A particular approach of the correlation between metals and health: arsenic removal from groundwater by Fe-rich geomaterials

Abstract

Arsenic is a very toxic element, observed in some groundwaters at levels above those suggested by the WHO (10 ppb). The geo-genetic origin is responsible for serious health problems, particularly the pathology known as Chronic Endemic Regional Hydroarsenicism (CERHA). In Argentina the arsenical grounwaters are consumed in the Chaco-pampean area, affecting more than 4 million people. In general, several technological strategies to remove the contaminant were used, but the adsorption arsenate/metal-oxide seems to be the most appropriate treatment, useful for areas of low population density and/or low income. In our case, the method was supported by the abundance of mineral species naturally rich in iron or possible to be modified with this metal. Chemical modification was carried out by using solutions of Fe (III) salts, through a hydrolytic process and pH adjustment, promoting the formation of Fe-O-H2O active clusters (precursors of nanoscopic ferrihydrite). Aluminosilicates such as clinoptilolite, pyrophyllite, pyroclastic material and kaolinite (Fe2O3 content lower or close to 5%) and Fe-rich clay minerals (~40% Fe2O3>), have been analyzed. The performance of the process was studied by means of Jar tests and physicochemical techniques (micro-Raman, XR diffraction, chemical analysis (ICP-AAS), scanning electron microscopy (SEM-EDS) and surface (BET) assays). It was noted that a small increase on the surface iron content (2-10%) correlates with an increase in mesoporosity and a marked increase in the arsenate(V) adsorption, measured from the number of treatment cycles. During the process, scorodite precursor is formed, whose stability in the clay matrix ensures the As isolation. Results revealed that the trigger alternative, depending on structural and surface mineral properties, constitutes a low-cost, effective, accessible and eco-friendly technology. Hence, several prototypes were successfully installed in rural and/or vulnerable localities of the affected region, producing water with As values lower than 10 µg/L.