SURFACE COMPLEXATION MODELING OF METAL REMOVAL BY RECYCLED IRON SORBENT

The triple layer surface complexation model (TLM) is used to describe equilibria for lead, cadmium, and zinc adsorption on a recycled iron-b earing material that is treated as a hydrous oxide in aqueous solution . Using model constants derived from surface titration experiments and literature recommendations, equilibrium constants are estimated for m etal adsorption reactions by calibration of pH-adsorption edge data. A method is then developed for integrating the TLM into a dual-resistan ce mass transport model in order to simulate the performance of comple tely mixed batch reactors and fixed beds for the treatment of heavy me tals by porous sorbents. A sequential scheme is employed in which the coupled liquid- and solid-phase material balance equations of the dyna mic model are solved at a given time step, followed by updating of the liquid-phase sorbate concentration at the sorbent particle surface by solving the set of nonlinear algebraic equations that define solid! l iquid-phase equilibrium according to the TLM. The result is demonstrat ed with laboratory-scale kinetic data in both batch and fixed-bed reac tors for lead adsorption onto the recycled iron sorbent.