The process of extracting scandium from scandium-containing waste molten salt, dust collection slag and hydrolyzed mother liquor produced by the production of titanium metal and titanium white. Titanium minerals are generally accompanied by trace amounts of scandium. When titanium tetrachloride is produced by molten salt chlorination, 70% to 80% of scandium in titanium minerals is (Na, K) 3ScCl6. The complex salt form is left in the waste molten salt, and the content of Sc2O3 is 0.01% to 0.03%; when titanium tetrachloride is produced by the fluidized chlorination method, most of the scandium in the titanium mineral enters the dust collection slag; it is produced by the sulfuric acid method In the process of titanium dioxide, more than 85% of scandium in the titanium mineral is stored in the mother liquor after the titanium liquid is hydrolyzed. Scandium is a precious metal with a special purpose. Recovering scandium from these scandium-containing materials has important technical and economic significance. A recovery method combining solvent extraction and precipitation is usually used.
The former Soviet Union used hydrochloric acid solution (HCl 20~40g/L) to leaching waste molten salt to transfer scandium into solution. Next, the scandium in the leaching solution is extracted into the organic phase with 70% TBP, the impurities are washed away with concentrated hydrochloric acid (HCl 220-240 g/L), and the scandium is back extracted into the aqueous phase with 7% hydrochloric acid solution. Oxalic acid is used to precipitate the scandium in the stripping solution to oxalate precipitation. The oxalate precipitate obtained by filtration is dried and calcined at a temperature of 973K to obtain crude scandium oxide containing 350% to 70% of Sc2O. The crude scandium oxide is then repeatedly purified by solvent extraction and precipitation methods to produce commercial scandium oxide with a purity of more than 99.9%.
China has studied two methods for recovering scandium from chlorinated dust: (1) water leaching-TBP extraction-oxalic acid precipitation; (2) hydrochloric acid leaching-two-stage extraction of TBP and P350-oxalic acid purification. The latter method has reached a certain production capacity, the scandium recovery rate is close to 60%, and the product purity is above 99.5%.
Internationally, scandium is recovered from the hydrolyzed mother liquor produced by the sulfuric acid method. It is generally extracted with P204 and back-extracted with NaF to obtain the Na3ScF6 precipitate. The precipitate is then leached with a solution containing 43% H2SO. The scandium recovery rate is 85% to 90%. China uses acidic and neutral extractants to synergistically extract scandium from mother liquor, and the organic phase is washed with sulfuric acid and hydrogen peroxide to remove titanium, and then back-extracted with NaOH. There are also P204+TBP synergistic extraction of scandium, and the organic phase is directly used to remove titanium without washing. For NaOH back extraction, hydrochloric acid dissolution, TBP or P350 extraction resin chromatography separation and purification methods, the purity of Sc2O3 exceeds 99.9%, and the scandium recovery rate exceeds 70%.
Ion exchange method or solvent extraction method can be used to purify Sc2O3 to 99.99%. The extraction resin chromatographic separation method (see rare earth element chromatographic separation) combines the characteristics of the above two methods, and can more effectively purify Sc2O3, which has been applied in China.