Method for processing red mud to obtain scandium oxide

Abstract

The invention relates to technology for the comprehensive processing of bauxites, specifically red mud, to obtain scandium oxide. The present method includes filtering red mud, reslurrying the red mud cake, sparging the mud slurry, and subjecting same to carbonate-bicarbonate leaching and filtration to obtain a scandium-containing product solution. The obtained solution is mixed with an alkali-aluminate solution to obtain a precipitate which is filtered and releached to obtain a scandium-containing alkali-aluminate solution and an insoluble precipitate. The precipitate is releached to obtain a scandium-containing sodium carbonate-bicarbonate solution. The scandium-containing solutions are mixed to obtain a concentrate from which scandium is extracted by two-stage sulphuric acid leaching to obtain basic scandium sulphate which is then treated with oxalic acid. The obtained scandium oxalate precipitate is filtered and calcined to obtain scandium oxide. The invention makes it possible to achieve high scandium extraction.

Description

[0001] METHOD OF PROCESSING RED MUD TO OBTAIN SCANDIUM OXIDE

[0002] Field of technology to which the invention relates

[0003] The invention relates to the field of non-ferrous metallurgy, namely, to the technology of complex processing of bauxite, in particular, waste generated during the production of alumina from bauxite using the Bayer process, the so-called red mud.

[0004] State of the art

[0005] Scandium is a classic trace element and is not found in nature in its free state, forming virtually no industrial-scale deposits of Sc-containing minerals. Scandium is obtained only through industrial production, primarily as its oxide, SC2O3, a white powder, or its salts. Scandium is one of the most expensive metals on Earth, which hinders its widespread use in innovative and high-tech applications, as well as as a component of light alloys. However, demand for scandium is growing. Scandium is primarily of interest for the production of alloys used as a structural material in aircraft construction, rail, road, and water transport, as it imparts improved properties to aluminum alloys. A few hundredths of a percent of metallic scandium in an aluminum alloy increases its electrical conductivity, strength, and other properties.torsion, improves plastic properties, increases resistance to stress-corrosion cracking, ensures weldability of these alloys in an air atmosphere, while the strength of the welded seams is greater than that of the material.

[0006] The world's largest commercially valuable scandium reserves are concentrated in red mud—a byproduct of bauxite processing into alumina. Disposal of this environmentally hazardous waste poses a major challenge for aluminum production. Developing scandium extraction technology can improve the properties of red mud and lower its hazard class, including significantly reducing the content of active caustic alkali and phytotoxic aluminum, and lowering the red mud's moisture content. This reduces the sludge's hazard class from 3 to 4, eliminating the need for costly red mud disposal and environmental fees for waste disposal. It also creates a source of additional revenue through the use of activated sludge in the construction industry or for the treatment of industrial wastewater from heavy metals, particularly molybdenum, copper, and strontium.

[0007] Patent RU 2247788, dated March 10, 2005, discloses a method for producing scandium oxide. This method involves the repeated sequential leaching of red mud with a mixture of sodium carbonate and sodium bicarbonate solutions, washing and separating the precipitate, adding zinc oxide dissolved in sodium hydroxide to the resulting solution, maintaining the solution at elevated temperature and stirring, separating the zinc and scandium precipitate, treating it with a sodium hydroxide solution at boiling point, separating, washing, and drying the resulting product, and then extracting scandium oxide using known methods. This method allows for the production of up to 58 g of high-grade scandium concentrate from 1 ton of red mud, with an average SC2O3 content of 30.0%, and a scandium oxide recovery of 13.9%.To obtain such a SC2O3 content in the concentrate (approximately 30.0%), it is necessary to recycle the primary Sc-containing solution at least 10 times for a new leaching cycle of a fresh portion of red mud, which reduces the productivity of the overall process. The main disadvantage of this method is the low scandium oxide recovery from red mud (13.9%), caused by high secondary scandium losses during the reuse of the Sc-containing soda-bicarbonate solution due to the binding of scandium from the solution at the beginning of the leaching process into poorly soluble Al2SCO3. Aluminum appears in the solution due to the decomposition of some of the calcium hydrogarnets and sodium hydroaluminosilicates contained in the red mud during interaction with sodium bicarbonate NaHCO3.

