Optimizing conditions of key factors influencing CN− producing ability of Pseudomonas biofilm to leach Ag from waste printed circuit boards

Abstract

Abstract With the sharp increase in the number of waste printed circuit boards, biocyanidation is adopted to recover the precious metals from waste printed circuit boards for its environmental friendliness. In this study, Pseudomonas biofilm with CN− producing ability was constructed to leach Ag from mixed metal particles of waste printed circuit boards. The optimal culture conditions for Pseudomonas biofilm to produce CN− were pH 7.0, 20 °C, 100 rpm and 1/25 NB medium. Polyethylene particles were more suitable as carriers than ceramsite. 500 ppm of Cu2+ and 2.5 ppm of Ag+ were beneficial for the CN− production while higher concentrations were adverse. With 0.05% of Ag content, the Ag leaching rate was the highest, which was up to 35.53% after 7 d of leaching. The Pseudomonas biofilm remained stable and active during the whole leaching process. This paper contributes to the construction of continuous bioreactor using biofilm and the industrialization of biocyanidation technology for recovering waste printed circuit boards.