土壤铁氧化物-亚铁的相互作用及其环境影响研究进展

铁氧化物和溶液相亚铁常在厌氧土壤环境中共存。铁氧化物能够加快亚铁的氧化速率，且控制亚铁氧化成矿产物的类型，同时，亚铁与铁氧化物组成的系统是一种良好的还原剂，能够有效还原重金属及降解有机污染物。另一方面，亚铁能够催化铁氧化物晶相转变，导致铁氧化物结构和表面性质发生改变，进而影响相关重金属、有机质的环境行为。本文综述了铁氧化物催化亚铁氧化成矿、铁氧化物-亚铁系统还原污染物以及亚铁催化铁氧化物相变的反应机制及影响因素，最后，对未来在自然土壤中研究铁氧化物-亚铁界面反应及其环境影响进行了展望。     

金属离子在铁(氢)氧化物与腐殖质微界面上的吸附机理和模型研究进展

铁(氢)氧化物和腐殖质是广泛分布在土壤中的重要天然活性物质,因其具有较大的比表面积并且铁(氢)氧化物表面的-OH与腐殖质表面的-COOH、-OH等活性官能团可通过静电作用、配体交换等多种机制对重金属离子产生较强吸附,从而影响重金属离子在环境中的迁移、转化和生物效应。深入了解重金属离子在铁(氢)氧化物-腐殖质复合体微界面相互作用的分子机理,对于阐明重金属离子在环境中的迁移、转化过程具有重要意义。本文综述了金属离子在铁(氢)氧化物与腐殖质上吸附机理和模型的研究进展,为重金属污染土壤的风险评估和控制提供理论依据。     

铁铝氧化物–层状硅酸盐矿物互作对Cr (Ⅵ)和As (Ⅴ)吸附的影响

以高岭石、蒙脱土、针铁矿和三水铝石四种单一典型土壤矿物以及针铁矿-蒙脱石和三水铝石-蒙脱石（质量比为1:1）两种代表性土壤矿物复合体为吸附材料，采用吸附平衡实验、能谱分析（(EDS）、红外光谱、扫描电镜、酸碱滴定和zeta电位测定等方法，研究了铁铝氧化物与层状硅酸盐矿物之间的相互作用对Cr(Ⅵ)和As(Ⅴ)吸附的影响及其机制。吸附平衡实验和EDS实验结果表明，两种复合体对Cr(Ⅵ)和As(Ⅴ)的吸附容量均小于其两种组成矿物单一体系吸附量的平均值，即铁铝氧化物与蒙脱石的互作降低了这些氧化物对Cr(Ⅵ)和As(Ⅴ)的吸附能力。表面性质表征结果表明，与蒙脱石复合后，针铁矿与三水铝石表面的正电荷均被完全中和，电荷符号发生反转。与理论值相比，三水铝石-蒙脱石复合体的表面位点总浓度无明显变化，比表面积减小。针铁矿-蒙脱石复合体的比表面积与理论值无明显差异，但矿物表面位点浓度减小，表面羟基红外吸收峰强度减弱。氧化物与层状硅酸盐矿物互作改变了矿物表面性质，这可能是导致氧化物对Cr(Ⅵ)和As(Ⅴ)的吸附能力降低的主要原因。当评估污染元素在土壤中有效性时应当考虑土壤固相组分间的互作对离子吸附的影响。     

长期秸秆还田对砂姜黑土矿质复合态有机质稳定性的影响

依托10 a定位试验研究了秸秆还田对典型砂姜黑土有机矿质复合体中有机质稳定性的影响机制。田间试验设置5个处理:氮磷钾配施下的小麦和玉米秸秆双季还田(WMS+F)、小麦秸秆还田(WS+F)、玉米秸秆还田(MS+F)、非秸秆还田(F)处理,以不施肥模式下的非秸秆还田为对照(CK)。结果显示,铁铝键合态和紧密结合态有机质含量累计占土壤总有机质的88.70%,且三者变化趋势一致,均呈现WS+F≈WMS+F≈MS+FFCK,并与土壤短程有序、有机结合态铁铝氧化物呈显著正相关,但与非晶型铁铝氧化物呈负相关性。秸秆还田显著促进了土壤有机质累积,并受到土壤铁铝键合态有机质的影响,但由于非晶型铁铝氧化物生成速度较慢,限制了土壤有机质的进一步累积。土壤紧密结合态有机质对其全量的贡献明显高于铁铝键合态有机质,相关机制值得进一步研究。     

