Shahrood University of Technology Journal of Mining and Environment 2251-8592 12 2 2021 04 01 Direct and Indirect Bio-Leaching of Co and Ni from an Iron-Rich Laterite Ore using Delftia Acidovorans and Acidithiobacillus Ferrooxidans 471 489 2037 10.22044/jme.2021.10528.2002 EN M. Hosseini Nasab Mining Department, University of Sistan and Baluchestan, Zahedan, Iran M. Noaparast School of Mining Engineering, College of Engineering, University of Tehran, Tehran, Iran H. Abdollahi School of Mining Engineering, College of Engineering, University of Tehran, Tehran, Iran Journal Article 2021 02 04 In this research work, the bio-leaching of Co and Ni from an iron-rich laterite ore is assessed using the acidophilic heterotrophic (<em>Delftia acidovorans</em>)and autotrophic (<em>Acidithiobacillus ferrooxidans</em>) bacteria. The metabolic products of the acidophilic bacteria play an important role in bio-leaching. The results obtained from the indirect bio-leaching indicate the highest nickel recoveries of up to 83.65% and 80.18%, respectively, by the supernatants of <em>Acidithiobacillus ferrooxidans</em> and <em>Delftia acidovorans</em>, both measured at 90 ^°C for 3 h with a stirring speed of 370 rpm and S/L of 0.1, while the corresponding cobalt recovery rates have reached 86.93% and 83.94%, respectively. The iron dissolution rates in these conditions for the two studied bacteria are 64.34% and 54.41%, respectively. The nickel and cobalt extractions by the indirect bio-leaching of <em>Delftia acidovorans</em> are, respectively, 29.84% and 23.75% higher than those for the direct bio-leaching, performed at 30 ^°C and 150 rpm of an incubator shaker for 30 days. For the indirect bio-leaching, the chemical control has a larger influence on the dissolution rate of the iron-rich laterite compared to the diffusion control. The activation energies of nickel and cobalt in the chemical control model are 40.07 and 39.08 kJ/mol, respectively. https://jme.shahroodut.ac.ir/article_2037_c14198951021bf578b0c35de5209fc9e.pdf