Abstract: Process for recovering coarsely crystalline alumina hydrate from bauxite according to the Bayer process wherein, in the presence of fine seed crystals, agglomerates are initially formed in a supersaturated sodium aluminate solution at 80.degree. to 65.degree. C. The agglomerates are then conducted through a first cascade of crystallizers and, after cooling to 55.degree. to 45.degree. C., through a second crystalizer cascade. A crystal suspension is extracted from the last crystallizer of the second crystallizer cascade and fractionated into fine seed crystals and coarse product crystals.

Abstract: An improved precipitation system is provided for the Bayer process production of alumina hydrate. In order to produce coarse and strong alumina hydrate at high yield, supersaturated Bayer process sodium aluminate liquor is seeded with a relatively small seed charge in a first precipitator at a relatively low temperature and the produced slurry is transferred to a second precipitator where without additional seeding, the solids content of the slurry is allowed to increase to about 250-700 g/l by accumulating solids in the line until the desired solids content is reached. After a suitable residence time, a coarse, strong product hydrate can be recovered in yields of or exceeding 80 g/l based on the alumina (Al.sub.2 O.sub.3) content of the supersaturated sodium aluminate liquor subjected to precipitation.

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: The invention relates to a process for the reduction of sodium hydroxide losses of the Bayer-cycle by modified causticization of red mud which comprisessubjecting an optionally previously concentrated red mud slurry led off from the red mud washing line by ramification and containing a liquid phase which has a concentration of 5-40 g. caustic Na.sub.2 0/1. caustification by adjusting the lime content expressed as CaO through addition of lime or lime milk to 1-3.2 moles per mole Al.sub.2 O.sub.3, preferably to 2-2.5 moles per mole Al.sub.2 O.sub.3, related to the total Al.sub.2 O.sub.3 content of the slurry;stirring the slurry for 0.3-5 hours at a temperature of 70.degree.-110.degree. C., preferably at 80.degree.-100.degree. C.;adding to the slurry 3-4 moles, preferably 3.2-3.4 moles, of soda related to 1 mole of the originally dissolved Al.sub.2 O.sub.3, and continuing the stirring for 1-4 hours at 80.degree.-100.degree. C., preferably at a temperature of 90.degree.-95.degree. C.

Abstract: A process for recovery of alumina and soda from materials containing sodium aluminosilicates, such as red mud and desilication products, comprises treating said materials with lime at elevated temperature and pressure. In a preferred embodiment of the invention, hydrothermal treatment of red mud with lime is integrated into a Bayer process to improve the overall efficiency of that process.

Abstract: During the final stages of Al(OH).sub.3 production, deliquoring the aluminum trihydroxide slurry of excess sodium ions in the form of caustic liquor is conventionally achieved by numerous water washes prior to drying the product. Addition of an effective amount of highly charged, high molecular weight anionic polymer flocculant to the aluminum trihydroxide slurry improves the filtration rate, i.e., increases the amount and rate of removal of caustic liquor from the slurry. Addition of the flocculant reduces the amount of washing necessary to remove sodium ions from the final cake and also provides higher cake solids which results in greater production per unit time and less expenditure of energy in the drying process. Anionic polymers derived from 80 to 100% of an anionic vinyl monomer such as acrylic acid and from 20 to 0% of a nonionic vinyl monomer such as acrylamide having molecular weights between 1.5 to 12.0.times.10.sup.6 are useful in deliquoring aluminum trihydroxide slurries.

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 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: Bauxite is reacted with spent caustic soda solution at 113.degree. C. to 205.degree. C. to produce a first pregnant liquor stream, a granular residue stream and a muddy substance stream wherein the granular residue stream is discarded, the muddy substance stream is reacted with or without a small portion of bauxite, but with a spent caustic soda stream at 206.degree. C. to 350.degree. C. to produce a second pregnant liquor stream and a red mud stream which is discarded; the first and second pregnant liquor streams are filtered, cooled to 50.degree. C. to 87.degree. C. and then seeded to precipitate alumina hydrate containing less than 0.017% Fe.sub.2 O.sub.3 by weight.

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: 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: In the production of alumina from aluminous ores containing alumina trihydrate and alumina monohydrate comprising a first-stage digestion by digesting alumina trihydrate from a slurry of the ores and a caustic solution and separating the resulting slurry into a caustic aluminate solution and an insoluble residue, and a second-stage digestion by digesting alumina monohydrate from a slurry of the insoluble residue separated in the first-stage digestion and a caustic solution, the present invention provides an improvement wherein scale formation onto a preheater for the slurry in the second-stage digestion is completely or substantially prevented and reduction in heat transfer coefficient of heat transfer surface is remarkably lowered. The improvement is attained by setting up a desilication reaction zone in the course of the first-stage digestion, whereby the slurry introduced into said zone is subjected to desilication reaction treatment.