α-氧化铝–细菌二元复合胶体对锑的吸附研究

锑(Sb)在土壤胶体微界面的吸附解吸深刻影响其迁移、转化和归趋.土壤矿物、有机物、微生物等胶体组分多结合在一起,形成复杂的矿物–有机复合体.目前,锑在单一土壤组分上的吸附研究颇多,但较少有学者关注锑在土壤矿物–有机复合胶体界面的吸附过程和机制.通过宏观吸附以及光谱学技术探究锑在典型铝氧化物–细菌复合胶体上的吸附行为,结...     

水分非饱和条件下土壤矿物界面有毒有机物转化机制研究进展

土壤矿物作为土壤重要活性组分，可驱动土壤有毒有机物化学转化，降低污染风险。以往土壤矿物与有毒有机物界面行为研究主要集中于水环境或矿物悬浊液体系，然而实际环境中土壤及其矿物常处于干燥、湿润等水分非饱和状态。近年来，水分非饱和条件下土壤矿物界面有毒有机物转化及机制已成为研究热点，相关研究获得一系列新发现。低含水量铁锰矿物、黏土矿物和金属离子饱和黏土矿物能驱动多环芳烃、抗生素等疏水性有毒有机物化学转化。水分非饱和环境会减弱矿物界面水分子与有毒有机物竞争活性位点，并使矿物发生脱水、向高活性结构转变。此外，土壤矿物水分状态也会影响有毒有机物转化产物，水分非饱和环境更有利于持久性自由基和卤代二噁英等中间产物的形成和稳定。以往研究认为，电子转移反应是土壤矿物界面有毒有机物转化机制，随着检测技术与理论计算的发展，自由基催化和水解作用机制逐渐被发现，相关机制研究精准至矿物晶型和晶面层面。虽然水分非饱和条件下土壤矿物界面有毒有机物转化及机制已逐渐清晰，但其研究广度和深度有待进一步拓宽和加深。建议未来在实际水分非饱和土壤和矿物中开展有毒有机物转化研究，深入探究还原转化过程，研发原位反应装置及检测方法，尝试从微纳米尺度和分子水平解析有毒有机物在矿物界面转化机制。     

基于不同分析方法研究磷酸根在矿物表面吸附机制的进展

磷素是植物生长必需的营养元素,也是联系生态系统中生物与非生物作用的关键元素。对磷酸根在矿物表面吸附反应机制的深入认识,有助于了解其在陆地和水环境中的形态、迁移、转化和生物有效性。本文主要综述了磷酸根在常见(土壤)矿物表面吸附机制的研究进展。各种分析技术或方法,如OH–释放量分析、Zeta电位分析(电泳迁移率测试)、等温滴定量热法、原子力显微镜、X射线光电子能谱、红外光谱、核磁共振波谱、X射线吸收光谱、表面络合模型、量子化学计算等,均以不同方式揭示磷酸根在不同矿物体系的吸附机制。磷酸根在矿物(尤其是铁、铝氧化物)表面的吸附通常伴随着水基和羟基的交换。一般认为磷酸根在矿物表面主要形成双齿双核、单齿单核内圈络合物,且受pH的影响较大。pH以及磷酸根在矿物表面的吸附密度影响内圈络合物的质子化状态。在低pH、高磷浓度、较高反应温度、较长吸附时间,以及弱晶质矿物吸附等条件下矿物表面吸附的磷可在矿物表面转化形成含磷的表面沉淀,造成矿物溶解转化以及磷生物有效性的进一步降低。最后展望了磷酸盐在矿物-水界面吸附有关的研究热点和方向。     

