土壤胡敏素对铜离子的吸附作用及其机理研究

Adsorption behavior and mechanism of Cu(II) on soil humin

以暗棕壤为供试土壤,研究了不同溶液pH值、离子强度、接触时间、反应温度和初始铜离子(Cu^(2+))浓度条件下,胡敏素对Cu^(2+)的吸附作用;利用扫描电子显微镜(SEM)、X-射线能量色散谱(EDS)、傅立叶变换红外光谱(FTIR)和X-射线光电子能谱(XPS),对胡敏素/胡敏素-Cu^(2+)复合物的表面形貌、元素分布和官能团组成进行了分析;应用延展X-射线吸收精细结构谱(EXAFS),对吸附态Cu^(2+)的局域配位结构进行了表征.结果表明:胡敏素对Cu^(2+)的吸附量随pH值、接触时间、反应温度和Cu^(2+)浓度的增加而增加,但随离子强度的增加而下降;吸附动力学符合准二级动力学方程,而吸附等温线用Langmuir方程的拟合效果较好;吸附过程需要能量,是自发、吸热和自由度增加的缔合反应;吸附Cu^(2+)之后,胡敏素表面产生了团聚现象,表面羧基、羟基、吡啶氮和N—O基团参与了Cu^(2+)的吸附作用,同时吸附态Cu^(2+)是以内层配位形式与胡敏素表面的O/N和C原子结合.

The adsorption of copper ion(Cu2+) on humin isolated from a dark brown soil was studied under different solution pH, ion strengths, contact time, reaction temperatures, and Cu2+ concentrations. The surface topography, elemental distribution, and functional group compositions of humin/humin-Cu2+ complex were characterized using scanning electron microscopy, X-ray energy dispersive spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The local coordination structure of Cu2+ adsorbed on humin was examined with extended X-ray absorption fine structure spectroscopy. The results showed that the adsorption amounts of Cu2+ increased with increasing solution pH, contact time, reaction temperatures, and Cu2+ concentrations whereas it decreased with increasing ion strengths. The adsorption kinetics agreed with pseudo-second-order kinetic equation, and the adsorption isotherms were well depicted by Langmuir equation. The adsorption process was an association reaction that required energy. Meanwhile, the adsorption was spontaneous, endothermic, and increasing random. After Cu2+ adsorption, the surface of humin aggregated slightly. Carboxyl, hydroxyl, pyridinic N and N-O groups on humin surface took part in the adsorption process of Cu2+. Cu2+ adsorbed on humin was combined with O/N and C atoms of humin surface via inner-sphere complexation.