Bioleaching of Lateritic Nickel Ores

Despite nickel-bearing sulfide deposits having a large share of the world's nickel extraction, lateritic ore deposits contain more than 70% of the world's nickel reserves. Considering the limitations of producing nickel from sulfide reserves, the use of oxide reserves (laterites) for the production of nickel will be of great importance in the future. In this chapter, the applications of nickel and cobalt in various industries were described. Nickel and cobalt are mainly used in alloys of other metals. In addition, the most effective methods for extracting nickel and cobalt from lateritic nickel ores were examined. Due to the need for high energy, pyrometallurgical methods, as well as acid leaching, which uses a high amount of acid, are rarely used today. Therefore, the bacterial and fungal leaching methods (bioleaching), which is another hydrometallurgical process, and their mechanisms were explained. Bioleaching is a new prospective method for extracting valuable elements from hard-to-treat ores. The benefits of bioleaching low-grade ores are numerous in comparison to traditional methods due to their simplicity, using unskilled labor, low capital and operating costs, low energy consumption, and also the lowest negative environmental effects. In this processing operation, metals are dissolved from low-grade deposits by using microorganisms and their metabolic products. In addition, the final concentrations of iron in PLS can be decreased by biological methods. The most effective factors in the bioleaching process such as pH, size of sample particles, type of microorganism species, type of substrate, amount of inoculation, type of produced metabolic acid, the pulp solid to liquid ratio, salinity, temperature, and leaching time were explained. Heterotrophic bacteria such as Aspergillus, Penicillium, Pseudomonas, and Delftia were also successful at dissolving laterites, in addition to autotrophic bacteria such as At.ferrooxidans and At.thiooxidans. The presence of O2 is considered a key factor in increasing the bio-reduction dissolution of nickel and cobalt of iron-containing minerals. In addition, high temperature, low density, and pH gained a higher dissolution rate of nickel and cobalt. The main mechanisms for autotrophic acidophilic (iron-oxidizing) and iron-reducing (dissimilatory iron-reducing bacteria) were acidolysis and redoxolysis. In general, biological dissolution and chemical control, respectively, had a greater effect compared with chemical dissolution and diffusion control on the dissolution rate of nickel and cobalt from the laterites. It was found that optimizing factors that affect the bioleaching of nickel and cobalt from nickel-containing laterites greatly increased the dissolution rate, recovered nickel and cobalt, and reduced iron dissolution.