Metal Oxyhydroxide Composites for Halogens and Metalloid Removal

The occurrence of pollutants in drinking water sources has become a serious problem worldwide. Sometimes, the contamination is not even related to human activities but occurs naturally during the weathering of minerals in water reservoirs. This is the typical case for arsenic- and fluoride-polluted human consumption water sources, which is a well-documented problem that impacts millions of people worldwide. Due to the health affectation to humans, the permissible concentration limit of arsenic and fluoride in drinking water is very low, 10 μg/L and 1.5 mg/L, respectively. Therefore, purifying water to reach those levels in a cost-effective way has become a real challenge. In this chapter, we first reviewed the full-scale strategies for the elimination of arsenic and fluoride from water, considering only physicochemical processes. Afterward, we make emphasis on adsorption, mainly by metal oxyhydroxides as adsorbent materials. The focus of the current research on this topic is the generation of new materials with superior characteristics, including higher adsorption capacity and selectivity. Metal and bimetallic oxyhydroxides have been developed and have shown to be promising materials to remove up to 200 and 250 mg/g of arsenic and fluoride, respectively. Also, researchers have oriented their efforts to transform metal oxyhydroxides into granular materials that can be applied in full-scale drinking water operations. Among the strategies are the synthesis of polymer composites, the agglomeration of metal oxide powder with various binders, and the anchorage of particles onto granular materials such as activated carbon: the processes involved are revised, with emphasis on the interactions between the carbonaceous matrix and the anchored metal oxyhydroxides.