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.     

Mineralogical and chemical properties of weathered magnetite grains from lateritic saprolite

Magnetite grains in lateritic saprolite have altered in situ to porous hematite (martite) grains. Hematite occurs as relatively large (～ 1 μm) platy crystals, triangular arrays of small (0.01–0.05 μm) lathlike crystals and very small (< 100 Å) platy anhedral particles. Titanium increased in altered grains and may substitute for Fe³⁺ in hematite. Mn, V, Cr and Zn remained approximately constant whereas the Ni content decreased. Halloysite crystallized from soil solution within pores resulting in a marked increase in the Si and Al contents of grains.     

A STATISTICAL EVALUATION OF THE INTER-RELATIONSHIPS BETWEEN PARTICLE-SIZE FRACTIONS,FREE IRON OXIDE,AND TRACE ELEMENTS1

A statistical approach was adopted to study the association between particle-size fractions and trace elements in soil, because conventional studies on the subject usually involve chemical methods of fractionation, which may lead to loss and upsets in natural distribution patterns. The results showed that both total and extractable contents of Zn, Al, Cu, Mn, Pb, and Fe are bound up either in clay or silt fractions, although variations as to the particular particle-size diameter range did occur among the different elements. An attempt to resolve these relationships fitting a linear mathematical function, y=a+bx, based on the statistical association of individual particle-size fractions with particular trace elements, gave satisfactory results. There was no evidence to indicate that certain size fractions could mobilize trace elements by virtue of their abundance in these soils. There was convincing statistical proof to show that amorphous Fe₂O₂, possibly by way of surface coating of finer particles, may retain a large proportion of the trace elements investigated.     

Potassium release from sand,silt and clay fractions in calcareous soils of southern Iran

The release of non-exchangeable potassium from 24 calcareous soils of divergent mineralogy, from southern Iran, was examined. Sand, silt and clay particles were fractionated after dispersion with an ultrasonic probe. Samples were extracted with 0.01 M CaCl₂ for 30 successive 2-h periods. The clay fraction released the largest amount of K in each soil. Cumulative K released ranged from 175 to 723, 35 to 128, and 71 to 146 mg kg^?1 contributing 20–90, 4–39 and 2–54% for clay, silt and sand fractions, respectively. The lower proportion of K released from sand and silt fractions can be explained by the presence of a high content of CaCO₃ and quartz in these fractions. The release kinetics for the non-exchangeable K data showed that parabolic diffusion and power function were the best fitting kinetic models. This indicated that slow diffusion of K from the mica interlayer positions is the main rate-controlling process. Cumulative K released and constant b values of parabolic diffusion model correlated significantly with the mica content of the clay fraction.     

Fractionation of organo-mineral complexes by sedimentation and density techniques

Soil samples were fractionated by sedimentation in water and by flotation in heavy liquids to separate complexed and uncomplexed organic and inorganic components. Flocculation of clays in heavy organic liquids was delayed by addition of a surfactant. Heavy liquids and surfactants sorbed by soil components were removed by washing with acetone-water mixtures.In a sample of a red-brown earth, the organic carbon and nitrogen contents were highest in the finest separates. In samples of a ground-water rendzina and a chernozemic soil, the coarse clay and silt separates had the highest organic carbon and nitrogen contents. Organic matter was concentrated in low density fractions in all separates. Carbon/nitrogen ratios were lowest in the finer and heavier separates. Calcium, and to a lesser extent manganese, iron and phosphorus, were concentrated in low density fractions: thus these elements appear to be associated with organic matter and may be important in organo-mineral complex formation. Carbonates, titanium, iron, silicon and potassium were concentrated at the highest densities.Organic fractions < 2.06 g cm^?3 from sand size separates were insoluble in alkali and had wide carbon/nitrogen ratios characteristic of plant debris. The light fractions from fine silt and coarse clay separates were more soluble in alkali but showed high ratios of humic to fulvic materials and high absorption at 280 nm. Such materials were considered to be microbial cell debris and were associated with high contents of disordered aluminium and iron oxides and expanding lattice silicates in 1 to 5 μm aggregates.Heavier fractions, particularly of finer clay separates, contained more fulvic and humic materials of a more aliphatic nature than those in < 2.06 g cm^?3 fractions. It is suggested that physical sorption on clay surfaces may be more important in these fractions. Ellite and kaolinite were concentrated in medium density fractions, and contents of some iron oxides and titanium minerals were highest in fractions > 2.06 g cm^?3. Such minerals plus quartz and feldspars were associated with minor amounts of organic matter or possibly were not involved in organo-mineral associations.     

