Impact of solution variables on the removal of heavy metals from wastewaters by a recycled iron sorbent

Waste shot-blast fines from surface finishing processes have been demonstrated to be effective for removing heavy metals from solution by adsorption. The technology offers the potential for inexpensive recovery and reuse of a material normally discarded as a solid waste. While metal removals compare favorably with those achieved by commercial sorbents, applications issues such as the impact of background metal-complexing agents require investigation. The presence of oxalic acid, a complexing organic compound, impacted cadmium and lead adsorption in accordance with predictions from metal speciation equilibria; i.e., a small but measurable reduction in lead removal was observed, but cadmium adsorption was relatively unaffected. The effects were repeated in dynamic column experiments, with lead removals reduced by 15 to 20% in the presence of the ligand. Efforts to model adsorption equilibria in the presence of oxalic acid did not fully capture the reduced lead removal, presumably because the model does not consider the complete formation of metal-oxalic acid complexes prior to contact with the sorbent.