ADSORPTION OF CADMIUM AND LEAD IONS USING BIOWASTE ADSORBENTS FROM AQUEOUS SOLUTIONS WITH ION-SELECTIVE ELECTRODES AND ICP-OES

Upon using low cost biowaste adsorbents as toxic metal ion removal substrates from aqueous solutions, it was found that they have a high potential of being used to generate a great environmental advantage. This thesis study evaluated pumpkin peels and potato peels for the adsorption of cadmium and lead ions. Chamomile tea residues, peanut shells, and ground coffee beans were also studied and showed less adsorption response for these heavy metals. The biowaste sorbents were treated with acid (HNO3) or base (NaOH). Batch experiments were carried by introducing a known concentration of metal ion solution into the biowaste sorbent at various pH levels. The pH and metal ions were monitored with a pH and cadmium or lead ion-selective electrode continuously for two hours, and the final concentration for the metal ions after 24 hours was measured with the ISE and then confirmed with ICP-OES. The characteristics of the biowaste sorbents were also studied with scanning electron microscope (SEM) and infrared spectra (FTIR). L-type isotherms were obtained that fit to Freundlich model. Adsorption isotherms showed chemical adsorption and kinetics following second order model. Equilibrium adsorption capacity is higher than 55 mg/g for both ions at pH 5.6 when the initial concentration is 500 ppm. Dynamic cadmium adsorption capacity is 12-15 mg/g from aqueous solution when the feed solution is 220 ppm. The biowaste materials can also be regenerated with acid washing. This work demonstrates that the ion-selective electrodes can provide simple and fast continuous determination of metal ion concentrations during the adsorption process