Abstract
Chromium has emerged as one of the extremely toxic heavy metals whose pollution has raised a lot of concerns globally. Due to the adverse impacts that hexavalent chromium (Cr(VI)) has on human health, a number of techniques such as; chemical precipitation, ion exchange and membrane filtration and so on have been dedicated to the remediation of this metal. However, such techniques generally suffer drawbacks related to low efficiency or high installation and operational costs.
The present study was therefore aimed at the use of tea factory waste (TFW) collected from a tea factory in Mpumalanga, South Africa, as a low cost adsorbent for the removal of toxic hexavalent chromium from water. The adsorbent was characterized using ATR-FTIR, FE-SEM, XRD, BET, etc. Batch and fixed bed studies were performed to determine its efficiency of TFW for Cr(VI) adsorption. From batch studies, effect of critical parameters such as pH, temperature, adsorbent dose, initial adsorbate concentration, coexisiting ions and contact time were investigated. The adsorption of Cr(VI) on TFW followed Langmuir model with maximum adsorption capacity of 192.30 mg/g at pH 2, at 25 °C. The adsorption was favored at low pH values due to the nature of functional groups found on the TFW. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were also calculated, and revealed that the adsorption process is endothermic and spontaneous in nature. Furthermore, the adsorption data were modelled using various kinetic models such as pseudo-first-order, pseudo-second-order and intraparticle diffusion model, and the results indicate that the pseudo-second order model best describes the kinetics of the adsorption of Cr(VI) on TFW. From fixed bed studies, effects of flow rate, initial concentration and bed mass was also investigated to check the performance of the adsorbent. 9.54 L of contaminated water was successfully treated with 6 g of TFW at 50 mg/L influent concentration. The performance of the TFW bed highly depended on initial influent concentration, flow rate and adsorbent bed mass.
M.Sc. (Chemistry)