The efficiency of raw and activated Pugu Kaolin clay in the removal of selected textile dyes from water

The study aimed at examining the efficiency of raw, thermally and acid activated Pugu kaolin clays in removing BB9 and DR28 representative textile dyes from polluted water. Thermal activation at 150 °C and acid activation with 0.2 M 112SO4 of RPK were performed to obtain TAPK and AAPK adsorbents, respectively. The adsorbents were characterized by XRF, XRD, ATR-FTIR and porosimeter instruments. RPK and TAPK adsorbents were composed of kaolinite, silica and microcline while AAPK consisted of silica and microcline phases. RPK was mainly composed of silica and alumina. The silica content increased from 44.18% to 46.95% and 58.81%, while alumina content decreased from 26.70% to 24.11% and 12.74% upon thermal and acid activation of RPK, respectively. Likewise surface area increased from 15.36 to 41.07 m2/g and 149.61 m2/g after thermal and acid activation of the RPK, respectively. Adsorption studies were performed through batch adsorption technique. Equilibrium concentration for determination of the adsorption efficiency were extracted from maximum absorbance measured at optimal wavelengths of 665 and 500 nm for BB9 and DR28 dyes, respectively. The optimal conditions of contact time of 3 h, temperature of 27 °C, adsorbent dose of 0.9 g, initial pH 11 for BB9 and 5 for DR28, and initial adsorb ate concentration of 90 mg/L resulted into maximum adsorption efficiency. AAPK, TAPK and RPK adsorbents exhibited strong affinity for BB9 with highest adsorption efficiency of 99, 91%, 98.73% and 96.82% compared to affinity for DR28 with adsorption efficiency of 95.04%, 88.52% and 86.33% for AAPK, TAPK and RPK, respectively. The small values of thermodynamic data (AG and OH) less than 20 kJ/mol suggested feasible, spontaneous, exothermic and physisorption adsorption process. Furthermore, the negative values of AS indicated increased orderedness of the adsorbates for both adsorb ate-adsorbent systems. The correlation coefficient, R values which are close to unity based on Langmuir and Freundlich models revealed feasible mono-multilayer BB9 and DR28 adsorption process while the surface of the adsorbents were homo-heterogeneous in nature. Significantly, this research study has revealed that raw and it’s activated Pugu kaolin clays have good adsorption efficiency enough to be used as ideal adsorbents in the removal of dyes from polluted water.