[0008] A method for obtaining scandium concentrate from red mud is known from patent RU 2536714 dated 27.12.2014, which ensures an increase in the degree of scandium extraction from red mud into a primary Sc-containing solution during carbonization leaching and the production of a productive solution purified from accompanying impurities and more concentrated in scandium before the precipitation of scandium concentrate. This method for obtaining scandium concentrate involves the sequential carbonization leaching of red mud with a carbonate solution with simultaneous gasification of the slurry pulp with a gas-air mixture containing CO2, filtration of the carbonized slurry pulp to obtain a scandium-containing solution, sequential separation of scandium from associated impurity components with appropriate concentration, precipitation of poorly soluble scandium compounds from the purified solution, filtration, washing and drying of the precipitate to obtain a scandium concentrate.In this process, carbonization leaching of red mud involves initial vibrocavitation treatment of the slurry pulp. Scandium is separated from impurity components and concentrated from the resulting scandium-containing solution by sorption onto phosphate ion exchangers, followed by desorption of scandium from the organic phase of the ion exchangers. Desorption is performed with mixed carbonate-chloride solutions in a pulsed mode, producing a scandium-containing eluate from which sparingly soluble scandium compounds are precipitated in stages. Initially, the sparingly soluble impurity compounds precipitate, separating the precipitate, which is titanium-zirconium concentrate, followed by precipitation of the scandium concentrate. This method enables an average scandium oxide recovery of 23.5% into the target product (concentrate).The main disadvantage of this method is also the low extraction of scandium from red mud into the production Seco holding solution.

[0009] It is known that the recoverable scandium in the red mud of alumina refineries in Russia (Ural Aluminum Plant (UAZ) and Bogoslovsky Aluminum Plant (BAZ)) is approximately 70%, so it is important to create conditions under which scandium recovery will be increased.

[0010] A method for obtaining scandium oxide is known from patent RU 2257348 dated 27.07.2005, according to which a scandium-containing concentrate is dissolved in a mineral acid (hydrochloric, sulfuric, nitric), the scandium solution is purified from impurities by treating the solutions with a sulfate-containing inorganic compound and then with barium chloride, the purified scandium solution is treated with alkaline reagents, in particular, NH4OH, to obtain poorly soluble scandium compounds: oxyhydroxide ScO(OH) or scandium hydroxocarbonate. This is followed by filtering the pulp to separate the scandium precipitate from the solution, treating the precipitate with formic acid H2CO2, separating the scandium formate precipitate from the mother liquor, washing the precipitate with formic acid, drying and calcining the precipitate to obtain commercial scandium oxide with a purity of > 99%. The disadvantages of the known method include its multi-stage nature, which requires a large amount of process equipment, increasing operating expenses., translated as “operating expenses (costs)”) and high specific consumption of materials, increasing CAPEX (capital expenditures - English, translated as “capital expenses (costs)”).

[0011] Patent RU 2478725, dated April 10, 2013, describes a method for extracting scandium oxide from scandium-containing concentrate. The process involves dissolving the Sc-containing concentrate in sulfuric acid, removing the acid-insoluble precipitate, and precipitating the scandium in the presence of an ammonium compound. The precipitate is then filtered, washed, dried, and calcined to obtain a scandium oxide precipitate. After removing the acid-insoluble precipitate, the sulfuric acid concentration in the filtrate is increased to 540-600 g / dm3. 3 , ammonium chloride NH4CI is used as an ammonium compound, introduced into the solution in an amount of 26.7-53.5 g / dm3 3At a temperature of 50-70°C, followed by aging for 1-2 hours with stirring. The resulting precipitate is washed with ethyl alcohol. The technical result is a simplified process for producing commercial, high-purity scandium oxide with a yield of up to 97-98% from low-grade scandium concentrate, such as waste generated during the processing of bauxite into alumina.

[0012] The invention under patent RU 2647398 dated 04.08.2016 of RUSAL for a method for obtaining a scandium-containing concentrate, including a single-stage soda-bicarbonate leaching of red mud to obtain a production scandium-containing solution, sorption of scandium from the solution on phosphonic resins, desorption of scandium with a concentrated soda solution at an elevated temperature to obtain a rich scandium-containing eluate, two-stage hydrolysis of the scandium-containing eluate to obtain a Sc-containing concentrate, was accepted as a prototype.The main disadvantages of this method are that, when implemented in practice, it results in a low scandium recovery rate from red mud, no more than 20-25%, high cost of scandium due to the high specific consumption of phosphonic resins, due to their intensive destruction during desorption with a hot concentrated soda solution, as well as the need for periodic regeneration of the phosphonic resin from iron and titanium with oxalic acid, poor process reproducibility during the two-stage hydrolysis of a scandium-containing soda-bicarbonate solution, which is a buffer solution, due to which the pH value changes abruptly, which leads to the inability to control the first stage of hydrolysis, as well as difficulties in separating the scandium-containing precipitate from the liquid phase in the second stage of hydrolysis. Disclosure of the essence of the invention.

