Platy Quartz Phytoliths found in the Fossil Forest Deposits,Axel Heiberg Island,Northwest Territories,Canada

The occurrence of quartz particles having a platy morphology found in the white layers within the fossil forest deposits of Axel Heiberg Island, was further confirmed by optical and electron microscopic examinations. The platy quartz crystals were concentrated in the finer fractions. The δ ₁₈O values of fractions enriched in platy quartz crystals ranged from +13.7 to +16.6 %₀. These values were higher than those obtained for coarser fractions. The platy morphology and crystallographic character of the quartz particles concentrated in the finer size fractions are uncharacteristic both of aerosol derived material and of secondary silica. These findings and information available for the paleoenvironment of the study area favor a biogenic origin for the platy quartz. The oxygen-isotope data are consistent with this hypothesis.     

安徽凤阳石英岩发育土壤的磁学性质及环境磁学意义

通过对安徽凤阳石英岩发育土壤典型剖面的磁学参数测量,结果表明,A层和B层中的磁性矿物含量明显高于C层,且A层和B层中磁性矿物的粒度明显比C层细.C层的磁学性质由磁铁矿主导,A层和B层的磁学性质由磁赤铁矿主导.磁赤铁矿是石英岩在成土过程中形成的次生矿物.土壤中磁赤铁矿的出现及含量的变化指示成土作用的强弱.石英岩的磁性对土壤的磁性影响甚小,而成土作用和生物作用对土壤磁性增强起到了主要作用.     

Intensive kaolinization during a lateritic weathering event in South-West Spain: Mineralogical and geochemical inferences from a relict paleosol

This study documents the mineralogical and geochemical record of a lateritic weathering event during the Pliocene in South-west Spain. The paleoweathering profile derived from arkosic sands and comprises a white sandy clayey saprolite, a red mottled clay zone overlain by a thick soft layer, and a ferruginous pisolitic hardcap partially dismantled by erosive processes. Kaolinite, quartz and degraded K-feldspars are the major minerals forming the saprolite, along with Al-goethite (mottled zone) as well as gibbsite and boehmite (soft layer), while the pisolitic duricrust is essentially composed of quartz grains embedded in a matrix of Fe oxy-hydroxides (hematite, goethite, and/or maghemite). Besides quartz, the phases most resistant to alteration were a variety of heavy minerals (mostly titanium oxides) that are present as minor impurities in the residual kaolin deposit.     

Strengths of a densipan,humus-pan and clay-pan in a Spodosol developed under kauri (Agathis australis) and the implications for soil classification

Three hard layers have formed in a Spodosol developed on aeolian coastal sands under the influence of litter from kauri (Agathis australis). A densipan in the albic horizon and a humus-pan in the spodic horizon slaked in water whereas a clay-pan in a buried soil only softened in 1 M HCl. Blocks sawn from these three pans showed a maximum of unconfined compressive strength in the humus-pan.Specimens made from remoulded pan materials with minimum compaction developed only a proportion of the original strength. Greater compaction enhanced the strength of all three materials. Raising the pH during remoulding caused a marked increase in strength, but above pH 10.5 all the pan materials lost strength when silicate was solubilised from surfaces of clay and quartz particles.Scanning electron micrographs showed that the densipan was a close-fit configuration of sand- and silt-sized quartz particles that attained a high density without cementation of particles. In the humus-pan organic matter bridged across a third of the surfaces of the quartz particles and prevented a close-fit configuration. The clay-pan below the spodic horizon had all its particles thickly coated with clay and humus and these were aggregated into an open-fit arrangement of lower density.According to Soil Taxonomy procedures, the Te Kopuru sand lies within the Aquod sub-group of Spodosols. In the absence of a non-slaking duripan it was the presence of a fragipan below the spodic horizon that directed the soil into being a Fragiaquod. It is the densipan in the albic horizon above the spodic horizon, however, that controls plant roots and cannot be ignored in soil classification. We suggest that a new great group, Densiaquod, be recognized for these soils.     

Effect of clay colloids on the zeta potential of Fe/Al oxide-coated quartz: a streaming potential study

Purpose

This study was conducted in order to examine the effect of colloidal particles on electrochemical properties of charged larger size materials.

