AU2018403419A1 - Method of producing scandium oxide from scandium-containing concentrates - Google Patents

Abstract

The present method comprises dissolving a scandium-containing concentrate in a mineral acid, purifying the scandium solution, separating the precipitate, treating same with an alkaline agent, and separating the precipitate of scandium compounds from the solution, wherein the concentrate is dissolved in sulfuric acid to obtain a scandium solution that is separated from the precipitate and treated with sodium sulfate; the double salt of sodium sulfate and scandium sulfate is precipitated, removed by filtration, washed with sodium sulfate solution and dissolved in water; barium hydroxide or a barium salt is added; the precipitate of impurities is removed by filtration, and scandium hydroxide is precipitated from the scandium solution at pH 4.8-6.0 by adding sodium hydroxide, the precipitate is removed by filtration and treated with a solution of oxalic acid to obtain scandium oxalate, which is separated from the solution, washed with water, dried and calcined to obtain scandium oxide.

Description

METHOD FOR OBTAINING SCANDIUM OXIDE FROM SCANDIUM-CONTAINING CONCENTRATES

The invention relates to the field of metallurgy of rare metals, in particular, to a method for producing scandium oxide from scandium containing concentrates, and can be used in the processing of scandium containing concentrates of various origins. In particular, scandium containing concentrates obtained simultaneously during the processing of ilmenite concentrates, uranium ores, red mud from alumina production and others. Scandium oxide has several advantages; the strength of scandium oxide increases when heated and reaches a maximum at 10300C. In an alloy with aluminum, scandium provides additional strength, forging property, superductility and high corrosion resistance, therefore, its use in such industries as aerospace engineering, rail transport manufacturing, shipbuilding, oil and gas production will not only let enhance their technical and economic performance, but also create a revolutionary product. There is a known method of producing 99% scandium oxide, which includes leaching scandium from a fluoride scandium-containing concentrate with a solution of NH 4F, precipitating scandium from a solution of leaching with crystalline NaF in the form of a double fluoroscandiate, hydrolysis of a double fluoroscandiate Na-NH4 to produce scandium fluoride and the conversion of ScF 3 intoSc20 3 at a temperature of 700 C in a stream of air. This method allows the separation of scandium from Ca, Mg, Al, Ti, Y,

