Absorbance Enhancement of a Treated Tanzanian kaolin for Removal of Synthetic Dyes from Water

Abstract

The absorbance efficiency of local kaolin clay from Tanzania (Pugu kaolin) has been enhanced to improve its utilization in removal of textile dyes from water. The clay was acid-activated using H2SO4, after calcination at 750oC. Characterization by XRF, XRD, ATR-FTIR and Porosimeter showed kaolinite [Al2Si2O5(OH)4], silica (SiO2) and microcline [KAlSi3O8] as the main phases. Upon acid treatment, silica increased from 44.18% to 58.81% due to the appearance of tridymite, and alumina decreased from 26.70% to 12.74% due to disappearance of the kaolinite. Surface area increased from 15.36 to 149.61 m2 /g due to removal of acid-soluble impurities. The chemical composition showed decrease of Fe2O3 and increase of other major oxides. The impact of acid-activation on contact time, temperature, adsorbent dose, initial pH and absorbate concentration was investigated through batch adsorption technique using basic blue 9 (BB9) and direct red 28 (DR28) dyes. The results at optimal conditions of 3 hours contact time, 27oC temperature, 0.9 g adsorbent dose, initial pH of 11 and initial adsorbate concentration of 90 mg/L, showed that acid modification of the clay increased its capacity to adsorb BB9 from 96.82% to 99.91%, and DR28 from 86.33% to 95.04%. These findings established the influence of modifying the raw clay for its dye removal applications.