Removal of Chromium Species by Adsorption: Fundamental Principles, Newly Developed Adsorbents and Future Perspectives

Parameter Influence, Characterization and Adsorption Mechanism Studies of Alkaline-Hydrolyzed Garcinia kola Hull Particles for Cr(VI) Sequestration

Despite the regulations by The World Health Organization (WHO) on the permissible limit of chromium, many industries still discharge wastewater polluted with chromium into the environment irrationally. This poses a lot of risk to aquatic lives and humans because of its carcinogenic and toxic attributes. Thus, treatment of industrial wastewater polluted with chromium is highly imperative before its disposal. Nonetheless, the hulls generated from Garcinia kola in our various farmlands also causes environmental pollution when dumped unknowingly. In this present study, Garcinia kola hull particles (GK-HP) was hydrolyzed using NaOH and applied as adsorbent for Cr(VI) sequestration. The raw Garcinia kola hull particles (rGK-HP) and modified Garcinia kola hull particles (cMGK-HP) were characterized using Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM), powder X-ray diffractometry (XRD), Fourier-Transform-Infrared (FTIR), thermogravimetric analysis (TGA), energy dispersive spectroscopy (EDS) and point of zero charge (pHpzc). The influence of pH, adsorbent dose, contact time, temperature and adsorbate initial concentration on Cr(VI) sequestration were examined. The cMGK-HP was able to remove 96.25% of Cr(VI) from solution and proved to be effective than rGK-HP. The amount of Cr(VI) removed from solution decreased as the pH and adsorbate initial concentration were increased. However, the amount increased as the adsorbent dose, contact time and temperature were increased. Change in morphological structure, textural property, spectral peak, phase composition and adsorbents chemical composition before and after Cr(VI) sequestration from solution were proved by SEM, BET, FTIR, XRD, and EDS analyses respectively. The isotherm and kinetic studies suggest Cr(VI) adsorption on adsorbents' surface to be monolayer in nature and adsorption data to be well-fitted into pseudo second order model respectively. The cMGK-HP possessed excellent reusability attribute and high thermal stability as shown by TGA. In conclusion, cMGK-HP could effectively be used as an adsorbent for Cr(VI) sequestration from solution.