A novel process for recovery of vanadium and chromium from vanadium-chromium sludge: Roasting pretreatment and thermal reduction co-alloying process

Abstract

Vanadium (V) and chromium (Cr) are significant strategic metals and has been widely used in many applications. In order to realize resource utilization and harmless disposal of this metallurgical solid waste, an effective and clean process was proposed in this paper to recover V and Cr from this wastewater purification sludge (WPS), namely roasting pretreatment and thermal reduction co-alloying process. After a roasting pretreatment at 1000 °C, water and more than 75% of sulfur in sludge were removed from the WPS. The pre-treated sludge was used to produce Fe-Cr-V alloy by carbon thermal reduction co-alloying method with Fe₂O₃ powders as an additive. The thermodynamics software Fact Sage 8.3 was utilized to assess the feasibility of the reduction reaction and to design the components of both the slag and the alloy. The recovery rate of V and Cr were 99.4% and 99.6%, respectively, under the conditions of theoretical reducing agent dosage ($W=n_C/n_O$) value of 1.0, binary alkalinity (R = $w_{\text{Ca}O}/w_{Si{O}_2}$) value of 1.06, and the temperature of 1550 °C. In addition, the mass percentages of Fe, Cr, and V in the left slag were 0.38%, 1.07%, and 0.09% (in Fe₂O₃, Cr₂O₃ and V₂O₅), respectively, which was tested to be non-hazardous waste. This work opens up a clean and efficient way of recovering valuable Cr and V from metallurgical solid wastes.