Removal of Cr(VI) and Zn(II) from an aqueous solution using an organic-inorganic composite of bentonite-biochar-hematite

Abstract

A bentonite/biochar/hematite composite was synthesized to develop an adsorbent with the properties of each constituent suitable for the removal of Cr(VI) and Zn(II) from aqueous solution. The compos - ite was prepared through slow pyrolysis and characterized using scanning electron microscope (SEM) and X-ray fluorometry (XRF). The developed adsorbent was used in a batch system for the removal of individual metal ion of Cr(VI) and Zn(II). The XRF results showed that the composite contained the elements found in the respective constituents, while the SEM results showed that the morphology of the composite resulted from the combination of the constituents, indicating a successful synthesis of the composite. The adsorption study showed the affinity of bentonite and biochar for the Zn(II) which was mainly due to the negative groups present in those adsorbents, while hematite with a net positive charge was mainly suitable for the removal of Cr(VI) present as dichromate in the working pH range (between 6 and 8). The adsorption behaviour of the adsorbent fitted the Freundlich isotherm model implying that the adsorption mostly occurred through a heterogeneous binding of metal to the surface of the adsor - bent. The composite did not exhibit the highest adsorption capacity but was the only adsorbent capable to remove both Cr(VI) and Zn(II), with an adsorption capacity of 5.414 mg/g and 5.167 mg/g respectively. The composite could therefore be used for the treatment of wastewater contaminated by both metals