Characterization of trace level Au(III) binding to alfalfa biomass (Medicago sativa) by GFAAS

Existing technologies for the extraction and recovery of gold include cyanidation which uses toxic cyanide. Because of the potential health threat created by many of these processes, an increasing need to develop new safer technologies to extract and recover gold from aqueous solution has arisen. Previous experiments have shown that gold(III) is adsorbed by alfalfa biomass at high concentrations in an almost pH-independent manner. However, little data exist for the bio-adsorption of trace levels of gold(III) by alfalfa biomass. Batch laboratory pH profile experiments were performed at trace levels with native alfalfa biomass using a 100 ppb gold(III) aqueous solution. The observed trend in the binding by the alfalfa biomass was highest at pH 2-3 (≈ 97%) and decreased to approximately 50% at pH 4.0 and 5.0. To explore the effects of hard cations on the trace level gold(III) binding, calcium, magnesium, and sodium cations were added to the gold(III) solutions and binding experiments were repeated to determine how these ions might interfere with the gold(III) bio-adsorption by the biomass. Experiments were also performed using all three cations combined in solution to further explore the effects of hard cations on the trace level gold(III) binding to the alfalfa biomass. All of the interference experiments showed that under optimal conditions the presence of the hard cations in concentrations as high as 3000 times the ppm concentration of gold(III) did not greatly effect binding by the alfalfa biomass.