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环境化学

摘要：为进一步了解土壤环境中有机物有效快速还原Cr(Ⅵ)的作用机理,通过批式试验研究了不同温度和pH条件下土壤中普遍存在的Al³⁺对酒石酸还原Cr(Ⅵ)反应速率的影响.结果表明,Al³⁺对酒石酸还原Cr(Ⅵ)有催化作用,且pH越低,Al³⁺的催化作用越明显;然而,当pH达4.5时,其催化作用几乎完全消失.前期试验结果指出,Al³⁺对只含有1个α-OH有机酸(如柠檬酸和乳酸)和只具有2个羧基的有机酸(如草酸和琥珀酸)还原Cr(Ⅵ)没有任何影响.因此,可得出Al³⁺的催化效应跟酒石酸分子中的2个α-OH与Al³⁺发生作用有关.在Al³⁺作用下,过量酒石酸对Cr(Ⅵ)还原反应符合零级反应动力学规律.

Abstract：The influence of Al³⁺ on the reduction of Cr(Ⅵ)by tartaric acid was studied in batch experimental systems at different pHs and temperatures to understand the mechanism of the rapid reduction of Cr(Ⅵ) by organic matter in soils. The results showed that Al³⁺ greatly accelerated the reduction of Cr(Ⅵ) by tartaric acid. The catalysis by Al³⁺ did not occur at pH4.5 or above, but increased as the pHdecreased. Our previous work had shown that Al³⁺ had no effect on the reduction of Cr(Ⅵ) by organic acids with one α-OH (such as citric acid and lactic acid) or with two-COOH groups (such as oxalic acid and succinic acid ). Based on these results, the catalysis of Al³⁺ must be related to a reaction between Al³⁺ and the two α-OHof tartaric acid. The reduction of Cr(Ⅵ)by tartaric acid followed zero order kinetics with excess tartaric acid in the presence of Al³⁺.