Cr^(Ⅵ) adsorption on four typical soil colloids: equilibrium and kinetics

It is observed that the adsorption of chromium are greater on kaolinite minerals, red soil (R) and laterite (L) colloids than that on montmorillonite, indicotic black (IB) and yellow brown (YB) soil colloids. The adsorption process of Cr Ⅵ on these media can be further described by Langmuir or Freundlich equation quite well. The adsorption reaction of Cr Ⅵ is fast, and the adsorption equilibrium can be reached within the first two hours in moderate temperature. The adsorption quantity of Cr Ⅵ to kaolinite mineral increased with the increasing pH in the range of 2.0 to 7.0, then decreased at higher pH. But it showed some consistence among the four soil colloids. The lower the pH, the stronger the adsorption. The possible mechanisms are further discussed here. Meanwhile the influence of temperature on Cr Ⅵ adsorption on different soil colloid and clay minerals are also investigated.

Amplification of plasmid DNA bound on soil colloidal particles and clay minerals by the polymerase chain reaction

Polymerase chain reaction （PCR） was used to amplify a 600-base pair （bp） sequence of plasmid pGEX-2T DNA bound on soil colloidal particles from Brown soil （Alfisol） and Red soil （Ultisol）, and three different minerals （goethite, kaolinite, montmorillonite）. DNA bound on soil colloids, kaolinite, and montmorillonite was not amplified when the complexes were used directly but amplification occurred when the soil colloid or kaolinite-DNA complex was diluted, 10- and 20-fold. The montmorillonite-DNA complex required at least 100-fold dilution before amplification could be detected. DNA bound on goethite was amplified irrespective of whether the complex was used directly, or diluted 10- and 20-fold. The amplification of mineral-bound plasmid DNA by PCR is, therefore, markedly influenced by the type and concentration of minerals used. This information is of fundamental importance to soil molecular microbial ecology with particular reference to monitoring the fate of genetically engineered microorganisms and their recombinant DNA in soil environments.

INFLUENCES OF SEVERAL SOIL COLLOIDS ON THE ADSORPTION AND PROPERTIES OF UREASE ENZYME

The present experiment was designed to elucidate the effects of the sterilized colloids separated from red soil,latosol and yellow brown soil,which are the typical zonal soils in central-south China, on the adsorption,activity,kinetic parameters and thermal stability of urease enzyme which plays significant role in the transformation of soil nitrogen compounds. Results show that the amount of enzyme adsorbed on the examined soil colloids followed the order: yellow brown soil>red soil=latosol. The residual activities of enzyme in different colloid systems are in the following sequence:red soil>latosol> yellow brown soil. The thermal stability of adsorbed enzyme is higher than that of free enzyme. The enzyme immobilized on yellow brown soil colloid had the highest stability at elevated temperature from 60 to 80℃. Both of the free and immobilized urease obey Michaelis-Menten kinetics. The Km values of immobilized urease (13. 5-20. 8 mM) on different soil colloids examined were in the same order of magnitude as that of free urease (9. 3mM). The kinetic constant of immobilized enzyme suggests that urease adsorbed on yellow brown soil colloid has a greater affinity for substrate. The Ku and Vmax values also indicate a mixed type of enzyme inhibition for the examined soil colloids. These results provide basic evidences for the understanding of the properties and kinetics of soil enzymes in tropic and subtropic regions.

Adsorption of Cadmium by Soil Colloids and Minerals in Presence of Rhizobia

Experiments were conducted to study the adsorption of Cd on two soil colloids (red soil and yellow- brown soil) and three variable-charge minerals (goethite, noncrystalline Fe oxide and kaolin) in the absence and presence of rhizobia. The tested strain Rhizobium fredii C6, tolerant to 0.8 mmol L-1 Cd, was selected from 30 rhizobial strains. Results showed that the isotherms for the adsorption of Cd by examined soil colloids and minerals in the presence of rhizobia could be described by Langmuir equation. Within the range of the numbers of rhizobial cells studied, the amount of Cd adsorbed by each system increased with increasing rhizobial cells. Greater increases for the adsorption of Cd were found in red soil and kaolin systems. Rhizobia influence on the adsorption of Cd by examined soil colloids and minerals was different from that on the adsorption of Cu. The presence of rhizobia increased the adsorption sanity of soil colloids and minerals for Cd, particularly for the goethite and kaolin systems. The discrepancies in the influence of rhizobia on the adsorbability and affinity of selected soil colloids and minerals for Cd suggested the different interactions of rhizobia with various soil components. It is assumed that bacterial biomass plays an important role in controlling the mobility and bioavailability of Cd in soils with kaolinite and goethite as the major colloidal components, such as in variable-charge soil.

