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

In this study, chitosan-blended composites were synthesised from chitosan, kenaf fibre and gamma-Fe2O3 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% Fe2O3 nanoparticles) and CF(20)N(20) (Chitosan 60%, kenaf fibre 20% and 20% Fe2O3 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 degrees C at a pH 2 when 1 g adsorbent was used. The composite CF(30) had the highest chromate ion (Cr2O72-) removal of similar to 70% at optimal conditions compared to the other prepared composites. The unmodified chitosan had a maximum chromate ion (Cr2O72-) removal of similar to 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 similar to 98% of the chromium (VI) and similar to 70% sulphates, while the composite CF(20)N(20) had the highest removal compared to other chitosan-blended composites, with a removal of similar to 97% chromium (VI) and similar to 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 mu g/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).

Automated summary

Chitosan-blended composites were synthesized and studied for their adsorption of chromium (VI) and sulphates. The composite CF(30) exhibited the highest removal efficiency for chromate ions.