Saraiva ÍCG, Ezaki S, Calabria GD, Shinzato MC. Groundwater defluoridation efficacy of manganese-oxide-coated alumina prepared via two-step heating.
Environ Technol 2022;
43:2684-2696. [PMID:
33615995 DOI:
10.1080/09593330.2021.1894242]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Accepted: 02/17/2021] [Indexed: 06/12/2023]
Abstract
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.
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