REE, Zr, Na, U, and Th impurities at the stage of selective leaching with NH4F solution, as well as from Ti, Zr, U, Fe, and Mg impurities at the precipitation stage scandium from a solution of NH4F in the form of fluoride salts (Patent RU 2040471, publ. 07.25.1995). The disadvantage of this method is the significant cost of implementing the method through the use of expensive fluoride treating agents, as well as the likelihood of gaseous fluorine compounds entering the atmosphere during the conversion of scandium fluoride to scandium oxide. The patent RU 2608033, publ. 01/12/2017 describes a method for producing scandium oxide, which consists in the fact that a scandium containing solution obtained after nitric acid leaching of scandium-containing raw materials with a residual acidity in the range from 5 to 40 g/ with nitric acid is sent to sorption of scandium into columns with a fixed layer of strongly acidic cation exchanger, scandium-saturated resin is washed in the column with aqueous saline, with a concentration of 1.5-5.0 g/l for cerium (IV) and 35-80 g/l for nitric acid at a speed of 3-30 rph at a temperature of 20 500 C, which is subjected to oxidation by electrochemical method before feeding into a column with cation exchange resin, the resulting washing solution containing scandium displaced from the cation exchange resin and impurities are sent for purification from impurities. After washing, the cation exchange resin is subjected to treatment with a 7-nitric acid solution to remove residual scandium and impurities, which are then sent to the regeneration of nitric acid by vacuum distillation. The moderately acidic scandium-containing wash solution is made alkaline with ammonia water to a neutral medium, scandium, together with impurities of rare-earth metals, iron, and aluminum, precipitates in the form of hydroxides, which are filtered and dissolved at a temperature of 850 C in a sulfuric acid solution, maintaining excess acidity for sulfuric acid at 10 -15 g/l, adjust the acidity of the solution with ammonia water to pH 3-4, and the resulting scandium-containing solution is sent to sorption on a strongly basic anion exchange resin converted to sulfate form, while scandium and iron (III) with biruyutsya, and other impurities remain in solution, which is fed to the precipitation of cerium hydroxide (IV) and reset after liming. Next, desorption of scandium is carried out with a solution of sodium carbonate or ammonium at a pH of 10.1-10.8, scandium hydroxide is precipitated from the eluate, which, after filtration, is dried and calcined to obtain the final product - scandium oxide containing 65.1% of scandium. The disadvantage of this method is the multi-stage process, the use in the technology of such expensive treating gents and materials as cerium salts, ion-exchange resins, the process of nitric acid regeneration, which is rather costly in terms of energy consumption and hardware design. There is also a method for producing scandium oxide from a poor scandium concentrate, which consists in dissolving a scandium-containing concentrate in sulfuric acid, removing an acid insoluble precipitate, increasing the concentration of sulfuric acid in the filtrate to 540-600 g/dm 3, and precipitating scandium in the presence of ammonium chloride at a temperature of 50- 700 C, followed by exposure for 1-2 hours with stirring, filtration, washing the precipitate with ethanol, drying and calcining the resulting precipitate. The result is a marketable scandium oxide Sc 203with a purity of 99.0%. The extraction of scandium from the concentrate to the oxide is 97-98%. Losses of scandium do not exceed 2-4%. (Patent RU 2478725, publ. 04/10/2013). The disadvantage of this method is the use of highly concentrated sulfuric acid solutions, which leads to high costs for corrosion-resistant equipment, the need to utilize the gaseous sulfur oxides generated by the calcination of scandium sulfate, and the use of expensive ethyl alcohol reagent for washing the precipitate of scandium sulfate. The closest to the claimed method according to the totality of the features and purpose is a method for producing scandium oxide from scandium-containing intermediate products and concentrates, including dissolving scandium-containing concentrate in a solution of hydrochloric acid with a concentration of 250-300 g/l at a temperature of 80-120° C for 1-4 h, purification of the scandium solution from impurities by treatment with sulfuric acid and/or sodium sulfate and then barium chloride, separation of the precipitate from the scandium solution, precipitation of scandium oxyhydrate from the solution when added to a target of sodium hydroxide or carbonate with a concentration of 20-120 g/ dm3 , separating the precipitate of poorly soluble scandium compounds from the solution, treating the precipitate with formic acid to obtain scandium formate, which is washed, dried and calcined at 700 0 C. After filtration of scandium formate the pregnant liquor is sent to the regeneration of formic acid and returned to the processing stage of scandium oxyhydrate. The method allows to obtain scandium oxide with a purity of up to 99.99%, the loss being 2.5 0.5% (Patent RU 2257348, publ. July 27, 2005). A significant disadvantage of the known prototype method is the high material costs for organizing the method due to the use of solutions of hydrochloric acid at the leaching stage of the scandium-containing concentrate, which entails the need for expensive acid-resistant equipment, as well as the need to create an additional technological unit for carrying out the process of regeneration of formic acid from the mother liquor. The basis of the proposed invention is the task of developing a new method for producing scandium oxide from scandium-containing concentrates of various origins, characterized by a simplification of the process with a reduction in the cost of implementing the method and maintaining a high quality product - scandium oxide, through the use of a certain sequence of technological stages and modes that allow maximally extract scandium into the final product - scandium oxide, and selectively separate it from impurities without using high-priced treating agents and equipment. According to the suggested method, scandium-containing concentrates obtained simultaneously with processing ilmenite concentrates, uranium ores, red mud from alumina production and other scandium-containing mineral and technogenic sources can be used as raw materials for producing scandium oxide. The content of scandium oxide in the starting concentrates should be at least 1 mass.0% Sc 2 0 3 , which provides high purity scandium oxide, not less than 99.5 wt %. The technical result of the invention is the solution of the problem, the simplification of the process with lower costs for the implementation of the method with obtaining scandium oxide of high purity. At the same time, it is important that highly concentrated acid solutions, expensive reagents and sorbents are not used, the creation of reagent regeneration, sorption and sorbent regeneration units is not provided, which can significantly simplify the technological scheme and reduce operational and capital costs for the process. This problem is solved, while the technical result is achieved in the proposed method for producing scandium oxide from scandium-containing concentrate, which includes the following stages: - dissolving the scandium containing concentrate in mineral acid to obtain a scandium solution, purifying the obtained scandium solution from impurities, - separating the precipitate from scandium solution, - treatment of the scandium solution with an alkaline agent, - separation of the precipitate of scandium compounds from the scandium solution. In this case, the dissolution of the scandium-containing concentrate is carried out in sulfuric acid at a pH of 1.5-3.0, preferably 2.0-

