Synthesis and Characterization of Zeolite-A from Kombolcha Kaolin by Hydrothermal Method for the Removal of Mg2+and Ca2+ from Aqueous Solution

Abstract

Zeolite-A is one of the most important synthetic Zeolites especially in water softening with high ion exchange ability due to its low Si/Al ratio. In this study, Zeolite-A was synthesized using a hydrothermal method from Kombolcha kaolin, and its adsorptive removal efficiency for Ca2+ and Mg2+ was investigated. The material prepared as such was characterized using different instruments including XRD, SEM, FTIR, and TGA. The Powder X-ray diffraction (XRD) patterns clearly show the presence of the characteristic 2𝜃 peaks (12.32 and 24.92°) of kaolin. X-ray diffraction measurements 2𝜃 peaks (7.18, 10.16, 12.44, 16.12, 21.68, 24.02, 26.14, 27.16, 30.00, 32.56, and 34.22°) and scanning electron micrographs clearly show the morphology of Zeolite-A. Characteristic OH, Al-OH, Si-OH, and Si-O-Al bands were confirmed in samples with Infrared spectroscopy studies. The thermal analysis indicated that the kaolin sample undergo de-hydroxylation from 563.73℃ to about 700 ℃ and converted to metakaolin. The potential of the material to remove Ca2+ and Mg2+ ions from water sample was evaluated using EDTA titration. Batch adsorption experiments demonstrated that solution pH, the adsorbent dose, contact time, initial concentration, and temperature have significant effects on Ca2+ and Mg2+ ions removal. Using the optimized experimental parameters, removal percentages 98.27 for Ca2+ and 97.12 for Mg2+ were obtained at pH 10, contact time 30 min, initial concentration 250 mg/L, and adsorbent dose of 0.5 g. In the Freundlich isotherm model, R2 values for Ca2+ and Mg2+ adsorption were found to be 0.9992 and 0.9985, respectively. The obtained highest R2 values for the Freundlich isotherm are approximately equal to unity that confirms the experimental data is well-fitted to the model and pseudo-second-order kinetic model, which suggests that the applicability of the model to the adsorption of Ca2+ and Mg2+ by Zeolite-A. Based on this study, it can be concluded that zeolite-A was successfully synthesized from Kombolcha kaolin by using a hydrothermal method and the results obtained showed that it can be used as an effective adsorbent for the removal of Ca2+ and Mg2+ ions from aqueous solution