三价锑（Sb(III)）和五价锑（Sb(V)）是环境中最为常见的两种锑的存在形态，但是两种形态的锑具有不同的毒性和迁移性能。铁化合物和锰化合物是自然环境中两种非常常见的金属化合物，可以通过催化氧化、直接氧化、吸附等多种方式对锑的形态转化和迁移产生影响。然而，目前对铁锰循环介导的锑地球化学循环的研究多以铁或锰单一体系为研究对象，对铁锰化合物共同作用下锑的迁移转化研究较少，对铁氧化物晶型转化过程中锑迁移转化行为的研究也较少。于是，本研究通过室内动力学模拟实验和原子荧光光谱（AFS）、电感耦合等离子发射光谱（ICP-OES）等光谱表征手段以及X射线衍射（XRD）、扫描电镜（SEM）等表面表征手段，开展了铁、锰化合物对Sb(III)的共吸附氧化以及铁氧化物晶型转化对锑迁移转化机理研究，研究结果对深入了解锑的环境地球化学过程和归趋具有重要的理论意义，对锑污染的预防与调控具有指导意义。本研究主要结果如下：

（1）系统研究了酸性水环境中Fe(II)对MnO₂吸附氧化Sb(III)的影响，通过对比MnO₂单独氧化Sb(III)/Fe(II)和同时氧化Sb(III)和Fe(II)以及改变Fe(II): Sb(III)摩尔比、Fe(II)预处理时间等多种方式探究反应机理。研究发现，在MnO₂同时氧化Fe(II)和Sb(III)过程中，MnO₂表面有Fe-Sb化合物生成，而在Fe(II)预处理MnO₂的过程中，MnO₂表面有施氏矿物生成。两种在MnO₂表面生成的化合物都对Sb(III)和Sb(V)具有较强的吸附能力，提升了对锑的吸附量，同时阻止了Sb(III)与MnO₂表面的直接接触，抑制了Sb(III)的氧化。尽管Sb(III)可以穿过Fe-Sb化合物和施氏矿物继续被MnO₂氧化，但由于Fe-Sb化合物和施氏矿物具有不同的化学特性，因此对Sb(III)氧化的抑制程度和对Sb(III)和Sb(V)的吸附能力也不相同。综上，酸性水环境中，Fe(II)的存在对MnO₂氧化Sb(III)有着显著的抑制作用，但对MnO₂吸附锑有着显著的促进作用。

（2）系统研究了溶解态Mn(II)对水铁矿/赤铁矿表面Sb(III)吸附氧化的影响，通过改变Mn(II): Sb(III)摩尔比和pH值以及添加Mn(III)络合剂和自由基掩蔽剂等方式探究反应机理。研究发现，由于铁氧化物的催化氧化作用，在Mn(II)存在时，水铁矿或赤铁矿表面有Mn(IV)/Mn(III)氧化物的生成，且生成量会因为pH值和Mn(II): Sb(III)摩尔比的升高或Mn(II)的预处理而增加。在铁氧化物表面生成的Mn(IV)氧化物是反应过程中主要的Sb(III)氧化剂，Sb(III)的氧化使得铁氧化物表面Mn(III)浓度升高，有助于锰循环的顺利进行。由于水铁矿对锑的吸附能力强于赤铁矿，导致水铁矿-Mn(II)体系对Sb(III)氧化的促进作用弱于赤铁矿-Mn(II)体系。铁氧化物表面生成的锰氧化物还会对整体的吸附能力产生一定的抑制，但抑制作用随着铁氧化物比表面积的增加而降低。综上，溶解态Mn(II)的存在会促进Sb(III)的氧化、抑制Sb(III)/Sb(V)的吸附，促进/抑制程度与铁氧化物的比表面积有关。

（3）系统探究了Fe(II)催化的水铁矿晶型转化过程对Sb(V)和Sb(III)迁移转化的影响，运用多种表征手段对水铁矿的晶型转化过程进行了动态监测，并通过对不同形态锑浓度的测定探究了水铁矿晶型转化对Sb(III)氧化和锑迁移的影响机理。研究发现，由于水铁矿具有较强的吸附能力，反应开始后Sb(V)和Sb(III)快速进入固相中，且反应过程中没有溶解态锑的释放，可见Fe(II)催化的水铁矿晶型转化对锑在固体和液体间的迁移没有显著影响。反应过程中，约42-80%的锑迁移性显著降低。在Sb(III)反应体系中，约62-80%的Sb(III)被氧化为Sb(V)，其氧化物可能是在Fe(II)催化的水铁矿晶型转化过程中生成的活性氧化物质。Sb(V)和Sb(III)的存在会对Fe(II)催化的水铁矿晶型转化产生一定的促进作用，且促进作用随着锑浓度的增加逐渐降低。Sb(III)对水铁矿晶型转化的影响相对较强，铁锑摩尔比100和80的条件下的主要产物是针铁矿，铁锑摩尔比40条件下的主要产物是纤铁矿。Sb(V)-水铁矿体系中，纤铁矿是主要转化产物。Sb(III)-水铁矿体系中，水铁矿先转化为纤铁矿，随后逐渐转化为针铁矿。综上，Fe(II)催化的水铁矿晶型转化过程会降低Sb(V)和Sb(III)的迁移性，且对Sb(III)有显著的氧化作用。

