Post by seveneleven711on Feb 07, 2023 2:24pm
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moreCURRENT INNOVATIONS ON SCANDIUM RECOVERY Successive Selective Precipitation All recovery processes to recover trace elements from highly impure aqueous solutions need intense purification steps or usage of advanced and expensive reagents due to co-extraction of impurity elements(25) . In the case of Sc, as it was mentioned before, impurity elements are also extracted with Sc both in SX and IX processes. Therefore reaching high purity Sc is an expensive and multi-stage operation. The major problem of the scandium recovery by precipitation from a multicomponent solution is the co-precipitation with ions present in the system, especially Fe. Since Fe interferes Sc in every extraction and purification operation, removal of this problematic ion beforehand makes all further processes much easier. In our previous studies, a simple triple-staged precipitation procedure has proven to have great potential to recover Sc from Sc containing aqueous solutions. This process showed that, the majority of Fe can be removed from the solution with dual step precipitation by NH3(aq) addition with negligible Sc loss(26,27) . A possible reason for low Sc co-precipitation as Fe is almost completely precipitated is because of the occurrence of scandium hexammine complex upon addition of ammonia to the system which can inhibit the interaction between Fe and Sc and prevent co-precipitation in the system. Addition of NH3(aq) to remove Fe in the system performed similarly in all three mineral acid media. Hence, this precipitation process can be applied to major acidic waste streams. In addition, there is a strong affinity of Sc, Fe and REEs towards PO4 (PHOSPHATE) 3- ion, which can be used to trigger selective Sc precipitation. Considering the behaviour of the major impurities of bauxite residue leachates, triple-staged precipitation processes to synthesize a scandium concentrate can be proposed for the possible mineral acid systems. After removing more than 95% of Fe using NH3(aq) with low Sc loss in the first two-stage Fe-removal operation, a phosphate precipitation step is applied as the 3rd part of this successive precipitation process. The process flow diagram can be seen in Figure 3. As a result, Sc concentrate containing 15-50% ScPO4 having Al as the major impurity was produced according to the initial impurity level. F