Arsenate adsorption on goethite and on Fe(III)-exchanged montmorillonite

LUENGO, CARINA; AVENA, MARCELO

Valencia. España

Congreso; 2nd Internacional Congress, Arsenic in the Environment; 2008

Sociedad Internacional de agua subterránea para el desarrollo sostenible (ISGSD).

Arsenic content in groundwaters is a topic of environmental interest because high concentrations of As limit the use of these resources. Arsenic is a known carcinogen and its effect in the human health is a topic of global interest (Nriagu, 2002). The Argentine Chacopampean region is one of the zones of Latin America with major arsenic concentrations in groundwaters (Smedley et al., 2002). In some provinces of Argentine levels of arsenic can be higher than 1 mg/l. It is very important to understand the factors that control As concentration of groundwaters and to develop materials capable of reducing this concentration. Arsenate mobilization in the environment is significantly influenced by mineral surfaces (Gao et al., 2001). The adsorption on these surfaces determines the quantity of arsenate that is retained in the solid phase controlling the concentration of these anions in surface and groundwaters. In this work a study of the arsenate adsorption on goethite and Fe-montmorillonite was performed. Adsorption measurements using a batch technique were performed at different times, pH, temperatures, stirring rates and initial concentrations of arsenate. The arsenate adsorption was very similar on goethite and Fe-montmorillonite. The adsorption takes place in two differentiated stages: a rapid one that is completed before 5 minutes of reaction, and a slow one that lasts between 1 and 3 hours. In the first stage around 60-80 % of the total arsenate is adsorbed, whereas in the second stage (probably a stage of diffusion within pores) the remaining percentage is adsorbed. The adsorbed amount increases by increasing the initial concentration of arsenate, by increasing temperature and by decreasing pH. It was also observed that the stirring rate does not have any effect on the adsorption. Duo to their good adsorptive capacities, goethite and Fe-montmorillonite might be used as decontaminant material of waters containing arsenate.