Phyllosilicates In Soils Research Articles

Role of Clay Mineralogy in the Stabilization of Soil Organic Carbon in Olive Groves under Contrasted Soil Management

Cropland soils are key systems in global carbon budgets due to their high carbon-sequestration potential. It is widely accepted that clays are one of the soil components that have a significant effect on the stabilisation of soil organic carbon (SOC), owing to its surface interactions with organic molecules. However, the identification of the direct effects of clays on SOC stabilization is complicated, mainly due to the difficulty of accurately characterizing the mineralogy of clays, especially phyllosilicates. In this study, the relationships between soil phyllosilicates and functional SOC pools in woodlands and comparable olive groves, under two contrasting management systems (bare soils versus soil under cover crops) and parent materials (calcareous and siliceous), were explored. The total mineralogy of soil and clay fractions and the soil-clay assemblages were analysed through the decomposition of X-ray diffraction patterns, and were then related to four SOC pools. Total and unprotected SOC was higher in olive groves under cover crops, and this was true independent of the parent material, proving the importance of herbaceous covers in SOC sequestration in woody crops. Some significant correlations between clay minerals and SOC fractions were found. Interestingly, mixed-layer content was correlated with the biochemically protected SOC fraction (r = 0.810, p < 0.05), and this was so even when the partial correlation coefficient was calculated (r = 0.761, p < 0.05). According to the partial correlation networks (PCN), four separated clusters of variables were obtained, which joined into only one at fdr < 0.25. The PCNs supported the direct correlation between mixed-layer content, especially those rich in smectite, and the biochemically protected SOC fraction, suggesting that smectite layers may stabilize organic molecules. Since potassium enrichment is higher in the rooted layers of woodland and soils under cover crops, and this increase is related to the collapse of swelling layers, these soils were poorer in smectite phases than the bare soils. This also would explain why the biochemically protected SOC was more abundant in the latter.

Thallium adsorption onto phyllosilicate minerals.

The adsorption of thallium (Tl) onto phyllosilicate minerals plays a critical role in the retention of Tl in soils and sediments and the potential transfer of Tl into plants and groundwater. Especially micaceous minerals are thought to strongly bind monovalent Tl(I), in analogy to their strong binding of Cs. To advance the understanding of Tl(I) adsorption onto phyllosilicate minerals, we studied the adsorption of Tl(I) onto Na- and K-saturated illite and Na-saturated smectite, two muscovites, two vermiculites and a naturally Tl-enriched soil clay mineral fraction. Macroscopic adsorption isotherms were combined with the characterization of the adsorbed Tl by X-ray absorption spectroscopy (XAS). In combination, the results suggest that the adsorption of Tl(I) onto phyllosilicate minerals can be interpreted in terms of three major uptake paths: (i) highest-affinity inner-sphere adsorption of dehydrated Tl+ on a very low number of adsorption sites at the wedge of frayed particle edges of illite and around collapsed zones in vermiculite interlayers through complexation between two siloxane cavities, (ii) intermediate-affinity inner-sphere adsorption of partially dehydrated Tl+ on the planar surfaces of illite and muscovite through complexation onto siloxane cavities, (iii) low-affinity adsorption of hydrated Tl+, especially in the hydrated interlayers of smectite and expanded vermiculite. At the frayed edges of illite particles and in the vermiculite interlayer, Tl uptake can lead to the formation of new wedge sites that enable further adsorption of dehydrated Tl+. On the soil clay fraction, a shift in Tl(I) uptake from frayed edge sites (on illite) to planar sites (on illite and muscovite) was observed with increasing Tl(I) loading. The results from this study show that the adsorption of Tl(I) onto phyllosilicate minerals follows the same trends as reported for Cs and Rb and thus suggests that concepts to describe the retention of (radio)cesium by different types of phyllosilicate minerals in soils, sediments and rocks are also applicable to Tl(I).

