Removal of nickel ions from aqueous solution by biomass and silica-immobilized biomass of Medicago sativa (alfalfa)

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 5 min. 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 more than 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 more than 90% of the retained nickel was recovered after four bed volumes of 0.1 M HC1 solution were passed through the column. After 12 cycles on the same column, the efficiency for nickel removal and recovery from solution was stable.