Synthesis and characterization of zinc oxide-kaolinite composite and its effect on the removal of aqueous lead(ii) ions

Abstract

The presence of ZnO coating significantly enhanced the adsorption of Pb²⁺ ions by kaolinite. This paper investigated synthesis, characterization of ZnO-kaolinite composite and its application in Pb²⁺ ions removal. Synthesis involved trimetric process and characterization involved the use of standard laboratory procedures. Lead adsorption on ZnO-kaolinite composite was investigated in batch experimental condition at ambient temperature. Reaction mechanism indicated less than one proton coefficient. The mass transfer rates were higher than values for the bare kaolinite. In addition, the intraparticle diffusion contained intercept c equals 592.31, ≠ 0. This was higher than the value for the uncoated kaolinite. Effect of Pb²⁺ initial concentration, concentration of particle and ageing, exhibited differences in magnitude and in other situations, different characteristics when compared with bare kaolinite. Reactions based on Pb²⁺ initial concentration, indicated that the active and reactive sites of the ZnO-kaolinite composite gradually became saturated as the concentration was increased. Reactions based on solid concentration -Cp, demonstrated a complex change in the capacity of adsorption over different Pb²⁺ concentrations (10mgL^-1 to 40mgL^-1).and solid concentrations (2gL^-1 to 10gL^-1). Here, reduction in specific surface area, particle size increase, mineral aggregation and concentration gradient effect, controlled the complex changes in adsorption. Based on pH variation, differences in magnitude and characteristics in adsorption percentage (89% to 93%), was linked to deprotonation, hydrolysis, the reactive support of ZnO coating and increased reorganization of active sites. This was because as pH was increased, protonation was reduced, and hydroxylation increased.