Binding of tetracycline on soil phyllosilicates with Cd(II) as affected by pH and mineral type

Antibiotics often coexist with heavy metals in contaminated soils, making their behaviors more complicated than their individual presences. Sorption to soil components deeply affects the mobility, bioavailability, and fate of contaminants. However, limited studies have investigated the cosorption characteristics of tetracycline (TC) and heavy metals to typical soil minerals, particularly phyllosilicates. This study investigates the effect of Cd(II) on TC sorption by kaolinite (Kao, 1:1-type) and montmorillonite (Mont, 2:1-type) via isothermal adsorption, coupled with X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Isothermal results show that TC sorption on both kaolinite (Kao, 1:1-type) and montmorillonite (Mont, 2:1-type) is little affected by Cd(II) at pH 4.5 but increases significantly at pH 8.5. The overall effect of Cd(II) on TC sorption depends on the intensities of two positive processes, i.e., (1) the formation of soluble Cd-TC complex increases sorption compared to free TC molecules and (2) the formation of a ternary clay-Cd-TC complex at clay variable edge sites increases sorption, and one negative process, i.e., competition of Cd(II) with cationic and zwitterionic TC species at the permanently charged sites decreases sorption. XRD analyses demonstrate that TC intercalates into the interlayer (d001 = 18.7 A) of Mont as one monolayer parallel molecule both with and without Cd(II) but adsorbs predominately on external surface of Kao. FTIR results suggest a flat-lying horizontal configuration of adsorbed TC molecules on clays, accompanied by a strong complexation between the carbonyl and amino groups of TC molecules and the surfaces. Besides, the presence of Cd(II) more or less facilitates this complexation. We propose that Cd(II) can significantly promote TC adsorption on clay minerals at alkaline pH rather than acidic pH. TC and Cd(II) interact intensely and form strong surface complexation on clay surfaces. Hence, coexistence with Cd(II) may lower the mobility and thus the bioavailability of TC in alkaline soils, which provides a new direction for soil remediation by regulating soil pH using alkaline materials.

Calcium isotopic fractionation during adsorption onto and desorption from soil phyllosilicates (kaolinite, montmorillonite and muscovite)

Abstract Mineral soil constituents play an important role in the storage/release of nutrients due to their ability to adsorb and desorb cations. Phyllosilicate minerals are particularly reactive due to their small size and high specific surface area (up to ∼800 m2·g−1). Previous work has highlighted the potential of Ca isotopes (δ44/40Ca) to identify secondary processes occurring within soils. Nevertheless, the mechanisms of isotopic fractionation (amplitude and nature) associated with Ca adsorption onto and desorption from different phyllosilicate minerals that are commonly found in soil remain poorly understood. This step is fundamental to improve our understanding of the Ca biogeochemical cycle at the water-soil-plant interface. Consequently, the study of the possible Ca isotopic fractionation during adsorption/desorption phenomena was approached experimentally using three “model” substrates representative of the phyllosilicate minerals frequently encountered within soils (KGa-2 kaolinite, Swy-2 montmorillonite and Tuftane muscovite). The experiments were carried out under abiotic conditions in “water-mineral” batch systems by precisely controlling the physico-chemical conditions: pH, solid/solution ratio, initial dissolved Ca concentration, particle size distribution, reaction time and other cations concentrations. Our results show no significant isotopic fractionation associated with Ca adsorption or desorption during KGa-2 and coarse size fraction of Tuftane muscovite (50–200 µm) experiments regardless of the physico-chemical parameters used. During Ca adsorption onto Swy-2 and fine size fraction of Tuftane muscovite (0.1–1 µm), light isotopes (e.g., 40Ca) are preferentially adsorbed to the clay mineral, and a positive apparent isotopic fractionation between 0.10‰ and 0.28‰ is measured in the supernatant recovered after adsorption experiments. Kinetic and thermodynamic isotopic fractionation are observed during the Swy-2 experiments while only a thermodynamic fractionation took place during the Tuftane muscovite (0.1–1 µm) experiments. The results obtained for the Ca desorption experiments performed with a chloride hexaamine cobalt solution suggest that Ca adsorption and the associated isotopic fractionation are fully reversible. Our results show that the Ca isotopic fractionation intensity during adsorption phenomena onto clay minerals is controlled by the layer charge and specific surface area of the considered phyllosilicate mineral, as well as the presence of an interlayer space open to cationic solute.