[0013] The objective of the proposed invention is to develop a technology for extracting scandium from large-tonnage alumina production waste—red mud—which, according to the accepted classification, is classified as hazard class 3. Due to the high alkalinity of this waste, areas near its storage sites (sludge ponds) are unsuitable for either construction or agriculture. As noted, demand for scandium is growing. Scandium is of interest for the production of alloys used as a structural material in aircraft manufacturing, rail, road, and water transport, as it imparts improved properties to aluminum alloys.

[0014] The technical result is the solution of the stated problem and the achievement of the highest possible scandium extraction during the processing of red mud under modern technological conditions.

[0015] In the proposed method, several main technological stages can be distinguished for obtaining primary scandium-containing concentrate during the processing of red mud using soda-bicarbonate leaching technology, and then re-cleaning the primary scandium-containing concentrate to scandium oxide with a purity of 2N (99% pure metal), given as an example of implementation below and shown in the process flow chart in Fig. 1.

[0016] First and foremost, this is the stage of filtering the red mud from the thickening and washing stage of alumina production, removing the liquid phase in a filter press. The liquid phase contains dissolved sodium carbonate (Na2CO3), caustic alkali (NaOH), and sodium aluminate (NaAlCl). After filtration, a cake with a moisture content of 28-35% is obtained, and the liquid phase is returned to the main alumina production process.

[0017] Next, it is necessary to note the stage of repulping the red mud cake with a recycled soda-bicarbonate solution containing at least 20 g / dm3 in terms of NaHCO3 (i.e. the amount of Na O contained in the solution in the form of sodium bicarbonate NaHCO3) and not less than 100 g / dm3 3 in terms of Na2O yra (i.e. the amount of Na2O contained in the form of sodium carbonate Na2CO3).

[0018] An important step is the activation of the slurry pulp at a temperature of < 40 °C for > 10 hours by bubbling with a gas-air mixture (e.g. exhaust gases from sintering and / or alumina calcination furnaces and / or a boiler house or plant combined heat and power plant and / or limestone kilns) containing at least 3 vol.% carbon dioxide to achieve a pH of < 10.5 in the liquid phase due to the conversion of part of the sodium carbonate to sodium bicarbonate (Na2CO3 + CO2 + H2O = 2NaHCO3). The use of the slurry activation step allows for an increase in scandium extraction from red mud in the subsequent leaching stage from 20-25% to 40-45%, including by opening the surface of the sludge particles due to the destruction of the so-called “network structure” of the red mud, as well as by reducing secondary losses of scandium due to the formation of insoluble double oxide of scandium and aluminum AlScO3 and other phases.It should be clarified that the pH (hydrogen potential) of a caustic alkali solution is approximately 14, the pH of a soda solution is approximately 12, and the pH of a sodium bicarbonate solution is approximately 8.4. Thus, achieving a pH < 10.5 indicates that, after bubbling with a gas-air mixture containing carbon dioxide, due to the sorption of CO2, all of the caustic alkali has converted to alkali carbonate, and some of the alkali carbonate has converted to sodium bicarbonate, and its content is > 20 g / dm. 3 in terms of Na2Obkb- The initial pH value of the slurry pulp is > 12.5. The minimum pH value of the slurry pulp during bubbling is about 8.5, however, achieving this value requires very long bubbling.

[0019] Next, the activated sludge pulp, consisting of red mud and a soda-bicarbonate solution of a given composition, selected experimentally, is heated to a temperature of 85-95 °C and subjected to soda-bicarbonate leaching to obtain a scandium-containing solution with a content of at least 10 mg / dm3 3 SC2O3. The pulp after soda-bicarbonate leaching is filtered in a filter press to obtain a scandium-containing product solution and a leached red mud cake with a pH close to neutral and a moisture content of 28-32%. The scandium-containing product solution is then mixed with the alkali-aluminate solution obtained at the stage of precipitation of the hydrolysis concentrate and its filtration, the composition (g / dm 3 ): IagTot = 90-320 (Na2O O6 is the sum of Na2O contained in the solution in various forms, including caustic alkali Na(OH), denoted as Na2O3, sodium carbonate Na2O3, denoted as Na2O3, sodium bicarbonate Na2HCO3, denoted as Na2O3, sodium aluminate NaAlO3). Na2O3 = 70-290, Al2O3 = 35-150 in a ratio of 10:1 to 20:1 (by volume). The mixture is kept with stirring for at least 3 hours at a temperature of 85-95 °C to obtain a precipitate of primary scandium-containing concentrate.

