Modification of natural zeolite by carboxylate compounds and minerals for removal of zinc ions from wastewater: equilibrium and kinetic studies

In this study, zeolite composite with different compounds (minerals containing: gypsum, gypsum–bentonite, bentonite, calcite and pumice, and carboxylates containing: tartrate, citrate and oxalate) was investigated as an adsorbent of zinc ions. The oxalate-loaded zeolite composite was recognized as the best composite to remove zinc. This composite was characterized by X-ray diffraction and FTIR spectroscopy. The effect of initial Zn(I) concentration and mass of adsorbent have been investigated on adsorption process. The equilibrium study was performed and followed by six different isotherm models which include two-parameter (Langmuir, Freundlich, Temkin and D–R) and three-parameter (Redlich–Peterson and Khan) models. The successful fitted results were obtained by using Langmuir model which indicated to homogeneity adsorption and the maximum adsorption capacity of oxalate-loaded zeolite composite for zinc ions (57 mg/g). Based on free energy of adsorption value (12 KJ/mol), interaction between zinc ions and oxalate-loaded zeolite composite is chemical adsorption, that is to say, ion exchange. The kinetic of adsorption has been investigated by considering four kinetic equations as pseudo-first-order, pseudo-second-order, intra-particle diffusion and Elovich models that kinetic mechanism is well described by pseudo-second-order model with correlation coefficient ( r2) more than 0.994. This means that amount of oxalate-loaded zeolite composite and concentration of Zn(II) are main rate of adsorption controller.