Description of titration curves of mixed materials with variable and permanent charge by a mathematical model. 3. Influence of the nature of the permanent charge mineral

A mathematical model, previously developed, is tested here for various clay minerals and their mixtures with iron oxides. The model yields good predictions of the permanent charge for non-swelling clay minerals, but clearly underestimates the permanent charge of montmorillonite. This result is interpreted as being caused by partial accessibility of the internal surface of the mineral.
In all cases, the values estimated for the permanent charge of the clay minerals fit the data for their mixtures with iron oxides. Nevertheless, important differences are found between the values of maximum densities of adsorption sites of potential-determining ions of the various minerals estimated when they are alone and when they are in mixtures, particularly in the case of montmorillonite mixtures. The differences are explained in terms of an intimate association between the particles in the mixtures, and some SEM and EDX results point to the same conclusion.     

有机酸和质子对淹水水稻土非交换性铵释放的影响

In a model experiment, which imitated the rhizosphere of rice, the effect of organic acids (oxalic acid, citric acid) and protons on the release of non-exchangeable NH4^ and the resin adsorption of N was studied in a paddy soil, typical for Zhejiang Province, China. Oxalic and citric acids under low pH conditions, in combination with proton secretion, favored the mobilization of NH4^ ions and increased resin adsorption of N. The release of non-exchangeable NH4^ was associated with less formation of iron oxides. These could coat clay minerals and thus hinder the diffusion of NH4^ ions out of the interlayer. Protons enhanced the release of NH4^ , and then they could enter the wedge zones of the clay minerals and displace non-exchangeable NH4^ ions.     

Charge Properties and Clay Mineral Composition of Tianbao Mountains Soils

The clay mineral association,oxides of clay fraction and surface charge properties of 7 soils,which are developed from granite,located at different altitudesof the Tianbao Mountains were studied.Results indicate that with the increase in altitude,1) the weathering process and desilicification of soil clay minerals became weaker,whereas the leaching depotassication and the formation process of hydroxy-aluminum interlayer got stronger;2)the contents of amorphous and complex aluminum and iron,and the activity of aluminum and iron oxides for soil clay fraction increased;and 3) the amount of variable negarive charge,anion exchange capacity and the values of PZC and PZNC also increased.The activity of aluminum and iron oxides,the accumulation of aluminum,and surface charge characteristics and their relation to clay oxides of the vertical zone soils were observed and recorded.     

Effect of soil composition on adsorption of lead as reflected by a study on a natural forest soil profile

The adsorption characteristics of lead on each genetic horizon of a natural brown forest soil profile were studied to recognize the possible immobilizing effect of a mineralogical diverse soil profile in the case of a possible lead contamination. Lead adsorption experiments were carried out on whole soil samples, soil clay fractions, as well as on their carbonate and organic matter free variant. TEM-EDS analyses were performed to characterize the adsorption capacity of individual mineral phases. The most important lead adsorbents in order of importance are the organic matter, the clay minerals, and the iron oxides. The most significant process is the ion exchange of calcium by lead with the respect to adsorption. The organic matter adsorbs more lead than clay minerals, and clay fractions adsorb more lead as compared to the whole soil samples. Among mixed layer clay minerals, those containing swelling component have the highest lead adsorption capacity, but the exact distinguishing of the individual clay mineral particles with the respect to their adsorption capacity is not possible. The calcite influences the lead adsorption through its buffering capacity: high calcite content results in lead precipitation. Soils characterized by high amount of organic matter, swelling clay mineral accumulation horizon and calcareous subsoil are suitable medium to immobilize a significant lead pollution.     

