Solvent extraction of vanadium with D2EHPA from aqueous leachate of stone coal after low-temperature sulfation roasting

The solvent extraction of vanadium from aqueous solution after the leaching of stone coal vanadium ore following low-temperature sulfation roasting was enabled by di-(2-ethylhexyl)phosphoric acid (D2EHPA). Firstly, the effects of main factors on vanadium extraction and iron removal were investigated. Secondly, density function theory (DFT) simulations using the DMol3 module (GGA/PW91) were conducted to elucidate the interactions between D2EHPA and vanadium, which concluded that the phosphoric acid oxygen atom formed a coordination bond with vanadium atoms to achieve the solvent extraction of vanadium. D2EHPA molecules also dimerized to form a cyclic chelate complex with vanadium, which contributed to the solvent extraction of vanadium. Lastly, the solution chemical behavior of the vanadium in the organic phase after extraction with D2EHPA was analyzed. After reduction and neutralization pretreatments, VV (VO2+) was reduced to VIV (VO2+), which could be more strongly coordinated by D2EHPA over the pH range of 1-4.03, while FeIII was reduced to FeII, which was not coordinated as strongly by D2EHPA, minimizing the amount of iron extracted from the aqueous leachate into the organic phase by D2EHPA. The vanadium extraction efficiency increased as the initial pH of the leachate increased, but the formation of VOSO4 at pH > 2.5 hampered the extraction of vanadium.