Materials and methods

A self-made streaming potential apparatus was used to measure the zeta potentials of Fe/Al oxide-coated quartz. The effects of colloidal particles of kaolinite and montmorillonite on the electrochemical properties of Fe/Al oxide-coated quartz were investigated through comparing the difference in zeta potential of the coated quartz in electrolyte and clay suspension.

Results and discussion

The change of zeta potentials of the coated quartz, when clay suspensions flowed through, increased with the increasing concentrations of kaolinite and montmorillonite and degree of coating with Fe/Al oxides, and decreased with increased ionic strength of the suspensions. Electrostatic attraction between clay colloids and the coated quartz was the key factor influencing the interaction between the oppositely charged particles. The deposition of colloidal particles of kaolinite and montmorillonite on coated quartz and the overlapping of the diffuse layers of electrical double layers between the oppositely charged particles were responsible for the change in zeta potential of Fe/Al oxide-coated quartz. The relative contribution of the deposition of clay particles to the change in zeta potential was greater than that of the overlapping of diffuse layers.

Conclusions

When clay suspensions flowed through the saturated sand of Fe/Al oxide-coated quartz, both overlapping of diffuse layers between charged sand and clay particles and deposition of clay particles contributed to change of zeta potential of the coated quartz.

     

Size and shape of fine quartz in the clay fraction of soils and geological materials

Fine clay fractions of two soils and five geological materials including three formed in late Wisconsinan glacial rock flour were separated by decantation and centrifugation procedures. X-ray diffractograms (XRD) showed mica and chlorite as the main components. Pyrosulfate fusion which removed the phyllosilicates and iron oxides revealed presence of quartz and some feldspars. After dilute H₂SiF₆ treatment, blade-shaped, platy and sheroidal particles mainly of 0.2–0.1 μm size were observed by scanning electron microscope. Fine feldspars and quartz were found to be susceptible to the chemical treatments. On treatment with diluted H₂SiF₆ + HF + H₃BO₃, the crystallinity of fine quartz was considerably decreased as indicated by a very broad diffraction maximum at a spacing of about 4 Å.     

氧化石墨烯和五价砷在改性多孔介质中的共迁移特征

砷是农田土壤重金属污染的主要元素之一,在砷污染农田土壤的修复过程中往往忽视纳米颗粒能够使结合态的砷重新释放,导致有效态砷浓度升高,探究土壤中黏土矿物对氧化石墨烯(Graphene Oxide,GO)和五价砷(As(V))在多孔介质中迁移行为的影响,对进一步完善农田土壤砷修复理论以及提高农作物产量、保护人体健康具有重要意义。该研究利用蒙脱石和高岭石改性石英砂,通过砂柱迁移试验系统地研究了GO、As(V)和GO-As(V)在填加0%、10%、30%和50%的蒙脱石和高岭石改性石英砂柱中的迁移行为。研究结果表明,随着高岭石和蒙脱石改性石英砂填加比例的增加,GO和As(V)的迁移能力均呈降低趋势,且GO和As(V)在不同条件下的迁移曲线均存在显著差异(P<0.05);GO在50%高岭石和蒙脱石改性石英砂柱中的回收率相对于石英砂柱分别下降了14%和17%,As(V)分别下降了15%和12%;在共迁移试验中,GO和As(V)在石英砂柱中回收率分别上升至99%和100%。分析表明,As(V)在蒙脱石改性石英砂柱中的迁移能力大于高岭石改性石英砂,而GO与之相反;当GO和与As(V)共迁移时,二者...     

