阴离子交换柱分离不同价态砷的研究及其应用

利用醋酸型AG 1-X8阴离子交换树脂和氯化物型AG 1-X8阴离子交换树脂对As(Ⅴ)和As(Ⅲ)吸附的差异,实现As(Ⅲ)和As(Ⅴ)的有效分离。过滤和酸化后的水样流经树脂交换柱(75mm×5.3mm i.d.)时,醋酸型AG 1-X8阴离子交换树脂可吸附As(Ⅴ);而As(Ⅲ)可通过树脂柱。被吸附的As(Ⅴ)用0.12mol/L HCl淋洗出来,在此过程中醋酸型树脂转化为氯化物型树脂。该树脂交换柱可多次循环使用。本方法简单易行,适用于野外现场条件下高砷地下水中As(Ⅲ)和As(Ⅴ)的分离和准确测定;用于检测水铁矿除砷过程中砷价态变化。结果表明,缺氧条件下水铁矿对As(Ⅲ)和As(Ⅴ)的吸附动力学特征遵循假二级反应动力学模式,内扩散不是控制As(Ⅲ)和As(Ⅴ)吸附的因素。随着时间的推移,膜扩散对吸附的控制作用增强。

Separation of Inorganic Arsenic Species from Aqueous Solution by Anion Exchange Column and Its Application in Study of Arsenic Removal

Arsenic(Ⅲ) and As(Ⅴ) can be separated with a strong anion-exchange resin(AG 1-X8) due to its adsorption of As in acetate form and neither As(Ⅴ) nor As(Ⅲ) in chloride form.The samples,which were filtered and acidified with concentrated HCl,flowed through the acetate-form resin column(75 mm×5.3 mm i.d.).Arsenic(Ⅲ) passes through the acetate-form resin column,and As is retained.Adsorbed As(Ⅴ) was eluted by passage of 0.12 mol/L HCl through the column,during which the resin was converted from the acetate form into the chloride form.The first 10 mL effluent gives the As(Ⅲ) concentration,and the last 10 mL the As(Ⅴ) concentration.The method is easy to handle and cost-effective,which is suitable for on-site separation and accurate determination of As(Ⅴ) and As(Ⅲ) in groundwater.The method has been used for determining As species in solutions during As removal by ferrihydrite.Results show that pseudo-second order kinetic model well describes the kinetics of both As(Ⅲ) and As(Ⅴ) adsorption on ferrihydrite in anaerobic condition.Intraparticle diffusion is not the major process controlling As adsorption.However,external mass transfer plays more and more important role during the adsorption as the reactive time increases.