Comparative analysis of cationic dye adsorption efficiency of thermally and chemically treated Tanzanian kaolin

Abstract The effectiveness of thermal and acid modified locally available kaolin clay in Tanzania (Pugu clay), for removal of cationic dye from water systems were tested. The raw Pugu kaolin (RPK) was thermally-treated at 150oC for 7 hours and acid-leached with 0.2 M H2SO4 under reflux for 3 hours, to obtain thermally-activated Pugu kaolin (TAPK) and acid-activated Pugu kaolin (AAPK), respectively. The raw and modified clays were characterized by XRF, XRD, ATR-FTIR and Porosimeter for their mineralogical compositions, chemical compositions, specific surface areas and pore sizes. A comparative analysis of their respective adsorption efficiencies was carried out using basic blue 9 dye (BB9) as a representative adsorbate. The results revealed that while RPK was mainly composed of 44.18% silica and 26.70% alumina, the modified adsorbents had higher silica content of 46.95% and 58.81%; decreased alumina content of 24.11% and 12.74%, and increased surface areas from 15.36 to 41.07 m2/g and 149.61 m2/g, for TAPK and AAPK, respectively. Batch adsorption analysis indicated that AAPK and TAPK exhibited respective adsorption efficiency of 99.91% and 98.73% against BB9, compared to 96.82% of RPK. The Langmuir and Freundlich models with correlation coefficients close to unity indicated that the surface of the adsorbents were homo-heterogeneous in nature and exhibited mono-multilayer BB9 adsorption. This study has revealed that both raw and modified Pugu kaolin have good adsorption efficiency as ideal adsorbents in removal of cationic dyes from polluted water. Moreover, acid-activation resulted into a more effective adsorbent than thermal treatment.