SANDSTONE-DERIVED SOILS OF A CATENA AT IPERU, NIGERIA

Chemical and mineralogical properties of five soil profiles of a catena in Iperu, Western State of Nigeria, are reported. The pH values of the subsoils are extremely acid. Acidity decreases with improved drainage in the subsoils (pH 4.0–5.8). The cation exchange capacity (C.E.C.) of the soils range from 3.0 to 16.2 me/100g of soil. The silt: silt+clay ratio, calcium: magnesium ratio and Fe₂O₃:Al₂O₃ ratio are used as weathering indices. The low values of the silt: silt + clay index indicate that the soils must have undergone advanced weathering. The magnitude of the Ca: Mg ratio indicates that more calcium than magnesium is available in the soils. The values for sodium and potassium are extremely low. More iron than aluminium was extracted from the soils by the dithionite-citrate method. Kaolinite is the most abundant clay mineral. Halloysite, interstratified clay materials, vermiculite, quartz, and mica are present in considerable amounts. The silt fraction in which quartz is the most abundant mineral, also contain some kaolinite and mica.     

Effects of Cow Dung Biochar Amendment on Adsorption and Leaching of Nutrient from an Acid Yellow Soil Irrigated with Biogas Slurry

Knowledge of the saturated hydraulic conductivity (K _sat) of porous filters used in water treatment technologies is important for optimizing the retention of nutrients and pollutants. This parameter determines the hydraulic capacity, which together with the chemical properties of the filter media, affects the treatment performance of the filter system. However, measuring K _sat is time consuming and expensive. This study developed a novel transfer function to predict K _sat of coarse porous media from easily measured parameters. The hydro-physical parameters determined were K _sat, grain size distribution, bulk density, uniformity coefficient, particle density, and porosity of 46 porous media fractions. The fractions ranged in grain size from 0.5 to 20 mm and were obtained from seven commercial available coarse filter materials. A backward stepwise regression analysis was performed between K _sat and 10 variables obtained from the grain size distribution and bulk density. The optimal model for predicting K _sat contained two parameters, D₂₀ and D₅₀, which describe respectively the particle diameters, where 20 and 50 % of all particles are finer by weight. The predicted K _sat values were in good agreement with the measured values (R ²?=?0.91). The transfer function can find potential usage in relation to dimensioning of permeable agricultural drainage filters or subsurface-flow constructed wetlands. The predicted values of K _sat can also be used as input to numerical models that simulate filter treatment performance.     

Effect of the particle-size distribution on the adsorption of copper, lead, and zinc by Chernozemic soils of Rostov oblast

The parameters of adsorption of Cu²⁺, Pb²⁺, and Zn²⁺ cations by soils and their particle-size fractions were studied. The adsorption of metals by soils and the strength of their fixation on the surface of soil particles under both mono- and polyelement contamination decreased with the decreasing proportion of fine fractions in the soil. The adsorption capacity of the Lower Don chernozems for Cu²⁺, Pb²⁺, and Zn²⁺ depending on the particle-size distribution decreased in the following sequence: clay loamy ordinary chernozem ∼ clay loamy southern chernozem > loamy southern chernozem > loamy sandy southern chernozem. According to the parameters of the adsorption by the different particle-size fractions (C _max and k), the heavy metal cations form a sequence analogous to that obtained for the entire soils: Cu²⁺ ≥ Pb²⁺ > Zn²⁺. The parameters of the heavy metal adsorption by similar particle-size fractions separated from different soils decreased in the following order: clay loamy chernozem > loamy chernozem > loamy sandy chernozem. The analysis of the changes in the parameters of the Cu²⁺, Pb²⁺, and Zn²⁺ adsorption by soils and their particlesize fractions showed that the extensive adsorption characteristic, namely, the maximum adsorption (C _max), was a less sensitive parameter characterizing the soil than the intensive characteristic of the process—the adsorption equilibrium constant (k).     

