Comparative assessment of thermal and thermochemical activation methods of South African kaolinite for effective adsorptive sequestration of humic acid from aqueous media

ABSTRACT

Current research has demonstrated that the adsorption capacity of raw kaolin is considerably low. Advances in kaolin activation for enhanced utility and improved adsoptibility of pollutants include thermal treatment, acidification, or combined treatment. In this work activation of South African kaolinite with sulfuric acid and calcination is studied. Comparing the FTIR spectra of the activated kaolin i.e thermochemical treated kaolin (HAK) and thermal treated kaolin (HK) with raw kaolin the following main observation were noted; the bands attributable to Si-O stretching vibration (1023 and 1095 cm⁻¹) increased in intensity by 61 and 59% for HK and HAK, respectively. Increasing the humic acid (HA) concentration (0.5–20 mg/L) increased the HA uptake for both adsorbents, HK increased from 0.52 to 0.75 mg/g while HAK increased from 0.59 to 0.86 mg/g. The adsorption of HA was delineated better by a pseudo-second-order model in both cases (Q_e = 0.810; 0.793 mg/g for HK and HAK, respectively). From the synchronous spectra, two auto peaks were observed at (1650;1650) and (3246;3246) indicating concurrent and similar HA adsorption behavior on either of the adsorbents. From the results, it can be concluded that activation of kaolin improved its adsoptibility capacity for HA.

KEYWORDS:

• Adsorption
• kaolinite
• humic acid
• acidification
• calcination
• isotherm

Acknowledgements

The authors are grateful for funding received from the University of South Africa, through the Postdoctoral fellowship fund

Disclosure statement

No potential conflict of interest was reported by the author(s).