Enhanced Bioleaching of Chalcopyrite Using Electron-Stimulated Bacteria

Bioleaching is a biotechnological process that applies microorganisms to extract valuable metals from usually  low-grade sulfidic ores and concentrates. Chalcopyrite (CuFeS2) is the most abundant and widespread copper-bearing mineral. Unlike many other copper sulfides, chalcopyrite is particularly recalcitrant to hydrometallurgical processes. Bioleaching of sulfide minerals is an electrochemical process, involving the transfer of electrons. In this work, we used low energy electron irradiation (LEEI) to promote the biotechnological process of chalcopyrite dissolution via stimulation the bacteria with low doses of external electrons.

A small scale setup was used to irradiate the bacterial suspensions. Briefly, a crystallizing dish was placed on a magnetic stirrer to stir the bacterial suspensions. For irradiation, the low-energy accelerated electron plant REAMODE with a 200 keV electron beam was used. The bacterial suspensions were irradiated at a beam current of 0.1 mA and 200 KV for different time periods. The deposited dose was routinely measured with radiochromic films. Additionally, a liquid research dosimeter based on a solution of triphenyltetrazolium chloride was used.

The electron stimulated bacteria were used as inoculum for bioleaching approaches. Bioleaching was performed with a solid load of 1 % (w/v) fine grained chalcopyrite. Samples were taken for determination of the pH, and the concentrations of dissolved ferrous-, ferric- and copper (Cu2+). These are crucial parameters for monitoring the success of the biotechnological process. It was deduced that electron-stimulated bacteria contributed to an enhanced copper leaching rate.