Reduction of pentavalent and trivalent arsenic by TiO2- photocatalysis: an innovative way for arsenic removal

Abstract

Arsenic in drinking water constitutes nowadays a serious problem, affecting the health of several million people all over the world. Only in the Gangetic delta regions of Bangladesh and West Bengal in India, it has emerged as an environmental health catastrophe with more than 100 million people estimated to be at risk (Naidu, 2012); in LatinAmerica, 14 million people could be affected (Litter et al., 2012). Ingestion of more than 100 mg of the element causes acute poisoning, but ingestion of small amounts of As for a long period leads to the occurrence of arsenicosis or Chronic Regional Endemic Hydroarsenicism (hidroarsenicismo crónico regional endémico, HACRE, in Spanish), responsible for skin alterations and cancer (Bundschuh et al., 2010; 2012; Figueiredo et al., 2010; Litter et al., 2008; 2010; 2012; Morgada et al., 2008, 2010a). The World Health Organization (2011) recommends 10 µg L−1 as the maximum allowable As concentration in drinking water, value taken by most national regulatory agencies. Arsenic pollution in water can be originated in anthropic activities (mining, use of biocides, wood preservers) but most pollution is natural, coming from dissolution of minerals in surface or groundwaters, or volcanic processes (Bundschuh et al., 2010; Litter et al., 2010). Predominant As forms in natural groundand surface waters (at neutral pH) are arsenate (As(V), as H2AsO − 4 and HAsO 2− 4 ) and arsenite (As(III), as neutral As(OH)3). Methods for As removal from waters are urgent, but they should take into account that while As(V) can be easily removed by conventional treatments such as ion exchange or adsorption techniques, As(III) removal is more difficult due to its nonionic form in aqueous solutions at pH < 9 (Litter et al., 2010). Recently, we focused on the study of the conversion of As(III) and As(V) to As(0) for immobilization of As dissolved in water by TiO2 photocatalysis (Levy et al., 2012).