Green recovery of gold through biosorption, biocrystallization, and pyro-crystallization

Abstract

Gold recovery from dilute solutions has always been a subject of great interest due to ever increasing demand of this precious metal. In the present study, an attempt had been made to recover this noble metal in ionic, nanocrystalline, and metallic form using a combination of biosorption, biocrystallization, and pyro-crystallization techniques with Sargassum biomass as biomaterial. Optimization of process parameters revealed that the biosorption capacity increased with a decrease in pH due to an ion-pairing effect. Kinetic studies showed that the biosorption of Au(III) onto Sargassum biomass was a rapid process with more than 90% removal at the initial 15 min. Nonlinear forms of pseudofirst-order and pseudosecond-order models were used to fit the experimental data. The adsorption capacity (Qmax) from the Langmuir model was found to be 32.94 mg/g at pH 2. Maximum desorption of 97.8% was achieved with 2 N NaOH used as desorption medium. Biocrystallization of ionic gold through bioreduction was observed from 30 min with high productivity at pH 8. The X-ray diffraction analysis (XRD) patterns of the gold nanoparticles revealed their biphasic nature. Recovery of the biosorbed ionic gold in metallic form through pyro-crystallization technique showed the possibility of 91.44% recovery of the metal in pure form as revealed by XRD analysis. The overall results indicate that gold from dilute solutions can be recovered through green processes in ionic, nanocrystalline, or metallic form as desired by the end-consumer using Sargassum biomass as biomaterial. © 2010 American Chemical Society.