Abstract
Abstract E-waste has become one of the greatest sources of environmental pollution. Bioleaching is known as a new, simple, and environmentally friendly technology for metal recovery requiring low energy input, unskilled labor operations, moderate conditions, and low costs. Acidithiobacillus ferrooxidans is a famous and puissant mesophilic bacterium applied extensively to recover metals from ores and different industrial and municipal wastes. It is necessary to identify the parameters affecting consumers E-waste recycling. Separating and recovering different types of E-waste is impossible for small recycling units. There should be a specific combination of E-waste, enabling the extraction of the maximum amount of precious metals. The main objective of the present study is finding the optimal combination of the most important printed circuit boards (PCBs) to maximize recovery of Cu, Ni, and Fe (as the most gold inhibitor metals) using adapted A. ferooxidans. The polymers and low-density materials were separated using the shaking table method to reach a concentrated sample. A. ferooxidans was adapted to the 15 g/l of the defined samples within 177 d. The D-optimal method was adopted to find the optimum E-waste combination. Pulp density, inoculum size, temperature, and stirring rate were fixed at 15 g/l, 10% (w/w), 30 °C , and 130 rpm in all experiments. The optimal percentages of computer PCBs plus CPUs, mobile phone PCBs, TV PCBs, copy machine PCBs, and fax PCBs were determined as 21.5%, 43.5%, 3%, 13.5%, and 18.5%. The application of this optimal E-waste composition resulted in 100% Cu and Fe extraction and 54% Ni recovery. It was concluded that increasing the concentration of a definite metal in PCB mixtures improves the recovery efficiency of that metal. Increasing Cu concentration in the bioleaching solution decreases Fe recovery. Significant amount of Cu and Fe in all samples reduces Ni recovery.
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