Groundwater defluoridation efficacy of manganese-oxide-coated alumina prepared via two-step heating.

Fluoride concentrations in groundwater can be high in some Brazilian aquifers and therefore these waters should be treated before consumption. This study assessed the properties of Mn-oxide-coated alumina (AM) prepared by two-step heating in water defluoridation. The release of secondary contaminants (e.g. Al3+ and Mn2+) from alumina was also examined, as their removal by vermiculite. The process of Mn-oxide coating changed some properties of the activated alumina (AA), decomposing the crystalline phases and reducing some parameters, e.g. specific surface area (from 295.90 to 94.51 m2 g-1) and pHPZC (from 7.34 to 5.74). These changes increased the efficiency and kinetics of alumina in removing F- from synthetic solutions and groundwater (from 80%/16 h to 100%/1 h). This efficiency was not affected by the presence of other anions in groundwater, such as HCO3- and SO42-. The optimum rate of F- removal occurred at pH 5; however, during the F- removal, Al3+ and Mn2+ ions were released, respectively, from the AA (0.61 mg L-1 Al3+) and from the AM ( 52 mg L-1 Mn2+). Vermiculite used to remove these cations adsorbed about 86% Al3+ and 90% Mn2+. However, only Al3+ concentrations fell below the standard limit for drinking water of <0.5 mg L-1. Therefore, AA has the advantage of not containing Mn, and after 3 h kept F- concentrations in solutions 5 mg L-1F- below the standard limit of 1.5 mg L-1. This study revealed that, depending on the groundwater characteristics, AA may be more efficient and sustainable for defluoridation than coated alumina.

Geochemical evolution, residence times and recharge conditions of the multilayered Tubarão aquifer system (State of São Paulo - Brazil) as indicated by hydrochemical, stable isotope and 14C data.

The Tubarão aquifer system constitutes a very complex, multilayered aquifer enclosed in the Paraná basin (central-southern part of Brazil). Despite the relatively low productivity of wells, groundwater represents an important source of water for the very populated and industrialized zones of the State of São Paulo. An extensive water sampling campaign was carried out followed by hydrochemical and isotopic (δ 2H, δ 18O, δ 13C and 14C) studies, aiming at a better understanding of the aquifer's geochemical evolution, recharge processes, and its groundwater residence times. Two main hydrochemical facies were recognized and divide the aquifer in two portions. The shallow portion - the active hydrological zone of the aquifer - is characterized by the Ca-HCO3 water type, evolving as a system open to atmospheric CO2. Mean residence times are typically lower than 5000 years. The lower portion is mostly characterized by the stagnant, Na-HCO3 water type, evolving under closed system conditions. Residence times average up to 15,000 years, but can reach 44,000 years, which indicates the exploitation of (possibly non-renewable) fossil waters. This study contributes to the establishment of proper policies regarding the sustainable groundwater exploitation of the Tubarão aquifer system.