Morphology and Solutes Content of Atmospheric Particles in an Urban and a Natural Area of São Paulo State, Brazil

The objectives of this work were to characterize and compare the chemical composition of the water-soluble fraction of the PM₁₀ particles (Dp < 10μm) in two sites: one inside the Metropolitan Area of São Paulo (MASP) and another, 250km apart, inside the State Park of Serra do Mar (CUNHA) part of the Atlantic Forest Reserve, both located in São Paulo State, Brazil. The atmospheric particles were collected during dry and wet season. The morphologic parameters of the particles were characterized for the different size fractions of the collected material. In the aqueous extract of the particulate fine fraction the major ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl^?, NO₃ ^?, NH₄ ⁺, SO₄ ^2?) and trace elements (Al, Mn, Fe, Pb, Cd, Zn, Ti, Ni, Cu, Co, Ba) were determined. The morphological characteristics of the particles collected within the MASP are typical of polluted environment while in CUNHA there is no evidence of this type of contribution. Regarding the solute concentrations it was observed that the most abundant major ions and trace elements were K⁺, Ca²⁺, Na⁺, Cl^? and Pb, for CUNHA and NO₃ ^?, SO₄ ^2?, NH₄ ⁺ and Mn, Ni, Pb, Co, Cd and Ba for MASP. These differences are associated with the different sources of the particles. In the urban area they are predominantly of pollution origin, mainly from vehicle emissions, and road dust suspension, while in the State Park they are mainly of biogenic, terrigenous and oceanic origins. For these reasons the CUNHA region can be considered to be a regional reference site for studies concerning eventual disturbances in the Cunha background site, derived from transported pollution.     

SIZE FRACTIONATION, DISSOLUTION ANALYSIS, AND INFRA-RED SPECTROSCOPY OF HUMUS COMPLEXES IN ANDO SOILS

Eight samples of Ando soil A₁ and buried A₁ horizons of different ages were fractionated into clay-, silt-, and sand-size separates, and the yields and carbon contents of these separates were determined. The clay-size separates were subjected to two series of successive extractions, 1) 0.1 M Na₄ P₂ O₇/2% Na₂ CO₃/0.5 M NaOH and 2) dithionite-citrate/2% Na₂ CO₃/0.5 M NaOH; and to difference infra-red spectroscopy for identification of the extracted constituents. The result indicated that humus evolves from forms with a very low complexing ability for Al and Fe into forms that complex Al and Fe in the A₁ horizon, and that humus further interacts with allophane-like constituents, allophane and imogolite in the buried A₁ horizon. These reactions between humus and inorganic constituents result in formation of silt- and sand-size aggregates which are stable to sonic wave treatment, but are broken down into finer particles upon boiling with H₂ O₂.     

Identification of vivianite formed on the roots of paddy rice grown in pots

Abstract

An understanding of the phosphate (P) dynamics in paddy rice fields is the basis for improving P fertilizer efficiency and reducing P loss from paddy fields. During the ripening stage of rice plants cultivated in pots, we identified vivianite on the roots. We placed 3?kg of air-dried soil in a pot with coated urea (1?g N), coated potassium sulfate (1?g K₂O) and granular superphosphate (1?g P₂O₅) as basal fertilizers. Three rice seedlings were transplanted into each pot and grown until the ripening stage under submergence outdoor conditions. The bulk soil showed a black color indicating the formation of amorphous FeS. According to the soil analysis data, the oxalate-extractable Fe content was much greater than the labile S and P contents, indicating that enough Fe(II) can be supplied to the S and P for the reaction. Bluish vivianite particles were observed on the roots using an optical microscope. Scanning electron microscopy revealed that the vivianite was an aggregate of platy crystals, and an energy dispersive X-ray analysis showed that Fe and P were the major elements in the crystal aggregates. The diffraction peak positions by the X-ray microdiffractometer were very close to the reported pattern for vivianite. Future research on the dynamics of P is expected based on vivianite formation in paddy field soils.     

盐渍土中盐结晶的显微研究——Ⅰ.芒硝无水芒硝的转换因素和蓬松盐土蓬松层的形成

应用偏光显微镜技术与扫描电子显微镜技术,对三种不同类型盐土的盐结晶进行观察研究。从土壤溶液的蒸发过程中,我们观察到石膏(CaSO₄·2H₂O)、芒硝(Na₂SO₄·10H₂O)、泻利盐(MgSO₄·7H₂O)、石盐(NaCl)结晶的析出过程,析出顺序受温度的影响。用这种方法可以快速确定土壤溶液中主要盐分类型。扫描电子显微镜的照片,展示出某些盐类结晶的自然特征,它们是:与土粒胶结紧密的石盐(NaCl)、由芒硝(Na₂SO₄·10H₂O)脱水转变成的无水芒硝(Na₂SO₄)、或由硫酸钠、硫酸钙形成的复盐——钙芒硝Na₂Ca(SO₄)₂。各种盐类在土壤中结晶出来形态清晰。以硫酸钠的溶解特性为例,扼要地讨论了土壤中芒硝—无水芒硝的转化条件及其对土壤结构产生的影响。     

