S.W. Leung, N. Basnet, K. Dejesus, J.C.K. Lai
Idaho State University,
United States
Keywords: MCM, adsorption, heavy metals, functionalized MCM, calcium, removal
Summary:
Mining operating and abandoned mines often have resulted in waste rock dumps and open pits that contain materials high in heavy metals and toxic elements. These contaminants are known to be present in groundwater, surface water, sediment, soils and plants and can be transported beyond the former mining areas through the surface and ground water system. Exposure to high level of these contaminants can cause adverse effects in humans, wildlife, and other animals. An effective technology to remove these pollutants is needed. MCM (Mobil Composition of Matter) is a mesoporous material that forms a family of silicate solids (such as MCM 41, MCM 48, etc.) that consist a regular arrangement of cylindrical mesopores that form an one-directional pore system. These mesoporous solids are widely used as absorbents, catalysts, or catalyst supports due to their large surface area to mass ratio. However, MCM materials are not structurally stable and their lattices may collapse with time, which will alter the properties of the materials. Addition of moieties on the surface of the MCM surface structure stabilizes the lattice but also changes the surface properties, thus this technique can serve as a “tuner” for the properties of MCM materials. The properties that are altered are depending on the molecules being attached onto the surface. This report will focus on MCM-41 and its functionalized product as an adsorbent to remove heavy metals and hardness simultaneously from polluted water and groundwater. In this study, MCM-41 was first synthesized by a hydrothermal method, functionalization was prepared by using ZnCl2 to form ZnCl2-MCM-41 with the use of a microwave procedure. MCM and ZnCl2-MCM-41 surface were characterized by SEM, TEM, AFM, and FTIR. Surrogate heavy metals used in the study were Hg, Pb, and Cr, while Ca was used as a major component of the hardness in water. Systematic experiments were performed to investigate the capabilities of these MCM adsorbents at various concentrations of absorbates and durations at neutral pH. Comparisons of adsorption capabilities with activated carbon were also performed. It was found that ZnCl2-MCM-41 could adsorbed 3 times as much as its original weight, and the amount of metal absorbed by ZnCl2-MCM-41 increased with molecular weight of the metals. Among other applications, the results of selective sorption phenonium can be useful for some particular water treatment alternatives, such as nuclear engineering industry.