[0020] Depending on the ratio of the production scandium-containing solution to the alkali-aluminate solution, two types of primary scandium-containing concentrate are obtained: 1) with an SC2O3 content from > 0.1 to < 1.0 wt.% and a low content of yttrium, thorium, but a high content of zirconium; 2) with a scandium oxide content from > 1.0 to 4.0 wt.% and a high content of yttrium, thorium, REE (rare earth metals).

[0021] Next comes the filtration of the obtained primary scandium-containing concentrate and washing on a cloth from the alkaline solution.

[0022] Primary scandium-containing concentrate with an SC2O3 content of 0.1 to <1 wt.% is used to produce scandium oxide with a purity of 2N. Primary scandium-containing concentrate with an SC2O3 content of >1 to 4.0 wt.% is a commercial product sold on the market and can also be used to produce scandium oxide with a purity of 2N.

[0023] Repeated leaching of the primary scandium-containing concentrate with an SC2O3 content of 0.1 to 4.0 wt.% is carried out with an alkali-aluminate solution of the composition (g / dm 3 ): NaarTot = 290-380 g / dm 3 ; ЯгОку = 260-350 g / dm 3 ; AI2O3 = 130-190 g / dm 3 , caustic modulus of about 3.5, at a temperature of 60-95 °C and a ratio of L (liquid): T (solid) of at least 3:

[0024] I (by weight) for > 1 hour. This operation allows for the maximum removal of AI2O3 from the primary scandium-containing concentrate.

[0025] The leached pulp is filtered to obtain a scandium-containing alkaline aluminate solution with a scandium concentration of > 0.05 g / dm3. 3 , sent for precipitation of hydrolysis concentrate to reduce the consumption of caustic alkali and insoluble precipitate-1 (see the process flow chart in Fig. 1). Precipitate-1 contains a residual amount of unleached scandium, therefore, to increase the through yield of scandium in the finished product, it is sent for repeated leaching with a soda-bicarbonate solution to extract additional scandium into the solution. Therefore, repeated leaching of the insoluble precipitate-1 is carried out with a soda-bicarbonate solution of the composition (g / dm 3): NagOtotal = 120-140, NagObkb = 10-20, at a temperature of 60-95 °C and a ratio of L:S> 3:1 (by weight) for > 1 hour, to obtain a scandium-containing soda-bicarbonate solution with a content of SC2O3> 0.05 g / dm3 3 Two stages of alkali-aluminate and soda-bicarbonate leaching allow for the extraction of up to 90-95% of scandium into solution and the retention of up to 95% of the main impurities in an insoluble precipitate.

[0026] The next stage is the filtration of the leached pulp, producing a scandium-containing alkali-aluminate solution and an insoluble precipitate (see the process flow diagram in Fig. 1). After several leaching stages, the precipitate contains virtually no scandium and consists of aluminum-, zirconium-, and rare-earth-metal-containing phases, so it can be returned to the main alumina production to reduce secondary alumina losses. The resulting insoluble precipitate

[0027] II is removed to the main alumina production process or can be used to produce zirconium and rare-earth metal concentrate. A scandium-containing alkaline aluminate solution and a scandium-containing soda-bicarbonate solution are mixed at room temperature and the mixture is stirred for 1 hour to produce a scandium-containing hydrolysis concentrate with an SC2O3 content of 4 to 12 wt%. The resulting scandium-containing hydrolysis concentrate is filtered to produce an alkaline aluminate solution, which is used to precipitate the primary scandium-containing concentrate.

[0028] This is followed by a two-stage sulfuric acid leaching of the filtered scandium-containing hydrolysis concentrate: in the first stage at a pH of 3.7-4.3 for at least 2 hours, and in the second stage at a temperature of at least 80°C at a pH of 2.0-2.3 for at least 2 hours, with the extraction of at least 90% of the scandium into the sulfuric acid solution. It should be clarified that the hydrogen potential (pH) value in the first and second stages of sulfuric acid leaching is obtained by adding the calculated amount of 72% technical sulfuric acid, and the pH is monitored with an industrial pH meter. After mixing the Sc-containing hydrolysis concentrate and the sulfuric acid solution, stirring, and heating are started, the pH is measured and adjusted with sulfuric acid. Next, the scandium-containing sulfate solutions filtered after the 1st and 2nd stages with an SC2O3 content of 0.8 to 3 g / dm are mixed. 3, and add an alkali solution to the mixed scandium-containing solution to achieve pH = 4.5-5.5. Scandium sulfate Sc2(SO4)3 is precipitated from a sulfuric acid solution at pH = 4.5-5.5, free of impurities, including thorium, REE, hafnium, zirconium, yttrium, titanium and other rare and trace elements.

