Effects of Solution Chemistry Conditions and Adsorbent Sur-face Properties on Adsorption of Ni(II) on Laiyang Bentonite

The effects of solution chemistry conditions and adsorbent surface properties on the adsorption of Ni(II) on Lai-yang 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 differ-ent ionic strength denoted pHPZNPC to be 8.2±0.1. The removal of Ni(II) from the solution increased with an increasing ben-tonite dosage, with the maximum removal efficiency equating up to 99%. The adsorption of Ni(II) on bentonite increased with an increasing pH value at a pH value of 99% at a pH value of >10.2. The Ni(II) adsorption performance exhibited different responses to cations (K+, Na+) but was not influenced by the back-ground anions (NO3-, Cl-, and ClO4-). The adsorption of Ni(II) was dominated by the outer-sphere surface complexation and ion exchange with Na+/H+ on bentonite surface at low pH value, whereas the inner-sphere surface complexation and surface precipitation were the main adsorption mechanisms at high pH 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.