AAS, XRPD, SEM/EDS, and FTIR studies of the effect of calcite and magnesite on the uptake of Pb2+ and Zn2+ ions by natural kaolinite and clinoptilolite

Abstract

In this study, the effect of magnesite and calcite on the uptake of lead and zinc ions by mixtures of these carbonates with kaolinite and clinoptilolite was investigated at various loadings and mixture compositions. The concentration of both ions in the liquid phase was in measured using AAS, while XRPD, SEM/EDS, and FTIR techniques were used in characterizing the solid samples. Thestudy included the determination of kinetics and sorption isotherms of lead and zinc on pure kaolinite and clinoptilolite. Moreover, the sorption behavior of lead and zincat different concentrations and pH conditions was investigated on mixtures of calcite and magnesite with kaolinite and clinoptilolite at carbonate mass percentage compositions of 5, 10, 25, 60 in addition to pure calcite and magnesite. The morphologies of theformed precipitates, the plausible structural change in the lattice of calcite, magnesite, kaolinite, and clinoptilolite originating from sorption of lead and zinc ions was examined. According to obtained results, the sorption affinity of kaolinite and clinoptilolite towards lead is larger than their affinity towards zinc. Within the operating experimental conditions, the sorption capacity increased with increasing the amountsof calcite, and magnesite. The overall order of retention of lead and zinc was observed as magnesite . calcite> clinoptilolite> kaolinite under neutral and alkaline pH conditions and high loadings. When the initialconcentration of zinc and lead ions is raised to saturation conditions, rapid overgrowth of cerussite and hydrozincite was observed. Increasing the initial pH to 10,0 causedenhancement in the dissolution of calcite and magnesite, leading to the enhancingthe precipitation of hydrozincite, and an increased formation of hydrocerussite instead ofcerussite. The uptake of Zn2+ and Pb2+ions by calcite and magnesite have lead to modifying the geometry of the carbonate groups, the thing reflected as variation in their vibrational bands.