In recent years, a significant increase in the amount of research published about the application of eggshells for the removal of metal ions from aqueous solutions has been observed. The paper presents different aspects of metal adsorption from aqueous solutions on untreated eggshells. Pretreatment procedures and tested parameters for the adsorption differ significantly across all the reviewed data, providing a source of variance for the results. For untreated eggshells, the range of the reported BET surface area is from 0.07 m2/g to 8.941 m2/g. Correlation between particle size and BET surface area has been highlighted. Reported removal efficiencies for the untreated eggshell have been compared. Reported results show that eggshell is most employed for the removal of Pb(II), Cd(II), and Cu(II) from aqueous solutions. Eggshell capacity to remove metal ions from the main group elements has also been demonstrated. While results look promising, not enough data are present to make reliable conclusions about its efficiency with other (mainly transition) metal ions – which makes it a possible research direction. Based on the reported data, multiple removal pathways are involved. Several eggshell modification methods and possibilities of creating new adsorbents using eggshells only as a part of the raw material have been assessed. Finally reported eggshell modification methods have been assessed and it is clear that to compare different material’s effectiveness as an adsorbent, comparing only materials adsorption capacities is insufficient. Certain environmental water pollution removal studies using adsorption demand further study, such as metal ion specification in aqueous solution, in different processing water, and even in wastewater.

中文翻译：

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未改性废蛋壳作为吸附剂从水介质中去除金属离子的数据模式识别

近年来，关于应用蛋壳去除水溶液中金属离子的研究数量显着增加。本文介绍了未经处理的蛋壳从水溶液中吸附金属的不同方面。预处理程序和测试的吸附参数在所有审查的数据中都有显着差异，为结果提供了差异来源。对于未经处理的蛋壳，报告的 BET 表面积范围为 0.07 m2/g 至 8.941 m2/G。颗粒尺寸和 BET 表面积之间的相关性已得到强调。已对未经处理的蛋壳的去除效率进行了比较。报告的结果表明，蛋壳最常用于去除水溶液中的 Pb(II)、Cd(II) 和 Cu(II)。蛋壳从主族元素中去除金属离子的能力也已得到证明。虽然结果看起来很有希望，但目前还没有足够的数据来对其与其他（主要是过渡）金属离子的效率得出可靠的结论，这使其成为可能的研究方向。根据报告的数据，涉及多种去除途径。已经评估了几种蛋壳改性方法以及仅使用蛋壳作为原材料的一部分来创建新吸附剂的可能性。最后对报道的蛋壳改性方法进行了评估，很明显，要比较不同材料作为吸附剂的有效性，仅比较材料的吸附能力是不够的。某些利用吸附去除环境水污染的研究需要进一步研究，例如水溶液、不同处理水、甚至废水中的金属离子规格。