Selective Dissolution Analysis Research Articles

Using the pedogenic oxide ratio in distinguishing volcanic soil weathering intensity in subtropical region

Pedogenic oxide ratio (POR) helps identify and understand pedogenic processes. However, POR is seldom used to study and distinguish the weathering intensity of volcanic soils that are moderately weathered in the subtropical region. The research was conducted by collecting thirty-three subtropical volcanic soils from the northeastern Tatung Volcanic Group (TVG) region in Yangmingshan National Park, near Taipei, located in northern Taiwan. These volcanic soils could be grouped into two groups with different weathering intensities based on three weathering indices, pedogenic Fe-oxides ratios (PORs) - Feo/Fed, ((Fed-Feo)/Fet), and total reserve in bases (TRB): the highly weathered (HW) group and the lower weathered (LW) group. The two PORs show significant differences between the two groups, but not for TRB, which indicates the PORs are a good indicator for providing quantitative measurements of weathering intensity. Except for the soil bulk density (BD) meeting andic soil properties, the soils of the HW group have a lower content of Al plus 1/2 Fe content (by ammonium oxalate) (Alo + 1/2Feo) and phosphorus (P) retention, and soils of the LW group only have a lower P retention. Within those soil physicochemical properties and selective dissolution analysis results and index values, Alo + 1/2Feo, pyrophosphate extractable C (Cp), P retention, and dithionite-citrate-bicarbonate (DCB) extractable aluminum (Ald) are four critical factors for the discrimination of the soils. The soils in the study area still have relict volcanic soil properties after moderately weathered. Our research results indicate that the PO and POR are good indicators of moderately weathered volcanic soils in the subtropical region, allowing for a more precise assessment of the soil weathering process, in addition to quantitative measurements of weathering intensity.

Exploring the applicability of thermodynamic modeling to predict the degree of reaction of supplementary cementitious materials in Portland cements

A reaction degree of supplementary cementitious materials (SCMs) in hydrated Portland cement is an important factor that enables prediction of the performance of concrete, while conventional methods for estimating the degree of reaction of SCMs are generally time-consuming and complicated. This study investigated the applicability of thermodynamic modeling as an alternative and potentially less complicated means of predicting reaction degrees of SCMs. The reaction degrees and bound water contents of slag- and fly ash-blended Portland cement were experimentally measured at various sample ages by selective dissolution and thermogravimetric analysis, respectively, and compared with thermodynamic calculations. The results suggest that reasonably accurate and comparable predictions of bound water and degrees of reaction of SCMs can be made, which is promising and shows the potential of this approach to be used as an alternative and simple approach to predict the degrees of reaction of SCMs in hydrated Portland cement.

Microstructural and selective dissolution analysis of 316L austenitic stainless steel

Austenitic stainless steels (ASS) are among the most used structural materials because of their excellent mechanical and corrosive properties. In addition, 316L ASS has excellent weldability because of its low carbon content. This steel normally contains 5–10% residual delta ferrite to avoid hot cracking and micro-fissuring of the weld metal. Many studies show that selective dissolution of austenite or ferrite can occur in 316L steel. In a survey of the selective dissolution of phases in duplex stainless steel (DSS), Lo and coauthors studied the effect of electrolyte composition (H2SO4 + HCl solutions) on the active–passive transition. They showed that corrosion occurred only in the austenitic phase in solutions of 2M H2SO4 + 0.25–1.2M of HCl. Increasing the % of HCl, > 1.2%, austenite, and ferrite contributed to the corrosion process. The present authors did not find the effect of this electrolyte in the study of selective corrosion in 316L ASS welded in the literature. Therefore, this study aims to determine how the phases behave on 316L ASS by applying 2M H2SO4 + 1.5M HCl solution. In this work, we welded the steel by the autogenous TIG process using three heat inputs. The purpose of welding was to obtain different amounts and morphology of ferrite and determine whether this affected the selective dissolution of the phases. After the corrosion tests, the samples showed selective austenite corrosion irrespective of the volume fraction and morphology of the ferrite. In summary, the corrosive etches severely consumed the austenite because of the significant difference in the electrochemical potential between the phases. Therefore, with more nickel, austenite functioned as an anodic region, and the δ-ferrite, with more chromium, worked as a cathodic region.

