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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. Al 3+  and Mn 2+ ) 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 m 2  g −1 ) and pH PZC  (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 HCO 3−  and SO 42− . The optimum rate of F −  removal occurred at pH 5; however, during the F −  removal, Al 3+  and Mn 2+  ions were released, respectively, from the AA (0.61 mg L −1  Al 3+ ) and from the AM ( 52 mg L −1  Mn 2+ ). Vermiculite used to remove these cations adsorbed about 86% Al 3+  and 90% Mn 2+ . However, only Al 3+  concentrations fell below the standard limit for drinking water of &lt;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 −1 F −  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.

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