Adsorption of Heavy Metal Ions from Aqueous Solutions by Zeolite Based on Oil Shale Ash: Kinetic and Equilibrium Studies

Na-A zeolite was successfully synthesized via the alkaline fusion method with oil shale ash as the raw material. The adsorption capacity of it was tested by removing Cu²⁺, Ni²⁺, Pb²⁺ and Cd²⁺ from aqueous solutions. The results reveal the maximum adsorption capacity of adsorbent for Pb²⁺, Cu²⁺, Cd²⁺ and Ni²⁺ were 224.72, 156.74, 118.34 and 53.02 mg/g, respectively. The effects of contact time and pH value of solutions on the adsorption efficiency of the zeolite were evaluated. Besides, The equilibrium adsorption data and the batch kinetic data were correlated with Langmuir and Freundlich models and the pseudo-first-order and pseudo-second-order models separately. The results show that the Langmuir isotherm and the pseudo-second-order equation were more suitable for the adsorption of Na-A zeolite for the metal ions. In addition, Thermodynamic parameters of the adsorption(the Gibbs free energy, entropy, and enthalpy) were also evaluated and discussed. The results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions and the synthesized zeolite was an effective adsorbent for the removal of metal ions from aqueous solution.