Interaction of aluminum and iron oxides and clay minerals and their effect on soil physical properties: A review

Abstract

Amorphous and crystalline aluminum and iron oxide minerals play a major role in stabilizing soil structure as measured by aggregate stability and clay dispersion. Aluminum and iron oxide interactions with clays are pH dependent. At low pH, where the oxides carry sufficient positive charge, they precipitate on clay surfaces. These coatings, once formed, are stable at higher pHs. Precipitation of oxides at high pH occurs as phases separate from the clays. Aluminum and iron oxides stabilize clay minerals by decreasing critical coagulation concentration, clay dispersion, water uptake, and clay swelling and by increasing microaggregation. The presence of aluminum and iron oxide minerals in soils has a favorable effect on soil physical properties, increasing aggregate stability, permeability, friability, porosity, and hydraulic conductivity, and reducing swelling, clay dispersion, bulk density, and modulus of rupture.     

土壤矿物质吸附砷的研究进展

砷是一种有毒的重金属元素,由于自然和人为的原因,世界上的许多国家存在砷污染问题,因此有关砷污染的研究与控制日益受到人们的关注。本文介绍了土壤砷污染的产生原因及污染状况,重点集中在探讨土壤中的各种矿物质对砷吸附行为的作用机理。这些矿物质包括铁铝氧化物和氢氧化物、锰氧化物、黏土矿物和碳酸盐类。关于砷在各类矿物质上的吸附机理,普遍接受的观点认为:砷氧阴离子与矿物质的表面发生了配位体交换过程并通过共价键的作用,形成了表面配位体。表面配位体以内层双齿双核鳌合形式为主,受矿物质的种类、pH值和氧化还原电位等因素的影响,外层吸附和其他鳌合状态可能存在。砷在土壤矿物质上的吸附效果强烈依赖于体系的pH值,这与吸附的理论模型和数学计算结果相一致。矿物质的种类、组成、结晶状态和表面积等影响了砷的吸附过程和吸附效果。土壤中存在的各种阴阳离子通过与砷阴离子竞争吸附位而影响砷在矿物质上的吸附。     

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.     

九宫山土壤剖面中黏土矿物的组成特征

以湖北省九宫山的4种垂直地带性土壤为对象,研究其剖面层次的黏土矿物组合和铁、铝氧化物的特征,揭示山地土壤中黏土矿物的变化特点。结果表明,随海拔升高,土壤中黏土矿物类型从以高岭石为主,逐渐变为以14.0?矿物、伊利石及三水铝石为主,有从1︰1型向2︰1型矿物过渡的趋势;不同层次的土壤中黏土矿物类型和相对含量变化明显;土壤随垂直高程的升高,其中游离态铁、铝减小,非晶形和络合态铁、铝增加,各种形态铁、铝氧化物的总量也增加。     

黄土高原淋溶土黏粒、氧化铁与颜色的关系及发生学解释——以山西土系调查的31个黏化层为例

以黄土高原山西省14个淋溶土剖面的31个偏红的黏化层(Bt)为研究对象,分析了其全铁、游离氧化铁、无定形态氧化铁的含量与土壤颜色参数、黏粒含量之间的相关性,并建立了定量关系模型。结果表明:Bt的黏粒含量与氧化铁含量之间呈极显著正相关(P<0.01);颜色的红度与全铁、游离氧化铁和无定形氧化铁含量之间均呈极显著正相关(P<0.01),其中游离氧化铁是最直接的土壤红色"染色剂";其他色调、明度与彩度等颜色参数与土壤全铁、游离氧化铁含量之间亦呈现出显著的相关性,这也间接说明了黏粒含量与土壤颜色具有一定相关性。野外观测发现,某些黏化层结构体表面颜色较结构体内基质颜色更红,证实了在土壤结构体表面氧化铁随着黏粒在土壤空隙中的迁移淀积。黄土高原淋溶土偏红的黏化层多是来自由于土壤侵蚀而出露地表或接近地表的第三纪保德红土和第四纪红黏土,其黏粒含量、土壤颜色等指标均表明第三纪的古气候条件较第四纪更为湿热。     

