Recovery of vanadium and nickel from petroleum flyash

Abstract

Flyash is a powdery residue generated by the power stations that use heavy oil as the source of fuel. The ash poses a threat to the environment due to the presence of certain heavy elements such as chromium. At the same time, it contains valuable metals, including vanadium and nickel, that are extractable if an economical and environmentally acceptable process can be developed. To this end, Mintek, in co-operation with Oxbow Carbon and Minerals, undertook a major research program over a two-year period in an attempt to find the most suitable technology to deal with this ash. After considering various alternatives, a process flowsheet was developed and used as a basis to identify the testwork required for the major processing units. The flowsheet consisted of a drying stage at moderate temperatures of about 150 °C, a de-carburization and de-sulphurization (pre-treatment) stage, and finally a smelting step in a DC arc furnace. Testwork carried out at the 40 kW scale, using pre-treated flyash, indicated the feasibility of producing a ferrovanadium alloy containing more than 15% vanadium and 6% nickel, with vanadium recovery of more than 89%, and a disposable slag based on USA EPA safe disposal criteria. Several parameters were studied in order to optimise the smelting stage including operating temperature, aluminium addition, the use of ferrosilicon as the reducing agent and lime (flux) addition. The results of the investigation are presented in this paper.