Monday, June 18, 2007 - 9:05 AM
Snake River (Boise Centre on the Grove)

Reduction of arsenic by humic acids adsorbed on mineral surfaces

Noel Palmer and Ray Von Wandruszka. University of Idaho, Moscow, ID

Previous work in this laboratory has shown that humic substances can abiotically reduce arsenic under a variety of conditions. The purpose of the present work was to determine how adsorption onto mineral surfaces affects the reduction potential of humates, and what consequences this has on their ability to reduce arsenate to arsenite. Reduction potentials of various mineral suspensions, including goethite, kaolinite and hectorite, were measured in the presence and absence of adsorbed humic acids. Reduction potentials of the bare minerals were generally higher than those of the adsorbed systems, meaning that the latter were more effective reducing agents for arsenic. The extent of redox change was directly related to the amount of humic material adsorbed, and also depended on the type of humate or fulvate used. Other parameters considered were particle size, surface area of the minerals, and pH of the sorbed systems. Selective adsorption of humic components onto the minerals was found to lead to segregation of redox characteristics, changing not only the surface potentials, but also the potentials of the humates remaining in solution.