镉砷复合污染土壤钝化材料研究进展

我国土壤重金属污染严重,尤以镉砷污染最为突出。镉砷复合污染土壤中各元素间表现为拮抗和协同等作用,其有效态含量受土壤pH变化和氧化还原电位等的影响,增加了镉砷复合污染土壤的修复难度,严重威胁我国粮食安全。综述了常见的镉砷复合污染土壤钝化修复材料的优缺点及其对镉砷复合污染土壤钝化修复效果和机理。常见的钝化材料有生物质炭类、磷酸盐类、金属及其氧化物类、含硅类材料、黏土矿物类、有机肥类和新型材料等。有大量研究表明生物质炭材料对镉有良好的吸附效果,为了同时钝化镉砷,通常使用改性生物质炭或与其他材料配合施用,常见的改性/配施材料有金属及其氧化物、黏土矿物、家禽粪便、复合肥等,其钝化反应机制包括离子交换、共沉淀和表面络合等;磷酸盐类主要与铁盐或铁粉配施,通过吸附和同晶替代钝化镉、点位竞争机制钝化砷;金属及其氧化物类多与生物质炭、石灰和黏土矿物等配施,通过专性吸附和共沉淀钝化镉、氧化还原和络合作用等钝化砷;铁硅肥、硅钙肥、硅钾肥等通过共沉淀钝化镉、专性吸附和点位竞争机制钝化砷;黏土矿物中多施用海泡石,主要与金属氧化物和钙镁磷肥等配施,通过离子交换、沉淀和络合反应钝化镉砷;污泥和动物粪便中含有腐殖化程度较高的有机质,主要通过吸附、氧化还原和有机络合以及微生物作用钝化镉砷;此外,富含巯基和氨基、谷聚多以及富含硫和硒的物质也可有效钝化镉砷。本文对镉砷复合污染土壤钝化修复材料进行总结,归纳了镉砷钝化材料特性,以期为镉砷复合污染土壤修复提供一定的指导。     

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。     

Clay mineralogy of the B horizons of two hydrandepts,a Torrox and a Humitropept in Hawaii

The mineralogy of the clay fractions separated from the B horizons of two Hydrandepts (Hilo and Akaka soils), a Torrox (Molokai soil) and a Humitropept (Kolekole soil) was determined by a combination of methods.The Hydrandept B horizons were characterized by predominance of hydrous non-crystalline alumina and iron oxides associated with considerable amounts of humus and with very small amounts of silica. Allophane, allophane-like constituents and imogolite were present but in minor amounts. Gibbsite, goethite, chlorite and illite were also present as accessory minerals.The Torrox and Humitropept B horizons were characterized by predominance of kaolinite, hematite and goethite. The iron oxide minerals were present as fine particles (40–80 A diameter) often clustered to form larger aggregates. Neither imogolite nor allophane and allophane-like constituents were detected. Considerable amounts of dithionite-citrate soluble Al and humus were, however, present in the Humitropept B horizon, which may reflect the effect of an admixture of volcanic ash to the parent material.     

我国北亚热带白浆化土壤矿物学特性的研究

本文对北亚热带地区七个白浆化土壤的原生矿物和次生矿物的特性进行了研究。重，轻矿物含量表明土壤继承了母质的特性，粘淀层与漂白层的母质沉积是间断的，前者风化强度大于后者。石英颗粒表现特征显示漂白层物来来源于黄土物质再堆积，粘土矿物以水云母为主，其结晶度较差，氧化铁类型以针铁矿和赤铁矿为主，也有非晶质氧化铁和硅酸盐中的Ｆｅ＾２＋，其形成条件与现代化成土条件一致。     