Investigation of the clay minerals composition of soils derived from basalt parent materials in the Early Miocene to Early Pleistocene on the Arabian Shield using multiple techniques: implications for paleoclimatic conditions

Knowledge of clay minerals composition can be used to understand paleoenvironmental and/or paleoclimatic conditions, particularly for soils derived from volcanic parent materials that were subjected to diverse climatic conditions during pedogenesis. In this study, the clay minerals composition in soils developed from basaltic parent materials during the Cenozoic (mostly during the Early Miocene to Early Pleistocene) in the harrats region of the Arabian Shield in Saudi Arabia were investigated. Forty-seven clay samples were examined using selective dissolution analyses, X-ray diffraction (XRD), thermogravimetric analysis (TG), Fourier-transform infrared spectroscopy (ATR/FT-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to obtain a better understanding of the clay minerals developed in basaltic parent materials, particularly under a dry-hot environment. The XRD results revealed that the clay mineralogy was dominated by smectite, kaolin (kaolinite/halloysite), and interstratified vermiculite–chlorite (Vm–Ch), with mica, pseudo-chlorite, palygorskite, and Ca–zeolites as minor components. The TEM provided strong evidence for the presence of allophane and imogolite, which is in line with numerous previous studies on soils formed from basaltic parent materials. The existence of poorly-crystalline minerals in these soils was strongly supported by the selective dissolution analysis results. The combined influence of paleoclimates and parent material is evidenced in the clay minerals in the studied soils. The formation of smectite, Vm–Ch, and chlorite minerals in the harrats soils could be attributed to the simultaneous effect of temperate paleoclimates that dominated the Pliocene and the wet transition periods that occurred through the Pleistocene into the mid-Holocene, while the minor palygorskite and Ca–zeolites could be related to the dry conditions that started in the late-Holocene and persist to the present day. Additional studies regarding the clay mineral assemblages in similar geoenvironmental settings are highly recommend and should account for paleoclimatic conditions to provide a better understanding of the relationship between clay minerals and paleoclimates.

Collaborative involvement of woody plant roots and rhizosphere microorganisms in the formation of pedogenetic clays.

Previous studies have described the laying down of specific B horizons in south-western Australian ecosystems. This paper presents biomolecular, morphological and physicochemical analyses elucidating the roles of specific woody plant taxa and rhizosphere bacteria in producing these phenomena. Clayey deposits within lateral root systems of eucalypts and appropriate background soil samples were collected aseptically at multiple locations on sand dunes flanking Lake Chillinup. Bacterial communities were profiled using tagged next-generation sequencing (Miseq) of the 16S rRNA gene and assigned to operational taxonomic units. Sedimentation, selective dissolution and X-ray diffraction analyses quantitatively identified clay mineral components. Comparisons were made of pedological features between the above eucalypt systems, giant podzols under proteaceous woodland on sand dunes at the study site of Jandakot and apparently similar systems observed elsewhere in the world. Bacterial communities in clay pods are highly diverse, resolving into 569 operational taxonomic units dominated by Actinobacteria at 38.0-87.4 % of the total reads. Multivariate statistical analyses of community fingerprints demonstrated substrate specificity. Differently coloured pods on the same host taxon carry distinctive microfloras correlated to diversities and abundances of Actinobacteria, Acidobacteria, Firmicutes and Proteobacteria. A number of these microbes are known to form biominerals, such as phyllosilicates, carbonates and Fe-oxides. A biogenic origin is suggested for the dominant identified mineral precipitates, namely illite and kaolinite. Comparisons of morphogenetic features of B horizons under eucalypts, tree banksias and other vegetation types show remarkably similar developmental trajectories involving pods of precipitation surrounding specialized fine rootlets and their orderly growth to form a continuous B horizon. The paper strongly supports the hypothesis that B-horizon development is mediated by highly sophisticated interactions of host plant and rhizosphere organisms in which woody plant taxa govern overall morphogenesis and supply of mineral elements for precipitation, while rhizosphere microorganisms execute biomineralization processes.

