University of Tehran

Removal of chromate ion from contaminated synthetic water using mcm-41/zsm-5 composite

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The increasing contamination of urban and industrial wastewater by toxic metal ions is a worrying environmental problem. These inorganic micro-pollutants are of considerable concern because they are non-biodegradable, highly toxic and have a probable  carcinogenic effect (Modani et al., 1996). In view of their high toxicity for human health, heavy metal concentrations in wastewater are restricted by strict standards. The risk of exposure to toxic oxy-anions in groundwater is a worldwide rising environmental risk. Among these anions, chromate is particularly hazardous. Chromate is one such toxic ion that requires considerable attention (Adam and Pribil, 1974). The chromate (CrO4 2-) oxyanion is soluble in aqueous systems and is readily transported in ground water and the EPA maximum contaminant level for Chromium in drinking water is 0.1 parts per million (Sadaoui, 1998). Aqueous solutions of chromate (CrO4 2-) are known to undergo oligomerization reactions upon acidification. These kinds of polymerization processes are in general very common in aqueous solutions as they apply for the precipitation mechanism of hydroxides and oxides at basic pH conditions (Stern, 2000). The traditional techniques for the removal of metal ions from aqueous effluents; such as lime precipitation are incapable of reducing concentration to the levels required by standards (Chai et al., 1997). Nowadays, utilizati on of ionexchange process to clean up the   contaminated solutions with toxic ions is attractive for scientists. Adsorption of toxic species on solid surfaces is considered to be an effective method for improving the environment. These methods have been aimed at searching for effective adsorbents or the development of geochemical models of chromate distribution. Conventional porous solids, such as coconut coir, zeolite, and clay minerals, modified with surfactants have been applied to the removal of chromate.

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