土壤中铁铝氧化物与黏土矿物交互作用的研究进展

铁铝氧化物与黏土矿物是土壤中最重要、最活跃的固相组分之一,一般占土壤质量的90%以上,它们之间的交互作用直接影响土壤界面活性、理化性质和肥力状况.本文以铁铝氧化物和黏土矿物胶结过程中的一些表观特征变化为出发点,重点阐述了交互作用前后对土壤理化性质的影响,以及宏观表现到微观交互作用的机理,并提出了宜加强二者交互作用的界面特性、非晶形向晶形转化过程等的研究,以期揭示土壤退化、团聚体形成、元素的保蓄与释放、土壤污染物的调控等土壤的基本属性问题.     

可变电荷土壤中特殊化学现象及其微观机制的研究进展

综述了近年来可变电荷土壤化学研究的进展,着重总结了可变电荷土壤中的盐吸附、铁铝氧化物对土壤自然酸化的抑制作用和离子强度对离子专性吸附的影响等特殊化学现象及其微观机制的研究进展。用颗粒表面扩散层重叠导致有效电荷数量减小的原理解释了盐吸附现象和铁铝氧化物对土壤自然酸化的抑制作用。阐明了可变电荷土壤和矿物中介质离子强度影响离子专性吸附的机制,用四层吸附模型解释了离子专性吸附随离子强度增大而增加的现象,并根据胶体zeta电位随离子强度改变而变化的趋势进一步证明了离子强度增大使胶体专性吸附面上静电电位的绝对值减小,是离子专性吸附随离子强度增大而增加的主要原因。带电颗粒表面双电层结构和双电层相互作用的深入研究,有助于阐明可变电荷土壤中一些特殊化学现象的微观机理,从而进一步完善土壤化学理论。     

亚热带土壤亚铁与厌氧反硝化

本文就亚热带土壤亚铁参与反硝化的可能性进行了探讨。研究结果表明:厌氧还原条件下加入KNO3的处理中,Fe2+浓度随培养时间延长而下降,且Fe2+浓度的降低和NO3–-N浓度的降低呈显著正相关。预培养结束后的亚铁浓度(In-Fe2+)和厌氧培养期间Fe2+浓度降低速率与反硝化势表征指标k、b、v7,以及与无定形铁氧化物(活性铁)含量的显著正相关性初步证明,活性铁通过不同价态铁离子(Fe2+和Fe3+)之间的转化,参与了反硝化的电子传递过程。当有机碳等电子供体受限时,Fe2+可作为电子供体参与反硝化还原NO3–-N。这一结果表明,NO3–-N作为电子受体参与厌氧条件下Fe2+氧化成Fe3+的反应可能在铁氧化物含量丰富的亚热带土壤中普遍存在。     

Surface chemical properties and pedogenesis of tropical soils derived from basalts with different ages in Hainan,China

Limited information is available on the changes of surface chemical properties of tropical soils with time during the pedogenesis. Soil samples of three profiles derived from basalts of 10, 1330 and 2290 kilo annum (ka) in age were collected from adjacent locations in a tropical region of Hainan Province, China. The changes in soil surface chemical properties and the mineralogy of the soil clay fraction with time were investigated using ion adsorption, micro-electrophoresis, and X-ray diffraction analysis. The content of 2:1-type clay minerals decreased, while those of kaolinite and gibbsite increased with increasing basalt age and degree of soil development. The content of pedogenic free iron (Fe) oxides and the ratio of free Fe oxides/total Fe oxides increased with soil development stage, while soil poorly crystalline Fe and aluminum (Al) oxides had an opposite trend. The positive surface charge of the soils increased with increasing basalt age and degree of soil development; this was consistent with the change in their contents of free Fe/Al oxides. However, the value of negative surface charge had an opposite behavior. The soil derived from 10-ka-basalt had much more negative charge than soils derived from 1330- and 2290-ka-basalt. Soil net surface charge and zeta potential of the soil clay-fraction decreased with the increase in basalt age. Both net charge–pH curves and zeta potential–pH curves shifted to positive values with increased basalt age and degree of soil development. Increasing age also elevated the point of zero net charge of the soil and the isoelectric point of soil colloids.     

