Treatment of acid mine drainage and chromium (VI) removal using synthesised chitosan composites blended with kenaf fibre and γ-Fe2O3 nanoparticles

• Published in: International journal of environmental science and technology (Tehran) 2023-04, Vol.20 (4), p.3599-3612
• Main Authors: Nkuna, C. N., Sadiku, E. R., Perry, G., Oboirien, B., Dludlu, M. K., Thompson, C.
• Format: Article
• Language: English
• Subjects: acid mine drainage; adsorbents; adsorption; Aquatic Pollution; chitosan; chromates; chromium; Earth and Environmental Science; Ecotoxicology; Environment; Environmental Chemistry; Environmental Science and Engineering; kenaf; kinetics; microstructure; nanoparticles; Original Paper; potassium; Soil Science & Conservation; South Africa; sulfates; temperature; Waste Water Technology; Water Management; Water Pollution Control
• ISSN: 1735-1472; 1735-2630
• DOI: 10.1007/s13762-022-04243-3

In this study, chitosan-blended composites were synthesised from chitosan, kenaf fibre and γ -Fe 2 O 3 nanoparticles. The chitosan-blended composites were used for the adsorption of chromium (VI) and sulphates from a potassium dichromate solution and an acid mine drainage (AMD) sample obtained from the CSIR, South Africa. Three chitosan-blended composites were synthesised namely CF(30) (Chitosan 70 and 30% kenaf fibre); CN20 (Chitosan 80 and 20% Fe 2 O 3 nanoparticles) and CF(20)N(20) (Chitosan 60%, kenaf fibre 20% and 20% Fe 2 O 3 nanoparticles). The adsorption of chromium (VI) on these three chitosan composites was compared with the adsorption on unmodified chitosan. The microstructure of chitosan and chitosan-blended composites was evaluated by SEM–EDS, XRD, FTIR and TGA. Batch experiments were carried out by varying the pH, temperature, adsorbent loading and contact time in order to optimise the conditions. The removal of chromium (VI) from the potassium dichromate solution was found to be optimal at 40 °C at a pH 2 when 1 g adsorbent was used. The composite CF(30) had the highest chromate ion ( Cr 2 O 7 2 - ) removal of ~ 70% at optimal conditions compared to the other prepared composites. The unmodified chitosan had a maximum chromate ion ( Cr 2 O 7 2 - ) removal of ~ 46% at optimal conditions. The unmodified chitosan and chitosan composites showed to follow a pseudo-second-order kinetic model, whereby adsorption of chromate ions was through chemisorption. The unmodified chitosan was found to remove ~ 98% of the chromium (VI) and ~ 70% sulphates, while the composite CF(20)N(20) had the highest removal compared to other chitosan-blended composites, with a removal of ~ 97% chromium (VI) and ~ 67% sulphate on AMD solution . Adsorption of chromium (VI) from AMD proved to be efficient since it is difficult to adsorb chromium (VI) at such a low concentration of 78 μg/L especially when sulphate concentration is at 21.82 g/L, whereby the adsorbent would had high affinity to adsorb sulphates instead of chromium (VI).