Comparison of Ni2+ sorption to bare and ACT-graft attapulgites: Effect of pH, temperature and foreign ions

Attapulgite was investigated to remove Ni2+ from aqueous solutions because of its strong sorption ability. Herein, the sample of attapulgite was modified with ammonium citrate tribasic (ACT) and used as an adsorbent to remove Ni2+ from aqueous solutions. XRD and FTIR analysis indicated that ACT was successfully grafted on attapulgite surfaces. The results indicated that ACT-attapulgite was better than bare attapulgite in the removal of Ni2+ from aqueous solutions. Sorption of Ni2+ on ACT-attapulgite was mainly dominated by ion exchange or outer-sphere complexes at low pH values, and by inner-sphere complexes or surface precipitation at high pH values. The thermodynamic data indicated that the sorption of Ni2+ to ACT-attapulgite hybrids was an endothermic process and was enhanced with increasing temperature. ACT-attapulgite is a suitable material for the preconcentration of Ni2+ from large volume of solutions and can be used in wastewater treatment because of its negative surface charge and large surface areas.