeration stage, the supersaturated aluminate liquor is introduce into the tank, with an equivalent amount of terms of Na.sub.2 O of between 110 and 175 g/liter, at a temperature of between 65.degree. and 80.degree. C.

Abstract: A process is provided for hydrometallurgical processing of steel plant dusts containing cadmium, lead, zinc, and iron values, along with impurities such as chloride and fluoride salts of sodium, potassium, magnesium, etc. The first step in the process involves leaching the dust in a mixed sulfate-chloride medium that dissolves most of the zinc and cadmium. Any iron and aluminum dissolved in this step is precipitated by oxidation and neutralization. Zinc is recovered from the resulting solution by solvent extraction which provides a raffinate which is recycled to the leaching step with a bleed stream also provided for recovery of cadmium and removal of other impurities from the circuit. The lead sulfate residue from the leaching step is leached with caustic soda, and zinc dust is used to cement the lead out from the caustic solution, which then joins the main solution for zinc recovery.

Abstract: The negative effects of sodium oxylate on the crystallization of aluminum trihydrate from Bayer process liquors may be eliminated or curtailed by adding an effective amount of a polyacrylic acid with a molecular weight about 1,000,000 and containing at least 50 mole percent acrylic acid monomer to pregnant Bayer process liquors.

Abstract: A process for purifying at least a fraction of a solution in the Bayer cycle, which is preferably taken off after decomposition of the sodium aluminate, before or after concentration thereof, by causing the precipitation of the sodium oxalate in solution by the introduction of an agent for destabilization of the state of supersaturation of the sodium oxalate, which is characterized in that the supersaturation destabilization agent introduced into the Bayer solution to cause precipitation of the sodium oxalate is selected from the group comprising calcium oxalate and barium oxalate and that, in the case of solutions charged with degraded organic materials which generally result from high-temperature attack on bauxites with high proportions of humic materials, an anionic synthetic polyelectrolyte of high molecular mass is previously introduced into said solutions in order to increase the efficiency of the purification effect.

Abstract: A process for the purification of spent liquor from an alumina precipitation stage is disclosed wherein the spent liquor is first contacted with 50 volume % or less ethanol to form a sodium oxalate precipitate and the, after removal of the sodium oxalate precipitate is contacted with over 50 volume % of ethanol extraction fluid to separate the mixture into a first layer comprising the ethanol and at least a portion of the caustic from the spent liquor and a second layer which comprises the remainder of the spent liquor. The spent liquor may then be subjected to a further precipitation to recover further alumina. The spent liquor remaining may be further treated in subsequent extraction steps to concentrate and dispose of undesirable impurities remaining.

Abstract: Bayer process liquors derived from the digestion of bauxites with a caustic solution are purified by removing at least a portion of the organic impurities present in the liquors. Removal of these impurities is accomplished by treating liquor containing dispersed therein solids generated by the Bayer process or added thereto, such as red mud particles, alumina trihydrate, oxalate salt, or filter aid with an organic polymeric, water-soluble cationic quaternary ammonium salt (POLYQUAT salt) which due to its cationic nature will adhere to the surface of the dispersed solids. The organic coating or layer adhered to the solids provides a receptive surface for the organic impurities, thus allowing formation of a solid-Polyquat-organic Adduct which is easily removed from the Bayer system.

Abstract: Acrylic acid copolymers and certain acrylic acid acrylamide terpolymers which contain amounts of 2-AMPS provide superior results when used to remove suspended red mud from aqueous solutions which contain alumina.

Abstract: In a process for the production of alumina from aluminous raw material, an ammonoalunite intermediate is formed. The raw material is preferably a clay which is leached with sulfuric acid to form an aluminous solution which is separated from the solid materials. After any required extraction of iron, such as by liquid ion exchange, the solution is subjected to elevated temperatures and pressures in the presence of ammonium ions to form ammonoalunite which is recovered as a precipitate. The liquor is recycled to leach the clay, while the ammonoalunite is thermally decomposed to alumina. Gases liberated during decomposition are scrubbed with recycled liquor to form clay leach liquor. The alumina may be purified by washing with sulfuric acid to obtain a purity suitable for aluminum electrolysis.

