Statistical modeling of Chevreul's salt recovery from leach solutions containing copper

In this study, oxidized copper ore was dissolved under optimum conditions [temperature 14 °C, average particle size 2.8 mm, stirring speed 500 rpm, ammonia concentration 2.824 mol L−1, ammonium sulphate concentration 0.236 mol L−1, solid-to-liquid ratio 0.167 g mL−1, leaching time 2 h] in an aqueous NH3-(NH4)2SO4 solution [T. Çalban, S. Çolak, M. Yeşilyurt, Optimization of leaching of copper from oxidized copper ore in NH3-(NH4)2SO4 medium, Chem. Eng. Commun., in press]. Chevreul's salt was precipitated by passing SO2 from these leach solutions. Chevreul's salt, a mixed valence copper sulfite Cu2SO3·CuSO3·2H2O, was characterized by XRD and SEM. The effects of parameters, such as temperature, pH, stirring speed and reaction time, were investigated on precipitation of Chevreul's salt. 2n factorial experimental design and orthogonal central composite design methods in the precipitation experiments were used. It was observed that the most effective parameters on the precipitation of Chevreul's salt were temperature, stirring speed and reaction time. The optimum conditions established for maximum copper precipitation were: temperature 62 °C, pH 3, stirring speed 600 rpm, reaction time 12 min. Fixed parameters chosen at the initial stage of the reaction were: SO2 flow rate 358 L h−1, concentration of CuSO4 solution 7.383 g Cu L−1. Under these optimum conditions, the percentage of copper precipitated from leach solution was 99.92.