Leaching kinetics of Cu, Ni and Zn from waste silica rich integrated circuits using mild nitric acid

Abstract

An inexpensive leaching method of metal values (Cu, Zn, and Ni) from waste electrical and electronic equipment (WEEE) is of economic importance in e-waste recycling process. In this study, characterization of well pretreated silica rich integrated circuits (SRICs) powder revealed the presence of quartz (SiO2), tenorite (CuO), willemite (Zn2SiO4), nickel zinc oxide (Ni0.8Zn0.2O), iron copper oxide (CuFe5O8), wustite (Fe0.945O), ilmenite (Fe2TiO4) and cassieterite (SnO2). Chemical analysis shows that the sample investigated was rich in Si (45.5%), Cu (35.5%), Zn (1.7%), Ni (1.2%) and Fe (7.2%). Effect of reaction temperature, leaching time, pulp density, and concentration of leaching agent on the leaching of Cu, Zn and Ni were investigated. Results obtained revealed maximum leaching efficiency of 100% for Cu with 1.0 M HNO3, 96.6% for Zn with 1.0 M H2SO4 and 76.8% for Ni with 1.0 M HCl. Trifluoromethanesulfonic acid (TFMS) was used for the first time in the leaching of SRICs at a temperature of 90 °C, where leaching efficiencies of 85.9, 60 and 28.4% were achieved for Cu, Zn, and Ni respectively. However, for further studies nitric acid was taken as the leaching agent. From the leaching studies it was found that the leaching efficiencies of Cu, Zn and Ni decreased with increasing pulp density from 20 to 100 g/L, but increased with increasing reaction time from 10 to 120 min. Kinetic data show that leaching of Cu and Zn fit with ash diffusion control, while that of Ni fits with chemical reaction control. The activation energy (Ea) values as per the Arrhenius equation are 46.03, 31.28, and 32.69 kJmol−1 for Cu, Zn and Ni respectively.