Distinctive Roles of Two Aggregate Binding Agents in Allophanic Andisols: Young Carbon and Poorly-Crystalline Metal Phases with Old Carbon

Interaction of organic matter (OM) with soil mineral components plays a critical role in biophysical organization (aggregate structure) as well as in biogeochemical cycling of major elements. Of the mineral components, poorly-crystalline phases rich in iron (Fe) and aluminum (Al) are highly reactive and thus contribute to both OM stabilization and aggregation. However, the functional relationship among the reactive metal phases, C stability, and aggregation remains elusive. We hypothesized that relatively young C acts as a binding agent to form the aggregates of weak physical stability, whereas the reactive metal phases and older C bound to them contribute to stronger aggregation. Using four surface horizons of Andisols having a gradient of soil C concentration due to decadal OM management, we conducted sequential density fractionation to isolate six fractions (from <1.6 to >2.5 g cm−3) with mechanical shaking, followed by selective dissolution and radiocarbon analysis. After 28 years of no-till with litter compost addition, not only C and N but inorganic materials including the reactive metal phases (pyrophosphate-, oxalate-, and dithionite-extractable metals) showed clear shifts in their concentrations towards lower-density fractions (especially <2.0 g cm−3) on a ground-area basis. This result was explained by the binding of compost-derived OM with soil particles. Major portions of the reactive metal phases in bulk samples were distributed in mid-density fractions (2.0–2.5 g cm−3) largely as sonication-resistant aggregates. Theoretical density calculations, together with depletion in radiocarbon (Δ14C: −82 to −170‰) and lower C:N ratio, implied that the sorptive capacity of the reactive metal phases in these fractions were roughly saturated with pre-existing OM. However, the influx of the compost-derived, modern C into the mid-density fractions detected by the paired-plot comparison suggests decadal C sink in association with the reactive metal phase. Our results supported the concept of aggregate hierarchy and further provided the following new insights. At the high hierarchy level where shaking-resistant aggregates form, soil organo-mineral particles appeared to be under a dynamic equilibrium and the changes in OM input regime controlled (dis)aggregation behavior due to the binding effect of relatively young C. At a lower hierarchy level, the reactive metal phases were bound to N-rich, 14C-depleted OM and together functioned as persistent binding agent. Our study suggests that the recognition of binding agents and aggregate hierarchy level would help to untangle the complex organo-mineral interactions and to better understand soil C stability.

Comparative study of reaction degree of mineral admixture by selective dissolution and image analysis

The reaction degrees of slag and fly ash in composite binder pastes were comparatively studied by selective dissolution and BSE image analysis. The reaction degree of slag or fly ash determined by selective dissolution is higher than that by image analysis at early age, but the inverse regularity is observed at later age. When the selective dissolution method is used, the reaction degrees of slag and fly ash may be overestimated at early age due to the loss of the superfine particles through the filtration and the partial dissolution of slag or fly ash, and underestimated at later age owing to the presence of cement and hydration products. The narrow reacted slag rims formed at early age cannot be accurately identified during image analysis procedure, which leads to an underestimation of the reaction degree of slag. Due to the destruction of fly ash particles during grinding or polishing process, the reaction degree of fly ash obtained by image analysis is overestimated. At later age, the small particles cannot be fully counted at low magnification and the outer part of particles cannot be calculated at high magnification, and thus high reaction degree may be obtained. BSE image analysis could give more reliable results with acceptable error than selective dissolution.

