Increasing interest in biomining process and the demand for better performance of the process has led to a new insight toward the mining technologies. From an engineering point of view, the complex network of biochemical reactions encompassed in biomining would best be performed in reactors which allow a good control of the significant variables, resulting in a better performance. The subprocesses are in equilibrium when the rate of particular metal ion; for example, iron turnover between the mineral and the bacteria, is balanced. The primary focus is directed towards improved bioprocess kinetics of the first two subprocesses of chemical reaction of the metal ion with the mineral and later bacterial oxidation. These subprocesses are linked by the redox potential and controlled by maintenance of an adequate solids suspension, dilution rate, and uniform mixing which are optimised in bioreactors during mining operations. Rate equations based on redox potential such as ferric/ferrous-iron ratio have been used to describe the kinetics of these subprocesses. This paper reviews the basis of process design for biomining process with emphasis on engineering parameters. It is concluded that the better understanding of these engineering parameters will make biomining processes more robust and further help in establishing it as a promising and economically feasible option over other hydrometallurgical processes worldwide. 1. Introduction Biomining is gaining importance as a unit process which involves biological organisms in mineral extraction industries worldwide. With the decreasing high grade ore reserves and increased concern regarding the effect of mining on the environment, biomining technology, which was nevertheless age old deserted technique, is now being developed as a main process in the mining industry to meet the demand [1]. Another important aspect is the feasibility of biomining technologies to treat ores deposits with complex mineralogy, which could be difficult to treat by conventional methods [2]. Besides, the most attractive feature of biomining is economic feasibility compared to other competitive techniques [2]. Gahan et al. [2] comparatively analysed how gold and copper biomining operations played a role with the increase or decrease in metal pricing over time. Their analysis indicated that most biohydrometallurgical innovations have been commercially implemented during leaner times [3]. Economic factors such as eliminations of net Smelter Royalties associated with smelting and refining and possibility of the use bioleaching for on-site acid
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