Leaching of nickel from a secondary source by sulfuric acid

In the present study, leaching of tailing containing 29.6 wt.% Ni in sulfuric acid was investigated. Tailing was characterized by X-ray powder diffraction (XRD), X-ray fluorescence (XRF) and inductively coupled plasma (ICP-OES) methods. Rinsing process for the separation of tungsten from tailing was conducted in distilled water at 80 °C for 240 min. After the filtration of solid residue from tungsten solution by vacuum filtration, batch leaching tests were carried out on solid residue at atmospheric pressure in stirred acid solution. The effects of sulfuric acid concentration (1-4 mol), pulp density (1/10-1/20 gmL−1), particle size (−600 +420 to −180 +125 mm) and temperature (25-80 °C) on the nickel dissolution were studied. The results showed that leaching of about 99% of nickel content of the washed tailing could be achieved using 4.0 mol sulfuric acid, pulp density of 1/20 gmL−1 and particle size of −180 +250 mm at 80 °C after 240 min. Kinetic analysis of the leaching data properly followed the shrinking core model, and the dissolution rate of nickel was found to be controlled by diffusion through the product layer for 25 and 40 °C and chemical reaction for 80 °C. Leaching rate of nickel at 60 °C at the first stage (0-60 min) was controlled by diffusion through the product; then, at the second stage, it was controlled by the chemical reaction (60-240 min).