（4）系统考察了草酸影响下Sb(V)-水铁矿/针铁矿再结晶过程中锑的释放行为，通过改变草酸浓度和pH值以及添加Fe(III)以提前达到溶解平衡等方式探究反应机理。研究发现，反应过程中锑的释放是非化学计量释放，不受铁氧化物净溶解的影响。锑释放的速率随pH值的升高逐渐降低，随草酸浓度的升高逐渐升高。草酸影响下Sb(V)-水铁矿/针铁矿的再结晶以及锑的释放过程大致为：草酸与铁氧化物表面Fe(III)结合导致铁氧化物的溶解，并生成溶解态Fe(III)-草酸络合物，这些络合物可能再次被吸附到铁氧化物表面。为了达到质量平衡，被吸附的Fe(III)-草酸络合物发生解离，解离产生的Fe(III)造成了局部的矿物生长，而草酸则回到溶液中并与矿物表面另一个Fe(III)生成络合物。矿物的溶解导致原先结合在矿物结构中的锑暴露于矿物表面，从而发生溶解，释放至溶液中。因此，草酸的存在会促进掺杂在水铁矿/针铁矿中锑的释放。

本研究结果表明，铁、锰化合物共存时会影响各自对Sb(III)的吸附和氧化，铁化合物的存在会促进锰化合物对锑的吸附，但抑制锰化合物对Sb(III)的氧化，而锰化合物的存在会提高铁氧化物对Sb(III)的氧化能力，但抑制铁氧化物对锑的吸附。此外，铁氧化物再结晶过程中锑的迁移性能会受到显著影响。锑可能在水铁矿晶型转化过程中进入铁氧化物晶体结构，迁移性显著降低，同时部分Sb(III)被氧化为Sb(V)。而掺杂Sb(V)的水铁矿和针铁矿在草酸影响下发生再结晶，晶体结构中Sb(V)发生迁移，释放至溶液中。本研究的结果为全面、深入地了解锑的地球化学循环提供了数据支持和理论基础，同时对锑污染的预防和控制也具有指导意义。

The two most common oxidation states of antimony (Sb) in the environment are Sb(III) and Sb(V), however, they have different toxicity and mobility. Iron and manganese compounds are two of the most common metal compounds in the natural environment and they may influence the Sb transformation and migration by catalytic oxidation, direct oxidation, adsorption, etc. However, existed research on the geochemical cycle of Sb mediated by the iron or manganese cycle mostly took the single system of iron or manganese compound as the study subject, there were few researches on the migration and transformation of Sb under the combined effect of iron and manganese compounds. Moreover, studies on the migration and transformation of antimony in the process of iron oxides recrystallization were also inadequate. In the present study, investigations on the mechanism of co-adsorption and oxidation of Sb (III) by iron and manganese compounds and the migration and transformation of antimony in the process of iron oxide transformation were conducted by carrying out kinetic experiments and spectral characterization for concentration detection (such as Atomic Fluorescence Spectrometry (AFS), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), etc.) and surface characterization (such as X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), etc.). The research results have important theoretical significance for an in-depth understanding of the environmental geochemical process and fate of antimony and have guiding significance for the prevention and regulation of antimony pollution. The main results are as follows:

(1) The effect of dissolved Fe(II) on the adsorption and oxidation of Sb(III) by MnO₂ in acidic waters was systematically studied. The reaction mechanism was explored by comparison of individual oxidation of Sb(III)/Fe(II) and simultaneous oxidation of Sb(III) and Fe(II) by MnO₂ and by conducting experiments under different Fe(II): Sb(III) molar ratios and Fe(II) pretreatment times. It was found that Fe-Sb compounds were formed on the surface of MnO₂ in the process of simultaneous oxidation of Fe(II) and Sb(III) by MnO₂, while schwertmannite was formed on the surface of MnO₂ in the process of Fe(II) pretreatment of MnO₂. Both compounds formed on the surface of MnO₂ had strong Sb(III) and Sb(V) adsorption capacity, which improved the adsorption of antimony. Meanwhile, direct contact between Sb(III) and the surface of MnO₂ was prevented, which inhibited the oxidation of Sb(III). Although Sb(III) can permeate Fe-Sb compounds and schwertmannite and continue to be oxidized by MnO₂, the inhibition of these two compounds on Sb(III) oxidation and adsorption capacity of Sb(III) and Sb(V) was different due to their different chemical properties. Therefore, in acidic waters, the presence of Fe(II) can significantly inhibit the oxidation of Sb(III) by MnO₂, but significantly promote the adsorption of antimony.