土壤电化学性质的研究——Ⅹ.红壤胶体的表面性状和离子专性吸附对表面电荷性质的影响

根据可变电荷和永久电荷共存的土壤体系的模式,研究了一个砖红壤和一个红壤胶体的表面电荷特性。由于两种土壤胶体的矿物成分和铁铝氧化物的含量不同,砖红壤胶体的pH。值、ZPNC和IEP都高于红壤胶体者。红壤胶体的永久负电荷量多,其pH₀与ZPNC的差值也大。土壤加3%的有机质淹水培育4个月后,胶体的腐殖质含量增加不足0.5%,对胶体的pH₀的影响不明显。砖红壤胶体用磷酸盐或硅酸盐处理后,表面正电荷减少,负电荷增多,pH₀值和IEP都降低。磷酸盐的效应较硅酸盐为甚。不同浓度的KCl溶液中存在少量SO₄^2-时,砖红壤胶体的正电荷减少,负电荷增加,ZPNC和pH₀值降低;如存在少量Ca²⁺,则pH₀值升高。以单一的K₂SO₄、为支持电解质时,pH₀值较KCl者为高。     

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。     

The Role of Soil Mineralogical Characteristics in Sustainable Soil Fertility Management: A Case Study of Some Tropical Alfisols in Nigeria

The pedogenic horizons of nine profile pits dug across three toposequences were studied to determine the soil mineralogical characteristics and its implications on sustainable management of the fertility of some tropical Alfisols in Nigeria. Results showed that the epipedon which were predominantly ochric had textures that ranged from sand to sandy loam, while the subsurface (B/Bt) horizons had sandy clay loam to sandy clay texture and were gravelly (31.79–83.04%). The soil reaction ranged from strongly acid to neutral (pH 5.10 to 7.05). Calcium and magnesium dominated the exchange sites and accounted for about 75% of the exchangeable bases. Illite/mica and kaolinite were the dominant minerals in the clay fractions, while quartz, mica, and feldspars dominated the fine sand and silt fractions of the soils. While the presence of illite and mica could be important for potassium nutrition in these soils, kaolinite and oxides of iron could also cause phosphorus fixation.     

平原区水田改林地后土壤黏土矿物及氧化铁的变化

近年来水田改为林地在我国南方地区非常普遍,为了解这种转变对土壤矿物(黏土矿物和氧化铁)演变的影响,在浙江省平原地区构建了4个水田改林地系列土壤,采用野外调查和室内分析相结合的方法,研究水田改林地后土壤剖面中氧化铁形态和黏土矿物类型的演变规律。结果表明,改林地后,土壤剖面中全铁含量变化不明显,耕作层和犁底层土壤游离氧化铁有轻微增加趋势。改林地15～20 a后,4个系列土壤耕作层活性铁和活化度降幅分别在18.0%～38.4%和24.7%～48.9%;耕作层土壤铁氧化物的晶胶比增幅在0.73倍～1.62倍;耕作层土壤亚铁含量明显下降,降幅最高达95.8%,变异系数达到143.9%;耕作层络合铁降幅在21.3%～36.2%,并与有机质呈极显著正相关(P<0.01)。改林地后,犁底层土壤中绿泥石相对含量及其与高岭石的比值都呈降低趋势,其他黏土矿物相对含量变化规律不明显,土壤有机质显著下降,土壤明显酸化。土壤铁氧化物形态和数量的变化对土壤结构以及土壤重金属的迁移转化等产生重要影响。     

STUDIES ON SOIL COPPER

Adsorption isotherms were determined for the specific adsorption of copper by soils and soil constituents. Adsorption was found to conform to the Langmuir equation. The Langmuir constants, a (adsorption maximum) and b (bonding term), were calculated. Soils were found to have specific adsorption maxima at pH 5.5 of between 340 and 5780 μg g^?1, and a multiple regression analysis revealed that organic matter and free manganese oxides were the dominant constituents contributing towards specific adsorption. Adsorption maxima for soil constituents followed the order manganese oxides > organic matter > iron oxides > clay minerals, which supported the findings for whole soils. The cation exchange capacities (non-specific adsorption) of the test soils were found to be far greater than the specific adsorption maxima. However, evidence suggests that, for the relatively small amounts of copper normally present in soils, specific adsorption is the more important process in controlling the concentration of copper in the soil solution.     

