A Microbial System for Recovering Noble Metals in Urban Mining

Microbial reduction and recovery of palladium was achieved at 25℃and pH 7 using resting cells ofthe metal ion-reducing bacterium Shewanella algae in batch and continuus -flow stirred tankThe bioreductive recovery of palladium with formate was a fast process：Within 60 min operation of batch reactor，1-10 mol/m^3 aqueous palladium(II) ions were completely reduced to crystalline nanoparticles of lessthan 10 nm in size. The microbial recovery capacity demonstrated that The 10 mol/m^3 （1060 ppm）aqueous PdCl2解决方案was concentrated up to 570-fold by the microbial deposition in the bacterialcells. In a continuus -flow reactor，the rate of palladium recovery reached a maximum of 95 kg/(h ^3) when the space time was veryshort, say,20s. Fast bioreductive deposition of gold(III) was also achieved even under acidic conditions. At pH2.0,larger gold particles approximately 350 nm in size was . The concept wassuccessfully applied to recover selectively gold from acidic leachate （200 ppm of gold(III)）electronic scraps. We furthermore proposed a conceptual flow sheet for the microbial recycling ofnoble metal from electronic waste.我们strongly believe that the microbial recovery is extremelyattractive system for recycling noble metals in urban mining。

Microbial reduction and recovery of palladium was achieved at 25℃ and pH 7 using resting cells of the metal ion-reducing bacterium Shewanella algae in batch and continuous-flow stirred tank reactors. The bioreductive recovery of palladium with formate was a fast process : Within 60 min operation of batch reactor, 1-10 mol/m^3 aqueous palladium(II) ions were completely reduced to crystalline nanoparticles of less than 10 nm in size. The microbial recovery capacity demonstrated that the 10 mol/m^3 (1060 ppm) aqueous PdCl2 solution was concentrated up to 570-fold by the microbial deposition in the bacterial cells. In a continuous-flow reactor, the rate of palladium recovery reached a maximum of 95 kg/(h・m^3) when the space time was very short, say, 20s. Fast bioreductive deposition of gold(III) was also achieved even under acidic conditions. At pH 2.0, larger gold particles approximately 350 nm in size were deposited extracellularly. The concept was successfully applied to recover selectively gold from acidic leachate (200 ppm of gold(III)) from electronic scraps. We furthermore proposed a conceptual flow sheet for the microbial recycling of noble metal from electronic waste. We strongly believe that the microbial recovery is extremely attractive system for recycling noble metals in urban mining.