Observed-Predicted Shifts in Thermodynamic Functions of Water Adsorption by Smectite at Nanoscale

The unique properties of nanoparticles have attracted a great deal of soil chemists' and geochemists' interest. The objective of this study was to evaluate the integral enthalpy (H), entropy (S), and free energy (F) of water vapor adsorption on nano-smectite surfaces. We used water adsorption isotherms at 28 and 35°C. The adsorbents were Na-nano smectite of diameter 59 to 72 nm and Na- and Ca-micro smectites of diameter 72 nm to 2 μm. The Na-nano smectite was prepared using centrifugation under prevailed diffusion motion in centripetal field that directed nanoparticles to assemble into hydrogel phase. X-ray diffraction (XRD) and selective dissolution analysis indicated separated smectite was the dominant phase. The means of ΔH were −8.6 ± 2.1, -11.6 ± 2.6, and -38.0 ± 7.4 kJ mol-1 for Na-micro smectite, Ca-micro smectites, and Na-nano smectite, respectively, indicating Na-nano smectite could function as effective thermal energy storage material and that bound water cannot be removed from Na-nano smectite aggregates without coarsening. The corresponding means of ΔS were −9.9 ± 4.7, -18.0 ± 3.2, and -104.9 ± 16.2 J mol-1 k-1, signifying ordered bound water cannot be disordered in Na-nano smectite aggregates without coarsening. The corresponding means of ΔF were −5.7 ± 2.9, −6.2 ± 2.5, and −6.1 ± 2.9 (averaged −6.0 ± 4.8 kJ mol-1), indicating that ΔF values, contrary to ΔH and ΔS, did not show definite nano-effect. These observed nano-effects were successfully predicted using facility in scaling the magnitudes of ΔH, ΔS, and ΔF, as the length scale L shrunk. The high heat of water vapor adsorption by nano smectite and ability to hydrate and dehydrate makes soil effective in the storage of thermal energy.

Micrometer-scale internal structure and element distribution of Fe-Mn nodules in Quaternary red earth of Eastern China

Fe-Mn nodules are the common feature of tropical and subtropical soils and contain abundant information of pedogenic processes, palaeoenvironmental changes, and element geochemistry. The main aim of the present study was to determine the internal structure and spatial distribution of elements in the Fe-Mn nodules to better understand the 3D internal structure, enrichment, and dynamics of heavy metals in nodules and to provide more aspects to explore the possible heavy metal sequestration and pedoenvironmental implications of Fe-Mn nodules in soils. The studied Typic Plinthudult was developed on Quaternary red earths in Eastern China. The Fe-Mn nodules in the Bs horizon of soil were separated and classified into four size fractions (5–8, 3–5, 2–3, and 1–2 mm). The 3D microstructure of Fe-Mn nodules was examined by means of synchrotron radiation-based X-ray microcomputed tomography (SR-mCT), and the spatial distribution of Fe and Mn in nodules was studied by scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). The association of heavy metals with Fe and Mn oxides in nodules was described by selective chemical dissolution, SEM/EDS, and principal component analysis. The SR-mCT images indicated that the 5–8, 3–5, and 2–3 mm nodules exhibited well-defined ring structures, while the 1–2 mm nodule exhibited homogeneous fabric. The internal microstructures of nodules could be divided into four parts: Fe-rich ring, Mn-rich ring, Fe and Mn overlapped ring, and the gap between ring structures. The Fe-Mn nodules were significantly enriched in Mn, Pb, Ni, Cu, and Zn relative to the soil matrix. In particular, the concentrations of Mn and Pb in the nodules were 150 and 90 times greater than those in the soil matrix, respectively. A clear partitioning of heavy metals between Mn and Fe oxide phases was observed in the nodules, indicating that Pb was mainly present in Fe oxides, while Ni, Cu, and Zn were mainly associated with Mn oxide phases. The SR-mCT and SEM-EDS revealed the detailed internal microstructure of the Fe-Mn nodules and geochemical dynamics of heavy metals in the soil system. The Fe-Mn nodules have very high scavenging ability in sequestrating toxic heavy metals in soils, such as Pb and Ni. The microstructure and spatial distribution of Fe and Mn in nodules reflected the cycle of alternating drying and wetting conditions and served as an important basis for inferring the pedogenic processes and pedoenvironmental conditions.

