锰离子与胡敏酸络合反应特征研究

CHARACTERISTICS OF COMPLEX REACTION BETWEEN HUMIC ACID AND Mn^(2+) ION

采用离子交换平衡法研究了在不同酸度、离子强度、温度条件下胡敏酸(HA)与Mn2+络合反应稳定性和热力学特征。结果表明,在相同离子强度、反应温度条件下,随着pH的升高,HA与Mn2+络合反应稳定常数增大;络合反应配位数在pH 3.0～5.0范围内随着pH的升高而增加,在5.0～7.0范围内随着pH的升高而降低;离子强度增加,HA与Mn2+络合反应表观稳定常数增加,离子强度从0.00升至0.10 mol L-1,HA与Mn2+络合反应配位数增加,但离子强度从0.10 mol L-1继续上升至0.15 mol L-1,配位数呈现下降的趋势;胡敏酸络合Mn2+标准自由能变ΔGmθ、焓变ΔHθm、熵变ΔSθm在298.2K、308.2K温度下均为负值,反应是自发进行的放热反应,较低的温度有利于反应的进行。

Humic acid （HA） was extracted from surface soil under evergreen broadleaf forest in Jingyun Mountains of China. Effects of acidity, ion strength and temperature on stability and thermodynamics of the complex reaction between the humic acid and Mn2~ ion were studied using the ion-exchange equilibrium method. Results showed that its stability constant increased with increasing pH when ion strength and temperature remained unchanged, and with increasing ion strength,as well. Ligancy of the complex reaction increased with pH rising from 3.0 to 5.0, but decreased with pH rising further up from 5.0 and 7.0, and increased as well with ion strength rising from 0. 00 to 0. 10 mol L-1 but decreased, too, with ion strength rising further from 0. 10 to 0. 15 mol L-1 The thermodynamic parameters of the complex reaction, including standard free energy change ΔG0, standard enthal- py change ΔH0, and entropy change ASOm , were all negative when the temperature fell within the range from 298.2 to 308.2K, suggesting that the complex reaction is a kind of exothermie one processing spontaneously and keeping it lower in temperature favors process of the reaction.