The effects of solution chemistry conditions and adsorbent surface properties on the adsorption of Ni(II) on Laiyang bentonite were investigated via the batch technique. Potentiometric and mass titration techniques were employed in the batch experimental methods, and the results showed that the point of zero net proton charge(PZNPC) of bentonite at different ionic strength denoted p HPZNPC to be 8.2±0.1. The removal of Ni(II) from the solution increased with an increasing bentonite dosage, with the maximum removal efficiency equating up to 99%. The adsorption of Ni(II) on bentonite increased with an increasing p H value at a p H value of <8.5, and reached a Ni(II) removal efficiency of >99% at a p H value of >10.2. The Ni(II) adsorption performance exhibited different responses to cations(K+, Na+) but was not influenced by the background anions(NO3-, Cl-, and Cl O4-). The adsorption of Ni(II) was dominated by the outer-sphere surface complexation and ion exchange with Na+/H+ on bentonite surface at low p H value, whereas the inner-sphere surface complexation and surface precipitation were the main adsorption mechanisms at high p H value. The adsorption isotherms of Ni(II) on bentonite can be described well by the Langmuir model. The thermodynamic parameters of adsorption, including the Gibbs free energy, the enthalpy change, and the entropy change, at different temperatures indicated that the adsorption of Ni(II) on bentonite was endothermic and spontaneous.
Cao XiaoqiangYan BingqiXue JianliangWang QianWang YapingHuang YongqingZhang YanLyu Xianjun
