Characterization and properties of hydroxyapatite with KOH modification for lead (II) removal

Adsorption has been widely used and proven to be a solid method to remove heavy metals from wastewater. Hydroxyapatite (HAP) is one of the adsorbents that can be produced from waste as raw materials (e.g., chicken bones, eggshells, cockle shells) which ultimately led to the utilization of biomaterial. Moreover, the cockle shell is a promising raw material as it is rich in calcium carbonate and abundantly available. Hence, this study aims to enhance the performance of cockle shell-based HAP for the lead (II) removal from the aqueous solution. The enhancement is done using a chemical modification of hydroxyapatite with the base solution of KOH. The concentration of KOH varies from 1.5 M, 2 M, and 2.5 M. The characterization of the sample was done using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), Thermogravimetric (TGA), and Zeta Potential to analyze the properties of hydroxyapatite after the treatment with KOH. Furthermore, the removal efficiency of lead (II) was performed using a batch adsorption experiment and Atomic Absorption Spectroscopy (AAS) to measure the final concentration of lead in the solution. The results of AAS in this study show a promising increment due to the chemical modification of KOH. The modified hydroxyapatite has a higher removal efficiency compared to the unmodified hydroxyapatite which is up to 73.35 % with the treatment using 2.5 M KOH. This has proven the ability of KOH to increase the adsorption performance of hydroxyapatite which happened due to the higher electrostatic interaction. The adsorption was also supported by the ion exchange mechanism of hydroxyapatite and lead ions. In this research, Langmuir is found to be the best fit of an isotherm study to explain the adsorption process of hydroxyapatite which indicates that the molecules are adsorbed on fixed sites where each site only holds one adsorbate molecule with the same energy. Moreover, hydroxyapatite can retain the removal efficiency of around 60 % after 5 cycles of usage.