Abstract: Coarse grains of aluminum hydroxide having high resistance to disintegration to powder in a calcination step are continuously produced from a supersaturated sodium aluminate solution of the Bayer process through(1) a first precipitation step of adding recycle seed aluminum hydroxide to a supersaturated sodium aluminate solution having a molar ratio of Na.sub.2 O as caustic soda to Al.sub.2 O.sub.3 in solution of less than 1.8 supplied to a precipitation tank of substantially complete mixing type in a ratio of 30-150 kg of the recycle seed to 1 m.sup.3 of the solution, thereby partially decomposing the seed-added solution until the molar ratio of the solution reaches 2.0-2.4 while keeping the solution at 65.degree.-80.degree. C.

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: A wet caustic aluminate process that comprises digesting a bauxite at a low temperature in caustic aluminate liquor to extract the alumina trihydrate, separating the supersaturated caustic aluminate liquor of low Fe.sub.2 O.sub.3 content from the mud, digesting the mud or a mixture of mud and bauxite at a higher temperature in caustic aluminate liquor to extract the majority of the remaining monohydrate and trihydrate, separating the supersaturated caustic aluminate liquor of higher Fe.sub.2 O.sub.3 content from the residue, precipitating alumina hydrate from the two supersaturated caustic aluminate liquors, recyling spent caustic aluminate liquor to digestion and calcining alumina hydrate to alumina with a Fe.sub.2 O.sub.3 content less than 0.03%.

Abstract: Coarse grains of aluminum hydroxide are economically produced in a high yield from sodium aluminate solution by dividing supersaturated sodium aluminate solution being prepared by the Bayer process and having a molar ratio of Na.sub.2 O as caustic soda to Al.sub.2 O.sub.3 in solution of less than 1.8 into two streams, adding a portion of recycle seed aluminum hydroxide and fine grains of aluminum hydroxide as seed to one of the streams of sodium aluminate solution, partially decomposing the sodium aluminate solution until the molar ratio of the sodium solution reaches 1.8-2.6, adding to the resulting partially decomposed sodium aluminate slurry the other stream of sodium aluminate solution, which has been cooled to a temperature low enough to lower the temperature of the partially decomposed sodium aluminate slurry by at least 3.degree. C.

Abstract: A precipitation system is provided for the production of strong, coarse alumina hydrate (Al.sub.2 O.sub.3.3H.sub.2 O) from Bayer process aluminate liquors. In the system three distinct, but interconnected processing stages are utilized which comprise an agglomeration stage, a growth stage and a seed generation stage. In the agglomeration stage hydrate particles agglomerate to form coarse particles; in the growth stage these particles grow and acquire strength; while in the seed generation stage alumina hydrate seed is generated to be used in the agglomeration and growth stages.The precipitation system combines the advantages of both the American and European Bayer processes in that it results in the production of a strong, coarse product hydrate and an increased yield.

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: Bayer liquor containing carbon compounds is freed from the carbon compounds by a method which comprises adjusting the molar ratio of the aluminum component to the sodium component in the liquid to a value in the range of from 1 to 5 calculated as Al.sub.2 O.sub.3 /Na.sub.2 O and heating the resultant Bayer liquor.

Abstract: Sodium oxalate in supersaturated solution in Bayer spent liquor stabilized by the presence of humic material is precipitated by the treatment with cationic sequestrants which interact with the humic material to give an insoluble product, thus removing it from solution and destabilizing the solution with respect to precipitation of sodium oxalate. Preferred cationic sequestrants are quaternary nitrogen compounds including medium or long chain alkyl groups. Precipitation of sodium oxalate can be expidited by addition of seed crystals and/or addition of sodium oxalate solution which is supersaturated at a temperature higher than that of the spent liquor.

Abstract: Sodium oxalate is supersaturated solution in Bayer spent liquor stabilized by the presence of humic material is precipitated by the treatment with an adsorbent which adsorbs the humic material to give an insoluble product, thus removing it from solution and destabilizing the solution with respect to precipitation of sodium oxalate. The preferred adsorbent is activated carbon. The activated carbon can be dispersed in the spent liquor as a fine powder or the spent liquor can be passed through a column of particulate carbon. Precipitation of sodium oxalate can be expidited by addition to seed crystals and/or addition of sodium oxalate solution which is supersaturated at a temperature higher than that of the spent liquor.

