Method of making scandium oxide from red slag

IPC classes for russian patent Method of making scandium oxide from red slag (RU 2483131):

C22B59 - Obtaining rare earth metals

C22B3/20 - Treatment or purification of solutions, e.g. obtained by leaching (C22B0003180000 takes precedence);;

C22B3/04 - by leaching (C22B0003180000 takes precedence);;

C01F17 - Compounds of the rare-earth metals, i.e. scandium, yttrium, lanthanum, or the group of the lanthanides

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FIELD: metallurgy.

SUBSTANCE: proposed method comprises multistep leaching of red slag by the mix of sodium carbonate and bicarbonate on forcing annealing furnace flue gases containing carbon dioxide there through to obtained solution. Then, three-step holding of said solution at increased temperatures is performed along with selective separation of precipitates after every said step. At first step, said solution is heated to temperature not exceeding 80°C for, at least, 1 hour. Thereafter, it is settled for, at least, two hours at natural cooling. At second step, said solution is boiled and mixed for, at least, two hours. At third step, said solution is evaporated to 50% of initial volume to add 46%-solution of sodium hydroxide to concentration of Na₂O_caustic of 1.5-2.0 kg/m³. Now, it is boiled for, at least, 2 hours and precipitate containing scandium oxide is settled for 10-16 hours at natural cooling.

EFFECT: simplified process, higher yield of scandium oxide.

1 ex

The invention relates to the metallurgy of non-ferrous metals, namely the recovery of scandium oxide from the waste in the processing of bauxite to alumina.

The method for extracting scandium in the processing of bauxite to alumina, for example, from the sludge by-product processing, including leaching of water and/or 5-10%solution of carbonate or sodium bicarbonate or mixtures thereof, which are conducted at least 3 times at a temperature not exceeding 50°C for at least 2 hours at a ratio of T:W=1:2.5-5.0 using each time new portions of the product refining of bauxite as raw materials, separating the precipitate, introducing the resulting solution of aluminum oxide or zinc, dissolved in sodium hydroxide, extract with temperatures below 80°C for at least 2 hours. The precipitate treated with a hot 10-20%sodium hydroxide solution, washed with 1.5%sodium hydroxide solution, and then dissolving the precipitate in a 1-5%solution of hydrochloric acid, filtered and the filtrate treated with 10-15%ammonia solution or 2-10%solution of hydrofluoric acid with an excess of 1-3% from stoichiometry accessing primary scandium concentrate (RF Patent No. 2201988, IPC SW 59/00, 2003).

The disadvantage of this method is the complicated process of obtaining primary scandium concentrate in private is the use of a large number of additional chemical reagents.

The closest technical solution to the claimed is a method of producing oxide of scandium from red mud, a waste of alumina production, including multiple, sequential leaching of the red sludge is a mixture of solutions of carbonate and sodium bicarbonate, washing and separating the precipitate, introducing the resulting solution of zinc oxide dissolved in sodium hydroxide, the extract solution at elevated temperature and stirring, separating the precipitate and treated with a solution of sodium hydroxide at boiling point, separating, washing and drying the resulting product, followed by removing the oxide of scandium known methods. When leaching through a mixture of solutions of carbonate and hydrocarbonate sodium miss air-gas mixture containing 10-17% CO₂(by volume), leaching repeat until you get a solution with a concentration of scandium oxide is not less than 50 g/m³injected in solution solid sodium hydroxide to a concentration of 2-5 kg/m³in Na₂O caustic and maintained at a temperature not higher than 80°C, followed by introduction of the flocculant, endurance and sludge separation, which is the titanium concentrate, the resulting solution is subjected to electrolysis with solid electrodes at the cathode density 2-4 A/DM², a temperature of 50-70°C for 1-2 hours to remove impurities,a solution of zinc oxide in sodium hydroxide added to purified after electrolysis solution to a ratio of ZnO:Sc ₂O₃=(10-25):1 and introducing the flocculant, the extract solution is carried out at 100-102°C for 4-8 hours, processing the separated precipitate lead 5-12%sodium hydroxide solution at boiling point, again enter the flocculant, stand and separate the precipitate, which is the target product. The content of scandium in the target product is 2.26 wt.% (RF patent 2247788, IPC SW 59/00, 2005 - prototype).

The disadvantage of this method is the complexity of the technological process of obtaining scandium concentrate, in particular the additional consumption of zinc oxide, the implementation stage of electrolysis, the use of organic flocculant.

Thus, the authors was to develop a technically simple method of producing oxide of scandium from red mud, providing a high percentage of extraction of scandium scandium concentrate.