Abstract: The process consists of two desilication stages. In the first stage the aluminate liquor resulting from digestion of the sinter is subjected to an autoclave treatment to remove the major portion of impurities of SiO.sub.2 and Fe.sub.2 O.sub.3. In the second stage the aluminate liquor is treated with a desilication agent comprising a lime pulp containing oxides CaO, Al.sub.2 O.sub.3, SiO.sub.2, Fe.sub.2 O.sub.3, Na.sub.2 O in a mass ratio of CaO:(SiO.sub.2 +Fe.sub.2 O.sub.3)=1,000 to 5,000:1 and Na.sub.2 Al.sub.2 O.sub.3 =0.25-0.60:1, wherein CaO is active, Na.sub.2 O--in the carbonate form. This lime pulp is employed in such an amount as to ensure the content of active CaO in the aluminate liquor within the range of from 5 to 10 g/l . The impurities of SiO.sub.2 and Fe.sub.2 O.sub.3 present in the liquor pass into the solid phase with the formation of calcium hydrogarnets of the formula 3 CaO(Al,Fe).sub.2 O.sub.3 mSiO.sub.2 (6-2m)H.sub.2 O, wherein m=0.01-0.5 which are separated as a mud.

Abstract: Aluminous siliceous starting materials are mixed and ground with correction materials to produce a raw mixture comprising oxides of aluminium, silicon, calcium and alkali metal having certain mole ratios, preheating the raw mixture by suspending the raw mixture in a hot gas, and sintering the preheated material to clinker.

Abstract: A process is disclosed which provides for the removal of sodium oxalate compounds from a Bayer-type process liquor, after prior precipitation of aluminum hydroxide, which comprises: treating the liquor with ethanol in an amount up to 50 vol. % of the liquor to form a first layer comprising the ethanol and at least a portion of the caustic in the liquor, and a second layer comprising the liquor; and filtering at least the liquor layer to recover a sodium oxalate precipitate. Preferably, the liquor is concentrated to provide a caustic concentration of at least 200 and, most preferably, about 250 grams per liter total caustic (measured as sodium carbonate).

Abstract: A leaching process employing acidic chloride solutions, whereby the iron content of aluminous materials such as lower grade iron-containing bauxite ores is reduced, enabling the obtention of valuable products such as metallurgical grade alumina and refractory grade bauxite, previously obtainable only from higher grade low-iron aluminous materials.

Abstract: A process for the recovery of valuable metals from roasted crude-oil sulfur-extraction catalyst waste is disclosed. In this process the value metals can be separated from aluminum in a single stage by treating the waste at elevated temperature and pressure with such an amount of sulfate solution that the waste dissolves and the aluminum simultaneously precipitates as alunite, which is separated from the solution which contains the other value metals. A sulfate solution is preferably added in such an amount that the concentration of sulfuric acid in the solution is 2-30 g/l at the end of the stage.

Abstract: A starting solid mixture of AlCl.sub.3 and Nacl, which may have been obtained by acid leaching of an aluminiferous mineral and precipitation of the AlCl.sub.3 and NaCl, is mixed with water in an amount to form an aqueous solution containing NaCl and AlCl.sub.3 in a weight ratio Na.sub.2 O/Al.sub.2 O.sub.3 of about 0.028. This is sparged with HCl to precipitate AlCl.sub.3, but the sparging is stopped before a substantial concentration of NaCl starts to come out of solution. The precipitated AlCl.sub.3 may be calcined to Al.sub.2 O.sub.3 and washed to remove any residual NaCl.

Abstract: A process for the production of alumina from aluminum-containing mineral ores, such as bauxite, comprising comminuting the aluminum-containing mineral ore, then reacting the comminuted mineral ore at an elevated temperature with an aqueous solution having at least 150 grams per liter of sodium bicarbonate which forms a solid reaction product containing dawsonite and impurities, and finally converting the dawsonite to alumina.

