Citric acid mediated leaching kinetics study and comprehensive investigation on extraction of vanadium (V) from the spent catalyst

Abstract The extraction and leaching kinetics of V from the spent catalyst (3.06 %V, 10.01% Fe and 0.52 % Mg) was investigated using organic citric acid. The characterization of the spent catalyst sample by XRD, EDAX and SEM was examined to ascertain the existence of V, Mg and Fe in the form of respective oxides. Different organic acids were tested to ensure the leaching performance towards extraction of V, Fe and Mg and based upon the efficacy, the metal extrication trend followed the order as; Citric acid > Tartaric acid > Acetic acid > Formic acid > Oxalic acid. The critical parameters such as citric acid concentration, agitation speed, temperature, S/L and particle size, affecting on either of the metal leaching was systematically examined at varying time extent to establish the leaching mechanism as well as for attaining suitable optimum condition for effective dissolution of vanadium. The leaching kinetics of V, Mg and Fe was governed by diffusion controlled mode while following to shrinking core model mechanism as evident from the correlation coefficient (R2 = 0.99) and the resultant activation energy (11.21 kJ/mole for V, 10.86 kJ/mole for Mg and 11.84 kJ/mole, for Fe). The dissolution behaviour of either of metals examined at various particle size ranges as well as citric acid concentrations follows the linearity trend with above proposed leaching kinetics model. More than 99% of Vanadium, 80% Fe and 75 % Mg leaching was resulted at the optimum condition: S/l: 4%, Citric acid: 1.0 M, temp: 373 K, Particle size: 46-75micron. The residue obtained after leaching at the above optimum condition was further analyzed by XRD and EDAX, indicating no peak due to Vanadium and confirms on almost all extraction of V from the spent catalyst phase.