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

Abstract

• Muscovite and hematite leaching thermodynamics in C 2 O 4 2- /F - solution were analyzed. • V and Fe speciation distributions in the leachate were determined. • Changes between Fe 2 O 3 , FeF 3 , Fe(C 2 O 4 ) 2 - /Fe(C 2 O 4 ) 3 3– and FeC 2 O 4 ·2H 2 O were investigated. • Mechanism of V selective separation from Fe of shale in C 2 O 4 2- /F - system was proposed. 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 C 2 O 4 2- /F - multiple ligands leaching system, the thermochemistry and solution chemistry calculations indicate that vanadium in KAl 3 Si 3 O 10 (OH) 2 reacted with H 2 C 2 O 4 /HC 2 O 4 - /C 2 O 4 2- , and then generated VOC 2 O 4 and VO(C 2 O 4 ) 2 2– . The Fe 2 O 3 reacted with H 2 C 2 O 4 /HC 2 O 4 - /C 2 O 4 2- and HF/F - , and then generated FeF 3 , Fe(C 2 O 4 ) 2 - and Fe(C 2 O 4 ) 3 3– . Meanwhile, the FeF 3 was dissolved as Fe(C 2 O 4 ) 2 - and Fe(C 2 O 4 ) 3 3– in oxalic acid. As a result, the Fe impurity in the leachate mainly existed as Fe(C 2 O 4 ) 2 - and Fe(C 2 O 4 ) 3 3– . In precipitation process, the Fe reductant combined with Fe(C 2 O 4 ) 2 - and Fe(C 2 O 4 ) 3 3– , reducing Fe(III) to Fe(II). Finally, the FeC 2 O 4 ·2H 2 O product with a high purity of 98.5% and a mean particle size of 5.41 μm can be obtained at 25℃. The revealed reaction mechanism can strengthen theoretical foundation of selective and clean vanadium extraction from shale.