Effect of acid deposition on the displacement of Al(III) in soils

This study represents an assessment of some of the key factors influencing the mobility of Al(III) and its displacement in acid soils. This assessment is based on the effect of pH and other solution variables on the solubility of Al(III) and its complex formation with OH^?, F^? and organic ligands (fulvates and humates). Above all, the adsorption behavior of Al(III) on iron(III) (hydr)oxides and on SiO₂ on one hand, and the adsorption of organic acids and of humic substances on mineral surfaces on the other hand was investigated. Adsorption is interpreted in terms of surface complex formation equilibria; the mass law constants derived permit the modeling of adsorption as a function of solution variables. It is illustrated that the distribution of oxides and hydroxides in the soil profile affects the pH buffering, determines the mobility of the organic acids while the mobility of Al(III) is primarily governed by the formation and dissolution of Al(III) (hydr)oxides.     

Aluminiumsubstitution in pedogenen Eisenoxiden – eine Übersicht

Al-substitution in Fe-oxides This article resumes the present knowledge on Al-substitution in Fe (III)oxides. Al-substitution is known for goethite, hematite, lepidocrocite, magnetite and maghemite. The extent of substitution is mineral specific and varies for different soil environments for which it may have some indicator value. Al-substituted Fe-oxides are easily to synthesize. A number of characteristics of the synthetic samples have been measured. The result was that most of the changes in characteristics except the unit cell size is more an indirect effect of Al-substitution because Al in the system also affects crystallinity. Crystallinity will, however, also be strongly influenced by other conditions during crystallization. Therefore, thermal behaviour, X-ray line intensity and width, magnetization, dissolution, OH-content, IR absorption characteristic etc. depend more directly on crystallinity than on Al-substitution. The variation of these characteristics for soil iron oxides is essentially unknown so far.     

Specific features of iron behavior in soddy-podzolic and alluvial gleyed soils of the Middle Cis-Urals region

The regime of observations revealed that the Eh dynamics in soddy-podzolic and alluvial soils in the Middle Cis-Urals region depends not only on the rate of iron (hydr)oxides reduction but also on the rate of opposite reactions in the gleyed horizons. Both processes depend on the temperature. The Eh value decreases on heating in automorphic soils, when the reduction of Fe(III)-(hydr)oxide particles accelerates. On the contrary, in gley soils, the Eh decreases on cooling, probably, because of the reactions opposing the reduction of Fe(III)-(hydr)oxide particles, including Fe(II) fixation on the surface of mineral particles. Fe(III)-(hydr)oxides are, for the most part, preserved in gleyed soils of the Cis-Urals; the content of (Fe₂O₃)_dit reaches 3.3% with iron minerals being usually represented by goethite. The increase in moistening influences the soil parameters (i.e., the redoxpotential rH and the content of conventional red pigment Hem_conv) in an intricate manner. Both direct and reverse branches on the curve of the Hem_conv-rH dependence point to the equilibrium and nonequilibrium conditions in the soil. The reverse branch probably stands for the initial phase of gleying in strongly humified soils, where, despite extra electrons in the solution, the brown pigment in the form of Fe(III)-(hydr)oxides is preserved.     

Speciation and sorption structure of diphenylarsinic acid in soil clay mineral fractions using sequential extraction and EXAFS spectroscopy

Purpose

The mobility of arsenic (As) in soils is fundamentally affected by the clay mineral fraction and its composition. Diphenylarsinic acid (DPAA) is an organoarsenic contaminant derived from chemical warfare agents. Understanding how DPAA interacts with soil clay mineral fractions will enhance understanding of the mobility and transformation of DPAA in the soil-water environment. The objective of this study was to investigate the speciation and sorption structure of DPAA in the clay mineral fractions.

