Preparation of High Purity V2O5 from a Typical Low-Grade Refractory Stone Coal Using a Pyro-Hydrometallurgical Process

The recovery of vanadium from a typical low-grade refractory stone coal was investigated using a pyro-hydrometallurgical process specifically including blank roasting, acid leaching, solvent extraction, and chemical precipitation. The appropriate role of parameters in each process was analyzed in detail. Roasting temperature and roasting time during the roasting process showed a significant effect on leaching efficiency of vanadium. Using H2SO4 as a leaching agent, vanadium leaching efficiency can achieve above 90% under the optimum leaching conditions of CaF2 dosage of 5%, sulfuric acid concentration of 4 mol/L, liquid to solid ratio of 2:1 mL/g, leaching time of 2 h, and leaching temperature of 95 ˝C. 99.10% of vanadium can be extracted from the leaching solution in three stages under the conditions of initial pH of 1.6, trioctylamine (TOA) extractant concentration of 20% (vol), phase ratio (A/O) of 2, and reaction time of 2 min. 1.0 mol/L NaOH was used to strip vanadium from the extracted solvent phase. After purification and precipitation, vanadium can be crystallized as ammonium metavanadate. The V2O5 product with a purity of 99.75% is obtained after ammonium metavanadate thermal decomposition at 550 ˝C for 2 h. The total vanadium recovery in the whole process is above 88%. This process has advantages of short operation time, high vanadium extraction efficiency, and high purity of the product.