Gold and silver uptake and nanoprecipitation on calcium alginate beads.

Calcium alginate beads were investigated for their biosorption performance in the removal of gold and silver from aqueous solutions. It was found that uptake capacities were significantly affected by the solution pH, with optimum pH values of 2 and 4 for gold and silver, respectively. Kinetic and isotherm experiments were carried out at the optimum pH. The maximum uptake capacities were 290 mg/g for Au and 52 mg/g for Ag. FTIR analysis indicated that both carboxylic and hydroxylic functional groups in alginate beads are involved in the metal binding and later reduction of gold (+3) and silver (+1) to gold (0) and silver (0). SEM and X-ray diffraction confirmed the formation of gold and silver nanoparticles.