没食子酸还原六价铬反应动力学规律研究

实验研究了不同pH值,温度和六价铬初始浓度等条件对没食子酸还原六价铬的反应动力学的影响,分别建立六价铬还原反应速率常数关于氢离子浓度和温度的函数方程.结果表明:pH值 为2.0~5.0时,没食子酸与六价铬发生的氧化还原反应符合准一级动力学反应;而pH值为6时,因H+]不足,二者的反应不符合准一级动力学反应.在pH值为2.0~5.0时,六价铬反应速率常数(103kobs)分别是是951.6、103.6、17.3和7.5h-1.pH值 为2.5时,温度升高,反应速率常数快速增加;温度为30℃时,没食子酸还原六价铬的反应速率常数分别是温度为20℃和10℃时反应速率常数的1.61倍和3.68倍.不同初始浓度六价铬的反应体系中,六价铬反应速率常数随着反应体系中六价铬与没食子酸初始浓度比值的增加而逐渐减小.利用最小二乘线性回归法和阿伦尼乌斯公式分别建立了六价铬还原反应速率常数关于氢离子浓度和温度的函数方程,为预测和分析没食子酸还原六价铬反应过程中六价铬的反应速率常数和浓度变化情况提供动力学模型参考.

Kinetics of the reduction of hexavalent chromium with Gallic acid

The objective of this work was to determine the effect of pH, temperature and initial Cr (VI) concentration on kinetics of Cr (VI) reduction, and to develop two kinetics models for the rate constants upon pH and temperature, respectively. Results indicated that the redox reaction of gallic acid and hexavalent chromium was the pseudo-first-order kinetics reaction at pH 2.0~5.0; because H+ is insufficient, the reaction was not pseudo-first-order at pH 6.5. The rate constants (103kobs) were 951.6, 103.6, 17.3and 7.5h-1respectively when pH was from 2.0to 5.0. At pH 2.5, increasing temperature could increase the kobs, and the kobs increased by 0.61 and 2.68 times when temperature was adjusted from 10℃ to 20℃ and 30℃. The rate constants of Cr (VI) reduction were gradually decreased with increasing initial concentration ratio of Cr (VI) and gallic acid. The kinetics equation of the rate constants and H+] was obtained through a weighted least-squares linear regression method, and Arrhenius formula was used to develop the kinetics equation of the rate constants and temperature. These provided a model reference for analysis and forecast the reaction rates and Cr (VI) concentration on reaction of Cr (VI) reduction with gallic acid.