胶体颗粒对不同粒径饱和多孔介质渗透性的影响

探讨胶体颗粒在多孔介质中迁移所发生的物理、化学及生物作用过程,在许多学科中具有重要的科学意义。采用室内石英砂柱实验,开展了定水头条件下不同浓度和粒径的胶体颗粒在饱和多孔介质中的运移行为研究。共使用了3种胶体粒径、3种浓度的胶体溶液和3种粒径范围的石英砂。实验表明:多孔介质的相对渗透系数K/K0(K为各时刻计算所得的渗透系数,K0为初始渗透系数)减小程度与颗粒浓度成正比;胶体颗粒越大,越易在表层沉积,而小颗粒易向下部迁移,但总体来看粒径效应没有浓度效应明显;当胶体颗粒在不同粒径的饱和多孔介质中迁移时,粒径大的多孔介质各段K/K0均有明显降低,而粒径小的只在表层变化明显。不同条件下总体相对渗透系数与时间之间呈二次方相关关系,但当多孔介质粒径较小时,相关性不显著。介质渗流流速及砂柱不同位置胶体颗粒浓度变化与介质渗透性变化相对应。用扫描电镜(Scanning Electron Microscope,SEM)进行定性表征,进一步说明胶体颗粒会堵塞多孔介质孔隙影响其渗透性。实验中发现当输入浓度C0小于0.5 g·L–1且dp/Dp>0.018(dp为胶体颗粒粒径,Dp为石英砂算数平均粒径)时,会出现多孔介质局部K/K0增大的现象。     

Community structure of bacteria on different types of mineral particles in a sandy soil

Various types of mineral particles in a soil probably provide different microenvironments for microorganisms. The purpose of this study is to investigate whether different types of mineral in a soil harbor different bacterial populations. DNA was extracted from five types (quartz, feldspar, pyroxene, magnetite, iron-coated reddish brown particles) of sand-size mineral particles separated from a sandy soil, and was amplified for partial 16 S rRNA gene by polymerase chain reaction (PCR). Twenty-nine to 69 amplicons per each type of mineral were cloned and sequenced, followed by phylogenetic affiliation of the sequences. As a result, some types of bacteria were detected on all of the types of mineral including the orders Rhizobiales, Bacillales, and Acidobacteriales. In the case of Acidobacteriales, higher percentages were found on magnetite and quartz. Some taxa were restricted to specific types of mineral; the class Actinobacteria was found on pyroxene but not on quartz, and rarely on magnetite and feldspar. Bacterial diversity at the order level estimated by Chao1 value was higher in feldspar and pyroxene than the other three types of mineral. The UniFrac Significance test indicated that the differences in bacterial communitiy structures among the particles were suggestive except that between feldspar and pyroxene. These results support the idea that different communities of bacteria were associated with each of the mineral types.     

THE MICROMORPHOLOGY OF GIBBSITE FORMS IN SOILS

Using optical and scanning electron microscopy various forms of gibbsite are described in some tropical soils. In a lateritic soil from Zaire gibbsite occurs on argillans, in randomly oriented crystal sheets, as nodular aggregates infilling vughs and on ped faces. The mineral also surrounds quartz grains and kaolinite pseudomorphs after biotite. In other soils gibbsite occurs as silt-size particles disseminated through the matrix, as large nodular aggregates, and as anatomizing sheets associated with crystal chambers. It is clear from these observations that alumina must be a mobile constituent and was probably translocated through the soil in solution.     

Technogenic Magnetic Particles in Alkaline Dusts from Power and Cement Plants

During this study, we investigated the mineralogical characterization of technogenic magnetic particles (TMPs) contained in alkaline industrial dust and fly ash emitted by coal burning power plants and cement plants. The reaction of tested dust samples varied between values of pH 8 and pH 12. Their magnetic properties were characterized by measurement of magnetic susceptibility (χ), frequency dependence of magnetic susceptibility (χ_fd), and temperature dependence of magnetic susceptibility. Mineralogical and geochemical analyses included scanning electron microscopy with energy dispersive spectroscopy, microprobe analysis and X-ray diffraction. The TMPs in fly ash from hard coal combustion have the form of typical magnetic spherules with a smooth or corrugated surface as well as a skeletal morphology, composed of iron oxides (magnetite, maghemite, and magnesioferrite) that occurred in the form of incrustation on the surface of mullite, amorphous silica, or aluminosilicate particles. The TMPs observed in fly ash from lignite combustion have a similar morphological form but a different mineralogical composition. Instead of magnetite and magnesioferrite, maghemite and hematite with lower χ values were the prevailing magnetic minerals, which explains the much lower magnetic susceptibility of this kind of ash in comparison with the ash from hard coal combustion, and probably results from the lower temperature of lignite combustion. Morphology and mineralogical composition of TMPs in cement dust is more diverse. The magnetic fraction of cement dust occurs mostly in the form of angular and octahedral grains of a significantly finer granulation (<20 μm); however, spherules are also present. A very characteristic magnetic form for cement dust is calcium ferrite (CaFe₃O₅). The greatest impact on the magnetic susceptibility of cement dust results from iron-bearing additives (often waste materials from other branches of industry), which should be considered the most dangerous to the environment. Stoichiometric analysis of micro-particles confirmed the presence of heavy metals such as Pb, Mn, Cd, and Zn connected with TMPs, which are carriers of magnetic signals in atmospheric dust. Therefore, in some cases, their presence in topsoil when detected by magnetic measurement can be treated as an indicator of inorganic soil contamination.     

