Microwave assisted leaching investigation for the extraction of copper(II) and chromium(III) from spent catalyst

Microwave (MW) assisted leaching of copper (Cu) and chromium (Cr) from Cu-Cr spent catalyst was investigated. The MW assistance have many advantages over the regular leaching process and in consequences, the leaching time has been significantly reduced from 240 min to 120 min. The optimum condition; 900 Watt MW power, 2.0 min MW treatment time, 10% H2O2 (v/v) and 1.0 M sulphuric acid for during MW irradiation followed by leaching with a very low concentration of H2SO4 (1% (w/w)) was suitable for quantitative extraction of both metals from the spent catalyst phase. The role of either of the oxidants (H2O2, NaClO4, K2S2O8 and HNO3) appears to be critical on enhancing the leaching efficiency of both copper and chromium in addition to the MW treatment. The leaching kinetics study was examined to ascertain the extraction mechanism. The activation energies were obtained to be 3.49 kJ mol(-1) and 3.33 kJ mol(-1) for Cu and Cr, respectively, indicating on the shrinking-sphere diffusion control leaching behaviour. The linear dependence log k(ap) on log 1/d(o) plot and a first order dependence for k(ap) with H2SO4 at 1.0 M was derived from the proposed leaching model. The FESEM characterization of spent catalyst before and after MW treatment showed a significant change of the particle morphology (shred type to porous type). The XRD and EDAX characteristics pattern of residue samples resulted at optimum leaching condition further ascertained on substantial extraction of copper (99.99%) and chromium (98.56%) from spent catalyst phase.