两性修饰剂修饰红壤对镉离子吸附的影响

Cadmium Adsorption Characteristics in Red Soil Modified with Amphoteric Modifier

采用不同比例的八烷基氨基酸表面修饰剂修饰红壤,研究了在单一Cd2+及Cd2+和苯酚混合条件下供试土样对Cd2+的吸附和热力学特征,目的在于探讨两性修饰剂修饰可变电荷土壤以增强对重金属离子吸附的效果。结果表明,除20℃混合条件下100%AA-8处理外,同一温度下不同修饰比例的供试土样对Cd2+的吸附量顺序均为CK>50%AA-8>100%AA-8,但差异并不显著。Cd2+的吸附具有化学吸附的升温正效应特征。苯酚的共存对Cd2+的吸附具有减弱作用。Langmuir模型是描述Cd2+吸附等温线的最佳模型。热力学研究结果表明供试土样对Cd2+的吸附为熵增控制的自发性反应,表面修饰剂羧基上的负电荷点位和土壤表面上的正电荷点位的结合可能是主要的修饰机理,八烷基碳链的疏水性则是Cd2+在供试土样表面上吸附阻力的主要形式。八烷基氨基酸不是一种较好的增强红壤吸附重金属能力的有机修饰剂。

Cd^2＋ adsorption and its thermodynamic characteristics at both Cd^2＋ single and Cd^2＋ phenol mixture treatments on red soil modified with different rates of N-octalkyl-β-amino-propylacid （AA-8） were determined, in order to study the effects of amphoteric modifier on enhancing adsorption ability of variable charge soils for heavy metal cation. The results showed that except for soil modified with 100%AA-8 at 20℃, Cd^2＋ adsorption followed the order：. CK〉50%A A-8〉100%A A-8 at the same temperature, but no significant difference was found in the adsorption of Cd^2＋ on soils modified with different rates of the modifier. Cd^2＋ adsorption increased with the temperature. Langmuir model was the best model used in describing the Cd^2＋ adsorption. Cd^2＋ adsorption on modified red soil was spontaneously controlled by entropy increment. The amino acid modifier might be modified on the surface of soil by combining negative sites on the carboxyl of modifier with positive sites on the surface of soil. The hydrophobicity of eight-carbon chain might be the main resistance of Cd^2＋ adsorption on modified soil. Octalkyl amino acid is not a better modifier for red soil to enhance its adsorption ability to heavy metals.