磷是生物生长的必需营养元素，但其在水中的过量存在造成了水体富营养化。近年来，随着水体富营养化程度的加深，水华和赤潮现象呈现多发趋势，因此，磷的去除越来越受到关注。水体中磷的去除，可降低水中磷含量、提高水质，进而有效降低水华、赤潮的发生率。吸附除磷技术具有高效、快速、操作简单等优点，近年来成为研究热点。铁氧化物作为磷吸附剂，具有吸附量高、环境友好、成本低等优点。近来，研究表明复合氧化物明显比单一氧化物具有更高的吸附量，更广的pH适用范围。因此，本研究以铁氧化物为基体，合成了两种性质不同的铁基二元金属复合氧化物吸附剂，一种是铁铜复合氧化物，一种是铁钇复合氧化物，以期获得高效、具有应用前景的磷吸附材料。

通过对吸附剂的表征、磷吸附行为、吸附机制以及再生方面的系统研究，主要取得了以下成果：

一．铁铜复合氧化物

1. 制备了一系列铁铜复合氧化物，确定了铁铜比为2:1，合成pH 7.0，陈化温度为室温 (RT) ，干燥温度为55℃的样品具有最高的吸附量。

2. 铁铜复合氧化物系纳米结构的无定型材料，具有类似于二线水铁矿结构和较大的比表面积 (282 m²·g^-1) 。材料等电点 (Point of Zero Charge, PZC) 为7.9，在pH<7.9范围内可保持材料表面显正电性。

3. Langmuir等温线模型可较好的描述铁铜复合氧化物对磷的吸附，经拟合，其最大吸附量为34.9 mg·g^-1 (pH 7.0时)。热力学参数表明铁铜复合氧化物与磷发生化学吸附，为自发的吸热过程。铁铜复合氧化物对磷吸附速率较快，30 min即可去除90%的磷，准二级动力学模型和内扩散模型均可对动力学数据进行较好的拟合，说明吸附过程为化学吸附。在较宽的pH范围 (3~8) 内，铁铜复合氧化物保持对磷有高吸附量；共存阴离子SiO₃^2-和F^- 随浓度增加对磷吸附的影响变大，当浓度高达0.01 mol·L^-1时，对磷的吸附量分别为对照组的59%和72%，其他离子对吸附效果影响不大，均保持在90%以上的去除率，共存离子对磷吸附影响顺序为SiO₃^2- >F^- >HCO₃^- >SO₄^2- >Cl^-；随再生次数增加，吸附量逐渐减小，第一次再生吸附量为初始吸附量的89%，但再生五次之后，吸附量仍可保持在初始时的65%以上，说明材料再生性能较好，具有良好的实用性。

二．铁钇复合氧化物

1. 合成的铁钇复合氧化物具有纳米结构，初级粒子平均粒径为15.2 nm；有较强的磁性，比饱和磁化强度为38.7 emu·g^-1，可方便、快速地实现固液分离。材料PZC为6.8，在pH<6.8范围内可保持材料表面显正电性。

2. Langmuir等温线模型可较好的描述铁钇复合氧化物对磷的吸附，其最大吸附量为60.6 mg·g^-1 (pH 5.0时)。铁钇复合氧化物对磷吸附速率较快，120 min可去除80%以上的磷，准二级动力学模型可对动力学数据进行较好的描述，说明吸附过程为化学吸附。溶液pH对铁钇复合氧化物吸附磷影响较为明显，在pH 5.0时有最大吸附量，为60.6 mg·g^-1，高于其他常见吸附剂。SiO₃^2- 对磷吸附的影响随着浓度升高逐渐增大，当浓度为0.01 mol·L^-1时，对磷的吸附量为初始的52%，其他常见阴离子对磷吸附影响不大，均保持在85%以上的去除率，共存阴离子对磷吸附影响的顺序为SiO₃^2- > CO₃^2- > SO₄^2- > Cl^-。