Abstract: When an alkali such as an alkali metal bicarbonate or carbonate is intimately mixed with bauxite or other alumina-containing raw material at an Al.sub.2 O.sub.3 /Na.sub.2 O molar ratio of from 1/1 to 1/3 and the mixture is molded into granules, then calcined and extracted with an aqueous medium, the alumina component can be recovered in a high yield in the form of an aqueous solution of an alkali metal aluminate. The alkali component is not substantially contained in the residue left after recovery of this aqueous solution.

Abstract: Impurities such as organic substances, i.e. sodium oxalate and inorganic impurities, i.e.

Abstract: A process for the production of sodium aluminate comprising drying an aluminate solution containing from 45 to 350 g/l of caustic Na.sub.2 O with a molecular ratio of caustic Na.sub.2 O to Al.sub.2 O.sub.3 from 1.1 to 1.8 in a fluidized bed of solid particles at 250.degree.-400.degree. C. of sodium aluminate using a gas heated to 750.degree.-950.degree. C. containing no carbon dioxide as a fluidizing medium and a heat carrier in an amount from 2000 to 25000 nm.sup.3 per 1 m.sup.3 of aluminate solution; feeding said aluminate, solution for drying by atomizing it at a velocity from 25 to 35 m/s thereby obtaining sodium aluminate in the form of pellets of a size from 0.5 to 8 mm with a bulk weight from 1.2 to 1.4 t/m.sup.3 completely soluble in water and alkaline solutions, with a maximum content of hygroscopic moisture of 0.3% by weight and a maximum content of water of crystallization of 5% by weight.

Abstract: An improved method for recovering aluminum values from alkaline aluminosilicate raw material by sintering a comminuted aqueous mixture of the alkaline aluminosilicate material, limestone and soda solution wherein the alumino-silicate material is first comminuted with the soda solution to form a mixture with a fraction of particles larger than 0.08 mm greater than 20 percent by weight, mixing limestone with the mixture and comminuting until the fraction of particles larger than 0.08 mm is between 2 and 15 percent by weight.

Abstract: The invention relates to a process for the disposal of bauxite processing wastes comprising the steps of:(a) filtering the bauxite muds in suspension coming from the washing decanter,(b) continuously washing the dehydrated filtration cake on the filter with hot water with recycling of the liquid phase containing the greater part of the soda into the basic chemical process of the bauxite treating plant.

Abstract: Process for the manufacture of coarse aluminum hydroxide, containing a maximum of 15 weight percent of the particles in a particle size under 45 micrometers, with a productivity that may be higher than 60 grams of precipitated Al.sub.2 O.sub.3.The process consists of a decomposition in two stages (an agglomeration phase and a growth phase); each stage proceeding within defined temperature ranges with seed material of different constitution. The first (fine) seed amount is added at the start of the decomposition in such an amount, that the ratio of the supersaturation of the aluminate liquor to the surface area of the seed hydroxide per liter of the aluminate liquor presented for decomposition exhibits a value of 7 to 25 grams per square meter. The process exhibits the advantage of the high productivity of the so-called European process and the advantage of the so-called American process by obtaining a coarse product hydroxide.

Abstract: An improved process for accelerating the digestion process in the Bayer alumina process is provided which promotes both the goethite-hematite conversion and a more perfect and quick dissolution of the diaspore. The above is achieved by carrying out the digestion in the process of 5-20% by weight calculated on the dry weight of the bauxite of a novel hydrogarnet catalyst.

Abstract: In a process for the production of alumina which comprises the steps of digesting bauxite to produce a precipitate of alumina trihydrate containing uncombined moisture, drying the alumina trihydrate to reduce the uncombined moisture content thereof, and feeding the dried alumina trihydrate to a calciner to convert the alumina trihydrate to alumina, improved economy is achieved by drying the alumina trihydrate in a fluidized bed in which the fluidized mass is heated indirectly by means of steam which is available from the digestion and recovery system. Drying of the alumina trihydrate in this manner prior to feeding it to the calciner also reduces the fuel requirement in the calciner and enables the throughput of the calciner to be increased.