Using chemometric analysis to classify and confirm the origin of bio-char

In this article, we present a method for detecting the amount of polymer added in the biomass pyrolysis process to obtain fuel for energy generation. The main aim of these research was to develop a new methodology to determine the amount of polypropylene added in the pyrolysis process, which was used as a case study of the type of impurities that can contaminate biomass. In our best knowledge these methods, based on chemometric methods combined with spectral data from Fourier transform infrared spectroscopy (FTIR) applied to bio-char analysis are new one and could allow a more accurate control of bio-char than existing methods such as selective dissolution analysis of the 14C content. As a chemomteric methods in this studies the classification analysis (CA) and principal component analysis (PCA) were applied. Thereby we could describe relation between the third principal component (calculated from FTIR spectra) and amount of polypropylene additive depending on the pyrolysis temperature.To the best of our knowledge, there have been no reports in the literature on determining the amount of polymer added in using a bio-char control instead of raw biomass for co-firing.

Podzolized soils and paleoenvironmental implications of white-sand vegetation (Campinarana) in the Viruá National Park, Brazil

The vast and complex system of hydromorphic sandy soils in northern Brazilian Amazonia remains little studied. We investigated the broader soil–vegetation relationships in white-sand areas under Campinarana vegetation in the Viruá National Park, discussing pedogenetic processes as well as some paleoenvironmental implications. Our hypothesis was that white-sand areas were not covered with savanna grassland during dryer periods, and remained under arboreal vegetation. Seven soil profiles were studied along a typical forest–shrub–grassland gradient. All soils are acid, depleted in bases, with a fine-sandy texture. The vegetation gradient is associated with decreasing soil organic carbon contents. Imogolite is present in some soils as indicated by selective dissolution and microchemical analyses. Podzolization, indicated by illuvial organic and Al-rich coatings on quartz grains is clearly observed in thin sections. The mineralogy of the clay fraction indicates the occurrence of residual kaolinite, hydroxy-interlayered 2:1 mineral and traces of gibbsite, from alteration of sedimentary parent material. Carbon isotope analysis suggests a predominance of arboreal-shrubby vegetation (C3-type) during past drier periods of the Late Quaternary. We conclude that the local distribution of vegetation is primarily associated with edaphic factors. Poor drainage, impermeable subsurface layers, very sandy soils and intense leaching created subtle but contrasting pedo-environments, closely related to vegetation types. Overall, these Amazon Spodosols and Podzol-like soils are associated with C3-plant-dominated vegetation.

Determination of uranium metal concentration in irradiated fuel storage basin sludge using selective dissolution

Irradiated uranium metal fuel was stored underwater in the K East and K West storage basins at the US Department of Energy Hanford Site. The uranium metal under damaged cladding reacted with water to generate hydrogen gas, uranium oxides, and spalled uranium metal particles which intermingled with other particulates to form sludge. While the fuel has been removed, uranium metal in the sludge remains hazardous. An expeditious routine method to analyze 0.03 wt% uranium metal in the presence of >30 wt% total uranium was needed to support safe sludge management and processing. A selective dissolution method was designed based on the rapid uranium oxide dissolution but very low uranium metal corrosion rates in hot concentrated phosphoric acid. The uranium metal-bearing heel from the phosphoric acid step then is rinsed before the uranium metal is dissolved in hot concentrated nitric acid for analysis. Technical underpinnings of the selective dissolution method, including the influence of sludge components, were investigated to design the steps and define the reagents, quantities, concentrations, temperatures, and times within the selective dissolution analysis. Tests with simulant sludge proved the technique feasible. Tests with genuine sludge showed a 0.0028 ± 0.0037 wt% (at one standard deviation) uranium metal analytical background, a 0.011 wt% detection limit, and a 0.030 wt% quantitation limit in settled (wet) sludge. In tests using genuine K Basin sludge spiked with uranium metal at concentrations above the 0.030 wt% ± 25 % (relative) quantitation limit, uranium metal recoveries averaged 99.5 % with a relative standard deviation of 3.5 %.

