Al(III)对糖浆溶液中有机还原物质还原六价铬的影响

通过批实验研究了Al(III)对糖浆溶液化学还原六价铬反应的影响,揭示了不同条件下Al(III)对六价铬还原反应动力学的影响.结果表明:Al(III)能够促进糖浆溶液还原六价铬反应进行;其作用机制是Al(III)与糖浆溶液中有机还原物质及Cr(VI)反应形成三者的络合物,降低糖浆中多酚等有机还原物质还原Cr(VI)的反应活化能,提高六价铬还原反应速率.Al(III)存在时,该六价铬还原反应符合准一级动力学反应; pH 2.0,2.5,3.0,3.5时,添加Al(III)的实验组中六价铬反应速率常数比对应的空白对照组中反应速率常数分别增加了0.0251,0.0139,0.0058, 0.0048h-1.添加Al(III)前后反应体系中六价铬还原的反应活化能(Eа)分别为66.38,62.80kJ/mol.当糖浆浓度不足时,Al(III)能够提高糖浆溶液还原六价铬的反应去除率.

Influence of Al(III) on the reduction of Cr(VI) by organic reducing substances from sugarcane molasses

The objective of this work was to investigate the effect of Al (III) on the reduction of Cr (VI) by organic reducing substances (contain phenolic hydroxyl and carboxyl groups) from sugarcane molasses, and to analyze the kinetics of Cr (VI) reduction in the presence of Al (III) under different conditions through batch experiments. Results indicated that Al (III) could catalyze the reduction of Cr (VI) by sugarcane molasses, and its mechanisms was organic reducing substances complexes of both Al (III) and Cr (VI) would reduce the reaction activation energy (Ea) of Cr (VI) reduction, and accelerated the reaction rate of Cr (VI) reduction by organic reducing substances from sugarcane molasses. This reaction could be described by the pseudo-first-order kinetic model with respect to Cr (VI) concentration in the presence of Al (III). At pH 2.0, 2.5, 3.0, and 3.5, the reaction rate constants increased 25.1, 13.9, 5.8, and 4.8h-1 respectively in the presence of Al (III) compared with that without Al (III). The reaction activation energy of Cr (VI) reduction by sugarcane molasses was 66.38 and 62.80kJ/mol respectively in the presence or no. When sugarcane molasses was insufficient, Al (III) would increase the removal efficiency of Cr (VI) reduction.