On the removal efficiency of copper ions in wastewater using calcined waste eggshells as natural adsorbents.

Eggshells offer many advantages as adsorbents, such as affordability without special preparations other than pulverization and calcination. However, the manufacturing industry generally has a severe problem with high concentrations of heavy metals in wastewater. The purpose of this study was to use eggshell byproducts and calcined eggshell treatment for the adsorption of copper in an aqueous solution. The reaction time, metal concentration, adsorbent dose, temperature, and pH were evaluated using primary factors followed by the response surface method (RSM) to investigate the optimum conditions for eggshell byproducts and calcined eggshell adsorption treatment. The results of the one-factor-at-a-time experiment showed that the optimal adsorption rate was obtained from treatment at 24 h, 25 mg/L, 10 mg, and 25 °C. In addition, the effect of pH on the adsorption rates of eggshells and eggshells with membrane were detected at pH values of 5 and 5.9 and found to be 95.2, 90.5, and 73.3%. The reaction surface experiment showed that the best adsorption rate reached 99.3% after calcination at 900 °C for 2 h and a 20 min reaction. The results showed that eggshells, eggshell membranes, eggshells with membrane, and calcined eggshells could be applied to remove copper ions from industrial wastewater. The adsorption capacity of the calcined eggshell is better than that of the non-calcined eggshell and has good neutrality in acidic industrial wastewater. Therefore, it is convenient and practical for practical production and application. Likewise, this study conveys promising findings in the context of improving wastewater treatment based on a circular economy approach to waste reuse in the food industry and represents a valuable direction for future research.