Effect of Cr(Ⅵ) and p-Chloroaniline Interaction on Their Reaction Behaviors on Soil Colloids

INTRODUCTIONStudiesonheavymetalororganicpollutantsinsoilhaverecedelymadegreatprogressboththeoreticallyandpractically.However,pollutionisusuallydevelopedbynotasinglebutamulti-substratecomplex.Furtherunderstandingthemechanismsandprocedureofmulti-substr...

Adsorption of Acid Phosphatase on Minerals and Soil Colloids in Presence of Citrate and Phosphate

The aim of this work was to study the influence of phosphate and citrate,which are common inorganic and organic anions in soils,on the adsorption of acid phosphatase by kaolin,goethite and the colloids separated from yellow-brown soil(YBS)and latosol(LS)in central-south China.The YBS colloid has the major clay mincral composition of 1.4 nm mincral,illite and kaolinite while the LS colloid mainly contains kaolinite and oxides.The adsorption isotherm of acid phosphatase on the examined soil colloids and minerals fitted to the Langmuir model.The amount of enzyme adsorbed in the absence of ligands was in the order of YBS colloid>LS colloid>kaolin≈goethite.In the presence of phosphate or citrate,the amounts of the enzyme adsorbed followed the sequence YBS colloid>kaolin>LS colloid>goethite.The presence of ligands also decreased the binding energy between the enzyme and soil colloids or minerals.With the increase of ligand concentration from 10mmol L^-1 to 400 m mol L^-1,different behaviors for the adsorption of cnzyme were found in the colloid and mineral systems studied.A sharp decrease in enzyme adsorption was observed on goethite while gradual decreases of enzyme adsorption were recorded in the two soil colloid systems.However,no any decrease was found for the amount of enzyme adsorbed on kaolin at higher ligand concentrations.When phosphate or citrate was introduced to the system before the addition of enzyme,the ligands usually enhanced the adsorption of enzyme.The results obtained in this study suggested the important role of kaolinite mineral in the adsorption of enzyme molecules in acidic soils in the presence of various ligands.

Surface Chemical Properties of Colloids in Main Soils of China

Surface chemical properties of soil colloids are the important factor affecting soil fertility and genesis.To provide scientific basis for soil genetic classification,promotion of soil fertility and reasonable fertilizqation,the specific surface area and electric charge of soil colloids in relation to clay minerals and organic matter are further discussed on the basis of the results obtained from the studies on surface chemical properties of soil colloids in five main soils of China.Results from the studies show that the effect of clay minerals and organic matter on the surface chemical properties of soil colloids is very complicated because the siloxane surface,hydrated oxide surface and organic matter surface do not exist separately,but they are always mixed together and influenced each other.The understanding of the relationship among clay minerals,organic matter and surface chemical properties of soil colloids depends upon further study of the relevant disciplines of soil science,especially the study on the mechanisms of organo-mineral complexes.

Characteristics of Phosphorous Adsorption and Desorption by Organo-Mineral Colloidal Complexes of Purple Paddy Soils

The kinetic characteristics of P adsorption and desorption by organo-mineral colloidal complexes (OMC)were studied using acid, calcareous and neutral purple paddy soils taken from Chongqing and Sichuan, China.The results showed that the P adsorption capacity of the organo-mineral colloidal complexes differed with the soil types, being higher for the acid and calcareous purple soils than for the neutral purple soils. Partial removal of the organic matter increased the adsorption capacity of the colloidal complexes. A very significant positive correlation was found between the amounts of P desorbed from OMC and the P saturation degrees.The P adsorption reaction was quick at the early stage and slowed later. The raise of temperature increased P adsorption capacity and P adsorption rate of the colloidal complexes. The adsorption processes could be described by the Elovich equation.

