Adsorptive Removal of Chromium from Tannery Wastewater by Chitosan Modified-Activated Carbon of Hyphaene Thebaica

Abstract

The continuous decline of freshwater resources has necessitated the quest for the
treatment of wastewater. Consequently, an adsorptive method of removal of major
pollutant (chromium) of tannery wastewater was initiated using chitosan-modified
activated carbon derived from shells of Hyphaene thebaica. The activated carbon was
initially synthesized by carbonization in an inert environment and chemically activated
with 1.0 M Zinc Chloride (ZnCl2) solution. The surfaces of both the native and chitosan-
modified-activated carbons were characterized by X-ray diffraction, Brunauer Emmett
Teller (BET) surface analysis, scanning electron microscopy (SEM), and Fourier transform
infrared spectroscopy (FTIR). The materials were also evaluated for Chromium (Cr) ions
removal bybatch adsorption experiment. High adsorption efficiency (97.2%) was observed
using chitosan-modified-activated carbon, which was largely influenced by facile
modification of the material which subsequently led to the effective synergy between
chitosan and the derived activated carbon. The batch adsorption of Cr ions revealed a
dependence on adsorbate concentration (11.5 mg/L), adsorbent dose (0.8 g/ 100 mL),
contact time (90 mins) and pH (4) with high adsorption efficiencies at optimum levels of
such operating parameters.The equilibrium adsorption data are well described by the
Freundlich model while kinetics data are favourably defined by the pseudo-second-order
model for both chitosan-modified and native activated carbons. In the context of its
environment-friendliness and abundance in the Sudano-Sahelian region of Africa,
activated carbon derived from shells of Hyphaene thebaica and modified with chitosan
demonstrated practical application in the removal of the environmentally deleterious level
of Cr ions from real tannery wastewater with high adsorption efficiency of 97.2%,
regardless of the presence of other competing heavy metal ions, tested at optimum
operating parameters. Hence, when the surface of activated carbon derived from
Hyphaene thebaica is properly engineered could be a material of great value for industrial
wastewater treatment of metal ions