Four kinds of ferrihydrite(Fh) have been prepared from iron nitrate as its raw materials,NaOH solution as precipitator,through constant pH(in the range of 3-9) precitation method. They are characterized through XRD, pH (pHpzc)determination at the point of zero charge and N2 adsorption-desorption technique. Taking methyl orange (MO) as a kind of simulated pollutant,their adsorption capacities are compared. The results show that the Fh (Fh5) prepared when pH=5 exhibits significantly higher adsorption removing capacity (92.8%) for methyl orange than those of Fh3,Fh7 and Fh9 prepared when pH=3(34.1%),pH=7(67.4%) and pH=9(53.7%),respectively. The adso-rption law of MO by the four kinds of Fh conforms to the Langmuir equation well,being monomolecular layer adsorption. Additionally,the influences of the types of precipitators(NaOH,and NH3·H2O) and the concentration of Fe (Ⅲ) on the adsorption capacity of Fh5 for MO are also investigated. The results indicates that the Fh5 prepared when NaOH solution is used as precipitator and Fe(Ⅲ) concentration is 0.2 mol/L has the best adsorption capacity.%以硝酸铁为原料，NaOH溶液为沉淀剂，通过恒pH沉淀法在pH为3～9范围内制得4种水合氧化铁（Fh），通过XRD、表面零电荷时pH（pHpzc）测定、N2吸附－脱附法对其进行表征，以甲基橙（MO）为模拟污染物比较其吸附性能。结果表明，pH为5时制备的Fh（Fh5）对MO的去除率为92．8%，明显优于Fh3（34．1%）、Fh7（67．4%）和Fh9（53．7%）。4种Fh 对MO 的吸附规律符合Langmuir 方程，为单分子层吸附。另外考察了沉淀剂类型（NaOH、NH3·H2O）和Fe（Ⅲ）浓度对Fh5吸附MO的影响。结果表明，以NaOH溶液为沉淀剂、Fe（Ⅲ）浓度为0．2 mol/L时制备的Fh5具有最佳的吸附性能。
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