Leaching of Vanadium from a Vanadium bearing slag using organic acids

Abstract: The bioleaching of Vanadium (V) from a V bearing slag with microorganisms such as Pseudomonas putida or Aspergellius niger was mimicked using commercial organic acids and a slag roasted in the presence of Na2CO3. A slag sample received from a steel making plant based in the North-West province of South Africa, was characterised using X-Ray Fluorescence (XRF), X-Ray diffraction (XRD) and Scanning Electron Microscope / Energy Dispersive X-Ray (SEM/EDX) in order to access the chemical composition, the mineralogy and surface morphology. The results revealed the presence of V in the form of indissoluble Vanadium oxide at a grade of 4.58% wt. To convert the Vanadium oxide into a soluble sodium vanadate, the slag sample was submitted to a sodium carbonate roasting process at various ratios and roasting temperatures in order to optimise the roasting process. XRD analysis of the slag roasted at lower temperature (800ºC) revealed a slight change of V-oxide phase into sodium vanadate. The middle roasting temperature (900ºC) showed a high modification of V-oxide phase into soluble sodium vanadate with appearance of impurities soluble phase such as sodium aluminate. Roasting at higher temperature (1000ºC) revealed a higher formation of soluble sodium vanadate and soluble impurity phase (sodium aluminate). The ratio of sodium vanadate was important due to the fact that lower ratios of sodium carbonate did allow lower sodium vanadate formation compared to higher ratios. The leaching tests were done on the slag roasted in different conditions of temperature (800, 900 and 1000ºC) and Na2CO3 ratio (10, 20, 30 and 40 % wt) using 50mM of commercial organic acids (Gluconic, Citric, Oxalic and Mixture of the three acids) to confirm the leachability of the roasted slag compared to the raw slag. Gluconic acid was the most effective in leaching of V followed by Citric, Oxalic and mixed acids. The optimum conditions for roasting the slag were found to be 900oC and 20% wt. Na2CO3. These conditions were used to prepare all the roasted slag used in the succeeding leaching experiments. The SEM/EDX of the selected roasted slag revealed the presence of V and Na scattered throughout the slag matrix confirming the presence of the soluble sodium vanadate phase. The roasted slag was leached using a mixture of Gluconic, Citric and Oxalic acid in the growing conditions of the microorganisms considered. Effect of different parameters such as acid concentration, solid-liquid ratio, particle size and temperature were investigated. It was found that the enhancement of the acid concentration has a positive effect on the V leaching...M.Tech. (Extraction Metallurgy