[0029] This is followed by the stage of repeated treatment of the sulfuric acid solution with caustic alkali to a pH of no more than 5.6 for the selective precipitation of scandium, and after filtration, a zirconium concentrate and a scandium-containing solution are obtained. The obtained basic scandium sulfate is treated with oxalic acid at a ratio of Sc(OH)SO4 : H2CrC^^H2O = 1 : 1.2 (by weight) for at least 1 hour at a temperature of at least 60 °C for conversion to scandium oxalate (8O2(02B)4)3). The resulting scandium oxalate precipitate is filtered and scandium oxalate is calcined at a temperature of at least 860 °C for at least 2 hours to remove all carbon from scandium oxalate 8O2(02B)4)3 and obtain pure scandium oxide.

[0030] The proposed technology allows to obtain scandium oxide with a purity of > 2N, namely, SC2O3 > 99 wt.%.

[0031] Key features of the new method include a red mud activation step prior to soda-bicarbonate leaching at a temperature of <40°C and an activation time of at least 8 hours, which allows for a roughly twofold increase in scandium recovery, from 20-25% to 40-45%. The activation step exposes the surface of the red mud particles by breaking down the "net" structure. This so-called "net" structure forms in red mud during the extraction of alumina from bauxite using the Bayer process. To quickly and efficiently separate the aluminate solution and red mud, the industry uses specialized synthetic flocculants based on organic compounds. Flocculants are long carbon chains of several million carbon units with active radicals at the ends of the chain.These flocculants, due to their chain length and active radicals, link the main phases of red mud into larger, more easily settled particles, forming a three-dimensional network. The nodes of this network contain large particles of iron oxide (hematite) with a low surface charge (zeta potential) and finely dispersed sodium hydroaluminosilicates with a high zeta potential, which "crosslink" the hematite. The recovered scandium is absorbed on the surface of the red mud particles, but due to the "network" structure, the soda-bicarbonate solution has no access to the surface. During the activation process, the network structure is destroyed, exposing the mud surface. The activation stage is important for breaking down the "network" structure formed by synthetic flocculants in alumina production and also reduces secondary scandium losses due to its binding to poorly soluble Al2SO4 at the beginning of the soda-bicarbonate leaching process.Aluminum appears in the solution due to the decomposition of some of the calcium hydrogarnets and sodium hydroaluminosilicates contained in the red mud, interacting with sodium bicarbonate (NaHCO3). Thus, the activation stage allows for the separation of the decomposition of sodium hydroaluminosilicates and hydrogarnets from the leaching of scandium into the liquid phase.

[0032] Another important distinction of this method is the use of freshly precipitated aluminum hydroxide as a scandium "collector," obtained by mixing the Sc-containing soda-bicarbonate solution with a high-modulus alkali-aluminate solution from alumina production. This operation replaces scandium sorption and / or two-stage scandium hydrolysis from the soda-bicarbonate solution. The process of concentrating scandium on aluminum hydroxide allows for the control of the impurity composition of the primary scandium-containing concentrate, i.e., the production of two types of primary scandium-containing concentrate with different impurity compositions.

[0033] Depending on the ratio of the production scandium-containing solution to the alkali-aluminate solution, the following is obtained:

[0034] - concentrate with a SC2O3 content from 0.1 to < 1.0 wt.%, with a low content of yttrium, thorium, and a high content of zirconium; mixing is carried out based on the content of Na2O caustic after mixing 1-5 g / dm3 3 ; this concentrate is used to obtain scandium oxide with 2N purity;

[0035] - a concentrate with a scandium oxide content of 1 to 4 wt.% and a high content of yttrium, thorium, and rare earth metals; mixing is carried out based on the Na2O content, caustic after mixing 5.1-20 g / dm3 3 ; the concentrate is a commercial product sold on the market or can be used to obtain scandium oxide with a purity of 2N.

[0036] Two-stage leaching of primary scandium-containing concentrate with an alkaline aluminate solution and a soda-bicarbonate solution removes over 90% of impurities, including titanium, zirconium, iron, aluminum, calcium, and others. Sulfuric acid refining of the concentrate, with an SC2O3 content of 0.1 to 0.3 wt.% and a pH of 4.5 to 5.5, removes thorium and other impurities from scandium and creates conditions for the subsequent production of zirconium concentrate, increasing the depth of bauxite processing.

[0037] Fig. 1 shows a general block diagram including the technology for producing scandium-containing concentrate with an SC2O3 content of 0.1 to 4.0 wt.%, its purification to scandium oxide with a purity of 2N, and zirconium concentrate.

