水合氧化铁的制备及其吸附性能研究

采用恒pH沉淀法,以NaOH溶液为沉淀剂,在溶液pH为3~9的范围内制得4种水合氧化铁(即水铁矿,Fh)。通过XRD、表面零电荷时pH(pHPZC)的测定、N2吸附-脱附对其进行了表征。研究了溶液pH对Fh的甲基橙去除率的影响。表征结果显示:4种Fh均为2-线Fh;它们的pHPZC为6.7~7.9;溶液pH为5,7,9时制备的Fh(Fh5,Fh7,Fh9)的N2吸附-脱附曲线均为IUPAC定义的第Ⅲ种类型。实验结果表明:4种Fh均在溶液pH为4时对甲基橙去除率最高;当甲基橙初始质量浓度为30 mg/L时,Fh5对甲基橙的去除率最高,为92.8%。Langmuir方程更适合描述Fh5对甲基橙的吸附行为,甲基橙在Fh5上产生单分子层吸附,该吸附是自发、放热的物理吸附过程。

Preparation of ferrihydrites and their adsorption properties

4 kinds of hydrous ferric oxide(ferrihydrite,Fh)were prepared at 3-9 of the solution pH by constant pH precipitation method using NaOH solution as precipitant,and characterized by XRD,pHPZC(pH at the point of zero charge)determination and N2 adsorption-desorption test. The effect of solution pH on removal rate of methyl orange (MO)on Fh was studied. The characterization results show that:All of the 4 products are Fh with 2 diffraction lines;The pHPZC of them are 6.7-7.9;And the N2 adsorption-desorption isotherms of Fhs prepared at pH 5,7,9(i.e. Fh5, Fh7,Fh9)are the curves of type Ⅲ classified by IUPAC. The experimental results show that:The MO removal rates on the 4 Fhs are all the highest at solution pH 4;When the initial MO mass concentration is 30 mg/L,the MO removal rates on Fh5 is 92.8%(the highest value). Langmuir equation is better to describe the adsorption behavior of Fh5 to MO,indicating that the adsorption of MO on Fh5 is monolayer adsorption,and the adsorption process is a spontaneous,exothermic and physical process.