Abstract: In the production of alumina from bauxite by the Bayer process, the present invention provides an improvement for effectively and economically removing organic substances from a circulating alkali aluminate solution by contacting the aluminate solution containing organic substances with molecular oxygen gas or a molecular oxygen-containing gas in the presence of copper ions as a catalyst at an elevated temperature, thereby oxidizing the organic substances, adding a chemical substance to the resulting aluminate solution which reacts with copper ions to deposit a water-insoluble precipitate, and separating the precipitate from the solution, and recycling the precipitate as a copper source to the above-mentioned wet oxidation procedure.

Abstract: In the production of alumina from aluminous ores by the Bayer process, the present invention provides an improvement for effectively and economically recovering caustic components consisting essentially of sodium aluminate from aluminum hydroxide cakes as seed classified from the product aluminum hydroxide by washing the seed with a washing liquor having a substantially saturated concentration of sodium oxalate and little content of caustic and then removing organic substances such as sodium oxalate from the washed seed by secondly washing said seed with hot water, thereby recovering caustic components without the dissolution of sodium oxalate from the seed into the recovered caustic solution and attaining the removal of sodium oxalate contaminant with high efficiency.

Abstract: A method for sampling and controlling the addition of suspended gases, liquids and solids in a control stream to a process stream is disclosed wherein the surface area of the suspended material acts as the determining feature for control of the process. The measured surface area is compared with a preselected surface area to control the addition of the suspended material. This method is particularly useful for the control of particulate seed material to the process stream in the Bayer process for the production of alumina. The method is also broadly applicable to physical and/or chemical control means in an analytical scheme for controlling and monitoring any process.

Abstract: Red mud slurries can be solidified by adding thereto certain fatty substituted quaternary ammonium salts.

Abstract: A first substance and a liquid are conveyed along a conduit at least part of which is arranged in heat-exchange relationship with a second substance. Upstream of this part of the conduit, a suspension of the first substance in the liquid is formed wherein the first substance has an average particle size between 10 and 150 microns and a concentration between 1 and 6 volume percent. The suspension is conveyed along the conduit under conditions of turbulent flow. In this manner, the efficiency of the heat-exchange between the suspension and the second substance is increased. The method may be used to increase the heat-exchange efficiency in the extraction of bauxite so that an apparatus of given size can extract greater quantities of bauxite or, conversely, so that a given quantity of bauxite can be extracted with an apparatus of smaller size.

Abstract: In a process for extracting alumina from alumina-containing ores on a two-stream system by individually preheating a slurry of alumina-containing ores and an aqueous alkali solution each in preheaters of indirectly heating, mixing the preheated slurry with the preheated aqueous alkali solution, and extracting alumina from the ores in a digester of either the heating type involving the direct injection of live steam or the heat-insulated type, the alumina is extracted from the ores by preparing the slurry of alumina-containing ores with water or a diluted aqueous alkali solution, such as from the drain obtained by recovering steam from an evaporator for cooling the slurry resulting from extraction, and utilizing the recovered steam in preheating the slurry of the alumina-containing ores or decomposition solution or both, preheating the slurry of alumina-containing ores, and mixing the preheated slurry with an aqueous alkali solution preheated as another stream as the decomposition solution.

Abstract: A pretreatment system is provided for transforming the goethite constituent [FeO(OH)] of goethitic bauxites to hematite and/or magnetite at high temperatures and pressures. The system employs a number of float-type, liquid displacement pressure pumps, both for charging caustic-containing bauxite slurries of high solids concentration to the system and for discharging the treated slurries. The system operates at temperatures in excess of 250.degree. C and up to temperatures required for the total conversion of the goethite content to hematite or magnetite which, in turn, significantly increases the yield of recoverable alumina. Since the slurry to be pretreated is of high solids concentration, e.g.

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: The invention relates to an improved process for the production of alumina according to the Bayer technology, of bauxites containing goethite and especially of boehmitic or diasporic bauxites, for the acceleration of the digestion process, for the transformation of goethite into hematite, for the increase of alumina yield and for the reduction of the caustic soda losses, the essence of which consists in carrying out the digestion in the presence of 2-6% CaO and 0.2-2.0% Mg.sup.++, Fe.sup.++, Mn.sup.++ Co.sup.++ ions based on the weight of the dry bauxite or of compounds or ores containing these ions in the indicated quantities.

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: The settling rate of caustic alkali-digested goethite-containing bauxite or laterite, or the like, is increased by carrying out the digestion in the presence of a reducing agent capable of reducing the trivalent iron component of the goethite to a lower valence so as to convert the goethite to hematite, magnetite, metallic iron, or combinations thereof, which enhance the settling rate of the digestion mass.