三．吸附机制

两种铁基二元金属复合氧化物与磷均发生了化学吸附。离子强度的变化对磷的吸附影响不大，结合傅立叶变换红外光谱的分析，复合氧化物与磷形成了内配位络合物。

Phosphorus, as an essential nutrient element, may cause eutrophication if excessively exist in water. In recent years, water blooms and red tide occurred more frequently and severely, due to the eutrophication. Therefore, the removal of phosphate from water is getting more attentions, which can improve the water quality and subsequently reduce incidence of water blooms and red tide. Recently, adsorption method has been extensively studied and was used to remove phosphate from water because of its high efficiency, fast and simple operation. As phosphate adsorbent, iron (hydr)oxides possess advantages of high adsorption capacity, environmental friendliness and low cost. Other researches show that metal binary oxides may have much higher adsorption capacity than single ones. Based on these, two kinds of iron based binary oxides (Fe-Cu binary oxide and Fe-Y binary oxide) were developed in this study, aiming at obtaining highly efficient and attractive adsorbents.

Through a systematical study of characterization, adsorption behaviors, mechanisms and regeneration, the following results were obtained through studies on:

I．Fe-Cu binary oxides

1. A series of Fe-Cu binary oxides were synthesized and the one with an Fe:Cu ratio of 2:1, synthesis pH of 7, aging temperature of RT and drying temperature of 55℃ was proved to possess the highest adsorption capacity.

2. The Fe-Cu binary oxide was amorphous, 2-line ferrihydrite-like and was aggregated with many nanosized particles, with a high surface area of 280 m²·g^-1. It has a PZC of 7.9, which makes the surface of oxide positively charged at pH<7.9.

3. The adsorption isotherm data is well described by Langmuir model (R²=0.96) with maximal phosphate adsorption capacity of 34.9 mg·g^‑1 at pH 7.0. Thermodynamic data indicates that the phosphate adsorption process is a spontaneous, endothermic and chemically sorptive process. The adsorption is fast and over 90% of the equilibrium adsorption capacity is achieved within 30 min. The adsorption kinetic data can be well described by both pseudo-second order model (R²=0.88) and intra-particle diffusion model (R²=0.88). The Fe-Cu binary oxide is effective in removing phosphate in a wide pH rage (3~8). The presence of coexisting SiO₃^2- and F^- decreased the phosphate adsorption. The adsorption capacities were reduced to 59% and 72%, respectively, when the concentration was 0.01mol·L^‑1. Other coexisting anions have little effect on phosphate adsorption. The effect of coexisting anions on phosphate adsorption on Fe-Cu binary oxide decreased in the order of SiO₃^2- >F^- >HCO₃^- > SO₄^2- > Cl^-. The spent Fe-Cu binary oxide could be effectively regenerated using NaOH solution. After the first regeneration, it had about 89% of the original adsorption capacity and maintained 65% of the original one, even after the fifth regeneration. These show that the adsorbent could be readily regenerated and repeatedly used.

II．Fe-Y binary oxide

1. Fe-Y binary oxide is formed with nano-structured fine particles with average primary particle size of 15.2 nm. The specific saturation magnetization of 38.7 emu·g^-1 shows that the adsorbent can be separated from water easily and fast. PZC of Fe-Y binary oxide of 6.8 makes the surface of oxide positively charged at pH<6.8.

2. The adsorption isotherm data is well described by Langmuir model (R²=0.99) with a maximal phosphate adsorption capacity of 60.6 mg·g^‑1. The adsorption kinetic data is well described by pseudo-second order model (R²=0.99) indicating adsorption may be a chemical process. Over 80% of the equilibrium adsorption capacity was achieved within 120 min. The phosphate adsorption is dependent on solution pH. Among the coexisting anions, the SiO₃^2- hindered greatly the phosphate adsorption. Other coexisting anions have little effect on phosphate removal. The effect of coexisting anions on phosphate adsorption on Fe-Y binary oxide decreased in the order of SiO₃^2- > CO₃^2- > SO₄^2- > Cl^-.

III．Adsorption mechanism

The adsorption of phosphate from water by iron based binary oxides is a chemical process. The change of ionic strength has little influence on the phosphate adsorption. The results of IS  (ionic strength) experiments and FTIR analysis suggest that phosphate anions may form inner-sphere surface complexes at the water/oxide interface.