Department of Integrated System Engineering, Hankyong National University, Anseong, 17579, Republic of Korea.
Department of Environmental and Safety Engineering, Ajou University, Suwon, 16499, Republic of Korea.
Environ Sci Pollut Res Int. 2021 Jul;28(27):35887-35901. doi: 10.1007/s11356-021-13284-z. Epub 2021 Mar 7.
In this study, the use of eggshells was suggested as an adsorbent for fluoride removal, and their mechanism of fluoride removal was investigated. The eggshells underwent thermal treatment to improve their adsorption capacity; 800 °C was found to be the optimal temperature for treatment. Eggshells thermally treated at 800 °C (ES-800) were mainly composed of Ca (82.4%) and C (15.9%), and the peaks of ES-800 obtained from X-ray diffraction (XRD) corresponded to calcite, portlandite, and lime. Fluorine adsorption by ES-800 reached 70% of the equilibrium adsorption amount within 15 min and gradually increased until 24 h. The maximum adsorption capacity of ES-800 at pH 7 and 25 °C was 258.28 mg/g, which is 18 times larger than that of activated alumina; this is classified as the best available technology by the United States Environmental Protection Agency. Both enthalpy and entropy increased in the process of fluoride adsorption onto ES-800. Fluoride adsorption of ES-800 decreased from 59.16 to 11.85 mg/g with an increase in pH from 3 to 11. Fluoride adsorption decreased in the presence of anions, whose impact follows the order: HPO > HCO >> SO > Cl. XRD, and X-ray photoelectron spectroscopy analysis revealed that fluoride removal was achieved by the formation of calcium fluorite (CaF). Thus, it can be concluded that eggshells can function as highly efficient adsorbents for fluoride removal, replacing bone char and activated alumina; further, their adsorption capacity can be improved by thermal treatment.
在这项研究中，蛋壳被建议作为一种用于去除氟化物的吸附剂，并且研究了其去除氟化物的机制。蛋壳经过热处理以提高其吸附能力；发现 800°C 是最佳的处理温度。在 800°C 下热处理的蛋壳（ES-800）主要由 Ca（82.4%）和 C（15.9%）组成，并且 ES-800 的 X 射线衍射（XRD）峰对应于方解石、水合钙和石灰。ES-800 对氟的吸附在 15 分钟内达到平衡吸附量的 70%，并逐渐增加直到 24 小时。在 pH 7 和 25°C 下，ES-800 的最大吸附容量为 258.28mg/g，是活性氧化铝的 18 倍；这被美国环境保护署归类为最佳可行技术。氟化物吸附到 ES-800 上的过程中焓和熵都增加了。随着 pH 值从 3 增加到 11，ES-800 的氟化物吸附从 59.16mg/g 降低到 11.85mg/g。阴离子的存在会降低氟化物的吸附，其影响顺序为：HPO > HCO > > SO > Cl。XRD 和 X 射线光电子能谱分析表明，氟化物的去除是通过形成氟化钙（CaF）来实现的。因此，可以得出结论，蛋壳可以作为去除氟化物的高效吸附剂，替代骨炭和活性氧化铝；此外，通过热处理可以提高其吸附能力。