The effects of chemical weathering on the morphology and strength of quartz grains–an example from S.W. Australia

In soils in south-western Australia rounded quartz pebbles and sand grains have been greatly modified by chemical dissolution. Evidence of dissolution was provided by thin sections, scanning electron microscopy and measurements of quartz grain strength. Dissolution is initiated at fractures and intercrystalline boundaries so that dissolution along intersecting microfractures produces various surface etch features including tessellated pyramidal surface textures. The alteration of quartz grains by dissolution prevents the use of quartz as a stable reference mineral in studies of pedogenesis in these soils.     

The formation of maghemite and hematite from lepidocrocite and goethite in a Cambisol from Corsica,France

The influence of a recent forest fire on the iron oxide phases, present in the A and the B horizon of a brown earth from Corsica, was examined by X-ray diffraction and chemical analysis. In the B horizon goethite and lepidocrocite, in the A horizon maghemite and hematite were identified. From the Al/(Al+Fe) ratio, which was determined for all four minerals by XRD, it was concluded that goethite was the precursor of hematite and lepidocrocite the precursor of maghemite respectively. The proportion of maghemite formed in the A horizon was calculated from the difference in Fe_d between the untreated sample and that free of maghemite. Because of substantial dissolution of clay minerals even after 5 citrate-bicarbonate treatments, it was not possible to determine Al_d correctly.     

The composition and formation of grainy void cutans in some soils with textural contrast in Southeastern Australia

Fine-grained, void cutans and grain cappings were observed in the A and upper B horizons of two podzolic soils at a site near Canberra. Optically these features are dark coloured and grainy textured in transmitted, plane-polarized light and generally isotropic in crossed-polarized light. They consist of fine particles ( < 5μm diameter) of quartz, clay minerals, and traces of feldspars and iron and titanium oxides. Electron microprobe analyses indicate high Si:Al ratios, which largely result from the high quartz content of the cutans. Transmission electron microscopy indicated the presence of some poorly structured and only weakly crystalline to possibly amorphous mineral phases consisting of iron, titanium and traces of silicon and aluminium as partial particle coatings and in voids. Mixed-layer clays in the cutans also appeared to have been attacked by weathering on their margins. The presence of euhedral quartz grains suggests that there may have been some authigenic quartz formation within the cutans. Illuvial clays in the lower B and C horizons consist of clear, reddish orange ferri-argillans. It is probable that the reddish orange ferri-argillans developed prior to the grainy cutans, the latter consisting partly of translocated aeolian deposits. Post-depositional weathering of both the grainy cutans and the ferri-argillans has occurred in the A and upper B horizons. Ferrolysis promoted by periodic waterlogging above the textural contrast may be an important weathering process in the A horizons.     

新疆天山天池景区表土磁性特征的时空变化

以天山天池5A级景区表土为研究对象,分别于2015年和2017年两次采集表土样品,采用磁测、统计和GIS方法对其磁学特征、时空变异性进行研究.结果表明:表土样品载磁矿物以低矫顽力亚铁磁性矿物(磁铁矿和磁赤铁矿)为主,同时含有一定不完全反铁磁性矿物(赤铁矿和针铁矿),磁性矿物含量适中,磁性矿物粒度主要由假单畴粗颗粒和含量...     

