Precipitation of iron with NaOH after oxidation of Fe2+, from lixiviation solutions containing rare earth

In obtaining concentrates of rare earth elements (REE) from local minerals techniques like acid lixiviation, solvent extraction and precipitation are used for the production of the final compound. In order to make the precipitation more efficient the solutions to be used should be concentrated and purified with solvent extraction techniques. The low selectivity of the cationic extractants with regard to the REE means undesirable elements such as iron should be eliminated. Solutions containing REE are rich in iron since they come from the lixiviation of davidite (Fe2,REE,U,Ca,Na,Zr,Th)(Ti4,Fe3,U,V3,Cr3)3(O2,OH)7. This study will determine the necessary operational conditions for the purification of lixiviation solutions containing REE through the elimination of the iron, in order to obtain cation-free solutions that do not interfere in the SX stage. Variations in the following parameters are studied: concentration of the precipitating agent (NaOH), intensity of agitation, working temperature, flow of reagent addition, maturing time, in order to obtain a precipitate with a suitable particle size that has filtering properties. After the precipitation the Fe2+ to Fe3+ so that removing this ion takes place at pH lower than 4 eliminating the presence of REE in the final solid. The oxidation of the ferrous ion was done with potassium permanganate (KMnO4) to obtain 96.6% efficiency. The resulting precipitate is an Akaganeite (FeO*OH), with a particle distribution size of 341.59 μm, an average size of 178.78 μm, and precipitation efficiency of 99.998% of the Fe3+