ABILITY OF MEDICAGO SATIVA (ALFALFA) TO REMOVE NICKEL IONS FROM AQUEOUS SOLUTION

J.L. Gardea-Torresdey¹, K.J. Tiemann¹, J.H. Gonzalez¹, I. Cano-Aguilera¹, 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

The characteristics of the roots and shoots from seven different populations of Medicago sativa (alfalfa) were examined for their ability to bind nickel ions from aqueous solution. Batch laboratory experiments were performed to determine the optimal pH for nickel binding to the alfalfa plant tissues which was between pH 5 and 6. From these experiments, pH profiles were performed to gain information about the chemical functional groups in the alfalfa plant tissues responsible for the nickel binding. Binding-time-dependency studies determined that approximately 80% of the nickel ions bound to the alfalfa plant tissues in less than five minutes. Binding capacity experiments showed that nickel binding was as much as 4.1 mg of nickel per gram of alfalfa biomass. Nickel recovery experiments showed that over 90% of the bound nickel was removed from the alfalfa biomass. Column experiments were conducted to examine the binding of nickel to silica immobilized alfalfa plant tissues under flow conditions. Results from these experiments showed that over 90% of the retained nickel was recovered after 4 bed volumes of 0.1 M HCl solution was passed through the column. After 12 cycles on the same column, the efficiency for nickel removal and recovery from solution was stable.

Key words: biofiltration, phytoremediation, alfalfa, Medicago sativa, nickel, binding, recovery