Abstract: Alumina dust, particularly partially calcined alumina dust, is coarsened by forming an aqueous admixture or slurry comprising the alumina dust and finely divided calcium carbonate and introducing the resulting aqueous admixture or slurry into Bayer pregnant liquor and precipitating alumina trihydrate from the resulting Bayer pregnant liquor.

Abstract: Aluminate mother liquor is passed countercurrent to the direction of feed of aluminum hydroxide crystals through at least two stages, each of which has a lower turbulent zone with a high suspension density and which is agitated under conditions which assure particle growth via crystal growth and an upper non-turbulent, stagnant liquid layer from which most crystals settle back into the respective lower turbulent zone. The suspension density in the stages is maintained at a constant level by sending crystal suspension from the lower turbulent zone in all the precipitation stages but the first to the preceding stage. Mother liquor is removed from the upper stagnant zone of all stages but the last stage and sent to the respective following stages. Coarse crystal suspension is removed from the turbulent zone of the first stage for separation of the crystals for further processing, while the mother liquor is returned to the system.

Abstract: A method is provided for removing harmful organic compounds from the aluminate liquor obtained in the production of alumina according to the Bayer process. A magnesium obtained is added to the aluminate liquor to form a hydroxide mixture containing magnesium hydroxide and aluminum hydroxide which precipitates from the aluminate liquor. The precipitated mixture is maintained in the aluminate liquor, while being stirred, until at least a part of the organic compounds have been eliminated from the aluminate liquor. The hydroxide mixture containing the organic compounds then is separated from the aluminate liquor.

Abstract: Sintered alumina of low porosity and Na content is made from calcined alumina of 2-6 micron average particle size and about 0.2-1% by weight Na.sub.2 O content by treating the calcined alumina with a synergistically acting combination of a magnesium salt and a boron compound. Suitable magnesium salts include magnesium halides, nitrate, sulfate, acetate and stearate, the water-soluble salts being preferred. As boron compound H.sub.3 BO.sub.3 or B.sub.2 O.sub.3 can be employed. The quantity of magnesium salt in the combination, calculated as Mg, is kept in the range of about 0.01-0.3% by weight of Al.sub.2 O.sub.3, while the boron content, calculated as B.sub.2 O.sub.3, is maintained in the range of about 0.1-1% by weight of Al.sub.2 O.sub.3. Used of the synergistically acting combination in the indicated range allows manufacture of sintered alumina products of less than about 3% total porosity and less than about 0.03% by weight Na content.

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 is provided which allows control of the impurity level of Bayer process streams with simultaneous generation of an environmentally acceptable effluent and recovery of valuable dissolved aluminum and sodium values. The process involves carbonation of a blow-down stream at 40.degree.-100.degree. C to produce sodium dawsonite [NaAl(OH).sub.2 CO.sub.2 ] and an effluent essentially free of dissolved alumina and significantly depleted in dissolved sodium. The sodium dawsonite can be used as such or returned to the Bayer process after thermal decomposition to sodium aluminate. The effluent can be directly discharged into natural receiving bodies without further treatment.

Abstract: The present invention provides for an improvement in the Bayer Aluminum manufacturing process wherein the digestion of goethite-containing bauxite is effected in higher yields, at lower temperatures and in a single step by carrying out said digestion in a wet caustic solution containing both calcium oxide and sodium chloride.

Abstract: Aluminum oxide having a sodium oxide content after calcination of less than 0.1% by weight is continuously precipitated as aluminum hydroxide from a Bayer process liquor by a controlled slow precipitation. The controlled, slow precipitation rate required to create a low soda product is achieved by controlling the residence time of liquor in the precipitation vessel so as to provide a constant, low ratio of aluminum oxide to sodium oxide. Residence time control in a Bayer process plant is achieved by controlling green liquor flow rate to the tank, or by sizing the tank for a constant flow. The use of heavy seed charges to increase the seed surface area permits the production of a low soda product at a faster precipitation rate.

Abstract: In a process for extracting alumina from alumina-containing ores by individually preheating a slurry of alumina-containing ores in alkali solution, and an alkali solution, and feeding the preheated slurry and the preheated alkali solution to a digester maintained at a temperature of about 200.degree. to about 300.degree. C, thereby extracting alumina from the alumina-containing ore. The alumina extraction is carried out without any formation of scales on the inside surface of the preheater with a considerably prolonged operating duration by preparing a slurry having a molar ratio of Na.sub.2 O/Al.sub.2 O.sub.