Cr(VI) Immobilization Process in a Cr-Spiked Soil by Zerovalent Iron Nanoparticles: Optimization Using Response Surface Methodology

The response surface methodology involving the five-level central composite design (CCD) was employed to model and optimize the Cr(VI) immobilization process in a Cr-spiked soil using starch-stabilized zerovalent iron nanoparticles (ZVIn). ZVIn were synthesized via a borohydride reduction method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). All Cr(VI) immobilization experiments were conducted in a batch system. The variables for the CCD optimization were the ZVIn dosage (% w/w), reaction time (min), and initial Cr(VI) concentration in soil (mg/kg). The predicted response values by the second-order polynomial model were found to be in good agreement with experimental values (R ²=0.968 and adj-R ²=0.940). The optimization result showed that the Cr(VI) immobilization efficiency presented the maximal result (90.63%) at the following optimal conditions: ZVIn dosage of 1.5% w/w, reaction time of 60min, and an initial Cr(VI) concentration of 400mg/kg. A five-level central composite design selected as a response surface methodology was employed to optimize the effect of influencing factors in the Cr(VI) immobilization process: zerovalent iron nanoparticles dosage, reaction time, and initial Cr(VI) concentration in soil. The results indicated that CCD could efficiently be applied for the modeling of reductive immobilization of Cr(VI).