天然腐殖酸对黄土吸附敌草隆的影响

为研究添加天然腐殖酸条件下黄土对有机农药的吸附过程及影响机制，以敌草隆为目标污染物，采用批量平衡试验法，分析黄土与黄土+HA（在黄土中添加腐殖酸）处理对敌草隆的吸附动力学、吸附热力学、解吸动力学过程及其主要影响因素（如pH、离子强度等）.结果表明:①与黄土相比，黄土+HA对敌草隆的吸附时间较短，且二者均符合颗粒内部扩散模型.②Freundlich等温吸附模型能够较好地拟合黄土及黄土+HA对敌草隆的吸附热力学过程.黄土和黄土+HA对敌草隆的吸附自由能（ΔGθ）、熵变（ΔSθ）均小于0，表明反应是一个自发进行且混乱度逐渐减小的过程；添加HA使黄土对敌草隆的焓变（ΔHθ）由负值变为正值，即由放热过程转化为吸热过程，表明温度升高使HA表面的微孔数量增多，为敌草隆提供了更多的吸附位点.③随着pH的升高，黄土和黄土+HA对敌草隆的吸附量均缓慢减小，当pH>7时吸附趋于平衡.④不同离子（Ca2+、Na+、Mg2+）及离子强度下，黄土和黄土+HA对敌草隆的吸附量随着c（Ca2+）的减小而增大，与同浓度的Mg2+和Ca2+相比，Mg2+存在下黄土对敌草隆的吸附量较大；与同浓度的Ca2+和Na+相比，Na+存在下黄土对敌草隆的吸附量较大.⑤由解吸动力学过程可以看出，添加天然HA可延长敌草隆在黄土中的滞留时间.研究显示，HA的存在提高了敌草隆在黄土中的迁移能力，并使其吸附机制发生了改变. 

Effect of Natural Humic Acid on Adsorption of Diuron by Loess

Adsorption is an important means for pollutant migration in aquatic environments and it''s also an important mechanism of pollutant transfer and transformation. In this study, in order to explore the process and influence mechanism of natural humic acid (HA) on the adsorption of organic pesticides onto loess, diuron was selected as the target pollutant. The adsorption kinetics, desorption kinetics, adsorption thermodynamics, and influence factors, such as ionic strength, pH values, were investigated by using batch adsorption experiments based on our previous study. The results showed that compared with the adsorption of diuron by loess soil, the addition of humic acid in loess shortened the adsorption time of diuron. The equilibrium adsorption capacity of loess + HA to diuron was greater than that of loess and both were in accordance with the fast and slow reaction mechanism. The kinetic data showed that the adsorption of diuron onto loess soil could be described by intraparticle diffusion model. The Freundlich isotherm adsorption model can better fit the adsorption thermodynamics of loess and loess + HA to diuron. Thermodynamic parameter of diuron adsorption onto loess and loess + HA analysis showed that the Gibbs free energy and entropy were less than zero, indicating that the adsorption was a spontaneous process with a reduced degree of chaos. Adding humic acid changed the enthalpy of diuron adsorption on the loess from negative to positive, which converted it from an exothermic process to an endothermic process. It indicated that the temperature increased, and the number of micropores on the surface of humic acid increased, providing more adsorption sites for diuron. The adsorption capacity of loess and loess + HA for diuron was weakened with increasing pH. When the solution was alkaline, the adsorption of diuron tended to be stable. Under different ionic and ionic strengthen, the amount of adsorption diuron on loess and loess + HA were increased with the decrease of Ca²⁺ concentration. Compared with the same concentration of Mg²⁺ and Ca²⁺, diuron adsorption was affected by Mg²⁺ more significantly than by Ca²⁺. Compared with Na⁺ and Ca²⁺ at the same concentration, the adsorption of diuron was more significantly affected by Na⁺ than Ca²⁺. Through desorption kinetics, it can be seen that the addition of natural humic acid can improve the retention of diphacuron in loess. The results have important implications regarding the enhancement effect of humic acid on the adsorption capacity and migration ability of diuron in loess, and its adsorption mechanism has changed, which also impact the adsorption/desorption under different environmental conditions and the fate of diuron in loess soil.