Bacterial Cyanide Generation in Presence of Metal Ions (Na+, Mg2+, Fe2+, Pb2+) and Gold Bioleaching from Waste PCBs

As an alternative to use cyanide chemical for gold extraction, the use of a cyanogenic bacterium viz. Chromobacterium violaceum (C. violaceum) in YP medium has been investigated. The catalytic role of metal ions such as Na+, Mg2+, Fe2+ and Pb2+, besides the addition of Na2HPO4, a nutrient, on the cyanide generation efficiency of the bacterium in this medium has been elucidated. While MgSO4 and FeSO4 in the medium were equally effective for the cyanide generation, presence of Na2HPO4 and Pb(NO3)2 was still better. In order to examine the effectiveness of C. violaceum in the YP media to generate cyanide ions, the dissolution of gold and copper from waste mobile phone printed circuit boards (PCBs), a good source of gold and copper in alkaline conditions was tested at 30°C at varying pH and metal ions. Gold leaching was found to be 11% in 8 days at pH 11.0 in presence of 4.0 × 10-3 mol/L MgSO4 whereas, copper recovery was high (11.4%) at pH 10.0. Addition of 1.0 × 10-2 mol/L Na2HPO4 and 3.0 × 10-6 mol/L Pb(NO3)2 in the YP medium increased copper leaching to 30.3% and 38.1%, respectively at pH 10.0 in 8 days, but these were not effective for gold leaching.