Specific Features of Profile Distribution and Crystallochemistry of Phyllosilicates in Soils of the Cisbaikal Forest-Steppe

The mineralogical composition of agrogray, dark gray, and agro-dark gray soils (Luvic Greyzemic Retic Phaeozems); agro-dark gray residual-calcareous soils (Calcaric Cambic Phaeozems); clay-illuvial agrochernozems (Luvic Chernic Phaeozems); and agrochernozems with migrational–mycelial carbonates (Haplic Chernozems) developed in the forest-steppe of Central Siberia within the Irkutsk Depression has been studied. The clay (<1 μm) fraction separated from these soils consists of mixed-layer minerals with alternating layers of hydromica, smectite, vermiculite, and chlorite; the proportions between them change within the soil profiles. The clay fraction also contains hydromicas, kaolinite, chlorite, and some admixture of the fine-dispersed quartz. Each type of the soils is characterized by its own distribution pattern of clay material with specific alternation of layers in the mixed-layer formations. Mixed-layer minerals of the chlorite–vermiculite type predominate in the upper horizons of texture-differentiated soils. Down the soil profile, the content of mixed-layer mica–smectitic minerals increases. In the clay fraction of arable dark gray-humus soils with residual carbonates, the distribution of the clay fraction and major mineral phases in the soil profile is relatively even. An increased content of well-crystallized kaolinite is typical of these soils. The parent material of agrochernozems has a layered character: the upper horizons are generally depleted of clay, and the middle-profile and lower horizons are characterized by the considerable kaolinite content. In general, the clay material of soils of the Tulun–Irkutsk forest-steppe differs considerably from the clay material of foreststeppe soils developed from loesslike and mantle loams in the European part of Russia. In particular, this difference is seen in the proportions between major mineral phases and between biotitic and muscovitic components, as well as in the degree of crystallinity and behavior of kaolinite and chlorite.

Investigation of acid hydrolysis reactions of polyphosphates and phytic acid in Bray and Mehlich III extracting solutions

Soil test phosphorus (STP) (Bray P-1, Mehlich III) was developed to predict the plant available P in agricultural soils in the USA. The acidic STP extracting solutions were intended to extract phosphate from alkaline earth metal-based solubility products and or adsorbed species on amorphous metal hydroxides or phyllosilicates in soils. However, the accuracy of STP in predicting plant available phosphate has often been questioned due to potential acid hydrolysis of poly- and organic-P in soils during the STP extraction. The objective of the study was to investigate the acid hydrolysis reaction of reference poly- and organic-P compounds (1.25–3.75 mM) in Bray and Mehlich III extraction solutions using spectrophotometric methods. The results showed that both tripolyphosphate and pyrophosphate readily underwent the acid hydrolysis reaction over 2 h, whereas phytic acid did not hydrolyze. The results suggest an overestimation of dissolved reactive phosphate from these polyphosphates should be considered when evaluating the STP data.

Is the geological concept of clay minerals appropriate for soil science? A literature-based and philosophical analysis

Data in the literature for soils that are dominated by each of the main types of clay minerals were examined and compared with those for reference clay minerals of the same types to determine the extent to which the nature and properties of clay-size minerals in soils could be explained by those of clay minerals with the same name from non-soil, ‘geological’ environments. Published information on soils from Australia, New Zealand and Iran was sourced for this study. The clay fractions of each of the soils are dominated by either one of the common phyllosilicates: kaolinite, halloysite, illite/mica, vermiculite, smectite, and palygorskite, or by the nanocrystalline mineral, allophane. Data for samples of kaolinite that had been extracted from soils from several countries (Australia, Thailand, Indonesia and Brazil) and purified before characterization have also been examined. In soils, each dominant clay mineral is generally associated with other materials, including iron oxides, other phyllosilicates and/or nanocrystalline minerals and organic matter. As the most studied example of an extracted phyllosilicate, kaolinite shows a wide range of properties in different soils, but a narrower range of properties within a particular locality. However, almost all of the soil kaolinites studied have larger specific surface areas and higher cation exchange capacities than reference kaolinites. The literature also reveals that, among phyllosilicates in soils, illites have a wide range of potassium contents, expandable minerals (vermiculites and smectites) may be interlayered by hydroxy-Al species particularly, and smectitic layers often occur interstratified with other layers, including those of illite, kaolinite and halloysite. The variability of soil phyllosilicates and their common association with other, often poorly crystallized but highly reactive minerals and compounds can be explained by their formation in the highly heterogeneous and dynamic soil environment. Phyllosilicates from non-soil or geological sources are poor models for the representation of secondary clay-size minerals in soils. In philosophical terms, the reduction of soil mineralogy to mineralogy as it is practiced within geology is misleading because of the differences between the minerals formed in soil and geological environments. In other words, clay minerals as they are defined as mineralogical entities for geology are of a different ‘kind’ to clay minerals in soils and cannot serve as ‘types’ or ‘stereotypes’ to enable explanation of the contribution of secondary clay-size minerals to soil properties or behavior. It is more useful to view clay minerals in soils as secondary inorganic compounds of clay-size than to follow their definition for non-soil purposes as plastic phyllosilicate minerals.

