重金属离子在胡敏酸-高岭石复合体上的吸附

Adsorption of heavy metal ions on humic acid-kaolinite complexes

本文研究了胡敏酸存在下高岭石对重金属离子的吸附行为。实验结果表明:①胡敏酸和Cu2+溶液按先后顺序或同时加入高岭石中反应,在Cu2+平衡浓度<10mg/L时,3种加入顺序对Cu2+的吸附量基本相同,当Cu2+平衡浓度>10mg/L时,(K+Cu)+HA和(K+Cu+HA)两种加入顺序对Cu2+的吸附量比(K+HA)+Cu的略大。②在pH=5时,胡敏酸-高岭石复合体对Cu2+的吸附量明显大于纯高岭石。这是由于胡敏酸含有大量的羧基和酚羟基等活性基团,吸附在高岭石上的胡敏酸增加了其表面吸附位,在复合体表面形成了S—HA—Cu三元配合物,且Cu2+的吸附量与复合体中胡敏酸的含量在一定范围内成正相关;③溶液pH值在4～7之间变化可调控复合体对Cu2+的吸附机制。④在Cu2+和Cd2+共存时,随着金属离子初始浓度的增大,Cu2+的吸附量呈直线上升,而Cd2+的吸附量增加缓慢,表明复合体对Cu2+的吸附能力比对Cd2+强。

This paper studied the adsorption of heavy metal ions on kaolinite in the presence of humic acid （HA）. Three adding sequences, composed of one co-adsorption process and two pre-adsorption processes, were compared with each other in this study. When Cu^2＋ equilibrium concentrations were lower than 10 mg/L, no significant difference in the amount of Cu^2＋ adsorption was observed in the three adding sequences. When Cu^2＋ equilibrium concentrations were higher than 10 mg/L, the Cu^2＋ adsorption amount for co-adsorption and kaolinite pre-equilibrated with two Cu^2＋ adding sequences were slightly higher than that for kaolinite pre-equilibrated with HA. In order to investigate the effect of HA on heavy metal retention, the authors first prepared the HA- kaolinite complexes by adding HA solutions of varied proportions to kaolinite, and then used the HA-kaolinite complexes to study Cu^2＋ adsorption at pH 5. The results show that complexes have higher Cu^2＋ adsorption capacity than pure kaolinite. When HA contains carboxylic and phenolic active groups, the adsorption sites on kaolinite increased by HA adsorbed on kaolinite and form the S-HA-Cu ternary structure on the complex surface. The Cu^2＋ adsorption amount was related positively to the proportion of HA in the complexes. The formation of the S-HA-Cu ternary structure is the main adsorption mechanism on HA-kaolinite complexes at pH 〈 5. Several mechanisms coexist in the complex system when the pH increases from 5 to 7. In the solution conmining Cu^2＋ and Cd^2＋ at 1 ： 1 molar ratio, the HA-kaolinite complex displays higher selectivity to Cu^2＋ as compared to Cd^2＋.