Efficient In Situ Utilization of Caustic for Sequential Recovery and Separation of Sn, Fe, and Cu in Microbial Fuel Cells

A novel strategy to sequentially recover and separate Sn(II), Fe(II) and Cu(II) from a synthetic wastewater from printed circuit board (PrCB) manufacturing in a single microbial fuel cell (MFC_Sn)-MFC_Fe-MFC_Cu process was achieved, where in-situ produced caustic was primarily utilized for Sn precipitation (MFC_Sn) and then secondly used for Fe deposition (MFC_Fe) and anaerobic Cu(II) reduction in the final MFC_Cu. An external resistance of 1000 Ω in the MFC_Sn and MFC_Fe, and a 10 Ω resistor in the MFC_Cu achieved predominant recovery of Sn (MFC_Sn: 80.8±0.8 %), Fe (MFC_Fe: 59.1±0.8 %), and Cu (MFC_Cu: 68.2±1.8 %) in the three MFCs, with separation factors of 32.1±1.6 for Sn (MFC_Sn) and 7.5±1.8 for Fe (MFC_Fe), and complete recovery of Cu (MFC_Cu, 42-mesh cathodes). The metal concentrations in the final effluent were below national discharge limits (Sn, 2.0 mg/L; Fe, 5.0 mg/L; Cu, 0.2 mg/L). The metal recoveries ranged from 2.6 (Sn, MFC_Sn)–12.0 (Cu, MFC_Cu), and the separation factors were 8.4 (Sn, MFC_Sn)–∞ (Cu, MFC_Cu) times those of the open circuit controls. Cathodes with 120-mesh size of stainless steel mesh produced lower metal recoveries [33.7 % (Sn, MFC_Sn) and 27.0 % (Fe, MFC_Fe) decrease] and separation factors than MFCs with 42-mesh cathodes. This study provides a viable approach for efficiently recovering and separating Sn, Fe and Cu from stripping solutions produced in PrCB manufacturing, with simultaneous power production.