3.0, to obtain a scandium solution, which is separated from the acid-insoluble precipitate and treated with sodium sulfate, while precipitating the double salt of sodium sulfate and scandium, which is filtered off, washed with sodium sulfate solution, dissolved in water and barium hydroxide or barium salt are added to precipitate impurities, the precipitate of impurities is filtered off, and scandium hydroxide is precipitated from the scandium solution at pH 4.8-6.0 by adding sodium hydroxide, the precipitate is filtered off and treated with a solution of oxalic acid to give the oxalate of scandium, scandium is separated from the solution, washed with water, dried and calcined. The greatest efficiency is achieved if the scandium solution is treated with barium hydroxide or barium chloride at a comfort temperature of 40-60° C, the scandium hydroxide is precipitated at an comfort temperature of 40 1000C and held for 1-10 hours, and scandium hydroxide is treated with ethane diacid at the comfort temperature is 40-100° C, the treatment of scandium hydroxide is carried out with ethane diacid with a preferred concentration of 80-120 g/dm 3, the calcination of scandium oxalate is carried out at the comfort temperature of 700-900 0 C. The content of scandium oxide in the initial scandium-containing concentrates should be at least 1 mass. % Sc2 0 3 ,which provides the proposed method of scandium oxide with a high degree of purification of at least 99.5 wt %.

The main non-obvious difference of the invention from the prototype method is the use of a diluted sulfuric acid solution at the stage of dissolution of the scandium-containing concentrate, which allows to reduce the degree of extraction of impurities in the solution while maintaining a high degree of extraction of scandium in the solution. In addition, purification of the scandalous solution from impurities is carried out step by step: first, a double salt of scandium sodium sulfate is precipitated (while zirconium, titanium, aluminum impurities remain in the pregnant liquor) by adding an excess of crystalline sodium sulfate as a salting out agent, then a double salt of scandium sulfate sodium is dissolved in water and the precipitates of Fe (+3) and other impurities remaining in the solution are precipitated by adding barium hydroxide or its salts. Another difference from the prototype is the stage of deposition of scandium hydroxide at pH 4.8-6.0 and an increase in the duration of the process up to 2-12 hours for high-quality separation of scandium from impurities of rare-earth metals and other metals. In contrast to the prototype, scandium purified from impurities is precipitated in the form of scandium oxalate with oxalic acid solution and sent to drying and calcination. The process of dissolution of scandium in a solution of sulfuric acid at pH 2-3 allows to achieve the maximum degree of extraction of scandium in solution with minimal extraction of impurities. Table 1 shows the experimental data on the effect of pH on the degree of extraction of scandium from a scandium-containing concentrate in a sulfate solution. With a decrease in pH of less than 2, an increase in the degree of extraction of scandium occurs with an increase in the amount of impurities of iron and aluminum in the solution; with an increase in pH above 3, a decrease in the degree of extraction of scandium in solution is observed.

