Eggshell as an adsorbent for removing dyes and metallic ions in aqueous solutions

Abstract

Contamination of water with metallic ions and dyes leads to several impacts on the environment and human health. The adsorption comes as an economic and simple process to remove these pollutants from water. The use of residues as adsorbents can make the process even more sustainable and cheaper. This work proposes the use of a solid residue (eggshells) as an adsorbent of dyes - Reactive Blue 198 (RB) and Direct Black 22 (DB) - and metallic ions (Cd2+ and Cr3+). The solid was characterized by SEM, EDS, FTIR, BET and pH-PZC; and the adsorption process was investigated for the adsorbent dosage, kinetic and isotherm analysis. The quantifications of dyes and metallic ions were determined by UV-VIS spectroscopy and atomic absorption spectroscopy, respectively. The eggshells presented a porous structure, with a surface area of 435 cm2.g−1, composed mainly of CaCO3 and a neutral surface charge at pH 7. It was verified that the phenomenon occurs by chemical interactions between the adsorbents and the adsorbates, having the external transport as the limit step. Regarding the isotherm models, the dyes fit the Langmuir model and the metallic ions to the Dubinin-Radushkevich model. 1.0 g of eggshells was sufficient to adsorb 96 % of RB; 97 % of BD; 99 % of Cd2+; and 95 % of Cr3+. Thus, the process analyzed in this research shows to be a promising alternative for removing these water pollutants while giving use to a solid residue.

Keywords

• Hazardous pollutants
• Textile dye wastewater
• Bioadsorbent
• Batch adsorption
• Wastewater treatment