[0038] As noted above, the primary objective of the invention and the overall scandium oxide production technology is to achieve the highest possible scandium recovery during red mud processing. For example, increasing scandium recovery from red mud obtained during the processing of a mixture of bauxites from the North Ural bauxite region and the Middle Timan bauxite region from 20-25% to 40-45% reduces the specific amount of processed mud from 28 to 16 tons per 1 kg of produced commercial scandium oxide with a purity of 2N. Extracting zirconium concentrate from red mud, in addition to scandium, reduces the cost of scandium oxide production by 20% or more.

[0039] Implementation of the invention

[0040] Table 1 shows a typical composition of red mud used for soda-bicarbonate leaching of scandium. Table 1

[0041] Table 2 shows examples of the influence of red mud activation modes on scandium extraction during soda-bicarbonate leaching (temperature, time, solution concentration according to Na2Obk6) on scandium extraction during soda-bicarbonate leaching.

[0042] Table 2

[0043] Examples 2 and 6 in Table 2 are the most effective, as they allow for the maximum transfer of scandium from the solid phase to solution.

[0044] The optimal temperature and time for the red mud activation stage were selected experimentally and depended on the following conditions:

[0045] - the need to separate two processes: 1) the decomposition of tricalcium hydroaluminate 3CaO*Al2O3*6H2O to calcium carbonate CaCO3 and calcium hydrocarboaluminate, and 2) the leaching of scandium from red mud into a soda-bicarbonate solution. The objective was to prevent the aluminum released during the first process from binding scandium into an inert compound, double oxide Al8CO3. Therefore, the activation process was carried out at a temperature of no more than 40 °C, and leaching at a temperature above 80 °C, which were selected experimentally as optimal;

[0046] - the activation time was also determined by the need to destroy the “mesh” structure of the red mud, which was formed due to the use of synthetic flocculants in the process to accelerate the thickening of the washing.

[0047] If the activation stage is not used, the scandium extraction is reduced, as shown in Table 2.

[0048] Table 3 shows the influence of the mixing ratio of the production scandium-containing solution and the alkali-aluminate solution of the following composition (g / dm 3 ): Na2O O 6 = 90-320; Na2O KV = 70-290; AI2O3 = 35-150 in a ratio of 10:1 to 20:1 (by volume) and a holding time with stirring for at least 3 hours at a temperature of 50-98 °C to obtain a precipitate of primary scandium-containing concentrate.

[0049] Table 3

[0050] Examples 1-4 in Table 3 show that mixing the production scandium-containing solution and the alkali-aluminate solution in the protected range of temperatures and volume ratios allows for the production of a filterable precipitate suitable for further processing into scandium oxide.

[0051] Table 4 shows the influence of hydrogen potential (pH) and temperature during two-stage selective sulfuric acid leaching of scandium-containing hydrolysis concentrate on the extraction of scandium into solution.

[0052] Table 4

[0053] In examples 1-4 of Table 4, the extraction of scandium from the solid phase into solution was more than 80 wt.%, which confirms the achievement of advantages by the proposed method in comparison with analogs and the prototype.

[0054] Taking into account the given description and examples, the scope of legal protection is claimed for a method of processing red mud to obtain scandium oxide, including filtering red mud from liquid phase, repulping the red mud cake with a soda-bicarbonate solution, bubbling the sludge pulp with a gas-air mixture containing carbon dioxide, carbonation leaching of the sludge pulp with a soda-bicarbonate solution to obtain a scandium-containing solution, filtration and washing with water on a cake filter to obtain a production scandium-containing solution, characterized in that bubbling is carried out to activate scandium compounds in the sludge and achieve a pH of < 10.5 in the liquid portion, after which carbonation leaching is carried out, after filtration the production scandium-containing solution is mixed with an alkali-aluminate solution to obtain a primary precipitate scandium-containing aluminum hydroxide with a scandium oxide content of 0.1 to 4 mass.%, the primary Sc-containing aluminum hydroxide is filtered and re-leached with an alkali-aluminate solution, then filtered to obtain a scandium-containing alkali-aluminate solution with a scandium concentration of at least 0.05 g / dm3. 3 and an insoluble precipitate, the insoluble precipitate is filtered off, the insoluble precipitate is re-leached with a soda-bicarbonate solution to obtain a scandium-containing soda-bicarbonate solution with an SC2O3 content of at least 0.05 g / dm3 3, the resulting solution is filtered, the scandium-containing alkali-aluminate solution and the scandium-containing soda-bicarbonate solution are mixed to obtain, upon mixing, a hydrolytic scandium-containing concentrate with an SC2O3 content of 4 to 12 mass.%, the filtered scandium-containing hydrolysis concentrate is subjected to two-stage sulfuric acid leaching, wherein at the 1st stage the pH is 3.7-4.3, at the 2nd stage the pH is 2.0-2.3 with the extraction of scandium into a sulfuric acid solution, the scandium-containing sulfuric acid solutions filtered after the 1st and 2nd stages are mixed and an alkali solution is added to achieve a pH of 4.5-5.5 with the precipitation of scandium sulfate that does not contain impurity elements, then re-treated with caustic alkali to a pH of no more than 5.6 for the selective precipitation of scandium, after which scandium sulfate is treated with a sulfuric acid solution to obtain basic scandium sulfate, the resulting basic scandium sulfate is treated with oxalic acid for conversion to scandium oxalate, the resulting precipitate is filtered scandium oxalate, calcining the scandium oxalate to remove carbon and obtain scandium oxide containing at least 99.0 wt.% SC2O3 in the calcined product.