Resistance of blended cement pastes subjected to organic acids: Quantification of anhydrous and hydrated phases

Concrete for agricultural construction is often subject to aggressive environmental conditions. Ground granulated blast furnace slag (GGBFS) or metakaolin (MK) largely improve the chemical resistance of the binder. Anhydrous particles seem particularly resistant to the acid solution. The purpose of this study is to quantify anhydrous particles in blended cement pastes as a function of acid exposition time in order to evaluate their acid resistance.Cement pastes were moist cured for 28days and then immersed in an acetic acid solution for 2months. The quantification of the anhydrous phases was carried out using 29Si MAS NMR, selective dissolution and back-scattered electron (BSE) images analysis, while the hydrated phases content was evaluated by TGA. After 28days of hydration, 60% of OPC, 44% of GGBFS and 76% of MK particles were hydrated. The amount of anhydrous particles drops for all materials during acid immersion. After 2months of immersion, the amount of anhydrous particles drops by 49%, 23% and 15% for OPC, GGBFS, and MK respectively. This study confirms that GGBFS and MK anhydrous and hydrates phases present higher acid resistance than OPC.

Clay composition and properties in termite mounds of the Lubumbashi area, D.R. Congo

The influence of Macrotermes falciger activity on clays, sesquioxides and water-dispersible clay (WDC) content was investigated by a physico-chemical, mineralogical and micromorphological study of termite mound and control soil profiles at various sites near Lubumbashi, SE Katanga, D.R. Congo. X-ray diffraction reveals that the termite-mound materials are enriched in 2:1 clays, especially mica and expandable clay minerals, and selective dissolution analyses show that they contain greater relative amounts of Mn oxides and poorly crystalline Fe oxides, relative to the surrounding Ferralsols. The water-dispersible clay (WDC) content is much higher (4–87 fold) in epigeal mound parts than in the control soils. Enrichment in 2:1 clays of the mounds is attributed to upward transport of mica and smectite as part of soil aggregates or saprolite materials used in mound construction. The difference in nature and abundance of sesquioxides between termite mound and control soil is related to a difference in moisture regime, whereby the basal part of the mounds are characterized by conditions with alternating reducing/oxidizing conditions, in contrast to the surrounding well-drained ferralitic soils. The much greater degree of clay dispersibility in termite mound materials than in the surrounding soils is mainly due to differences in clay properties, primarily surface charge characteristics, and to differences in Fe oxide content and mode of occurrence. The high water-dispersible clay content of termite mound materials is confirmed by micromorphological features, including abundant clay coatings and fragments of coatings.

Soil formation on the Karadag volcano at a semi arid environment from the Central Anatolia

Studies on soils developed on volcanic materials in Turkey in light of the wide distribution of these soils and soils defined as Andisols in the Soil taxonomy have not yet been recognized in Turkey. The aims of this study were to: i) show whether some Turkish soils developed in volcanic parent materials found on Mt. Karadag (Karaman Turkey) are Andisols and; ii) investigate their pedogenetic development. For this purpose, 3 representative soil profiles were evaluated. The results revealed that the amount of sand and coarse silt fractions were higher than 30% in all profiles. The bulk density is higher than 0.90 g.cm-3 in all profiles, while phosphate retention is low ( Fep > Feo (in profile 1) and Fed > Feo > Fep (in profiles 2 and 3) and, in most horizons Alp > Alo > Ald. According to selective dissolution analysis, non-crystalline minerals like allophane and imogolite were not found. The only non-crystalline minerals found in great quantities were Al-humus complexes and in small quantities ferrihydrite. The semiarid climate and long and dry summer season of volcanic areas, a low rate of weathering, inadequate Si leaching as a result of low precipitation and also very small amount volcanic glass content of parent materials of studied soils prevents andic soil properties. The major factors determining soil genesis on Mt. Karadag would appear to be climate, by affected leaching regime and weathering rates and the volcanic glass content of the parent material. Key words: Karadag mountain, soil formation, andisols, volcanic material, selective dissolution analysis.

