Adsorption performance and mechanism of different modified eggshell membranes for Ni(II) in aqueous solutions

Eggs are high-quality protein commonly consumed around the world, which leading to the generation of large amounts of waste eggshell (ES) and eggshell membrane (ESM). In this study, the natural ESM was prepared and modified by thioglycolate, polyethyleneimine, hydrogen peroxide, and glutaraldehyde, respectively. The different membranes were characterized by scanning electron microscope, contact angle meter, particle analyzer, and FTIR spectra. The effects of pH, contact time, temperature, and Ni(II) concentration on the adsorption capacity of membranes were studied in detail. The results displayed that thioglycolate-modified ESM was the best adsorbent to Ni(II) in five membranes, and its maximum adsorption amount was 2.07 times to ESM. Thermodynamic parameters for Ni(II) adsorption were calculated. The negative Delta G degrees indicated that adsorption were spontaneous processes. Three models were employed to fit the data of equilibrium concentrations. According to the Es of DR model, we inferred that the combinations of Ni(II) and membranes are physical adsorption. Furthermore, the modification processes of ESM and the adsorption mechanism of Ni(II) were speculated. After 6 cycles, the adsorption capacities of membranes were lost no more than 40%. So modified ESM had the potential to be applied to industrial production for adsorption of Ni(II).