Kinetics of hexavalent chromium reduction by grey cast iron powder

Abstract

ABSTRACTThe kinetics of Cr (VI) reduction by grey cast iron powder (HT250 as per Chinese standard GBT 9439-2010) was investigated in this paper. Factors such as pH, initial Cr (VI) concentration, particle size, stirring speed and temperature on Cr (VI) reduction were first examined at a moderate reducing agent dosage. It was found that Cr (VI) reduction could only occur at an initial pH of 2.0 and above this value, the reaction nearly stopped. Additionally, the obvious dependence of Cr (VI) reducibility on other parameters was also revealed. The changes of pH, ORP and the concentration of Fe ions during the reaction were investigated. The correlations between the experimental data and reaction models involving homogeneous and heterogeneous reactions were studied. The results indicated first-order kinetics for the Cr (VI) reduction, which was a homogeneous reaction with an apparent activation energy of 20.718 kJ/mol. A semi-empirical equation was proposed to describe the kinetics of Cr (VI) reduction by HT250 powder. It was concluded that HT250 powder was a promising zero-valency iron (ZVI) material offering excellent reducibility and its use can be extended to the pre-treatment of wastewater containing other heavy metal ions such as Cu(II) and Pb(II).