To solve the common problem of Cu bioleaching from waste printed circuit boards (PCBs), a slightly modified bioleaching method was used in this work. This method was concentrated on preventing the iron loss, which would promote Cu bioleaching, reduce FeSO₄·7H₂O consumption from up to 60 g/L and bring cost savings. Herein, we firstly compared the bioleaching performances between 1.5SO₄^2- system and 1.5S⁰ system. The results showed that 1.5S⁰ system was practicable to inhibit the production of Fe(III)-precipitates, and the sustaining low pH should be the main factor for the suppression. Then, different initial content of FeSO₄·7H₂O was combined with multi-stage bioleaching mode under 1.5S⁰ system. It was found that 0.25 g/L FeSO₄·7H₂O was sufficient for bioleaching of Cu from 50 g/L PCBs, the increasing Cu²⁺ content was achieved by the unsuppressed circulation between Fe²⁺ and Fe³⁺. Compared to previous reports, the input quantity of FeSO₄·7H₂O was reduced remarkably (up to 239 times) and the capital cost of bioleaching could be saved by 37–284 USD m^-3. Hence, this work significantly promoted the Cu bioleaching performance through controlling the iron loss, which appears very promising for the development of practical applications.

Concentrations of Fe²⁺ (a), Total Fe (b), pH (c) and Cu bioleaching efficiency (d) with respect to time under two bioleaching systems (experimental conditions: pH=1.5; 22g/L FeSO₄·7H₂O for 1.5SO₄^2-; 8 g/L FeSO₄·7H₂O for 1.5S⁰; 10 g/L PCBs).