Adsorption of Cr(VI) from aqueous solution by a litchi shell-based adsorbent

Abstract

Cr(VI) is a toxic metal pollutant existing in industrial effluents. In this study, Fe₃O₄ and layered double hydroxide (LDH) were inserted into the litchi shell (LS) successively by the co-precipitation method to synthesize the modified magnetic litchi shell adsorbent (MMLS) for removing Cr(VI). The advantageous structure characteristics of MMLS were confirmed by XRD, FT-IR, SEM and the hysteresis loop characterization. The batch experiments of optimizing the conditions (pH, adsorbent dosage, initial concentration, coexisting ions) for removing Cr(VI) were accomplished to in simulated wastewater at room temperature. And the optimal pH of 3 and initial concentration of 100 mg/L in simulated wastewater were similar to that in the actual chrome-plated rinse water with the stable MMLS. The effect of coexisting ions indicated anions and Cr(VI) competed with each other for the adsorption site, but the interactions were negligible in actual chrome-plated rinse water. Chemisorption as a rate-limiting step was confirmed with a good fit of pseudo-second-order kinetics. And the adsorption behavior of MMLS can not be explained by a single theory according to Sips model. The desorption and recycle experiments demonstrated MMLS was reusable in actual chrome-plated rinse water.

Keywords: Adsorption; Chrome-plated rinse water; Layered double hydroxide; Litchi shell; Modified magnetic adsorbent.