Soil formation overlying volcanic materials at Mount Erenler, Konya, Turkey

Studies of soils developed on volcanic materials are insufficient in Turkey in light of the wide distribution of these soils. The objectives of the present work were to assess the influence of climate and other soil-forming factors on physical, chemical, and mineralogical characteristics and pedological processes in the soil genesis and soil classification of 4 volcanic soil profiles derived from andesitic parent material, and to determine whether they meet the requirements for classification as Andisols. Collected from a semiarid climate in Konya, Turkey, these soils are characterized as medium- and fine-textured with low organic matter content, low cation exchange capacity, and low soil moisture retention. Bulk density was greater than 0.90 g cm^{-3} in all profiles. In general, phosphate retention was low, and lower than 85% in all profiles. The Al + ½ Fe percentages (by ammonium oxalate) were lower than 2% in all profiles. The pH values in NaF were less than 9.5 in the soils studied. Selective extraction yielded the following relationship in all extractions: Fe_d > Fe_o > Fe_p. Additionally, in most horizons: Al_p > Al_o > Al_d. According to selective dissolution analysis results and index values, noncrystalline minerals such as allophane, imogolite, and iron-humus complexes have not formed in these soils. Only noncrystalline minerals were present, such as Al-humus complexes in great quantities, and, in small quantities, ferrihydrite. Crystallized Fe minerals were more common than other Fe minerals. Feldspar, cristobalite, and quartz were the most common primer minerals. Hematite, cummingtonite, and magnetite were also found in some profiles. X-ray diffraction indicated that kaolinite and illite were dominant minerals in the clay fraction; furthermore, a considerable amount of smectite was found in the clay fraction. The local climate, characterized by low precipitation and a long dry season, obstructs the formation of andic soil properties because of the low rate of weathering and inadequate Si leaching. As a result, the soils of Mount Erenler were not classified as Andisol but rather as Entisol. The major factors determining soil genesis on Mount Erenler appear to be climate, topography, and the nature of the parent material

Possible influence of termites (Macrotermes bellicosus) on forms and composition of free sesquioxides in tropical soils

Abstract There has been less concern about soil mineralogical alteration than about soil physical, chemical and biological changes induced by termite nest-building activity. Furthermore, much less attention has been paid to free sesquioxides than to phyllosilicate minerals. In the present study, we conducted field morphological observations and selective dissolution analysis to characterize free sesquioxides in termite ( Macrotermes bellicosus ) mounds as compared with surrounding pedons in different toposequence positions, i.e., seasonally flooded valley bottom, hydromorphic fringe and well-drained upland sites. Distinctive redoximorphic features, such as surface yellowish layers on mound structures from the fringe site, indicate possible alteration of iron sesquioxide forms in the mounds due to the transportation of soil from reductive (aquic subsoil) to oxidative (epigeal mound) environments by the nest-building activity of M. bellicosus . On the other hand, the iron-soluble content in the dithionite–citrate–bicarbonate (DCB) system (Fe d ) was generally higher in the mound structures than at the adjacent sub-surface (Ap2) horizon at each toposequence position, while there was less difference in the content of acid ammonium oxalate (AAO) extractable iron (Fe o ) as compared to Fe d . As a consequence, the iron activity index (Fe d /Fe o ratio) was found for the most part to be lower in the mound structures than in the neighboring Ap2 horizon. In addition, the content of Fe d , AAO-soluble Al (Al o ) and DCB-extractable Al (Al d ) was significantly correlated with clay content in these soils. These findings suggest that M. bellicosus preferentially collects clay particles, probably from the clay-rich subsoils, such as the argillic horizon, which has been formed by the co-migration of phyllosilicate minerals and relatively crystalline sesquioxides. The species then likely incorporates them into the mounds, which induces an increase in the Fe d content relative to that of Fe o , resulting in a decreased iron activity index in the mound structures.

