REMOVAL OF COPPER IONS FROM SOLUTION BY SILICA-IMMOBILIZED MEDICAGO SATIVA (ALFALFA)

J.L. Gardea-Torresdey¹, K.J. Tiemann¹, J.H. Gonzalez¹, J.A. Henning² and M.S. Townsend²
¹Department of Chemistry, University of Texas at El Paso, El Paso, TX 79968, 915-747-5359, FAX 915-747-5748; and ²Department of Agronomy & Horticulture, New Mexico State University, Las Cruces, NM 88003

ABSTRACT

Previous screening laboratory batch experiments to determine the binding ability of seven different populations of Medicago sativa (alfalfa) showed good copper binding characteristics of the biomasses studied. All seven populations examined had similar trends for binding copper as a function of pH. The copper binding by the different alfalfa populations occurred in less than five minutes. All the alfalfa biomasses showed high copper binding, but the capacities varied according to the alfalfa population studied. The pH dependence of the copper ion binding to the alfalfa biomasses suggested that it might be possible to recycle the system much like an ion-exchange resin. However, the alfalfa cells can not be packed into a column since the cells clump together and restrict the flow. We have immobilized the cells of alfalfa Malone shoots in a silica matrix. Column experiments for copper binding by the silica-immobilized Malone demonstrated that the alfalfa tissues were capable of removing considerable amounts of copper ions under flow conditions. After every copper binding cycle most of the copper was desorbed with a few bed volumes of 0.1 M HCl. Our work indicates that the Malone-silica preparations are highly durable. We have subjected the biomaterial to as many as 10 cycles of binding and elution without observing any significant decrease in copper binding capacity.

Key words: biofiltration, phytoremediation, Medicago sativa, alfalfa, copper, removal, recovery