The removal of selected heavy metals from water by ion exchange

The adsorption of four heavy divalent metals, cadmium, zinc, nickel, and copper in water buffered to pH of 6.0 is studied in batch equilibrium and kinetic experiments and fixed bed experiments. The objective is the removal of heavy metals by ion-exchange, using two commercial resins independently, SR-5® and Diphonix resins®. This is an area of interest for the following reasons: to meet federal regulations for effluent discharge limits, which are frequently less than 5 ppm for regulated metals, recycling process streams, clean-up of existing groundwater problems, and the economic value of some metals. When compared to other commonly used methods, ion-exchange can reduce solution concentrations to extremely low levels and may be a feasible and economical method for the removal and recovery of heavy metals. In this work, the results of batch equilibrium experiments for single cation species on each resin are described by the Langmuir and the Toth models. Modeling the results of the kinetic experiments for cadmium and copper on Diphonix resin by simple ion transport through the resin beads yields an effective diffusion coefficient. These experimental results may then be used in future modeling work for a fixed bed ion exchange process. The fixed bed experiments in this work investigate the adsorption of multi-component feeds, of cadmium, zinc, and nickel, operated primarily in the displacement mode, using a copper displacer. One run gives results using a frontal analysis method. This data is interpreted qualitatively, with information provided on effective flow rates, breakthrough times, and cation elution curves.