QUANTITATIVE PEDOLOGICAL STUDIES ON SOILS DERIVED FROM SILURIAN MUDSTONES

The uniformity of the parent material between and within five soil profiles representing a typical catenary sequence in upland mid-Wales was investigated using as criteria of uniformity the constancy of the ratios Zr: Sr and quartz: illite in the silt fractions. No lithologic breaks could be detected in the soil profiles. ZrO₂, TiO₂, quartz, and tri-acid residue were assessed for use as internal standards. TiO₂ appeared to be mobile during pedogenesis. Of the other three standards tri-acid residue was considered to be most suitable.     

ADSORPTION ON HYDROUS OXIDES: II. OXALATE, BENZOATE AND PHOSPHATE ON GIBBSITE

Adsorption isotherms, the infrared spectra of adsorbed species, and the amount of hydroxyl released when oxalate is adsorbed, all indicate that adsorption of oxalate, benzoate and phosphate at low solution concentrations occurs only on A1(OH)(H₂ O) sites exposed on edge faces of the platy gibbsite crystals studied. This is confirmed by the finding that the vibrations of surface hydroxyl groups on the principal plate faces are unaffected when excess oxalate is present, and further supported by the low affinity for oxalate of imogolite, a tubular mineral with a very large gibbsite-like surface, but with a very low concentration of edge sites. Infrared spectra indicate that oxalate is adsorbed in bidentate form. Near neutrality and at low solution concentrations, gibbsite adsorbs more oxalate than does goethite of comparable surface area.     

华中南部某些土壤针铁矿的形态

The morphologies of goethites in latosol, red soils, yellow-brown soil and the paddy soils developed from red soils were studied in comparison with the morphology of synthetic goethite by means of the X-ray diffraction, transmission electron microscopy and energy dispersive X-ray analysis. The synthetic goethite displayed acicular particles elongated in the c-direction. The goethites in the latosol, red soils and yellow-brown soil were platy particles stretched in two directions or isodimensional particles, and those in the paddy soils from red soils were acicular, short columnar, platy or isodimensional particles. Various morphologies of the goethites probably suggested their different dominant crystal faces, surface charge distribution and surface adsorption characteristics.     

Distribution of Heavy Metals and Minerals in the Various Size Fractions of Soil from Copșa Mică, România

The Cop?a Mic? area is one of the most polluted anthropic sites in Romania. Because higher heavy metal concentrations occur in finer fractions, this research focuses on the size fraction <?500 μm. Two kilograms soil sample was sieved on the 500-μm sieve and was air classified into size fractions down to the low micrometer range. The size fraction’s composition was investigated by ICP-OES IC, XRD, and FTIR spectrometry. Approximately 80 and 62% of the material was smaller than 2 mm and <?500 μm, respectively. The predominant size fraction had a mass median diameter (MMD) of approximately 75 μm. The smallest size fraction with a MMD of 2.2 μm had a share of 3.6% and contained the highest amount of heavy metals. The concentrations of Pb, Zn, Cd, Cu, Sb, and As exceeded the legally regulated values for soils according to Romanian legislation. The respective concentrations were 26,900, 27,600, 415, 2130, 466, and 915 mg·kg^?1. In the coarser size fractions 5, 4, and 3, the predominant minerals were quartz and alkaline feldspar, while in the finer size fractions 1 and 2, the clay minerals and total carbon (TC) were predominant. Illites and montmorillonites in the fine fraction composition retain heavy metals due to the high levels of cation exchange capacity. Black carbon accumulated in soil acts as a heavy metal adsorbent due to its porosity and high specific surface area. The good correlation between heavy metals and TC in the top soil can be an indicator of the level of heavy metal pollution.     