The problem is solved in the proposed method of producing oxide of scandium from red mud, including multiple sequential leaching of the red sludge is a mixture of solutions of carbonate and bicarbonate of sodium by passing the mixture of flue gas containing CO₂, separating, washing and drying the resulting product, followed by removing the oxide of scandium known methods, in which, after the three-stage leaching is performed is ederico filtrate at an elevated temperature with separation of the precipitate after each stage, at the first stage filtrate is heated to a temperature not higher than 80°C and maintained for at least 1 hour, then defend for at least 2 hours when natural cooling; at the second stage, the filtrate is brought to a boil and kept boiling and stirring for at least 2 hours; on the third level, the filtrate is evaporated by boiling to reduce the volume by 50%, then add 46%sodium hydroxide solution until the concentration of Na₂O_caustic1.5-2.0 kg/m³can withstand boiling for at least 2 hours and then defend for 10-16 hours at natural cooling.

At the present time of patent and technical literature is not a well-known method of producing zinc oxide from red mud, in which the removal of impurities from the initial solution obtained by diluting the slurry of red mud, the waste product of the Bayer process, is carried out by a three excerpts of the filtrate at an elevated temperature with separation of the precipitate after each stage, the first stage filtrate is heated to a temperature not higher than 80°C and maintained for at least 1 hour; at the second stage, the filtrate is brought to a boil and incubated for 2 hours; on the third level, the filtrate is evaporated by boiling to reduce the volume by 50%, then add 46%sodium hydroxide solution to the concentrations of Na ₂O_caustic1.5-2.0 kg/m³.

Research conducted by the authors, has led to the conclusion that the three hydrolysis under certain conditions of holding temperature and time regimes provides the removal of harmful impurities (Ti, Fe, Zn, Zr, Ca, U) and the concentration of scandium in the filtrate after leaching without the technological complexity of the process (optional introduction to the solution of compounds of zinc or aluminum, additional processing chemicals, the additional operation of electrolysis). Is quite a high percentage recovery of scandium in the end scandium concentrate. The removal of harmful impurities while conducting stepwise hydrolysis due to several reasons. When heated filtrate after leaching at a temperature of not more than 80°C is released in the precipitate of oxides of iron, silicon, magnesium, zinc. The result at the end of the first stage is the separation of the precipitate, containing mainly compounds of iron and calcium. In the second stage hydrolysis results in the release of sediments already compounds of elements such as titanium, calcium, aluminum, zirconium. The result at the end of the second stage to separate the precipitate, which is a titanium-zirconium concentrate.

The third stage is provided by the concentration of scandium in the solution and add in this case, sodium hydroxide, as a precipitator of scandium, contributes to its rapid transfer into the sediment (scandium concentrate). If in the known method hydroxide is added to the solution to precipitate impurities (iron, silicon, calcium, aluminum, titanium and others), in the proposed method, the chemistry of its use in the process at the final stage of hydrolysis is of a fundamentally different nature, namely the creation of such conditions, which reduce the solubility of scandium oxide in alkali carbonate solution and transfer it to precipitate from the concentrated mother liquor.

The proposed method of producing oxide of scandium from red mud can be carried out as follows. Pre-pressed at a press filter red mud is a waste in the production of alumina - filled with a mixture of solutions of carbonate and sodium bicarbonate and subjected to repeated leaching. Thus the solution to leach slurry of red mud is made from soda (100-150 g/DM³Na₂CO₃with the preliminary carbonization of solution gas furnaces sintering/calcined to the content of sodium bicarbonate (NaHCO₃) not less than 20% of the total content of Na₂O in the solution, the leaching of the next portions of the sludge spend carbonate-bicarbonate solution, obtained from previous transactions with the ratio of solid:liquid = 1:3-, corrected by sodium bicarbonate before each new batch of downloadable sludge by additional aeration (flue) flue gases of furnaces sintering/calcined, the treatment is carried out at a temperature of 60°C to achieve in the solution content of scandium oxide is not less than 20 g/m³. Then separated from the bulk of the sludge and a filtrate and wash water are mixed and subjected to three-step aging at elevated temperature with separation of the precipitate after each stage, the first stage filtrate is heated to a temperature not higher than 80°C and maintained under stirring for at least 1 hour, and then defend for 2 hours with a natural cooling; at the second stage, the filtrate is brought to a boil and incubated for 2 hours at this temperature; the third stage, the filtrate is evaporated by boiling to reduce the volume by 50%, then add a solution of sodium hydroxide to a concentration of 1.5-2.0 kg/m³in Na₂O_causticand incubated with stirring for 2 hours, and then advocate for 10-16 hours at a natural cooling. Received scandium concentrate is separated, washed and dried. The content of scandium in the concentrate reaches 5.0 wt.%.

The proposed method is illustrated by the following example.

