**3. Application of clay in arsenic and fluoride removal**

The presence of arsenic and fluoride has attracted worldwide attention due to their toxicity in human health after a prolonged period of exposure [30]. Excessive intake of fluoride can lead to dental and skeletal fluorosis while the intake of arsenic can lead to various types of cancer. The World Health Organization (WHO) has set the standard of fluoride and arsenic in water for human consumption at 1.5 and 0.01 mg/L, respectively [31]. Recently much attention is being driven into developing a technique that can be used to remove excess of fluoride and arsenic in drinking water to acceptable levels. Adsorption using clay mineral has emerged to be the promising technique and several studies pertaining to removal of fluoride and arsenic using clay minerals has been reported in the literature. This is because clay minerals are abundantly available in nature at little or no cost. Furthermore clay minerals are more chemical and mechanical stable, poses larger specific surface are and higher cation exchange capacity making them good adsorbents.
