Selective recovery of vanadium from chloride titanium dioxide effluent and preparation of high-purity thermotropic vanadium dioxide(M): An ammonia-free process

Abstract

Vanadium recovery is critical for the hazard-free treatment and resourceful utilization of chloride titanium dioxide effluent (CTDE). Traditional ammonia precipitation vanadium recovery process from chloride titanium dioxide effluent suffered issues of the long process, high cost, and severe ammonia pollution risk. To solve these issues, an ammonia-free method consisting of V extraction from chloride titanium dioxide effluent by D2EHPA, direct VO2+ hydrolysis precipitation, and vacuum calcination was designed to produce VO2(M). The effect of conditions on V recovery, impurities behaviors, and vacuum dehydration mechanisms in each step was systematically investigated. Experimental results demonstrated that over 96.50% of vanadium was precipitated in the form of VO2∙xH2O by mixing CaO powder at 25 °C for 5 min until pH reached 4.20. And then, high purity VO2(M) (VO2 >99.50%) was prepared by vacuum calcined at 500 °C for 2 h in the tube furnace. Further characterizations revealed that the crystal structure of the calcined product was a monoclinic crystal structure with the space group of P21/c (VO2(M)), and the phase transition temperature was 57.8 °C. This demonstrated that the produced VO2(M) had met the established market standards and exhibited stable thermotropic degeneration, making it suitable for use in thermistors and other related fields. Compared with the conventional ammonia precipitation V recovery process, the proposed process exhibits a promising industrial application due to the short flow, near-zero wastes, higher economic efficiency, and superior product performance. In conclusion, it provides a clean and efficient vanadium recovery strategy from chloride titanium dioxide effluent.