Adsorption of Ni(II) on detoxified chromite ore processing residue using citrus peel as reductive mediator: Adsorbent preparation, kinetics, isotherm, and thermodynamics analysis

Abstract

Chromite ore processing residue (COPR) is a kind of hazardous industrial solid waste produced in the chromium salt industry that needs to be disposed of properly and safely. In this work, an agricultural waste of citrus peel (CP) was used to detoxify COPR by the pyrolysis process, and the resulted residue (DT-COPR) was used as the adsorbent to treat simulated nickel ion (Ni2+) wastewater. The effects of pyrolysis parameters on the COPR detoxification efficiency and adsorption performance of Ni2+ were investigated simultaneously. Besides, operating parameters on the adsorption efficiency and capacity of Ni2+ were also studied and the adsorption kinetics and equilibrium isotherms were summarized correspondingly. The results show not only water-soluble but also insoluble (Cr(Ⅵ)) in the COPR can be effectively reduced by the pyrolysis process, and the total Cr(Ⅵ) decreased from 1641.98 mg/kg to 8.04 mg/kg that can be used safely as an adsorbent. The characterization results of DT-COPR also show that the new adsorbent exhibits good thermal stability and full of chemical functional groups, and adsorption equilibrium of nearly up to 100% of Ni2+ removal efficiency with DT-COPR was achieved within 10–60 min. The adsorption process of Ni2+ can be accurately described by the pseudo-second-order model and Langmuir isotherm, and the theoretical maximum adsorption capacity (qmax) for Ni2+ could reach as high as 18.18 mg/g. This study provided an alternative treatment of bio-safety disposal and resource-oriented utilization of the COPR.