Soil solution aluminium activity related to theoretical A1 mineral solubilities in four Australian soils

Four soils were treated with HNO₃, CaCO₃ and K₂SO₄ to enable observation of the response of the soil solution composition and the solution A1 ion activity (Al³⁺) to the treatments and to time. The clay fraction of three of the soils was dominated by illite, kaolinite and quartz. The fourth was minated by kaolinite and iron oxides. The initial pH in 0.01 M CaCl₂ varied between 4.0 and 5.0 and the organic carbon content from 0.7 to 1.1%. The soil solutions from soils dominated by kaolinite, illite and quartz were generally supersaturated with respect to quartz and well ordered kaolinite, and unsaturated with respect to illite. The soil solutions from the soil dominated by kaolin and iron oxide were generally unsaturated with respect to quartz but still saturated with respect to ell crystallized kaolin. Within mineral groups such as Al₂SiO₅ compounds, A1₂Si₂O₅(OH)₄ (kaolinite group), and Al(OH)₃ (A1 oxide) minerals, the more soluble forms became less supersaturated or unsaturated with time for many treatments. Lime treatment usually increased the ion activity product of AI(OH)₃ in all soils, and of minerals with the composition, Al₂SiO₅, in the illite/kaolinite soils. Acid treatment reduced the apparent solubility of Al(OH)₃, and the A1 silicates in the Al₂SiO₅, and Al₂, Si₂, O₅,(OH)₄, mineral groups on all soils. These results are interpreted to indicate that lime treatment led to the formation of trace quantities of more soluble A1 minerals that subsequently controlled (Al³⁺), whereas acid treatment dissolved trace quantities of such minerals leaving less soluble minerals to control (Al³⁺). The results suggest that, in mineral soils such as these, (Al³⁺) is under the control of inorganic dissolution and precipitation processes. These processes conform to expectations given the free energy of various inorganic aluminium compounds. Furthermore the sequence of dissolution and formation processes appears to be governed by the Gay-Lussac—Ostwald step rule.     

Fe,Al, Mn,and S chemistry of Sphagnum peat in four peatlands with different metal and sulfur input

Comparisons among 4 peatland sites representing a gradient of increasing Fe, Al, Mn, and S loading revealed significant accumulation of total Fe, Al, and S, but not Mn, in surface (0 to 20 cm deep) peat along the gradient. Iron and Al accumulation were contributed mainly by organically bound fractions, with oxides contributing to a lesser extent. Although SO₄ ^2? and Fe sulfides showed significant increases in concentration along the gradient, most of the accumulation of total S was contributed by organic, rather than inorganic S. Laboratory studies of Fe²⁺ adsorption by peat indicated that increasing the pH of added Fe²⁺ solutions (pH values of 3, 4, 5, and 6) did not significantly affect Langmuir equation estimates of either maximum Fe²⁺ adsorption capacity or the affinity of peat for Fe²⁺. Regardless of the pH of the added Fe²⁺ solutions, final solution pH values were relatively uniform, averaging about 3.4, reflecting a considerable bufferring capacity of Sphagnum peat. Factors affecting the accumulation of metals and S in peat remain topics for further investigation.     

Factors affecting the structural stability of three contrasting soils of China

The structural stability of eight samples representing three soil profiles from tropical and subtropical regions of China (Latosol, Red Earth and Yellow Brown Earth) was studied by dispersion treatments. The samples were treated with the following solutions in order without previous mechanical disruption: (I) H₂O, (II) 0.1 N NaCl, (III) 0.002% Na₂CO₃, (IV) 0.1 N NaOH, (V) acid oxalate, (VI) 0.1N NaOH. These procedures were designed to disperse soil samples by removal of potentially aggregating substances and by anion adsorption. After each treatment the clay dispersed was separated by sedimentation and its mineralogical composition was studied by XRD, Mössbauer spectroscopy and magnetic susceptibility measurements to assess the role of mineralogy in the maintenance of soil structure. The amounts of iron extracted by Na-dithionite–citrate–bicarbonate were 9.6–10.8% in the Latosol, 3.1–3.4% in the Red Earth and 0.9–2.1% in the Yellow Brown Earth. It was concentrated in clay fractions and existed mainly as superdispersed particles. The hematite/goethite ratio varied from 1.7 for the Latosol to 0.2 for the Yellow Brown Earth. The clay fraction of the Yellow Brown Earth is vermiculitic and has a permanent negative charge. This soil's structural stability is mainly influenced by exchangeable Ca²⁺. In the Latosol and the Red Earth, surfaces with variable (pH-dependent) charges prevail because of the large free Fe-oxides contents. Alkaline treatment (IV) promoted most dispersion of these soils, indicating the mainly electrostatic nature of interactions between mineral particles. Thus, the role of the Fe oxide minerals in these soils is one of aggregation rather than cementation. The aggregation properties of the Latosol and Red Earth are relict paleosol features inherited from an earlier period of cooler and wetter climate than the present.