Recovery of gold(III) by alfalfa biomass and binding characterization using X-ray microfluoresence

There is a need for the development of a system that can extract gold from solutions without the use of hazardous chemicals. A biorecovery system using alfalfa biomass may be the answer for the recovery of gold(III) from aqueous solutions in an environmentally friendly manner. Batch laboratory experiments indicate that alfalfa binds gold(III) quickly and in a pH-independent manner. Gold(III) binding capacity experiments performed with the alfalfa roots and shoots have shown the following capacities: 40 mg gold per gram of shoot tissues; 19 mg gold per gram of root tissues. We were able to recover up to 99% of the bound gold metal by treatment with 0.2 M acidic thiourea. Surprisingly, we discovered that the bound gold turned purple in color, indicating that gold(III) could have been reduced to gold(0). In addition, column experiments were performed with silica-immobilized alfalfa to determine the gold(III) binding ability under flow conditions. XRMF analysis corroborated the presence o