Pattern identification in data about unmodified waste eggshell application as an adsorbent for metal ion removal from aqueous media

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.