Instituto de Ciências Ambientais, Químicas e Farmacêuticas da Universidade Federal de São Paulo, Diadema, Brazil.
Instituto Geológico - Secretaria de Infraestrutura e Meio Ambiente, São Paulo, Brazil.
Environ Technol. 2022 Jul;43(17):2684-2696. doi: 10.1080/09593330.2021.1894242. Epub 2021 Mar 4.
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 and Mn) 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 g) and pH (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 and SO. The optimum rate of F removal occurred at pH 5; however, during the F removal, Al and Mn ions were released, respectively, from the AA (0.61 mg L Al) and from the AM ( 52 mg L Mn). Vermiculite used to remove these cations adsorbed about 86% Al and 90% Mn. However, only Al concentrations fell below the standard limit for drinking water of <0.5 mg L. Therefore, AA has the advantage of not containing Mn, and after 3 h kept F concentrations in solutions 5 mg LF below the standard limit of 1.5 mg L. This study revealed that, depending on the groundwater characteristics, AA may be more efficient and sustainable for defluoridation than coated alumina.
地下水中的氟化物浓度在巴西一些含水层中可能很高，因此这些水在饮用前应进行处理。本研究评估了两步水热处理制备的 Mn 氧化物包覆氧化铝（AM）在除氟中的性能。还研究了氧化铝中释放的次生污染物（如 Al 和 Mn），因为它们可以被蛭石去除。Mn 氧化物涂层的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 降至 94.51 m²/g）和 pH 值（从 7.34 降至 5.74）。这些变化提高了 AA 从合成溶液和地下水（从 80%/16 h 到 100%/1 h）中去除 F 的效率和动力学。这种效率不受地下水中原位存在的其他阴离子（如 HCO 和 SO）的影响。最佳的 F 去除速率发生在 pH 5；然而，在 F 去除过程中，Al 和 Mn 离子分别从 AA（0.61 mg/L Al）和 AM（52 mg/L Mn）中释放出来。用于去除这些阳离子的蛭石分别吸附了约 86%的 Al 和 90%的 Mn。然而，只有 Al 浓度低于饮用水 <0.5 mg/L 的标准限值。因此，AA 的优势在于不含有 Mn，并且在 3 h 后，溶液中的 F 浓度保持在 5 mg/L 以下，低于 1.5 mg/L 的标准限值。本研究表明，根据地下水的特性，AA 可能比包覆氧化铝更高效、更可持续地用于除氟。
