Reduction and Accumulation of Gold(III) by Medicago sativa Alfalfa Biomass:  X-ray Absorption Spectroscopy, pH, and Temperature Dependence

• Published in: Environmental science & technology Vol. 34; no. 20; pp. 4392 - 4396
• Main Authors: Gardea-Torresdey, J. L, Tiemann, K. J, Gamez, G, Dokken, K, Cano-Aguilera, Irene, Furenlid, Lars R, Renner, Mark W
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.10.2000
• Subjects: Applied sciences; Chemistry; Exact sciences and technology; Flowers & plants; Gold mines & mining; Industrial wastewaters; Metals; Pollution; Wastewaters; Water treatment and pollution; Material recovery; Medicago sativa; Temperature effect; Bioadsorbents; Gold III; Biomass; Chemical reduction; Sorption; Leguminosae; Adsorption; Industrial waste water; Medium effect; Colloidal suspension; Dicotyledones; Angiospermae; Reaction mechanism; pH; Spermatophyta; Physicochemical purification; Fodder crop; Waste water purification; Mining industry
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es991325m

We report herein the use of Medicago sativa alfalfa shoot biomass for the removal of gold from aqueous solutions. The accumulation process involves the reduction of Au(III) to colloidal Au(0) and is shown to increase at elevated temperatures and at lower pH. X-ray absorption spectroscopy (XAS) was used to determine that gold(III) was reduced to form gold(0) colloids, which varied in size depending on the pH of the initial solution. The gold cluster radius was 6.2 ± 1 Å at pH 5 and 9.0 ± 1 Å at pH 2. Our findings indicate that essentially another layer of gold atoms was deposited onto the colloid surface at pH 2. Possible mechanisms of bioreduction and accumulation are discussed.