以色列Har Keren沙漠黄土环境磁学特征研究

风成黄土是研究古气候变化的良好载体,在全球陆地分布广泛,而不同区域地理环境差异显著,其记录气候变化的机制亦有所不同。以色列南部黄土区地处亚热带沙漠边缘,为探究该区域黄土磁性特征及其对区域环境的响应机制,对内盖夫沙漠边缘黄土区进行野外考察并测试系统环境磁学及粒度参数。结果表明,Har Keren(HK)剖面中磁性矿物主要为碎屑磁铁矿和磁赤铁矿,磁性矿物含量较少,磁性颗粒主要为粗单畴(SD)和多畴(MD),磁性特征与中国西北干旱区黄土较为相似。HK剖面常温磁学参数整体变化范围较小,仅在剖面亚表层有所升高,可能是受现代成土作用影响。HK剖面中值粒径自底部至顶部呈减小趋势,但粒度整体偏粗,其频率分布曲线显示为正偏态,分选较差,反映出多种搬运方式的混合特征,与典型风成黄土有所差异。     

Surface textures of intrafault quartz grains as an indicator of fault movement

Quartz grains obtained from gouges which accompany faults are observed by means of a scanning electron microscope. It is assumed that quartz grains in the gouge are formed from the breakage of quartz in the parent rock due to fault movement, with corrosion by groundwater occuring on grain surfaces after the movement. Therefore, surface textures or morphology of the grains can become a good indicator in examining the mode of fracture at the time of faulting, or the length of time elapsed since the fault moved.     

Concentration and size distribution of airborne particles in a broiler house

Airborne dust particles were sampled in a broiler house using the quartz crystal microbalance cascade impactor designed for the measurement of mass concentration and size distribution from 0.05 to 25 gm. No significant difference was noticed in the dust concentration from morning to evening or at different sampling sites in the broiler house. The concentration of airborne dust particles decreased as the age of the chickens increased. Ratio of dust particles smaller than 0.8 pm to the total dust ranged from 10 to 50%. The highest concentration of dust was in the particle size range of 3.2 μm. The fogging system in use reduced the concentration of larger particles but not that of the smaller particles.     

台湾红壤及森林土壤中之氧化铁

本文综合汇整近年来在台湾，应用高梯度磁场分离技术，配合一般化学分析，Ｘ－射线衍射法，磁测分析，电子显微镜观察与电子衍射鉴定，以及铁－５７穆期堡尔谱学分析等方法，研究红壤与森林土壤中，氧化铁的分布及其结构性质之成果回顾；关于氧化铁之分布情形，其研究结果显示：台湾红壤中普遍存在有赤铁矿与针铁矿等氧化铁矿物，而在化育自大屯山更新世纪安山岩母质与澎湖列岛更新世纪玄武岩母质的红壤中，以及兰屿绿岛海边之银白色     

微灌石英砂过滤器反冲洗数值模拟验证与流场分析

微灌石英砂滤层的反冲洗,是实现滤料再生的有效途径,为了对反冲洗过程流场进行分析,并确定合理的反冲洗速度。该文建立了石英砂过滤器几何模型并进行了网格划分,采用Eulerian模型作为石英砂滤层反冲洗数值模拟模型,分别对石英砂当量粒径为1.06、1.2和1.5 mm的3种滤层的反冲洗过程进行了瞬态模拟,并将滤层整体压降和整体密度的模拟结果与试验结果进行对比,结果显示,整体压降的最大模拟误差为7.03%,整体密度的最大模拟误差为1.93%,说明数值模拟准确可信。在此基础上,分析了石英砂滤层反冲洗过程压降的波动规律、压降均值和压降标准偏差随反冲洗速度的变化趋势;并分析了滤层密度的分布规律、密度均值和密度标准偏差随反冲洗速度的变化趋势。根据压降波动的稳定性,结合滤层密度分布的稳定性,确定了石英砂滤层反冲洗强度的合理范围,3种滤层分别为0.0149~0.0212、0.0146~0.0218和0.0191~0.0261 m/s。该研究为石英砂滤层反冲洗过程的机理研究提供了参考,为砂过滤器反冲洗性能参数的确定提供了依据。