Table 1. The effect of pH on the 0,5 1,0 2,0 2,5 3,0 4,0 degree of extraction of scandium from a scandium-containing concentrate in a sulfate solution. PH Degree of extraction Sc, % 99,5 99,0 98,5 97,5 97,0 86,0

The process of sedimentation of scandium sodium double sulfate from scandium sulfate-containing solution at a dosage of Na 2 SO 4 toa concentration

of 200-300 g/dm 3 at a temperature of 60-90° C, followed by cooling to room temperature due to the fact that at a temperature of 60-90° C is observed the maximum rate of formation of scandium-sodium double sulfate, and at room temperature the minimum solubility of scandium compounds with significant solubility of zirconium, titanium, and aluminum impurities. Table 2 shows the effect of the temperature of the solution at the stage of formation of the double salt on the concentration of scandium in the mother liquor after cooling and filtering the precipitate of the double salt. A decrease in temperature below 60 C leads to a decrease in the rate of formation of scandium sodium double sulfate, which, upon subsequent cooling of the solution and filtration of the precipitated double salt, leads to loss of scandium with the pregnant liquor. An increase in temperature above 900C is impractical from the point of view of increasing energy consumption in the absence of the effect of increasing the extraction of scandium from the solution into the precipitate of the double salt.

Table 2. The effect of the temperature of the solution at the stage of formation of the double salt on the concentration of scandium in the mother liquor after cooling and filtering the precipitate of the double salt. The temperature of the solution at the 50 60 70 80 90 stage of formation of the double salt of scandium, 0 C Sc 2 0 3 concentration in solution, g/dm3 2,5 0,8 0,7 0,6 0,5

The process of precipitation of impurities from a scandium-containing solution obtained by dissolving scandium sodium double sulfate in water with the addition of crystalline barium hydroxide to achieve a concentration in the solution of 1.5-4 g/dm3 for 2-4 hours is due to the maximum degree of precipitation of iron impurities (+3) and other elements while maintaining scandium in solution and a minimum consumption of barium hydroxide. With a decrease in the deposition time, an increase in the amount of impurities in the solution is observed; with an increase in the process time, part of the scandium is adsorbed on the surface of the solid precipitate of impurities. The precipitation of scandium hydroxide from a scandium solution obtained after coprecipitation of impurities with barium compounds is carried out at pH 4.8-6.0 and a temperature of 40-100° C, due to the fact that under these conditions REM impurities (rare-earth metals) remain in the solution, scandium transfers to the solid phase of scandium as much as possible. Table 3 shows the results of experiments to study the effect of pH at the stage of scandium hydroxide deposition on the REM content in the final product of scandium oxide and the loss of scandium oxide with the mother liquor after filtering the scandium hydroxide precipitate with a deposition process of 1 h and a temperature of 60 0 C. Table 3. The effect of pH at the stage of deposition of scandium hydroxide on the content of rare-earth metals in the final product of scandium oxide and loss of scandium oxide at the stage of deposition of scandium hydroxide. pH 3,5 4,0 4,5 5,0 5,5 6,0 6,5 Losses of Sc 2 0 3 during the 89,4 52,7 28,3 14,1 4,1 0,5 0,0 deposition of scandium hydroxide ,% The total content of rare-earth - - 0,005 0,009 0,02 0,08 0,1 metals in the final product of scandium oxide, mass. %

Table 4 shows the results of experiments to study the effect of the deposition time of scandium hydroxide on the loss of scandium oxide with the mother liquor after filtering the precipitate of scandium hydroxide at pH 5.5 and a temperature of 60° C.

Table 4. The effect of the duration of the deposition of scandium hydroxide on the loss of scandium oxide at the stage of deposition of scandium hydroxide. Duration, h 1 2 4 6 8 10 12 14 Losses of Sc203 at the 4,1 3,8 3,5 2,5 1,9 1,4 1,1 0,9 stage of scandium hydroxide precipitation,%

