钙基蒙脱石对氟离子吸附及解吸实验

Experimental study on fluoride adsorption and desorption by Ca-montmorillonite

一般根据研究认为粘土中的氟以可交换态的形式存在,对环境中氟的迁移具有重要意义,可用1M MgCl2进行提取,但其有效性却未进行验证.在不同初始pH和初始质量浓度条件下,但用钙基蒙脱石进行氟吸附.实验表明:钙基蒙脱石对氟的吸附与初始pH呈负相关关系,而与溶液初始质量浓度呈正相关关系.同时用MgCl2对粘土吸附的氟进行解吸,其解吸率在0%～30%之间,低初始氟质量浓度(<20 mg/L)时氟主要交换蒙脱石中的OH2基团,中初始氟质量浓度(20 mg/L^100 mg/L)时氟主要交换蒙脱石中的OH基团而与Al结合,高初始氟质量浓度(>100mg/L)时氟主要是与层间Ca结合,由于Al结合态氟稳定性最强,导致用1M MgCl2解吸粘土吸附的氟时中等初始质量浓度氟的解吸率最低.

It is generally believed that fluorine as exchangeable form in clay plays an important role during its transportation in nature environment.It can be extracted using 1M MgCl2,however,the extraction effectiveness is not verified.In this study,a fluoride adsorption on Ca-montmorillonite was conducted with various initial pH and fluoride concentrations.The results show that fluoride ion adsorption on Ca-montmorillonite decreases with the increase of initial pH,while it increases with the increase of initial fluoride concentrations.In addition,the desorption efficiency for fluoride adsorbed by Ca-montmorillonite ranges from 0 to 30% with 1M MgCl2 to extract so-called exchangeable fluorine in clay.It is concluded that fluoride ions exchange-OH2 of montmorillonite at low initial fluoride concentrations(<20 mg/L).As the initial fluoride concentration increases,the fluoride in solutions could be exchanged with surface-active OH and bounded with Al in Ca-montmorillonite to form a quasi-cryolite structure.At initial fluoride concentration higher than 100 mg/L,fluoride ions are combined with Ca in the interlayer of Ca-montmorillonite.As a result,fluoride has the lowest desorption efficiency at medium initial fluoride concentrations when extracted by 1M MgCl2.