Development and optimization of hydroxyapatite/kaolin-based ceramic materials as potential adsorbents for water purification

In this study, porous hydroxyapatite/kaolin-based ceramic (PHKC) materials were fabricated using beneficiated kaolin, starch as a pore former, and hydroxyapatite (HAp) as potential adsorbents for water purification. The effect of different raw materials content and sintering temperature on the physical, chemical, and mechanical properties of the ceramic materials was investigated, and grey relational analysis was used to optimize the process. A PHKC filter was produced using parameters from the grey relational analysis and the filter was used to treat tannery wastewater. The pH, electrical conductivity (EC), total dissolved solids (TDS), temperature, chromium, and turbidity of the raw tannery effluent and treated effluent were determined. The volumetric porosity of the PHKC materials ranged between 35 and 43% and this shows that all samples obtained in the study can be considered as porous materials. Surface area analysis (B.E.T) showed that the samples with pore formers had a greater number of small pores, and increasing the sintering temperature led to the reduction of the number of pores. The brittleness index of the ceramic materials were in the range of 0.19 and 0.46. Using the grey relational analysis, the sample with the highest grey relational grade was sample S8 (0.72), and the least was sample S3 (0.38). From the findings, it could be concluded that the ceramic samples (S3 and S8) have inherent properties for use as adsorbent materials in the purification of wastewater. From the adsorption experiments, the chromium removal rates of 67.91 %, 98.67%, and 98.74% were obtained for kaolin, kaolin + HAp, and kaolin + HAp + starch filters, respectively. The filter made from the optimum material composition of kaolin, HAp, and starch gave the maximum adsorption capacity of chromium (98.74%) at pH 7.12, and temperature of 25.23°C, while the turbidity removal was 97.07%.