基于Web of Science对土壤胶体影响重金属行为研究的计量分析

为全面了解土壤胶体影响重金属行为方向的研究现状和前沿动态,基于Web of Science(WoS)核心合集数据库,利用WoS自带分析工具、HistCite引文图谱分析软件、VOSviewer和Citespace可视化分析软件对1990—2021年间土壤胶体影响重金属行为的文献进行了计量分析。结果表明,在世界范围内该方向的发文量逐年稳步增长,我国相关研究起步较晚,但近些年呈现迅猛发展的势头。目前土壤胶体影响重金属行为研究发文量最多的国家和研究机构分别是美国和中国科学院,发文量最高的期刊为Environmental Science&Technology,主要研究学科为环境科学与生态学的交叉学科。关键词聚类分析显示“土壤胶体颗粒粒径分级与重金属的形态分布”、“土壤胶体的释放、沉积及对重金属的吸附作用”和“土壤胶体颗粒的迁移机制与迁移模型研究”为主要的研究主题,人工纳米颗粒在土壤中的行为、迁移转化以及生物有效性是现阶段的研究热点。利用场流分离技术结合单粒子电感耦合等离子体质谱等技术,探讨土壤胶体与人工纳米颗粒之间发生的复杂相互作用及其对人工纳米颗粒迁移归趋与环境命运的影响,是未来的主要研究方向。

Tracing Water Flow and Colloidal Particles Transfer in an Unsaturated Soil

In recent years, many studies have been carried out on colloidal particle transfer in the unsaturated zone because they can be a risk to the environment either directly or as a vector of pollutants. A study was conducted on the influence of porous media structure in unsaturated conditions on colloidal particle transport. Three granular materials were set up in columns to replicate a fluvio-glacial soil from the unsaturated zone in the Lyon area (France). It is a sand, a bimodal mixture in equal proportion by weight of sand and gravel, and a fraction of bimodal mixture. Nanoparticles of silica (SiO2-Au-FluoNPs), having a hydrodynamic diameter between 50 and 60 nm, labeled by organic fluorescent molecules were used to simulate the transport of colloidal particles. A nonreactive tracer, bromide ion (Br-) at a concentration of C0,s = 10-2 M was used to determine the hydrodispersive properties of porous media. The tests were carried out first, with a solution of nanoparticles (C0,p = 0.2 g/L) and secondly, with a solution of nanoparticles and bromine. The transfer model based on fractionation of water into two phases, mobile and immobile, MIM, correctly fits the elution curves. The retention of colloidal particles is greater in the two media of bimodal particle size than that in the sand, which clearly demonstrates the role of textural heterogeneity in the retention mechanism. The increase in ionic strength produced by alimenting the columns with colloidal particle suspension in the presence of bromide, increases retention up to 25% in the sand. The total concentration profile of nanoparticles collected at the end of the experiment shows that the colloidal particles are retained primarily at the entrance of the columns. Hydrodispersive calculated parameters indicate that flow is more heterogeneous in bimodal media compared to sand.

外源秸秆对污染土壤氧化还原过程水分散性胶体态重金属的影响

土壤胶体尤其是水分散性胶体,作为一种重要的污染物载体,在重金属吸附、迁移以及生物吸收过程起着重要作用。通过土壤培养试验探讨了外源添加水稻秸秆在氧化还原波动条件下如何影响土壤液相中及水分散性胶体中重金属的分布。结果表明,外源秸秆增加厌氧过程液相中溶解性有机碳(DOC)、砷(As)、铁(Fe)、锰(Mn)、钙(Ca)、钾(K)、硅(Si)、铝(Al)、镁(Mg)等浓度,降低了厌氧过程氧化还原电位(Eh)及铜(Cu)、铅(Pb)等浓度,提高了好氧过程Pb浓度。利用非对称流场流分馏-紫外可见-电感耦合等离子体-质谱联用技术(AF4-UV-ICP-MS),测得水分散性胶体颗粒主要分布在0.3~3 kDa、3~40 kDa和130 kDa~450 nm三个粒径范围,各粒径颗粒的组成有所差异,主要含有机质、无机黏土矿物和铁矿物等。外源秸秆促进液相中Fe和As由胶体态向溶解态转化,促进镉(Cd)和Cu由溶解态向胶体态转化。本研究有助于揭示农业活动影响重金属迁移转化及有效性的界面机制。