Dissimilar pH-dependent adsorption features of bovine serum albumin and α-chymotrypsin on mica probed by AFM

We studied bovine serum albumin (BSA) and α-chymotrypsin adsorption onto mica surfaces over a large pH range by atomic force microscopy (AFM) measurements in liquid. Data analyses (height, roughness and roughness factor) brought new insights on the conformation of proteins in soil environments, with mica as a model of soil phyllosilicates and non-hydrophobic surfaces. Validation of AFM approach was performed on BSA, whose behavior was previously described by nuclear magnetic resonance and infra-red spectroscopic methods. Maximum adsorption was observed near the isoelectric point (IEP). A stronger interaction and a lower amount of adsorbed proteins were observed below the IEP, which contrasted with the progressive decrease of adsorption above the IEP. We then studied the adsorption of α-chymotrypsin, a proteolytic enzyme commonly found in soils. AFM pictures demonstrated a complete coverage of the mica surface at the IEP in contrast to the BSA case. Comparison of the AFM data with other indirect methods broadened the understanding of α-chymotrypsin adsorption process through the direct display of the protein adsorption patterns as a function of pH.

Estimation of Vermiculite Content Using Rubidium‐Fixation Procedures in Four California Soils

Quantification of phyllosilicates in soils often depends on a combination of methods, including x‐ray diffraction (XRD), cation exchange and fixation capacities, and microscopy. We examined a Rb fixation method to quantify vermiculite content in California soils derived from granitic and nongranitic alluvium. Whole soil (&lt;2‐mm) samples were saturated with Rb and heated to 110°C followed by Rb displacement with NH4 (Rb110°C). Fixed Rb was determined directly by instrumental neutron activation analysis. The amount of vermiculite (g kg−1) was calculated as fixed Rb content (cmolc kg−1)/0.154 (based on a cation exchange capacity for vermiculite of 154 cmolc kg−1). For comparison, Rb fixation was also estimated after a 1‐h incubation (Rb1hr) with 2 mmol L−1 RbCl followed by a 30‐min extraction with NH4Cl. The more rigorous heating treatment (Rb110°C) fixed almost 35 times more Rb than the 1‐h method. The Rb110°C fixation was positively and significantly correlated with soil clay content. The XRD data showed, however, that clay fractions were dominated by smectite, mica, and chlorite, while vermiculite, the major K‐ and Rb‐fixing mineral, was a dominant mineral in most silt fractions. The Greene‐Kelly test showed that, in soils with smectitic clays, some of the charge originated in the tetrahedral sheet. Silt content was correlated with Rb1hr fixation but was not correlated with Rb110°C fixation. Our data suggest that Rb fixation by heating to 110°C overestimates the amount of vermiculite when tetrahedrally substituted smectites are dominant in clay fractions, and includes fixation by minerals in the silt fraction.

Origin and Properties of Smectite in Loess‐derived Soils of Western Ohio

AbstractExpanding phyllosilicates have been identified in soils of western Ohio for &gt;40 yr, yet little is known about the origin or properties of these clays. The objective of this study was to ascertain the origin of the smectite component of the expanding phyllosilicates from a representative Udalf‐Aqualf‐Aquoll toposequence derived from Peoria loess in western Ohio. The content, distribution, and layer charge of the smectite were evaluated using chemical and x‐ray techniques. Results from these analyses show the smectite present in these soils is a medium‐charge dioctahedral species. Alkylammonium chloride exchange indicated the layer charge of the smectite is between 0.36 and 0.38 mole charge per half unit cell. The smectite generally comprised 50% or more of the total clay content in the B and C horizons of each pedon. The presence of high contents of smectite in the C horizons of all three pedons demonstrates a detrital origin and suggests that Peoria loess was an important source of expanding phyllosilicates in soils of western Ohio.

Forest Fire Effects on Soil Phyllosilicates in California

AbstractThousands of hectares of forests are burned annually in wildfires and prescribed burns nationwide. Our objective was to determine the effects of such fires on soil phyllosilicates. At five sites throughout California representing Inceptisols, Andisols, and Mollisols, surface soil samples from similar depths were collected in burned and nearby unburned areas. Fires produced no visible soil alterations except in 1 to 2% of the land area where concentrated fuel such as logs or stumps burned slowly and at higher temperatures, effectively baking the underlying soil. Within the upper 1 to 8 cm at these severely burned areas, kaolin was completely destroyed or substantially depleted and d001 spacings of clay‐sized vermiculite, chlorite, chlorite‐vermiculite, and hydroxy‐interlayered vermiculite collapsed toward 1.0 nm or were decomposed as shown by x‐ray diffraction. Dehydroxylation of severely burned Fe‐bearing phyllosilicates was indicated by Mössbauer spectroscopy. The decomposition of virtually all phyllosilicates in the upper 2 cm of the soil was observed at one site after burning. The effects of severe burning on the soil phyllosilicates remained clearly expressed at least 3 yr after a fire.

