Ability of silica-immobilized Medicago sativa (alfalfa) to remove copper ions from solution

Preliminary 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 within 5 min. All the alfalfa biomasses showed high copper binding, but the capacities varied according to the alfalfa sample 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 cannot be packed into a column because the cells clump together and restrict the flow. We immobilized the cells of Malone alfalfa shoots in a silica matrix. Column experiments for copper binding by the silica immobilized alfalfa 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 subjected the biomaterial to as many as 10 cycles of binding and elution without observing any significant decrease in copper binding capacity.