Preparation of NaA and NaY zeolites from kaolin and their use as adsorbent for the removal of Ni2+ and Co2+ in aqueous solution

Abstract

Heavy metal ions can cause environmental problems and affect human health if they are not properly removed before waste water released into the environment. Adsorption is one of the most widely used method for removal of heavy metal ions due to its simplicity and efficiency. Among many adsorbents, NaA and NaY zeolites showed good ability to remove metal ions in aqueous solution due to their high ion exchange capacity. However, the cost of zeolites NaA and NaY, synthesized from pure chemical sources, is still quite high. Therefore, this paper presented the synthesis of NaA and NaY from kaolin, a commercial available and cheap material. Experimental results showed that kaolin calcined at 500°C was appropriate to be used as and source for synthesis of zeolite. NaA and NaY zeolites were synthesized by reaction at 100°C in 24 hours. NaA zeolite was synthesized in a gel with the molar ratio in term of 1.0 Al2O3/2.0 SiO2/1.6 Na2O/76 H2O and NaY zeolite was synthesized with the molar ratio of 1.0 Al2O3/3.7 SiO2/2.7 Na2O/76 H2O with the addition of from industrial fly ash. XRD results of both synthesized NaA and NaY zeolites showed that the diffraction peaks of these zeolites matched with simulated XRD pattern of NaA and NaY zeolite. Synthesized NaA and NaY zeolites were used as adsorbents to remove Ni2+ and Co2+ in aqueous solution. NaY zeolite showed the highest adsorption capacity of 56.5 mg/g and 58.2 mg/g for Ni2+ and Co2+, respectively. NaA zeolite showed higher metal removal efficiency than that of NaY zeolite, with the highest adsorption capacity for Ni2+ and Co2+ at 80 mg/g and 123.2 mg/g, respectively. Experimental data fit the pseudo-second-order model and Langmuir isotherm adsorption model well. The results showed that the removal of Ni2+ and Co2+ ions by NaA and NaY zeolites was of the .