Abstract: In accordance with the invention, spent liquor from an alumina precipitation stage is contacted with an extraction fluid to separate the mixture into a first layer comprising the extraction fluid and at least a portion of the caustic from the spent liquor and a second layer which comprises the remainder of the spent liquor. The spent liquor may then be subjected to a further precipitation to recover further alumina. The spent liquor remaining may be further treated in subsequent extraction steps to concentrate and dispose of undesirable impurities remaining.

Abstract: The bayerite form of crystalline alumina, Al(OH).sub.3, contained within a macroporous ion exchange resin is converted to the gibbsite form of Al(OH).sub.3 by reaction with hot MgX.sub.2, where X is halide, followed by water-washing the MgX.sub.2 portion from the product, thereby causing the conversion of bayerite to the gibbsite form of crystalline Al(OH).sub.3. The gibbsite form may then be reacted with hot LiX solution, where X is anion, to form crystalline 2-layer LiX.2Al(OH).sub.3.nH.sub.2 O.

Abstract: The present invention relates to the production of alumina and, more specifically, to a process for desilication of aluminate solutions.The process of desilication according to the present invention comprises treatment of the aluminate solution first with a calcium-containing reagent "a" which is a product of the reaction of desilication of the aluminate solution; reagent "a" contains mainly calcium hydrogarnet of the formula:3CaO.Al.sub.2 O.sub.3.nSiO.sub.2 (6-2n)H.sub.2 Owherein n.ltoreq.1, and then with a reagent "b" of the formula:4CaO.Al.sub.2 O.sub.3 (0.1-0.6)X.mH.sub.2 Owherein X is CO.sub.2 and/or SO.sub.3 ; m=8 to 15. The treatment of the aluminate solution with reagent "a" is carried out for 0.5 to 2 hours at a temperature ranging from 40.degree. to 105.degree. C. Weight ratio of reagents "a" and "b" is maintained within the range of from 1:1 to 3:1.The process according to the present invention is useful in the manufacture of alumina.

Abstract: A gravity fed water bath process treats waste water from spray rinses containing compounds of copper and like heavy metals. For displacing heavy metals, such as copper, the bath has a substantially pure metal with an electrode potential greater than the heavy metal contained in the rinse water. A system for controlling the pH level of the water bath treatment and for supplying acid at the beginning of the bath, and alkaline material at the bath's end provides a highly acidic pH level for the water bath and heavy metal removal chamber, and adjusts the pH level of the discharged water for satisfactory deposit in municipal sewer systems.A method for displacing the heavy metal from the compound in solution requires exposing the heavy metal compound to a substantially pure metal having an electrode potential greater than the heavy metal of the compound, in an acidic bath whose pH level is controlled.

Abstract: Sodium oxalate impurity is removed from oxalate-enriched Bayer process caustic liquor by gradual increase of the caustic concentration of the liquor, thus providing a staged precipitation of the sodium oxalate in a well-crystallized and readily filterable form.

Abstract: A process is described whereby gadolinium and gallium containing by-products can be reprocessed to yield the oxides of these elements in sufficient purity to be re-used in the process for manufacturing Gd.sub.3 Ga.sub.5 O.sub.12 (GGG) single crystal boules thereby improving the economics of production of GGG wafers significantly. The gadolinium and gallium oxides are recovered and separated from transition metal impurities introduced during fabrication of GGG wafers by precipitating the gadolinium as oxalate which is thereafter pyrolyzed to gadolinium oxide and eluting the gallium containing filtrate over an ion exchange resin and precipitating therefrom as an oxalate the gallium present. The gallium precipitate is also pyrolyzed to the gallium oxide. The process can be extended to include purification and re-use of by-products generated in other grinding and polishing operations which may result in the recycling of the order of 80% of the generated by-products.

Abstract: Bayer process caustic liquors are purified by treating the liquors with an organic solvent of relatively low boiling point, such as methanol, which causes the precipitation of inorganic carbonate and/or sulfate salt from the treated liquor. The treating solvent can be readily recovered for reuse.

Abstract: Disclosed is a process for recovering phosphate (P.sub.2 O.sub.

