Determination of Trace-level Gold(iii) Binding to Alfalfa Bio- Mass Using Gfaas with Zeeman Background Correction

Due to current technologies used to extract gold, increasing environmental pollution has occurred. Existing technologies for the extraction and recovery of gold include cyanidation, which uses toxic cyanide. Because of the potential health threat and waste generated by the cyanidation process, an increasing need to develop new technologies to extract and recover gold from aqueous solution has arisen. Previous experiments performed have shown that alfalfa has the ability to bind and subsequently to reduce gold(III) to gold(0). These experiments have also shown that gold(III) at high concentrations is adsorbed by the alfalfa biomass almost independently of pH. Batch laboratory pH profile experiments have been performed at trace levels for both native biomass and chemically modified biomass using a 100 ppb gold(III) aqueous solution. However, at trace gold(III) concentrations, the adsorption of gold(III) has been observed to be pH dependent. The pH profiles performed for both the native and esterified biomass were between pH 2.0 and pH 5.0. The observed trend in the binding by the native alfalfa biomass was highest at pH 3.0 (97%) and decreased to (approximately 50%) pH 4.0 and pH 5.0. However, the esterified biomass had an opposite binding trend, a low binding at pH 2.0 and 3.0 (50%) and a sharp increase in binding at pH 4.0 with a maximum binding at pH 5.0 (90%). To explore the effects of hard cations on the trace-level gold(III) binding, calcium, magnesium, and sodium were used. In addition, experiments were performed using all three cations combined in solution to further explore the effects of multiple hard cations on the trace-level gold(III) binding to the alfalfa biomass. All experiments showed that under optimal conditions, the binding was not greatly affected by the presence of the hard cations.