Biomining: A sustainable approach for metal recovery in low-grade ores

The rising proportion of low-grade ores, has forced mining companies to invest significantly in order to sustain their existing outputs to meet the current demand. Studies have shown that high grade ore deposits are expected to reduce over the next few decades. Thus, securing a sustainable and environmentally friendly technique to recover metals from low grade ores must be prioritized. Subsequently, mine wastes and waste electrical and electronic equipment (WEEE) has become sources of recovering valuable metals thereby transforming waste into wealth. Biomining has become a highly attractive and widely implemented technique for metal extraction. It involves bioleaching and biooxidation, which enhance the breakdown of mineral structures by liberating metals. Bioleaching harnesses acidophilic bacteria to produce Fe3+ and H2SO4, thereby oxidizing metal sulfide minerals and releasing metals into solution. Biooxidation uses microorganisms to degrade the mineral structure which contains the desired metal such as gold or silver, making the metal accessible to the oxidizing slag. The commercial application of acidophilic and chemolithotrophic microorganisms in oxidizing iron and sulfur to extract metals from copper-, uranium-, and gold-containing ores or concentrates is firmly established. These microorganisms convert insoluble metal sulfides into soluble metal sulfates through oxidation. Similarly, acidophilic biocatalysts like Acidithiobacillus, Leptospirillum, and Ferroplasma propel eco-friendly bioleaching of sulfide ores. In bioleaching, greenhouse gas (GHG) emissions produced are lower relative to the traditional pyrometallurgical techniques. Aside its metal extraction efficiency from low-grade ores, mine tailings and electronic wastes, biomining represents an environmentally sustainable method that enhances the separation of metals from solid matrices e.g. waste dumps. Bioleaching techniques deliver enhanced specificity in metal recovery, which is challenging to attain through conventional chemical leaching methods. Prudent management of mine tailings and sub-economic ore deposits through biomining offers dual advantages in environmental protection and cost-effectiveness.