Abstract: A process is described whereby the "saw kerf" can be reprocessed in sufficient purity to be re-used in the process, thereby improving the economics of production of GGG wafers significantly. Gadolinium and gallium oxides are recovered and separated from transition metal impurities introduced during fabrication of GGG wafers. The process "saw kerf" produced from slicing the crystal boule is dissolved by refluxing in HNO.sub.3, treated with oxalic acid and the resulting oxalates and nitrates separated. Pyrolysis of these salts at temperatures of at least 850.degree. C. resulted in their conversion to Ga.sub.2 O.sub.3 of purity >99.99%. The process can be extended to include purification and re-use of by-products generated in other grinding and polishing operations which may result in the recycling of the order of 80% of the generated by-products.

Abstract: A process is described whereby the by-products derived from the fabrication of Gd.sub.3 Ga.sub.5 O.sub.12 (GGG) wafers sliced from boules grown from Gd.sub.2 O.sub.3 and Ga.sub.2 O.sub.3 can be reprocessed in sufficient purity to be re-used in the process of growing GGG boules, thereby improving the economics of GGG wafer production. Gadolinium and gallium oxides are recovered and separated from transition metal impurities introduced during fabrication of GGG wafers. The "saw kerf" produced from slicing the crystal boule is dissolved in HCl and filtered to remove residual solids. Gasolinium oxalate is precipitated from the acidic solution by the addition of oxalic acid. Calcination at 850.degree. C. resulted in the isolation of Gd.sub.2 O.sub.3 of >99.99 purity.The pH of the filtrate is adjusted to about 11 with alkali metal hydroxide followed by the addition of sulfide ion. The precipitated transition metal sulfides are removed by filtration. Excess sulfide is removed by treatment with 30% H.sub.2 O.sub.

Abstract: Gd.sub.2 O.sub.3 and Ga.sub.2 O.sub.3 are currently used for the fabrication of Gd.sub.3 Ga.sub.5 O.sub.12 (GGG) wafers which are employed as substrates for bubble domain memory devices. In the processing, in the order of 25% of the starting material ends up as process "saw kerf" contaminated with variable amounts of iron, nickel, magnesium, aluminum, zirconium, iridium and silicon. A process is described whereby the "saw kerf" can be reprocessed in sufficient purity to be re-used in the process, thereby improving the economics of production of GGG wafers significantly. Gadolinium and gallium oxides are recovered and separated from transition metal impurities introduced during fabrication of GGG wafers. The process "saw kerf" produced from slicing the crystal boule is dissolved in HCl, treated with H.sub.2 SO.sub.4, and the resulting sulfates separated. Metathesis with (NH.sub.4).sub.2 C.sub.2 O.sub.4 results in conversion of the sulfates to the ammonium oxalates which were calcined at 850.degree. C.

Abstract: In a process for converting UF.sub.6 into UO.sub.2, the UF.sub.6 is brought into contact with an aqueous aluminum nitrate solution. The resultant product is solvent extracted with tributyl phosphate to remove uranyl nitrate. The raffinate has a fluorine/aluminum (F/Al) weight ratio within the range of from about 0.5 to about 1.2. A sufficient quantity of hydrofluoric acid is added to the raffinate to minimize the solubility of aluminum fluoride (AlF.sub.3) therein and thereby maximize the precipitation potential of AlF.sub.3. Generally this occurs when sufficient hydrofluoric acid has been added to cause the F/Al weight ratio to be within the range of from about 1.8 to about 2.2. As a result of this treatment, the raffinate is divided into an uranium-containing aqueous solution and an AlF.sub.3 precipitate which contains substantially no uranium.

Abstract: The invention relates to a new method of reducing the organic substance content of alum earth production cycle performed according to the Bayer technology. By the method of the invention the majority of the organic substances present in the circulating lye can be removed easily and with only slight losses in sodium content.According to the invention one proceeds so that soda present in the hydrate wash and/or in the soda salt solution is caustified with lime, the solution is evaporated to reach a total sodium oxide concentration of 200 to 400 g/l, the precipitated solid is separated and removed from the system, and the liquid is recycled.

Abstract: The production process for pseudoboehmite from leach liquors produced in the acid treatment of clays, which liquors contain Fe and alkaline earth ions.

