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 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 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.

摘要

在巴西的一些含水层中，地下水中的氟化物浓度可能很高，因此这些水在饮用前应进行处理。本研究评估了在水脱氟中通过两步加热制备的氧化锰涂层氧化铝 (AM) 的性能。还检查了从氧化铝中释放的二次污染物（例如 Al ³⁺和 Mn ^{2+ ），因为它们被蛭石去除。}氧化锰涂层过程改变了活性氧化铝 (AA) 的一些性质，分解了结晶相并降低了一些参数，例如比表面积（从 295.90 到 94.51 m ²  g ^-1）和 pH _PZC（从 7.34 到 5.74 ）。这些变化提高了氧化铝去除 F 的效率和动力学⁻来自合成溶液和地下水（从 80%/16 小时到 100%/1 小时）。这种效率不受地下水中其他阴离子的影响，例如 HCO ₃ ^-和 SO ₄ ^2-。F ^-去除的最佳速率发生在 pH 值为 5 时；然而，在F ^-去除过程中，Al ³⁺和Mn ²⁺离子分别从AA（0.61 mg L ^-1 Al ³⁺）和AM（52 mg L ^-1 Mn ²⁺）中释放出来。用于去除这些阳离子的蛭石吸附了大约 86% 的 Al ³⁺和 90% 的 Mn ²⁺。但是，只有 Al ³⁺浓度低于<0.5 mg L ^-1的饮用水标准限值。因此，AA 具有不含 Mn 的优点，3 小时后溶液中的 F ^-浓度保持在 5 mg L ^-1 F ^-低于标准限值 1.5 mg L ^-1。这项研究表明，根据地下水的特性，AA 可能比涂层氧化铝更有效和更可持续。