Preparation of Vanadium Oxides from a Vanadium (IV) Strip Liquor Extracted from Vanadium-Bearing Shale Using an Eco-Friendly Method

In the traditional vanadium precipitation process, the use of ammonium salts can produce serious pollution problems from the ammonia waste-water and the ammonia gas generated during the processing. In this reported study, an eco-friendly technology was investigated to prepare vanadium oxides from a typical vanadium (IV) strip liquor, obtained after the hydrometallurgical treatment of a vanadium-bearing shale. Thermodynamic analysis demonstrated that VO(OH)₂ could be prepared as a precursor over a suitable solution pH range. Experimental results showed that by adjusting the pH to around 5.6, at room temperature, 98.6% of the vanadium in the strip liquor was formed into hydroxide, in 5 min. After obtaining the VO(OH)₂, it was washed with dilute acid to minimize the level of impurities. VO₂ and V₂O₅ were then produced by reacting the VO(OH)₂ with air or argon, in a tube furnace. The XRD analyses of the products showed that VO₂ had been produced in air and V₂O₅ had been produced in argon. The purity of the VO₂ was 98.82% after calcining for 2 h at 550 °C, in argon flow, at a rate of 50 mL/min. It was found that the purity of the V₂O₅ was 98.70%, using the same reaction conditions in air. Compared to the traditional precipitation method that uses ammonium salt, followed by calcination, this proposed method is eco-friendly and employs less quantities of reagents and energy, and two types of products can be produced. Consequently, this process could promote the sustainable development of the vanadium chemical industry.