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-bearing 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 metal adsorption reactions by calibration of pH-adsorption edge data. A method is then developed for integrating the TLM into a dual-resistance mass transport model in order to simulate the performance of completely mixed batch reactors and fixed beds for the treatment of heavy metals by porous sorbents. A sequential scheme is employed in which the coupled liquid- and solid-phase material balance equations of the dynamic 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! liquid-phase equilibrium according to the TLM. The result is demonstrated with laboratory-scale kinetic data in both batch and fixed-bed reactors for lead adsorption onto the recycled iron sorbent.