Mechanism of vanadium selective separation from iron in shale under an environmentally friendly oxalate ligand system

Iron impurity ion is easy to precipitate or co-extracted together with vanadium in the process of vanadium extraction from shale, reducing vanadium product purity. In our previous research, the technological parameters of vanadium separation over iron from shale using oxalic acid were systematically investigated. In this paper, the reaction mechanism of vanadium selective separation from iron in leaching-precipitation process was detailed studied. In the C2O42-/F- multiple ligands leaching system, the thermochemistry and solution chemistry calculations indicate that vanadium in KAl3Si3O10(OH)2 reacted with H2C2O4/HC2O4- /C2O42-, and then generated VOC2O4 and VO(C2O4)22-. The Fe2O3 reacted with H2C2O4/HC2O4- /C2O42- and HF/F-, and then generated FeF3, Fe (C2O4)2- and Fe(C2O4)33-. Meanwhile, the FeF3 was dissolved as Fe(C2O4)2- and Fe(C2O4)33- in oxalic acid. As a result, the Fe impurity in the leachate mainly existed as Fe(C2O4)2- and Fe(C2O4)33-. In precipitation process, the Fe reductant combined with Fe(C2O4)2- and Fe(C2O4)33-, reducing Fe(III) to Fe(II). Finally, the FeC2O4.2H2O product with a high purity of 98.5% and a mean particle size of 5.41 mu m can be obtained at 25celcius. The revealed reaction mechanism can strengthen theoretical foundation of selective and clean vanadium extraction from shale.

Automated summary

This study investigated the separation mechanism of iron impurity in the process of vanadium extraction from shale. By using oxalic acid to separate vanadium and iron, a high-purity FeC2O4.2H2O product can be obtained.