Stirred-tank leaching of coarse-grained waste, printed circuit boards with Acidithiobacillus ferrooxidans

Stirred tank leaching of metals from coarse-grained waste, printed circuit boards (WPCB) used Acidithiobacillus ferrooxidans (A. ferrooxidans) at ambient temperature (20-35°C). The effect of the baffle size, WPCB concentration, and inoculation volume was tested. 95.92% of Cu, 93.53% of Al, 92.58% of Zn, 65.27% of Ni, and 95.33% of Sn in WPCBs were leached under the optimal conditions: no baffle, WPCB concentration of 5.0% (w/w), and inoculation volume of 5% (v/v). The alkaline substance and reactivity metal of WPCBs, and the oxidation of Fe2+, consume H+. Adding acid can maintain the pH value of the leaching solution, which is conducive to the growth and reproduction of the bacteria and improves the leaching efficiency of WPCBs. The second-order dynamics model can describe the acid consumption in the bioleaching process of coarse-grained WPCBs. Moreover, the Avrami equation can successfully explain the bioleaching kinetics of Cu, Al, Zn, Ni, and Sn from the coarse-grained WPCBs. The key factors controlling the bioleaching of coarse-grained WPCBs are metal reactivity and specific surface area. These results revealed that bioleaching metals from coarse-grained WPCBs using A.ferrooxidans is feasible, and has important significance to guiding its industrialization.