(446e) Treated Laterite As Potential Adsorbent for Removal of Heavy Metals from Drinking Water

Somak Chatterjee, Sirshendu De.

Department of Chemical Engineering, Indian Institute of Technology, Kharagpur, Kharagpur â?? 721302, India.

Contamination of groundwater by heavy metals is serious threat to environmental safety. These heavy metals undergo chemical transformation and pollute the water, which causes harmful diseases in the human body. Some of the inorganic form of the material is not metabolized and accumulates in the tissues and blood stream of human body. According to world health organization, maximum permissible limit of these heavy metals in drinking water should not be greater than 10 µg/L. Processes like advanced oxidation, precipitation ion exchange and membrane separation are some of the water treatment techniques and can be used in the removal of heavy metals. However, each of these processes has inherent limitations. Adsorption is an age old famous process which has been continuously used for these problems. Adsorbing agents are treated either physically (roasting, calcination) or by use of common chemicals (like zinc activation of charcoal made from coconut fibers). In most of the cases, the chemical agent is leached to the treated stream and becomes a potential threat in addition to the persistent danger. Also, cost of starting material and treatment becomes important parameters in judging the sustainability of these treatment procedures. Therefore a cost effective, environment friendly and high performance yielding material is required to address this issue. Laterite is present in Rarh region of the eastern part of India (Kharagpur, 22.32° N, 87.32° E) and can be chemically treated in bulk scale for arsenic removal from ground water [20]. Preparation of treated laterite occurs in three steps, i.e., acid dissolution followed by hydrolysis of the dissolved mass and finally washing [20]. Treated laterite (TL- prepared using hydrochloric acid and sodium hydroxide) was successfully utilized for this purpose. However, change in the treatment procedure has been done to make the material viable for cationic metal removal (lead, cadmium, zinc, nickel and copper). The adsorbent was characterized using scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), and Fourier Transform Infrared Spectroscopy (FTIR) to highlight its physical and chemical properties. Optimized equilibrium conditions were 1 g/L adsorbent concentration, 0.26 mm size and a pH of 7±0.2. Adsorption capacity of heavy metals was evaluated and was obtained to be 16 mg/g (Lead), 4.5 mg/g (cadmium), 3.5 mg/g (zinc), 2 mg/g (nickel) and 3 mg/g (copper). The adsorption was observed to be exothermic for lead whereas it was endothermic for other heavy metals. Equilibrium time of 24 to 30 hours is required to attain a 99 % adsorption of heavy metals by TL. Adsorption kinetics is explained by second order kinetics.

Keywords: heavy metals; laterite; adsorption; equilibrium; kinetics