土壤胶体磷环境效应及其影响因素

胶体是磷素在环境中迁移转化的重要载体,土壤胶体磷对磷素生物地球化学循环具有重要作用,其活化迁移对土壤、水环境具有十分重要的影响。本文介绍了国内外土壤胶体磷的分类、分离和分析技术。重点阐述了土壤胶体磷活化、土壤基础理化性质(矿物组成、其他胶体元素、土壤孔隙结构、pH、氧化还原电位)、肥料及土壤改良剂应用对土壤胶体磷环境效应的影响。并针对目前土壤胶体磷流失存在的问题,提出相关对策及展望,以期为后续胶体磷研究和胶体磷污染的治理提供参考。

Effects of different concentrations of super-absorbent polymers on soil structure and hydro-physical properties following continuous wetting and drying cycles

Super-absorbent polymers(SAPs)are widely used chemical water-saving materials,which play an active role in the accumulation of soil water and the improvement of soil structure.Little is known about their performance with repeated usage or about factors influencing their efficiency under alternate wetting and drying cycles.In this study,various concentrations of SAP(0,0.1,0.2 and 0.3%)in soil following three continuous wetting and drying cycles(T1,T2 and T3),were studied to determine effects on soil structure stability and hydro-physical properties.The results indicated that the SAP improved soil water supply capacity under conditions of mild drought(T2)and sufficient irrigation(T3)at concentrations of 0.2 and 0.3%,but a reduction was observed under severe drought conditions(T1),which was negatively correlated with the SAP concentration.The physical adsorption of the SAP by soil and the chemical connection between the SAP and soil mineral colloids as Si-O-Si bonds,-OH bonds and different crystalline silica were the important factors that directly lead to the reduction of water retention capacities of the SAP with alternating wet and dry conditions.Compared with the control,the soil liquid phase ratios of the SAP treatments were increased by8.8-202.7%in the T1 and T2 cycles,which would have led to a decrease in the soil air phase ratios.After repeated wetting and drying cycles,the SAP treatments increased the amount of>0.25 mm soil aggregates and the contents of water-stable macro-aggregate(R_(0.25)),and decreased the amount of<0.053 mm soil aggregates,especially with higher concentrations of the SAP.Increases in mean weight diameter(MWD)and geometric mean diameter(GMD),and declines in fractal dimension(D)and unstable aggregates index(E_(LT))were all observed with the SAP treatments,which indicated an improvement in soil stability and structure.It was concluded that the distribution and stability of soil aggregates and soil water supply capacity was closely related to SAP concentration,soil moisture condition and the interaction between the SAP and soil particles.

