Leaching kinetics of nickel extraction from hazardous waste by sulphuric acid and optimization dissolution conditions

In this study, dissolution kinetics of nickel in sulphuric acid was investigated. The effects of various parameters were studied to optimize the dissolution conditions and to determine the kinetics of the leaching. The results indicated that the increase in the leaching time, temperature, sulphuric acid concentration, and decrease in solid-liquid ratio and particle size enhanced the leaching rate of nickel. The results showed that the 96% of nickel content was extracted from the sample of particle size -250 mu m after 30 min leaching in 8% (v/v) sulphuric acid concentration and solid/liquid of 0.10. The experimental data were best fitted by a diffusion-controlled model indicated that diffusion through the product layer was the rate-controlling step during the dissolution. The activation energy was 9.06 kJ/mol and it was also an indication of the diffusion-controlled process. The following expression based on diffusion-controlled model can be used to describe the dissolution kinetics of nickel: 1-3(1 - alpha)(2/3) + 2(1 - alpha) = k(d)t = k(0)[H2SO4](1.36)(S/L)(-1.12)r(0)(-0.22) exp(9.06/RT)t gypsum was formed as the main leaching product and tended to inhibit the leaching rate. The leaching mechanism was confirmed by characterizing the original sample and the leach residues using XRD and SEM analysis. (c) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.