Gold‐cyanide biosorption with L‐cysteine

L ‐Cysteine increased gold‐cyanide biosorption by protonated Bacillus subtilis, Penicillium chrysogenum and Sargassum fluitans biomass. At pH 2, the maximum Au uptakes were 20.5 µmol g⁻¹, 14.2 µmol g⁻¹ and 4.7 µmol g⁻¹ of Au, respectively, approximately 148–250% of the biosorption performance in the absence of cysteine. Au biosorption mainly involved anionic AuCN₂⁻ species adsorbed by ionizable functional groups on cysteine‐loaded biomass carrying a positive charge when protonated (biomass–cysteine–H⁺)–(AuCN₂⁻)]. Deposited gold could be eluted from Au‐loaded biomass at pH 3–5. The elution efficiencies were higher than 92% at pH 5.0 with the Solid‐to‐Liquid ratio, S/L, = 4. Increasing solution ionic strength (NaNO)₃ decreased Au uptake. FTIR analyses indicated that the main functional groups involved in gold biosorption in the presence of L ‐cysteine are probably N‐, S‐ and O‐containing groups. The present results confirm that certain waste microbial biomaterials are capable of effectively removing and concentrating gold from solutions containing residual cyanide if applied under appropriate conditions. © 2000 Society of Chemical Industry