磷肥不同施用量对紫色土坡面胶体态磷流失的影响

[目的]农田磷流失风险与磷肥用量密切相关,鉴于土壤胶体在土-水界面磷素迁移转化过程中的重要作用,探讨施用磷肥对紫色土坡面胶体态磷流失的影响及其与产流产沙之间的关系,为从土壤胶体视角认识磷素迁移机制提供科学依据。[方法]试验采用人工模拟降雨和室内分析相结合的方法,开展4个磷肥施用量0(P0)、20(P20)、40(P40)和100(P100)mg·kg-1下紫色土坡面产流产沙及胶体态磷流失特征研究。[结果]地表径流量受磷肥施用量影响较小,侵蚀产沙量受磷肥施用量影响较大,施磷后坡面初始产沙量显著降低了49.3%-68.7%,P100处理累积产沙量较其他施磷处理显著降低了26.5%-30.9%。地表径流是紫色土坡面水分散性总磷(WTP)和胶体态磷(CP)的主要流失途径,其流失比例分别占总流失量的57.5%-93.9%和62.3%-94.8%,且CP是地表径流WTP流失的主要形态,占WTP流失量的72.1%-80.7%。施磷显著增加了磷素流失风险,与P0处理相比,施磷后地表径流WTP、CP、DP(溶解态磷)累积流失负荷量分别提高了2.56-20.97倍、2.72-22.21倍、1.17-10.40倍,侵蚀泥沙WTP、CP、DP的累积流失负荷量分别提高了0.24-0.92倍、0.05-1.09倍、0.47-0.76倍。[结论]紫色土坡面胶体态磷流失的主要途径为地表径流,胶体态磷流失与产流过程密切相关,流失负荷量主要取决于磷肥施用量。水分散性总磷与胶体态磷呈极显著相关关系,胶体态磷是紫色土坡面磷素流失主要形态,可以通过调控地表径流,合理减施磷肥以减少坡面CP流失。

铁还原菌对土壤胶体吸附与释放砷的影响

为研究铁还原微生物对土壤胶体调控砷(As)地球化学行为的影响机制,选用铁还原菌Geobacter metallireducens作用于土壤胶体,设计开展了土壤胶体的As吸附实验和不同pH条件下载As胶体的释放实验。结果表明:铁还原菌作用下胶体悬液Eh降至-222 mV,有助于形成强还原环境;当无菌作用时,土壤胶体随Fe(II)产生及释放量的增多对As(V)的吸附能力逐渐减弱;当有铁还原菌作用时,土壤胶体对As的最大吸附量较无菌组低6.14 mg/kg,但随厌氧处理时间的增加,其对As(V)的吸附能力呈增强趋势。在释放试验中,在pH=3条件下,铁还原菌对土壤胶体吸附As(V)的释放影响较弱,铁氧化物还原释放的As(III)仅占14.26%,以酸溶解为主;初始pH=7时总As释放量与悬液pH、Fe(II)含量呈线性关系,As(III)释放量较酸性条件提高6.7倍。该成果可为深入认识土壤微生物对As迁移转化的影响提供理论依据。

长期施用有机肥对苏打盐碱土胶体组分及有机无机复合状况的影响

基于松嫩平原苏打盐碱土有机肥长期改良试验,以未施用有机肥为对照(CK),研究不同改良年限(4,11,15,20 a)对土壤胶体组分、土壤有机碳组分及土壤有机无机复合程度的影响。结果表明,随着改良年限的增加,土壤水分散组胶体(G_(0))含量显著降低(P<0.05),而土壤钙结合的复合体(G_(1))含量显著增加(P<0.05),土壤铁铝氧化物结合的复合体(G_(2))含量及(G_(0)+G_(1)+G_(2))含量并无显著性变化;G_(0)、G_(1)和G_(2)组有机碳含量随改良年限的增加均呈增加趋势。与CK相比,施用有机肥处理显著提升了土壤有机碳和重组有机碳含量(P<0.05),并分别在4,11 a处理中达到最大值。改良年限在11 a及以上处理的复合体对土壤固碳的总贡献率为35.51%~54.64%。相对于CK,施用有机肥处理的苏打盐碱土有机无机复合程度均有不同程度提高,改良11 a及以上处理其增幅明显。综上所述,长期施用有机肥促进了苏打盐碱土水分散组胶体向水稳性复合体转化,显著增加了复合体对土壤固碳的贡献率,也显著提升了土壤的有机无机复合程度。