Example. In industrial carbonization pour the prepared PU is GPU of the pre-pressed at a press filter red mud of the Bayer process in the range of 50 m ³if T:W=1:4,0. In the pulp contains 1200 kg sludge, calculated on the dry product composition of sludge following, wt%: Fe₂O₃44,8; Al₂O₃14,2; SiO₂7,1; CaO 12,1; TiO₂4,1; Na₂O 2,8, other 8,6; PPP (loss when puncturing) of 5.3. The content Sc₂O₃110 g/ton of sludge. In the apparatus poured soda in the amount of 265 kg include stirring and let the exhaust gas furnaces sintering (~10% CO₂) barbata pulp. After barbatia within days the composition of the solution next, kg/m³: Na₂CO₃- 68, NaHCO₃- 28 (Na₂O_total50,1); the content of other elements, g/m³: 130 K, Ti 25, Zr 44.5, Ca 15, Si 1.0, Fe 3.4, Cr 1.5, 15.0 V, Hf 1.1, 2.1 W, Th, 0.17, 0.34 U, Sc 3.4 (Sc₂O₃5.20). The extraction of scandium is 15.8% of the initial content in the sludge.

After settling of the pulp, decanting the solution, separating and washing the slurry at a press filter sludge repulping and pumped to a sludge field. The liquid phase (filtrate and wash water) back into carbonization, where to download the new portion of the original waste sludge (pre-pressed at a press filter). The amount of sludge in the second game loaded in carbonization is 1180 kg, counting on the dehydrated sludge. The total amount of pulp in carbonizate is 52 m³. The second batch of slurry is subjected to carbonization during the day. After removal of the slurry composition of the solution trace is in store, kg/m³: Na₂CO₃- 55, NaHCO₃- 51 (Na₂O_total51); the content of scandium is increased to the value g/m³: 6,4 (Sc₂O₃9,8). The extraction of scandium from the second portion of the sludge is 14.5%. Similarly with the second loading of the slurry to leaching with barbotirovanie flue gases of furnaces sintering spend another 5 operations. As a result, after the last (7th) operations receive the following composition of the solution volume of 40 m³kg/m³: Na₂CO₃- 72, NaHCO₃- 89 (Na₂O_total70); the content of scandium is increased to the value g/m: 31,9 Sc₂O₃. The extraction of scandium from all processed waste red mud is 13.6%.

Phase separation of the main part of the dissolved and suspended impurities is carried out by heating the obtained scandium-containing solution to a temperature of 80°C With stirring for 1 hour at this temperature, and then standing still for 2 hours with natural cooling. The composition of the filter cake, wt.%: Al 5.21, CA 3.9, Ti 5.2, Fe 26.14, Zr 0.18, Na 3.23, 0.42 Mg, Th 0.005, U 0.0007, SiO₂4.5, Sc 0.01 (humidity 15%).

Then heat obtained from the previous operation the filtrate to boiling (100-102°C) and boiled for 2 hours, after which the precipitate is filtered through a press filter immediately, not defending. The composition of the filter cake, wt.%: Al 0.05, Sa 0.17, Ti 35.08, Fe 1.8, Zr 7.2, Na 3.38, 0.02 Mg, Th 0.003, 0.0001 U, SiO₂1.5, Sc 0.009 (16%moisture content).

Obtained after the second hydrolysis filtrate evaporated by boiling to reduce the volume by 50%, then enter a 46%solution of sodium hydroxide to a concentration of 1.5-2.0 kg/m³and maintained at the boiling temperature (100-102°C) With stirring for 2 hours and then the precipitate advocate for 10-16 hours at natural cooling, is separated, washed and dried. The resulting concentrate of the following composition, wt.%: Al 1.2, Sa 1.5, Ti 3.72, Fe 3.6, Zr 8.2, Na 4.87, 0.63 Mg, Th 0.1, U 0.037, SiO₂1.5, Sc 3.4 (18%humidity).

Thus, the proposed method of producing oxide of scandium from red mud allows to significantly simplify the technology of extraction of the target product and virtually minimizes his loss, which will allow us to fully remove the oxide of scandium in the concentrate, to significantly reduce the content of impurities already in the first two stages of hydrolysis, and also allows you to use the solution after separation of all precipitation, repeatedly returning to the beginning of the next cycle leaching.

The method of producing oxide of scandium from red mud, including multiple sequential leaching of the red sludge is a mixture of solutions of carbonate and bicarbonate of sodium by passing the mixture of flue gases of furnaces sintering containing CO₂, separating, washing, grinding the mA with subsequent extraction of scandium oxide from the resulting solution, characterized in that after leaching is performed three-stage shutter-mentioned solution at elevated temperatures with the selective separation of precipitation after each stage, the first stage solution is heated to a temperature of not higher than 80°C and maintained for at least 1 h, and then defend for at least 2 h at natural cooling in the second stage the solution is brought to a boil and kept boiling and stirring for at least 2 h, at the third stage the solution is evaporated by boiling to reduce the volume by 50%, then add 46%sodium hydroxide solution until the concentration of Na₂O_caustic1.5-2.0 kg/m, can withstand boiling for at least 2 h and then defend the precipitate containing the oxide of scandium, for 10-16 h at natural cooling.