Investigation of the kinetics of the hydrothermal reduction of sodium chromate with starch

In order to avoid environmental pollution caused by by-products containing chromium(Ⅵ),which are produced by conventional chromium oxide technology,this paper presented a new production process for preparing chromium oxide by hydrothermal reduction of sodium chromate using starch as a reductive. On the basic of analyzing reaction mechanism,the kinetics of hydrothermal reduction of sodium chromate by starch(St) have been studied and the affecting factors for the rate of reduction of Cr(Ⅵ) have been investigated. The results show that reaction temperature,reaction time and reactant concentration are the main factors affecting the rate of reduction of Cr(Ⅵ). A constant-temperature,constant-volume and irreversible reaction kinetic model was selected to describe its reaction process and the kinetic equation can be expressed as:r=-d[Cr(Ⅵ)]/dt=1.367×1013 e(-100.566×1000)/RT [Cr(Ⅵ)][St],i.e.,the pre-exponential constant,apparent activation energy and overall reaction order are 1.367×1013 L/(mol·h),100.566 kJ/mol and second-order or pseudo-second-order,respectively. The reaction is of the chemical reaction controlled type and the reaction order is first-order or pseudo-first-order with respect to Cr(Ⅵ) and starch.