[0055] Preferably, bubbling is carried out at a temperature of no more than 40 °C for > 10 hours to activate scandium compounds in the sludge and achieve a pH of < 10.5 in the liquid portion, after which carbonation leaching is carried out at a temperature of at least 80 °C, after filtration, the scandium-containing production solution is mixed with an alkali-aluminate solution in a ratio of 10:1 to 20:1 by volume at a temperature of 50-98 °C to obtain a precipitate of primary scandium-containing aluminum hydroxide with a scandium oxide content of 0.1 to 4 wt.%, the primary Sc-containing aluminum hydroxide is filtered and re-leached with an alkali-aluminate solution at a temperature of 60-95 °C and a Liquid: Solid ratio of at least 3: 1 by weight for at least 1 hour, filtered with obtaining a scandium-containing alkali-aluminate solution with a scandium concentration of at least 0.05 g / dm3 3and insoluble precipitate, filter off the insoluble precipitate, re-leach the insoluble precipitate with a soda-bicarbonate solution of the composition (g / dm 3 ): Na2O O 6 = 120-140, Na2O3 = 10-20 at a temperature of 60-95 °C and a Liquid: Solid ratio of at least 3: 1 by weight for at least 1 hour to obtain a scandium-containing soda-bicarbonate solution with an SC2O3 content of at least 0.05 g / dm3 3 , whereupon the obtained basic scandium sulfate is then treated with oxalic acid at a ratio of Sc(OH)SO4: H2C2O4X2H2O = 1: 1.2 by weight for at least 1 hour at a temperature of at least 60 °C for conversion to scandium oxalate, the resulting scandium oxalate precipitate is filtered, and scandium oxalate is calcined at a temperature of at least 860 °C for at least 2 hours to remove carbon and obtain scandium oxide.

[0056] It is advisable to carry out bubbling at the activation stage with a gas-air mixture containing at least 3 vol.% carbon dioxide. At the stage of mixing the production scandium-containing solution and the alkali-aluminate solution, it is preferable to use the composition of the alkali-aluminate solution (g / dm 3 ): Ыа2О О bsh = 90-320; Na2O KV =70-290; Al2O3 = 35-150, while the mixture is stirred and held for at least 3 hours. Repeated leaching of scandium-containing aluminum hydroxide is carried out with an alkaline aluminate solution of the composition (g / dm 3 ): Ыа2О О b Щ = 290- 380 g / dm 3 ; Na2O KV = 260-350 g / dm 3 ; A120z = 130-190 g / dm 3 The scandium-containing sulfate solution filtered after two-stage sulfuric acid leaching contains 8С2О3 from 0.8 to 3 g / dm3 3 The concentration of sulfuric acid H2SO4 during the processing of scandium sulfate is 100-350 g / dm3 3 .

