Effect of environmental conditions on the sorption of radiocobalt from aqueous solution to treated eggshell as biosorbent

Carbonate hydroxylapatite (CHAP), prepared from eggshell waste, was used to remove Co-60(II) from aqueous solutions. The sorption of Co-60(II) on CHAP as a function of contact time, pH, ionic strength and foreign ions in the absence and presence of humic acid and fulvic acid under ambient conditions was studied. The sorption of Co-60(II) on CHAP was strongly dependent on pH and ionic strength. The thermodynamic parameters (Delta H (0), Delta S (0), Delta G (0)) of Co-60(II) sorption on CHAP were calculated from the temperature-dependent sorption isotherms, and the results indicated that the sorption process of Co-60(II) on CHAP was endothermic and spontaneous. At low pH, the sorption of Co-60(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on CHAP surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. Experimental results also indicated that CHAP was a suitable low-cost adsorbent for pre-concentration and solidification of Co-60(II) from large volumes of aqueous solutions.