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环境化学

The stability and thermodynamics of the coordination reaction of humic acid with Fe³⁺ion

王强
1. 西南大学农产品质量与安全检测中心, 重庆 400716; 2. 西南大学资源环境学院, 重庆市农业资源与环境研究重点实验室, 重庆 400716; 3. 西南大学药用资源化学研究所, 重庆 400716

摘要：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Fe³⁺络合反应的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Fe³⁺络合表观稳定常数和配位数均增加,有利于络合反应的进行;相同pH和温度下,离子强度从0到0.10 mol·L^-1,HA与Fe³⁺络合反应表观稳定常数和配位数增加,但离子强度从0.10 mol·L^-1继续上升到0.15 mol·L^-1,则上述2个特征常数呈现下降的趋势;胡敏酸络合Fe³⁺标准自由能变△G_m^θ、焓变△H_m^θ、熵变△S_m^θ在298.2、308.2 K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.

Abstract：The stability and thermodynamics of humic acid coordination with Fe³⁺ ion at different acidity, ion strength and temperature were studied, using ion-exchange equilibrium method. The results showed that the condition stability constant and coordination number were increased with the increasing of pH at constant ion strength and temperature, suggesting that higher pH could be advantage to the process of coordination reaction. At constant pH and temperature, the stability constant and coordination number were increased when ion strength changed from 0 to 0.10 mol·L^-1, while these character constants were decreased when ion strength continually rose to 0.15 mol·L^-1. The thermodynamic parameters of coordination reaction, including standard free energy change ΔG_m^θ, the thermodynamic standard enthalpy change △H_m^θ and entropy change △S_m^θ, were all negative when temperature were in the range of 298.2 to 308.2K, which suggested that coordination reaction was spontaneous and exothermic. Consequently the lower temperature could be favor to the process of reaction.