Absorbance enhancement of a treated Tanzanian kaolin for removal of synthetic dyes from contaminated water

Abstract

Kaolin possesses unique features suitable for removing pollutants from aqueous solutions, in this regard, improving its effectiveness as an adsorbent is important. This study focused on refining the absorbance efficiency of Pugu kaolin clay from Tanzania to enhance its utilization in removing textile dyes from contaminated water. The process involved acid-activation after calcination at 750oC. Characterization using X-ray Fluorescence (XRF), X-ray diffraction (XRD), Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Porosimeter techniques revealed the presence of kaolinite [Al2Si2O5(OH)4], silica (SiO2) and microcline [KAlSi3O8] as the main phases. Acid treatment resulted in an increase in silica content from 44.18% to 58.81% due to the appearance of tridymite, while alumina decreased from 26.70% to 12.74% due to the removal of kaolinite. Surface area significantly expanded from 15.36 to 149.61 m2/g as acid-soluble impurities were eliminated. Chemical composition was also altered, with a decrease in Fe2O3 and increase in other major oxides. The impact of acid activation on the adsorption capacity of the clay was investigated by studying various parameters such as contact time, temperature, adsorbent dose, initial pH and adsorbate concentration. Basic Blue 9 (BB9) and Direct Red 28 (DR28) dyes were used as model adsorbates. The results obtained 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 underscore the positive impact of modifying the raw clay, enhancing its suitability for dye removal applications.