Extensive use of heavy metals in industrial activities causes environmental problems and health issues in the past decades. Unlike organic pollutants, heavy metals cannot be biodegraded once introduced into the environment. The major heavy metal exposure is consumption of contaminated drinking water or food; thus heavy metals need to be removed from water supplies. Adsorption is a promising separation technology based on the affinity between adsorbate and adsorbent; and has been widely used in water and wastewater treatment. Various kinds of adsorbents have been developed and employed in heavy metal contaminated wastewater treatment. This research project aims at studying the sorption capacity, uptake kinetics and sorption mechanism of cadmium, lead and copper onto a aluminosilicate bas...[ Read more ]

Extensive use of heavy metals in industrial activities causes environmental problems and health issues in the past decades. Unlike organic pollutants, heavy metals cannot be biodegraded once introduced into the environment. The major heavy metal exposure is consumption of contaminated drinking water or food; thus heavy metals need to be removed from water supplies. Adsorption is a promising separation technology based on the affinity between adsorbate and adsorbent; and has been widely used in water and wastewater treatment. Various kinds of adsorbents have been developed and employed in heavy metal contaminated wastewater treatment. This research project aims at studying the sorption capacity, uptake kinetics and sorption mechanism of cadmium, lead and copper onto a aluminosilicate based material derived from waste non-metallic fraction.

Firstly, non-metallic fraction was recycled from waste printed circuit board separation process and activated using a moderate-temperature thermal alkaline method. After the activation process, the activated material was characterized and tested, showing strong ability of heavy metal removal. Secondly, the equilibrium sorption of cadmium, lead and copper on activated non-metallic fraction with varying initial metal concentration, pH and adsorbent dosage were studied and simulated with six conventional single-component isotherm models. Thirdly, the sorption kinetics of cadmium, lead and copper onto activated non-metallic fraction were studied using batch agitating contacting system with varying initial metal concentrations, pH and adsorbent dosage. Three conventional kinetic models were used to calculate the overall rate constant. Based on the adsorption behaviour of the system, the adsorption is supposed to occur via ion-exchange. In order to further investigate the adsorption mechanism, aquatic adsorption experiments in combination with spectroscopic characterization of exhausted materials were carried out. The mole balance between the adsorbed amount of metal ions and the liberated amount of ions was the direct evidence that the metal ions were exchanged out by potassium and calcium present on the surface of the material. X-ray photoelectron spectroscopy (XPS) spectra, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) elemental mapping and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) results of the exhausted material further verified the ion-exchange mechanism. Finally, based on the adsorption mechanism and the experimental data, a novel kinetic model in correlation of two different adsorption sites was proposed to describe this adsorption system, it can also be applied to other adsorption or ion-exchange systems with two adsorption sites. Apart from the single-component adsorption systems, binary adsorption systems have been investigated to evaluate the selectivity of the adsorbent material. The results indicate that the activated material shows preference to lead.