Materials and methods

Twelve soils were collected from nine Chinese cities which known as chemical weapons burial sites and artificially contaminated with DPAA. A sequential extraction procedure (SEP) was employed to elucidate the speciation of DPAA in the clay mineral fractions of soils. Pearson’s correlation analysis was used to derive the relationship between DPAA sorption and the selected physicochemical properties of the clay mineral fractions. Extended X-ray absorption fine structure (EXAFS) L_III-edge As was measured using the beamline BL14W1 at Shanghai Synchrotron Radiation Facility (SSRF) to identify the coordination environment of DPAA in clay mineral fractions.

Results and discussion

The SEP results showed that DPAA predominantly existed as specifically fraction (18.3–52.8%). A considerable amount of DPAA was also released from non-specifically fraction (8.2–46.7%) and the dissolution of amorphous, poorly crystalline, and well-crystallized Fe/Al (hydr)oxides (20.1–46.2%). A combination of Pearson’s correlation analysis and SEP study demonstrated that amorphous and poorly crystalline Fe (hydr)oxides contributed most to DPAA sorption in the clay mineral fractions of soils. The EXAFS results further demonstrated that DPAA formed inner-sphere complexes on Fe (hydr)oxides, with As-Fe distances of 3.18–3.25 Å. It is likely that the steric hindrance caused by phenyl substitution and hence the instability of DPAA/Fe complexes explain why a substantial amount of DPAA presented as weakly bound forms.

Conclusions

DPAA in clay mineral fractions predominantly existed as specifically, amorphous, poorly crystalline, and crystallized Fe/Al (hydr)oxides associated fractions. Amorphous/poorly crystalline Fe rather than total Fe contributed more to DPAA sorption and DPAA formed inner-sphere complexes on Fe (hydr)oxides.

     

Effect of iron oxide removal on heavy metal sorption by acid subsoils

The adsorption of Cd, Cu, Pb, and Zn from 0.025 M NaClO₄ solutions by two ferruginous subsoils, Christiana silty clay loam and Dothan sandy clay, was investigated. Under acidic conditions, selective dissolution and removal of the Fe oxide soil component by dithionite-citrate-bicarbonate (DCB) generally increased heavy metal adsorption by the soils. This effect was attributed to increased electrostatic attraction of cations to the DCB-washed soils as evidenced by substantial reduction in the zero point of charge (ZPC) for the Dothan soil following DCB extraction. Alternately, the DCB extraction stripped Fe and Al species bound to structural exchange sites or eliminated coatings which reduce cation accessibility to such sites. Addition of low levels (10^?6 M) of ferric iron suppressed heavy metal adsorption capacity of the DCB-extracted Christiana soil to values comparable to the unmodified whole soil system. While hydrous oxide surfaces represent highly reactive sites for cation binding, Fe oxides can modify both the pH-dependent and structural exchange sites in a manner which hinders heavy metal adsorption. Thus, a soil's Fe-oxide content is unlikely to be a reliable guide to heavy metal adsorption capacity.     

低分子量有机酸对可变电荷土壤铝活化动力学的影响

从动力学角度研究了几种低分子量有机酸对2种酸性土壤中铝的活化和活化铝在土壤固/液相之间分配的影响。结果表明:对于络合能力弱的醋酸和乳酸,主要通过质子作用活化铝,且活化作用明显小于盐酸。而络合能力较强的苹果酸、草酸和柠檬酸,主要通过络合作用促进铝的释放,且这种作用随有机酸根阴离子络合能力的增强而增加。在氧化铁含量较高的砖红壤中,苹果酸、草酸和柠檬酸通过专性吸附增加土壤表面负电荷,从而增加土壤交换态铝;但在氧化铁含量较低的红壤中,草酸和柠檬酸主要通过形成可溶性铝络合物降低交换态铝。活化铝在土壤固/液相间的分配主要决定于溶液中有机阴离子与土壤固相表面对铝离子的竞争。醋酸和乳酸活化的铝主要以交换态铝存在;而草酸和柠檬酸活化的铝主要以有机酸-铝络合物存在于溶液中,特别是在氧化铁低的红壤中,这将促进铝在土壤-水体中的迁移。