Claims

CLAUSES OF THE INVENTION 1. A method for processing red mud to obtain scandium oxide, comprising filtering red mud from liquid phase, repulping red mud cake with a soda-bicarbonate solution, bubbling the sludge pulp with a gas-air mixture containing carbon dioxide, carbonation leaching of the sludge pulp with a soda-bicarbonate solution to obtain a scandium-containing solution, filtration and washing with water on a cake filter to obtain a production scandium-containing solution, characterized in that bubbling is carried out to activate scandium compounds in the sludge and achieve a pH of < 10.5 in the liquid portion, after which carbonation leaching is carried out, after filtration the production scandium-containing solution is mixed with an alkali-aluminate solution to obtain a precipitate of primary scandium-containing aluminum hydroxide with scandium oxide content from 0.1 to 4 mass.%, the primary Sc-containing aluminum hydroxide is filtered and re-leached with an alkali-aluminate solution, then filtered to obtain a scandium-containing alkali-aluminate solution with a scandium concentration of at least 0.05 g / dm3. 3 and an insoluble precipitate, the insoluble precipitate is filtered off, the insoluble precipitate is re-leached with a soda-bicarbonate solution to obtain a scandium-containing soda-bicarbonate solution with an SC2O3 content of at least 0.05 g / dm3 3 , the resulting solution is filtered, the scandium-containing alkali-aluminate solution and the scandium-containing soda-bicarbonate solution are mixed to obtain, upon mixing, a hydrolytic scandium-containing concentrate with an SC2O3 content of 4 to 12 wt.%, the filtered scandium-containing hydrolytic concentrate is subjected to two-stage sulfuric acid leaching, wherein at the 1st stage the pH is 3.7-4.3, at the 2nd stage the pH is 2.0-2.3 with the extraction scandium in a sulfuric acid solution, the scandium-containing sulfate solutions filtered after the 1st and 2nd stages are mixed and an alkali solution is added to achieve a pH of 4.5-5.5 with the precipitation of scandium sulfate that does not contain impurity elements, then re-treated with caustic alkali to a pH of no more than 5.6 for the selective precipitation of scandium, after which scandium sulfate is treated with a sulfuric acid solution to obtain basic scandium sulfate, the obtained basic scandium sulfate is treated with oxalic acid for conversion into scandium oxalate, the resulting scandium oxalate precipitate is filtered, scandium oxalate is calcined to remove carbon and obtain scandium oxide containing at least 99.0 wt.% SC2O3 in the calcined product.

2. The method according to claim 1, in which bubbling is carried out at a temperature of no more than 40 °C for > 10 hours to activate scandium compounds in the sludge and achieve a pH of < 10.5 in the liquid portion, after which carbonation leaching is carried out at a temperature of no lower than 80 °C, after filtration, the scandium-containing production solution is mixed with an alkali-aluminate solution in a ratio of 10:1 to 20:1 by volume at a temperature of 50-98 °C to obtain a precipitate of primary scandium-containing aluminum hydroxide with a scandium oxide content of 0.1 to 4 wt.%, the primary Sc-containing aluminum hydroxide is filtered and re-leached with an alkali-aluminate solution at a temperature of 60-95 °C and a Liquid: Solid ratio of at least 3:1 by weight for for at least 1 hour, filter to obtain a scandium-containing alkaline aluminate solution with a scandium concentration of at least 0.05 g / dm3 3and insoluble precipitate, filter off the insoluble precipitate, re-leach the insoluble precipitate with a soda-bicarbonate solution of the composition (g / dm 3 ): Na2O O 6 = 120-140, Na2O3 = 10-20 at a temperature of 60-95 °C and a Liquid: Solid ratio of at least 3: 1 by weight for at least 1 hour to obtain a scandium-containing soda-bicarbonate solution with an SC2O3 content of at least 0.05 g / dm3 3 , and then the resulting main scandium sulfate is treated with oxalic acid at a ratio of Sc(OH)SC>4: H2C2O4X2H2O = 1:1.2 by weight for at least 1 hour at a temperature of at least 60 °C for conversion to scandium oxalate, the resulting scandium oxalate precipitate is filtered, and scandium oxalate is calcined at a temperature of at least 860 °C for at least 2 hours to remove carbon and obtain scandium oxide.

3. The method according to item 1 or item 2, characterized in that bubbling at the activation stage is carried out with a gas-air mixture containing at least 3 vol.% carbon dioxide.

4. The method according to item 1 or item 2, characterized in that at the stage of mixing the production scandium-containing solution and the alkali-aluminate solution, the composition of the alkali-aluminate solution (g / dm3) is used. 3 ): IagTot = 90-320; Na2O KV =70-290; A1203 = 35-150, while the mixture is stirred and kept for at least 3 hours.

5. The method according to paragraph 1 or paragraph 2, characterized in that the repeated leaching of scandium-containing aluminum hydroxide is carried out with an alkali-aluminate solution of the composition (g / dm 3 ): NaarTot = 290-380 g / dm 3 ; ЯгОку = 260-350 g / dm 3 ; A120z = 130-190 g / dm 3 .

6. The method according to item 1 or item 2, characterized in that the scandium-containing sulfate solution filtered after two-stage sulfuric acid leaching contains SC2O3 from 0.8 to 3 g / dm3. 3 .

7. The method according to item 1 or item 2, characterized in that the concentration of sulfuric acid H2SO4 during the processing of scandium sulfate is 100-350 g / dm3 3 .

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