In the previous research, the effects of different addition time and amount of printed circuit boards (PCBs) on cells growth and metals recovery in separated and mixed culture of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans were investigated. This paper aimed to optimize mixed culture of both acidophiles for maximizing PCBs addition amounts and copper leaching percentage simultaneously. Initially, influences of inoculums ratio between two acidophiles on their cells growth were studied. Then, initial medium pH and concentrations of FeSO4 · 7H2O and elemental sulfur (S(0)) were optimized by response surface methodology (RSM) to improve copper recovery. Finally, multiple-point PCBs addition was tested to determine maximal amounts. Results showed that with initial inoculums ratio (Af:At) 1:2, pH 1.56, FeSO4 · 7H2O and S(0) at 16.88 and 5.44 g/L, and PCBs addition 28.8 g/L, copper recovery reached 92.6% after 240 h cultivation. It was indicated that copper could be efficiently leached out from increased PCBs addition amount and FeSO4 · 7H2O was remarkably reduced from 22.1 to 16.88 g/L.
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