Soils in the semi-arid area of the El Melah Lagoon (NE Tunisia) — Variability associated with a closing evolution

Soils of the semi-arid area of the El Melah coastal lagoon (NE Tunisia), with a closing evolution dynamic, were studied aiming: (1) the chemical and mineralogical characterization of surface and subsurface layers of soil profiles from locations previously submerged and of soils developed on dunes; (2) to evaluate the dependence on the environment conditions of the geochemical patterns of the soils; and (3) to determine chemical and mineralogical variations with the emersion of the sediments resulting from the decrease in the extent of the area permanently covered by water in the lagoon. The compositional results obtained showed significant differences depending on the environment (littoral plain, old dunes and sandy spit), but soils of the different environmental zones studied do not appear to be significantly polluted as far as trace elements are concerned. Among the elements studied, high element/Sc ratios and variations were found for As, Sb and Zn. Antimony is more concentrated in coarser samples suggesting its adsorption in Fe or Mn oxides coating quartz grain surfaces. Arsenic and zinc may be incorporated into the carbonates structure, as well as adsorbed on, or coprecipitated with, iron oxides. Zinc may also be significantly incorporated in clay minerals. Iron was found to be more oxidized in the cultivated soil from the old dune strand; and more reduced in the sandy spit where ankerite occurs suggesting the reduction of Fe³⁺ in oxide/hydroxides by microorganisms and incorporation of Fe²⁺ in carbonates. REE patterns, particularly the HREE/LREE are correlated with carbonates, indicating preferential incorporation of the HREE in carbonates, and of the LREE in clay minerals/iron oxides. High Ga contents were found in soils and sediments rich in clay minerals/Al, suggesting its incorporation in clay minerals structure. Therefore, Ga may be used as an indicator of the clay minerals proportion in sediments and soils. Carbonates, sulphates, besides Fe and/or Mn oxides and clay minerals, appear to play an important role on the trace elements distribution.     

Factors Affecting the Formation,Nature, and Properties of Iron Precipitation Products at the Soil–Root Interface

Abstract

A number of iron oxides (hematite, goethite, lepidocrocite, maghemite, and magnetite) or short‐range ordered precipitates (ferrihydrite) may be found in soil environments, but in the rhizosphere the presence of organic ligands released by plants (exudates) or microorganisms promote the formation of ferrihydrite. Iron ions are liberated into soil solution by acidic weathering of minerals and then precipitated either locally or after translocation in soil environments. Humic and fulvic acids as well as organic substances produced by plants and microorganisms are involved in the weathering of primary minerals. Organic compounds play a very important role in the hydrolytic reactions of iron and on the formation, nature, surface properties, reactivity, and transformation of Fe oxides. Organic substances present in the rhizosphere interact with Fe promoting the formation of ferrihydrite and organo‐mineral complexes. The solubility of Fe precipitation products is usually low. However, the formation of soluble complexes of Fe(II) or Fe(III) with organic ligands, usually present in the rhizosphere increases the solubility of Fe‐oxides. Mobilization of Fe from Fe oxides by siderophores is of great importance in natural systems. They can form stable Fe(III) complexes (pK up to 32) and thus mobilize Fe from Fe(III) compounds. These higher Fe concentrations are important for the supply of Fe to plant roots which excrete organic acids at the soil–root interface. Iron oxides adsorb a wide variety of organic and inorganic anions and cations, which include natural organics, nutrients, and xenobiotics. There is competition between anions and cations for the surfaces of Fe‐oxides. Root exudates suppress phosphate or sulfate adsorption on Fe‐oxides. This is a mechanism by which plant roots mobilize adsorbed phosphate and improve their phosphate supply. Anions adsorption on iron oxides modify their dispersion/flocculation behavior and thus their mobility in the soil system. That can increase or decrease the possibility of contact between Fe‐oxides and organics or organisms able to dissolve them.