Abstract: Platinum, palladium and other precious metals are recovered from aqueous media containing precious metal ions in solution by contacting the metal-containing solution with a proteinaceous material selected from the group consisting of feathers, hair, hoof meal and horn meal to collect the metals in concentrated insoluble form, and recovering metal from the proteinaceous material.

Abstract: In a process of the preparation of alumina from an alumina value containing material wherein a caustic sodium aluminate process liquor is subjected to a treatment to reduce the level of zinc impurity by the addition of ZnS seed in the presence of sulfide ion, the improvement comprising:(I) forming the zinc sulfide seed a by process comprising the steps of:(A) dissolving ZnO in NaOH to produce a caustic Na.sub.2 ZnO.sub.2 solution; and(B) reacting the solution of (A) with Na.sub.2 S to form ZnS, the Na.sub.2 S being present at a level sufficient to provide a concentration of Na.sub.2 S of at least about 0.150 g/l of Na.sub.2 S when the product of this step is added to the process liquor;(II) adding the product of step (B) to the process liquor to precipitate as ZnS, zinc contained as sodium zincate in the process liquor; and(III) filtering the process liquor to yield an NaAlO.sub.2 liquor containing less than 15 mg/l and preferably below about 10 mg/l zinc as ZnO.

Abstract: A process for obtaining pure aluminum oxide (Al.sub.2 O.sub.3) from siliceous aluminum ore is disclosed. The aluminum ore is digested in a hydrochloric acid solution to obtain aluminum chloride, the aluminum chloride is crystallized as the hexahydrate, the aluminum chloride hexahydrate is purified and, subsequently, decomposed to give pure aluminum oxide and secondary products. The mother liquor of the crystallization step and the secondary products of the decomposition step are recycled.

Abstract: Gallium and gadolinium are recovered and separated from scrap material of substances which contain both of these elements in the form of oxides or compounds which can be transformed to the oxides.The scrap is finely ground and then dissolved in a strong, aqueous mineral acid. The gadolinium is precipitated from the purified solution as the oxalate; then the gallium is deposited in the metallic form by means of electrolysis. The electrolytic deposition of the gallium can also take place before the gadolinium is precipitated out as the oxalate.

Abstract: The method comprises processing slime and off-gases resulting from the production of phosphorus with an aqueous solution of copper sulphate having a concentration of from 15 to 50% at a temperature within the range of from 20.degree. to 80.degree. C. As a result, two products are obtained, i.e. a liquid product and a solid one.The solid product containing mainly copper phosphide as well as fluorides and chlorides of alkali metals and silicon, and silicates of calcium and aluminum, is used as a modifying and refining agent for hypereutectic silumines and for the manufacture of a copper-phosphorus alloy.The liquid product containing phosphoric acid, sulphuric acid and copper sulphate is used as starting product for the preparation of a copper-containing fertilizer.The method according to the present invention makes it possible to modify the production of phosphorus so as to eliminate the formation of secondary wastes and improve the environmental control.

Abstract: A process for the removal of aluminum chloride from a liquid solution thereof with the liquid metal chlorides resulting from the chlorination of titaniferous materials by mixing water and sodium chloride with the liquid solution in amounts such that the amount of water is less than equimolar with respect to the total amount of aluminum chloride and the combined amount of water and sodium chloride is at least equimolar with respect to the total amount of aluminum chloride. This process significantly decreases the corrosion of apparatus associated with the presence of aluminum chloride and substantially eliminates losses of titanium tetrachloride and ferric chloride present in the liquid solution and reduces the formation of HCl.

Abstract: Process for treating solutions from the Bayer process, enabling amounts of sodium carbonate and sodium oxalate or sodium salts of organic acids corresponding to the amounts of these compounds dissolved during the attack on a bauxite to be removed by means of a barium compound, and without consumption of the latter.