农田土壤胶体对微塑料颗粒迁移的影响及机制研究进展

【目的】土壤胶体因具备巨大比表面积、较小粒径、携带大量电荷的特性,在吸附微塑料颗粒、影响微塑料颗粒迁移过程中发挥着重要作用。但是有关土壤尤其是农田土壤胶体对微塑料颗粒迁移的影响及其协同迁移机制尚不清晰。土壤胶体与微塑料颗粒定义模糊、分类标准各异等问题形成的认知误区也阻碍了对两者更为深入的研究。梳理国内外关于农田土壤胶体与微塑料颗粒的相关研究,旨在厘清农田土壤胶体与微塑料颗粒迁移过程中两者间的相互作用过程,为制定微塑料污染防治政策和措施提供理论依据。【主要进展】农业活动改变了土壤胶体颗粒的组成,影响了微塑料颗粒的迁移行为。土壤胶体、微塑料颗粒自身与多孔介质特性、土壤理化性质以及环境条件,通过协同促进和抑制两种机制影响着农田土壤胶体与微塑料颗粒的协同迁移。在此过程中,土壤胶体组成处于主导地位,土壤胶体颗粒的稳定性大小决定着其与微塑料颗粒的协同迁移状态。土壤胶体颗粒的吸附行为改变了微塑料颗粒的迁移路径和速率;微塑料颗粒的存在反过来也能影响土壤胶体颗粒的稳定性,改变其聚集态势,进而影响胶体颗粒的迁移能力。【展望】今后应细化不同性质农田土壤胶体与微塑料颗粒迁移机制研究,定量分析深入评估微塑料颗粒迁移的环境效应,探索土壤微生物−胶体−微塑料三者之间交互作用过程,从土壤物理、化学和生物学角度为修复微塑料污染土壤,守护土壤健康提供新的思路和借鉴。

苯并[a]芘降解菌在不同土壤无机胶体表面的吸附研究

基于等温吸附实验,结合扩展DLVO(Ex-DLVO)理论、傅里叶红外光谱(FTIR)等方法与手段,探究高岭石、蒙脱石和赤铁矿胶体对苯并[a]芘的高效降解菌噬氨副球菌(Paracoccus aminovorans)HPD-2的界面相互作用机制。结果表明,3种典型土壤无机胶体对菌株HPD-2的等温吸附曲线符合Langmuir吸附模型,其理论最大吸附量由大到小为赤铁矿>>蒙脱石>高岭石。Ex-DLVO理论计算结果表明,赤铁矿对菌株HPD-2细胞的吸附过程是自发的,而高岭石和蒙脱石对降解菌的吸附均需要越过能障;胶体颗粒与细胞之间的静电力作用在吸附过程中起到关键作用,其产生的作用能远高于范德华力和疏水作用力。FTIR结果表明,高岭石和蒙脱石对菌株HPD-2的作用力主要为细胞表面蛋白质构型的变化,相互作用较弱。除氢键外,赤铁矿与菌株HPD-2发生吸附的作用力还形成了较强的P—OFe化学键。研究结果阐明了不同性质无机矿物胶体与菌株HPD-2细胞间的界面作用机制,为研究无机矿物对降解微生物活性和微生物在无机矿物表面定殖的影响机制提供理论依据。

炭基质钝化剂对土壤Cd、Cu的阻控效果与老化机制

炭基质钝化剂对污染土壤Cd、Cu的钝化/稳定化效果与机制研究一直是阻控材料研发的关键与难点。本文以Cd、Cu复合污染水稻土为供试土壤,以未改性生物炭(BC)、铁改性生物炭(FeBC)和铁改性活性炭(FeC)为钝化剂,通过高温模拟自然老化过程,研究上述钝化剂对土壤Cd、Cu的阻控效果和老化机制。结果表明,上述3种材料均能有效钝化土壤中的Cd和Cu,钝化剂施用后土壤中Cd的可交换及碳酸盐结合态(F1)含量分别降低3.0%、9.4%、8.8%;土壤中Cu的F1含量分别降低2.2%、4.4%、3.8%。施用3种钝化剂后,土壤胶体中Cd、Cu的非晶质氧化铁结合态(C-Feo)含量分别提高3.5%、4.9%、4.5%和14.5%、18.8%、18.1%,这是重金属生物有效性短期降低的主要原因和途径。高温老化试验结果显示,胶体Cd、Cu的C-Feo向晶质氧化铁结合态(C-Fec)、残渣态(C-Fr)转化,3种钝化剂对土壤Cd、Cu的阻控效果具有长效性。