(2) The effect of dissolved Mn(II) on Sb(III) adsorption and oxidation on the surface of ferrihydrite/hematite was systematically studied. Experiments were conducted under different Mn(II): Sb(III) molar ratios, pH values, and in the presence and absence of Mn(III) complexing agent and free radical masking agent. It was found that Mn(IV)/Mn(III) oxides were formed on the surface of ferrihydrite/hematite in the presence of Mn(II) due to the catalytic oxidation of iron oxides, and the amount of formed Mn(IV)/Mn(III) oxides increased with the increase of pH value and the molar ratio of Mn (II): Sb(III) or due to the pretreatment of Mn(II). Mn(IV) oxide formed on the surface of iron oxide was the main oxidant for Sb(III). The oxidation of Sb(III) led to the increases of Mn(III) concentration on the surface of iron oxide, which enabled the manganese cycle. The adsorption capacity of ferrihydrite for antimony is stronger than that of hematite, as a result, the promotion effect of the ferrihydrite-Mn(II) system on Sb(III) oxidation was weaker than that of the hematite-Mn(II) system. Manganese oxides formed on the surface of iron oxide also inhibited the adsorption capacity of the solid, but the inhibition decreased with the increase of the specific surface area of iron oxides. It can be concluded that the presence of dissolved Mn (II) will promote the oxidation of Sb(III) and inhibit the adsorption of Sb(III)/Sb(V). The degree of promotion/inhibition was related to the surface area of iron oxides.

(3) The effect of Fe(II)-catalyzed transformation of ferrihydrite on the migration and transformation of Sb(V) and Sb(III) was systematically investigated. Multiple characterization methods were conducted to monitor the dynamic transformation process of ferrihydrite. Furthermore, the influence mechanism on Sb transport and Sb(III) oxidation of ferrihydrite transformation was explored by measuring the concentrations of different forms of Sb. It was found that Sb(V) and Sb(III) quickly entered the solid phase after the initiation of the reaction due to the strong adsorption capacity of ferrihydrite, and the transformation of ferrihydrite catalyzed by Fe(II) had no significant effect on the migration of antimony between solid and liquid phases. During the reaction, about 42-61% of antimony eventually transformed into the phosphate-unextractable phase, and this part of antimony existed in the solid phase as a more stable binding state. In the Sb(III) reaction system, about 62-80% of the initial Sb(III) was oxidized to Sb(V), and the oxidant may be reactive Fe(III) compounds generated in the process of ferrihydrite transformation catalyzed by Fe(II). The existence of Sb(V) and Sb (III) promoted the transformation of ferrihydrite, and the promoting effect decreased with the increase of antimony concentration. Moreover, Sb(III) had a relatively strong influence on the transformation of ferrihydrite. The main product under the condition of Fe/Sb(III) molar ratio of 100 and 80 was goethite, and the main product under the condition of Fe/Sb(III) molar ratio of 40 was lepidocrocite. In the Sb(V)-ferrihydrite system, lepidocrocite was the main transformation product. In Sb(III)-ferrihydrite system, ferrihydrite was firstly transformed to lepidocrocite, and then eventually transformed to goethite. In conclusion, the Fe(II)-catalyzed transformation of ferrihydrite reduced the mobility of Sb(V) and Sb(III) and had a significant oxidation effect on Sb(III).

(4) The release and mechanism of antimony in the recrystallization process of Sb(V)-ferrihydrite/goethite under the influence of oxalate were systematically investigated. The reaction mechanism was explored by changing the concentrations of oxalate and pH values and the addition of dissolved Fe(III) to reach the dissolution equilibrium of iron oxide. It was found that the release of antimony in the reaction process was non-stoichiometric and was not affected by the net dissolution of iron oxides. The release rate of antimony decreased with the increase of pH value and increased with the increase of oxalate concentration. Under the influence of oxalate, the release of antimony in the recrystallization process of Sb(V)-ferrihydrite/goethite was as followed: The complexation of oxalate and Fe(III) on the surface of iron oxide led to the dissolution of iron oxide and the formation of dissolved Fe(III)-oxalate complex, and these complexes could be reabsorbed to the surface of iron oxide. To achieve mass balance, these adsorbed complexes were dissociated, as a result, Fe(III) caused local mineral growth while oxalate returned to the solution and formed a complex with another Fe(III) on the mineral surface. The antimony originally entrapped in the mineral structure was exposed at the region of the mineral surface where the dissolution occurred, which dissolved and was released into the solution. Therefore, the presence of oxalate will promote the release of antimony structural incorporated in ferrihydrite/goethite.

The present study found that the coexistence of iron and manganese compounds affected their adsorption and oxidation of Sb(III). The presence of iron compounds promoted the adsorption of antimony but inhibited the oxidation of Sb(III) by manganese compounds. The presence of manganese compounds improved the Sb(III) oxidation ability yet reduced the Sb adsorption ability of iron oxides. In addition, the mobilization of antimony was significantly affected by the recrystallization of iron oxide. Antimony might be incorporated into the structure of iron oxides which led to a significant decline in Sb mobilization and oxidation of Sb(III). Moreover, recrystallization of Sb(V) incorporated ferrihydrite and goethite occurred in the presence of oxalate, causing Sb(V) release into the solution. The results of this study provide data support and a theoretical basis for a comprehensive understanding of the geochemical cycle of antimony, and also have certain guiding significance for the prevention and control of antimony pollution.