Abstract: A process is described for the recovery of gallium from scrap materials in which the gallium occurs as gallium compounds containing at least one element selected from the group consisting of aluminum, antimony, arsenic and phosphorus. The process comprises the steps of leaching said gallium compounds with an oxidizing agent selected from nitric acid and a combination of nitric acid and hydrogen peroxide to form a gallium-containing leach solution, forming a gallate solution from said gallium-containing solution, and recovering gallium from said gallate solution. The leach solution can be treated with a calcium compound chosen from the group consisting of lime and calcium hydroxide for precipitation of calcium arsenate and calcium phosphate. An alkaline material such as sodium hydroxide may then be added to said leach solution in an amount sufficient to raise the pH to a value of at least 11 to form gallate solution. Gallium metal preferably is recovered from said gallate solution by electrolysis.

Abstract: A method of beneficiating kaolin clay by the addition of non-dispersing neutral salts to assist in the removal of discolored impurities, such as titanium and iron bearing minerals from a clay slurry. This process is capable of producing clays having a brightness in the 90- 95 range.

Abstract: Sufficient anionic polyacrylamide having molecular weight of at least 2,800,000 is contacted with alkali metal aluminate liquor containing ferrous iron until a substantial proportion of the ferrous iron is precipitated, and said precipitate and liquor are separated. The process is particularly useful as an improvement in the Bayer process for preparing alumina from bauxite.

Abstract: Metal powders, metal oxide powders, and mixtures thereof of controlled particle size are provided by reacting an aqueous solution containing dissolved metal values with excess urea. Upon heating, urea reacts with water from the solution leaving a molten urea solution containing the metal values. The molten urea solution is heated to above about 180.degree. C. whereupon metal values precipitate homogeneously as a powder. The powder is reduced to metal or calcined to form oxide particles. One or more metal oxides in a mixture can be selectively reduced to produce metal particles or a mixture of metal and metal oxide particles.

Abstract: A monovalent thallium compound is converted to a trivalent thallium compound by treating the thallium (I) compound with molecular oxygen in the presence of a Group VIII noble metal catalyst and in the presence of a promoter comprising a heterocyclic tertiary amine to oxidize the thallium (I) compound to a thallium (III) compound.

Abstract: An improvement in the process for the recovery of aluminum from alunite in which the alunite in particulate form is dehydrated, sulfur and alkali metal compounds removed from the dehydrated ore leaving a particulate residue containing aluminum values, the residue digested with at least one alkali metal hydroxide to convert the aluminum values to soluble aluminates, silicon removed from the soluble aluminate solution, and aluminum values precipitated from the aluminate solution, the improvement comprising: multiple stage digestion of the particulate residue accomplished by dividing the particulate residue into two fractions, digesting one fraction first and using the first stage liquor from the first digestion step to digest the remaining fraction. The fraction digested first may be the one having the smaller particle size, or the one having the larger particle size.

Abstract: In order to control the sodium oxalate level in the liquor employed in the Bayer process for the production of alumina, a part of the spent liquor recovered from alumina trihydrate precipitation stage is concentrated by evaporation to render it supersaturated with respect to sodium oxalate. The thus concentrated liquor is then sprayed onto a packing in an enclosed space under conditions such that the supersaturation of the droplets at impact on the packing exceeds a critical supersaturation. The sprayed liquor deposits sodium oxalate on the packing and is recovered for recirculation to the process circuit.

Abstract: A process for recovering aluminum from alunite ore directed to providing a residue for the Bayer leach step substantially free of impurities so that a high A/C ratio Bayer leach liquor is produced, which comprises roasting the ore in particulate form to drive off water and sulfur as SO.sub.2 and to convert aluminum sulfate to alumina, leaching the residue containing aluminum values with water and filtering to remove potassium sulfate and other soluble sulfates, hot leaching the residue with sulfuric acid to convert the alumina therein to soluble aluminum sulfate followed by filtering to remove silicon dioxide and other solid impurities, crystallizing the aluminum sulfate to further remove impurities, heating the residue to convert the aluminum sulfate to alumina and drive off any remaining sulfur as SO.sub.2, and digesting the alumina calcine with sodium hydroxide under standard Bayer conditions at a high A/C ratio to provide a high A/C ratio solution from which a "sandy" aluminum hydroxide is precipitated.