The process of precipitation of scandium oxalate by treating scandium hydroxide with ethane diacid having a concentration of 80-120 g / dm3 at a temperature of 40-100° C for 1-6 hours is due to the minimal solubility of scandium oxalate under these conditions with a maximum degree of conversion of scandium from hydroxide to oxalate with optimal consumption of ethane diacid. Scandium oxalate is dried and calcined at a temperature of 700-900° C for 1-5 hours, under these conditions, scandium oxalate is completely decomposed to obtain a dense finely divided scandium oxide precipitate. An increase in the process temperature and/or calcination time leads to unreasonable energy costs, a decrease in the process temperature and/or calcination time leads to a decrease in the quality of the product. The set of impurities accompanying scandium in scandium-containing concentrates does not fundamentally affect the process. It is essential that the content of scandium oxide in the concentrate be at least 1 mass. %

As a result of studies on the production of scandium oxide from scandium-containing concentrates, the optimal modes of the basic operations of the process were determined, namely: a) Dissolution of the scandium-containing concentrate in a solution of sulfuric acid: - pH 1.5-3.0, preferably 2.0-3.0;

- process temperature 10-90° C, preferably up to 20-60° C; b) Precipitation of scandium sodium double sulfate: - adding crystalline sodium sulfate to achieve a Na 2SO 4 concentration of 200-300 g/dm. - the temperature of the process is 60-90° C, preferably 70-80°C, followed by cooling to room temperature; - the obtained precipitate of double sodium sulfate-scandium is filtered and washed with a solution of sodium sulfate c) Dissolution of scandium sodium double sulfate in water - process temperature 40-90 0 C, preferably 50-70 0 C d) Precipitation of impurities when barium compounds are added: - adding crystalline barium hydroxide to achieve a concentration in the solution of 1.5-4 g / dm3, preferably 2-2.5 g / dm3; - the duration of the deposition process is 2-6 hours, preferably 3-4 hours e) Scandium hydroxide precipitation: - adding a solution of sodium hydroxide to achieve a pH of 4.8-6.0; - process temperature 40-100 0 C, preferably 50-70 0 C - the resulting scandium hydroxide precipitate is filtered and washed with water - the duration of the deposition process is 2-12 hours, preferably 6-10 hours f) Scandium oxalate precipitation - treatment of scandium hydroxide is carried out with oxalic acid with a concentration of 80-120 g/dm3 , preferably 95-105 g/dm; - process temperature 40-100° C, preferably 50-70° C - the duration of the deposition process is 1-6 hours, preferably 2-4 hours. g) Calcium scandium oxalate calcination to produce scandium oxide - the process temperature is 700-900° C, preferably 750-850° C. - the duration of the calcination process is 1-5 hours, preferably 1-3 hours.

A schematic flow diagram of the production of scandium oxide from scandium-containing concentrate is shown in PIC.1 and consists of the following operations: - dissolution of scandium-containing concentrate in a solution of sulfuric acid; - filtration to obtain a scandium-containing sulfate solution and the leach residue of the concentrate; - precipitation of double scandium sodium sulfate by adding sodium sulfate as a salting out agent; - filtration to obtain double scandium sodium sulfate and the pregnant liquor sent for processing; - dissolution of double scandium sodium sulfate in water; - precipitation of impurities from a scandium-containing solution by adding barium compounds; - filtration to obtain a purified scandium-containing solution and a solid precipitate of impurities; - precipitation of scandium hydroxide with sodium hydroxide solution; - filtration to obtain scandium hydroxide and the pregnant liquor sent for processing; - obtaining sparingly soluble scandium oxalate by treating scandium hydroxide with ethane diacid; - drying and calcination of scandium oxalate to obtain scandium oxide, purity > 99.3%. The implementation of the proposed method and its advantages over the prototype are confirmed by the following example. Example Take 27.7 g of scandium-containing concentrate of the following chemical composition, mass.%: Sc 2 03- 32,4; TiO2 - 0,67; ZrO 2 - 7,8; A1 2 0 3 - 0,28; Fe 2 03- 1,7; moisture content 49,3 %; dissolve in 200 g of a solution of sulfuric acid at pH 3 for 2 hours. The acid-insoluble precipitate is filtered off and the scandium-containing solution is treated with sodium sulfate (Na2 SO 4 ), bringing its concentration to 280 g/dm 3, double salt of scandium sodium sulfate is formed, which precipitates. The resulting precipitate is filtered off, washed with a solution of sodium sulfate at a concentration of 200 g/dm 3 and dissolved in water. 0.8 g of barium hydroxide Ba(OH) 2 is added to the obtained scandium-containing solution and kept at pH 3.8 for 5 hours. The slurry is filtered to obtain a precipitate of barium sulfate and impurities and a scandium-containing solution, from which scandium hydroxide is precipitated by treatment with a 45% sodium hydroxide solution. The precipitate of scandium hydroxide is filtered off, washed with water and treated with a 10% solution of ethane diacid to obtain scandium oxalate, which is separated from the solution, washed with water, dried and calcined at a temperature of 8500 C for 2 hours. Scandium oxide is obtained with aSc203 content of 99.5%. The total loss of scandium with impurities is ~ 2%. Thus, by using the proposed method for producing scandium oxide from scandium-containing concentrates, a degree of extraction of scandium oxide of 98% is achieved to obtain scandium oxide with a purity of > 99.5 mass. % while simplifying the process with reducing costs for the implementation of the method due to the use of a certain sequence of technological stages and modes that allow maximum extraction of scandium in the final product scandium oxide and selectively separate it from impurities without the use of consumptive treating agents and equipment.