Selective Dissolution Analysis of Major and Trace Elements in an Allophanic Andisol Acidified by Long‐Term Fertilizer Application

A long‐term (61 years) experimental field was used to examine the effect of acidification on the chemical composition of an allophanic Andisol in northeastern Japan. The pH values of the 1:10 water extract of the plow layer soils were 4.1, 4.7, and 6.2 for three fertilizer application treatments: chemical fertilizers only (CF), CF and compost (CFC), and CFC with liming, respectively. Three batch dissolution analyses were conducted to determine water‐soluble and exchangeable (D1), D1 plus, inorganically bound elements to noncrystalline clays and organically bound elements (D2), and total concentration of elements (TCE, 45 elements). The D1 fraction of 20 elements increased, and that of eight decreased with acidification. The D2 fraction of lithium increased, and that of eight elements decreased with acidification. Because the D2 fraction of many other elements and TCE were not strongly altered, present acidification of this soil can be restored with liming and other necessary amendments.

Corrosion Products from Carbon Steel Formed in Compacted Bentonite under Reducing Conditions

For safety assessment of high-level radioactive waste disposal, the sorption of radionuclides on corrosion products that migrate from overpack material into compacted bentonite and the dissolution of corrosion products, which may cause the alteration of smectite to Fe-smectite due to the increase in Fe2+ concentration in the pore water, are possibly dependent on the kinds of minerals formed in compacted bentonite as corrosion products. In this study, carbon steel, previously corroded electrochemically under aerobic conditions, was left in contact with compacted Kunigel V1 and Kunipia F under reducing conditions for 3 to 4 years at room temperature. The corrosion products, which migrated from the carbon steel into compacted bentonite, were investigated by selective dissolution analysis, which can estimate the crystal-linity of Fe-bearing compounds, and by spectrophotometry to determine the valence of iron in the corrosion products. From these analyses, the corrosion products in compacted bentonite were identified to be amorphous, noncrystalline or poorly ordered Fe(OH)2 and Fe(OH)3. Furthermore, the alteration of smectite to Fe-smectite in compacted bentonite was analyzed by X-ray diffraction (XRD). In the XRD analysis, Fe-smectite was not identified in Kunipia F from the variation in basal spacing as a function of relative humidity.

Investigation of montmorillonite alteration and form of iron corrosion products in compacted bentonite in contact with carbon steel for ten years

In high-level radioactive waste disposal, the alteration of montmorillonite due to the corrosion of carbon steel possibly affects the swelling and self-healing capacity of compacted bentonite used as a buffer material. The nature of the corrosion products in compacted bentonite is also important to evaluate not only the diffusion and sorption behavior of radionuclides but also the chemical composition and redox potential of pore water. In this study, the alteration of montmorillonite in compacted bentonite due to the interaction with carbon steel was analyzed by X-ray diffraction (XRD). The possibility of montmorillonite alteration was also investigated from the cation exchange capacity (CEC) of compacted bentonite and scanning electron microscopy (SEM) observation. The corrosion products distributed in the compacted bentonite were investigated by selective dissolution analysis, which can estimate the crystallinity of Fe-bearing compounds. The valence of Fe in the corrosion products was spectrophotometrically determined. From the XRD analysis, newly formed phyllosilicates resulting from the alteration of montmorillonite could not be identified in compacted bentonite. CEC of compacted bentonite adjacent to the carbon steel, in which high concentration of Fe was extracted, was hardly decreased. No significant differences of clay particles were observed with SEM. Thus, the alteration of montmorillonite was scarcely detected in compacted bentonite in contact with carbon steel for ten years. The selective dissolution and valence analyses suggest that most of the corrosion products of carbon steel existed in Kunipia F, which consists of over 95 wt% montmorillonite, was amorphous, non-crystalline or poorly ordered Fe(OH) 2. This means that Fe(OH) 2 distributed into compacted bentonite was scarcely crystallized within ten years at 80 oC. From the XRD analysis, small amount of green rust one containing Cl − at the interlayers (GR1(Cl −)) and lepidocrocite were also identified in Kunipia F. Therefore, under this experimental condition, Fe(OH) 2 formed in Kunipia F due to the corrosion of carbon steel was oxidized to GR1(Cl −) as intermediates, and then GR1(Cl −) was possibly oxidized to lepidocrocite. On the other hand, GR1(Cl −) was hardly detected in Kunigel V1, which contains 46–49 wt% montmorillonite, from the XRD analysis.