Extraction of vanadium from direct acid leaching solution of clay vanadium ore using solvent extraction with N235

Solvent extraction of vanadium from a direct acid leaching solution, generated by the direct leaching of clay vanadium ore, was conducted using tertiary amine N235, and the effects of the main factors on the extraction of vanadium and iron were investigated. Through a three-stage countercurrent extraction under the following optimum conditions: N235 concentration of 10% (v/v), initial aqueous phase pH of 1.8-2.0, phase ratio (A/O) of 2.5, and extraction time of 5 min, vanadium extraction efficiency reached above 98% whereas iron and other impurities were barely extracted. In addition, the solution chemical behavior of the vanadium extraction with N235 was analyzed. After oxidation and neutralization, V(IV) was oxidized to V(V), and VO2+ was converted to various forms of anions. N235, acidified by H2SO4 to convert R3N to (R3NH)2SO4, was able to extract vanadium through anion-exchange reaction. When vanadium was in the specific form of [H2V10O28]4−, high extraction efficiency was obtained, and vanadium was extracted more easily. As the pH increased, the concentration of [H2V10O28]4− and the dissociation of HSO4− also increased, which improved extraction efficiency. Vanadium existed in form of [H2V10O28]4− within a wide pH range of 1-3.5, but dissociation of (R3NH)2SO4 occurred at pH > 2.0, which hampered the extraction. Moreover, Fe(III) was precipitated by hydrolysis at pH > 2.0, which prevented the two phases from separating and caused a coprecipitation loss of vanadium.