SUMMARY OF THE INVENTION

1. A method of obtaining scandium oxide from a scandium-containing concentrate, comprising successive stages: - dissolving the scandium-containing concentrate in mineral acid to obtain a scandium solution, - purification of the obtained scandium solution from impurities, - separation of the precipitate from the scandium solution, - treatment of scandium solution with an alkaline agent, - separation of the precipitate of compounds of scandium from scandium solution, is characterized by following: the dissolution of the scandium-containing concentrate is carried out in sulfuric acid at a pH of 1.5-3.0, preferably 2.0-3.0, to obtain a scandium solution, which is separated from the acid-insoluble precipitate and treated with sodium sulfate, while the double salt precipitates sodium sulfate and scandium, which is filtered off, washed with sodium sulfate solution, dissolved in water and barium hydroxide or barium salt are added to precipitate impurities, the precipitate of impurities is filtered off, scandium hydroxide is precipitated from the scandium solution at pH 4.8-6.0 by adding sodium hydroxide, the precipitate is filtered off and treated with a solution of oxalic acid to obtain scandium oxalate, which is separated from the scandium solution, washed with water, dried and calcined. 2. The method according to p.1, characterized in that the treatment of scandium solution with barium hydroxide or barium chloride is carried out at a temperature of 40-60° C 3. The method according to p.1, characterized in that the precipitation of scandium hydroxide is carried out at a temperature of 40-100° C with exposure for 1-10 hours.

4. The method according to p. 1, characterized in that the treatment of scandium hydroxide with oxalic acid is carried out at a temperature of 40-100 ° C. 5. The method according to p.1, characterized in that the treatment of scandium hydroxide is carried out with oxalic acid with a concentration of 80 120 g / dm3 .

6. The method according to p.1, characterized in that the calcination of scandium oxalate is carried out at a temperature of 700-900° C. 7. The method according to p.1, characterized in that the content of scandium oxide in the original scandium-containing concentrate is at least 1 mass. %, while scandium oxide is obtained with a purity of not less than 99.5 mass. %

1/1

H2SO4 Sc-concentrate Solution DISSOLUTION Unleached residue for disposal FILTRATION

Sulfate Sc-containing solution

Na2SO4 PRECIPITATION Pregnant liquor for processing FILTRATION

Sodium and Scandium Sulfate H2O DISSOLUTION

Ba(OH)2 PRECIPITATION BaSO4 precipitate and impurities for disposal FILTRATION

Sc-containing solution NaOH Solution PRECIPITATION Pregnant liquor for processing FILTRATION

Sc(OH)3 H2C2O4*2H2O OBTAINING SCANDIUM OXALATE Pregnant liquor for processing FILTRATION

Sс2(С2O4)3

DRYING, CALCINATION

Sc2O3 ≥ 99,5%

Fig. 1