Kinetics of two-step bioleaching of Ni and Co from iron rich-laterite using supernatant metabolites produced by Salinivibrio kushneri as halophilic bacterium

Abstract

In the laterite leaching process using sulfuric acid, the addition of NaCl, for example at amount of 10% of solid weight, at 70 °C resulted the increase of nickel and cobalt recoveries up to 18.13 and 25.07%, respectively, and significant decrease in iron dissolution to 39.94% in leaching solution. Due to the role of salts in increasing the dissolutions of nickel and cobalt and decreasing iron dissolution, in this study, the possibility of using salt-friendly bacteria to extract nickel and cobalt from iron-rich laterite was investigated. The halophilic bacterium was isolated from Shorgaz Hamoon soil and grown in the medium with 10% NaCl. Results of HPLC analysis showed that gluconic acid (14.84 g/l), lactic acid (4.58 g/l) and citric acid (1.56 g/l) were the main organic acids in the supernatant metabolite of Salinivibrio kushneri as halophilic bacterium. Leaching experiments were performed at temperatures of 45 °C, 75 °C and 90 °C at pH of 0.5, stirring speed of 370 rpm, solid percentage of 6.67% w/v for 3 h. The results showed that recoveries of nickel and cobalt could reach to 58.40% and 60.6%, respectively after 3 h at 90 °C using supernatant metabolites of halophilic bacterium. Activation energies (Ea) for the chemical control model were 41.32 kJ/mol for nickel, and 40.24 kJ/mol for cobalt that these values indicated chemical control had more effect on the iron-rich laterite dissolution rate using supernatant metabolites produced by Salinivibrio kushneri than diffusion control.