K‐fixing phyllosilicates in soils: the role of inherited components

SUMMARYK‐fixing potential of 29 illite/smectite mixed‐layer minerals, covering a broad range in layer ratios and stacking arrangements, has been investigated utilizing X‐ray diffraction as the principal investigative tool. Samples were derived from a borehole core transecting Permian sedimentary rocks. In 93% of all samples, K+ was retained against replacement with Mg2+ from a 1 M MgCI2 solution in an average of 33% of the smectitic interlayers, defined via expansion to 1.7 nm upon ethylene glycol solvation after Mg‐saturation. This non‐ideal smectite behaviour points to a vermiculite‐type layer charge. Ordered structures fixed on average 20% more K than did random ones, but results were widely scattered. The Greene‐Kelly test revealed predominantly tetrahedral substitution, intercalation with dodecylammonium chloride molecules a high interlayer charge density in samples with a high K‐fixing capacity.The findings have implications in two fields: in pedology, soils developed from thermally altered sedimentary rocks may inherit a considerable potential for K–fixation; in mineral identification, interlayers in illite/smectite interstratifications fully expanded to 1.7 nm upon ethylene glycol solvation despite their vermiculite–type layer charge. Glycerol solvation provided equally inconsistent results, while dodecylammonium spacings seemed to correlate reasonably well with interlayer charge density characteristics.

Concentration of Iron Oxides from Soil Clays by Density Gradient Centrifugation

AbstractHigh speed centrifugation with a large‐scale zonal rotor and a linear, tetrabromoethane‐ethanol density gradient (1.0–2.8 Mg m−3) was utilized to fractionate the &lt;0.2µm clay materials from three soils with differing Fe‐oxide mineralogy. Hematite, goethite, and lepidocrocite were concentrated 4‐ to 10‐fold in the high density range (&gt;2.4 Mg m−3) while the low density fractions (&lt;2.2 Mg m−3) were depleted in reductant‐soluble Fe. Density gradient centrifugation also produced useful mineralogical separations of the soil phyllosilicates. In particular, smectite was concentrated in the 1.8 to 2.1 Mg m−3 density range whereas the 2.1 to 2.3 Mg m−3 density range was enriched with kaolinite, vermiculite, and clay mica. Electron microscopy and x‐ray diffraction analyses indicated that Fe‐oxides were present in the materials studied as discrete particles rather than as “coatings” on associated minerals.

Charge Heterogeneity and the Calorimetry of K-Ca Exchange-Adsorption in Clays and Soils

Current evidence for surface heterogeneity of the permanent negative charge in some soils and phyllosilicates, which is based on the thermodynamic interpretation of K-Ca exchange isotherms and on other methods, is summarized and reviewed. The relationship between differential heats of K-Ca exchange and K-saturation of the permanent negative charge in the phyllosilicates, especially the Smectites and the Kaolins, is described and related to their known interlayer expansion with ethylene glycol intercalation. From these descriptions, their surface charge heterogeneity and new definitions of ‘pure’ phyllosilicates, especially ‘pure’ montmorillonite and ‘pure’ kaolinite are inferred. The heterogeneity of cation-exchange sites in some English soils is compared with those of the 2:1 phyllosilicates. Differences in the ‘differential heat:fractional K saturation’ relationships between soil phyllosilicates before and after treatment with potassium salts and with farmyard manure illustrate the effects of such treatments on site heterogeneity.

Inherited and Detrital 2:1 Type Phyllosilicates in Soils Developed from Mazama Ash

AbstractPrevious studies of soils developed from Mazama ash have indicated the occurrence of a complex suite of 2:1 and 2:2 type phyllosilicates. Before interpreting the phyllosilicates as weathering products from the ash, it must be established that they have formed in situ. Origin of 2:1 and 2:2 type phyllosilicates in soils of the coarse Mazama pumice in central Oregon was traced to the pyroclastic lithic fragments in the deposit. Clay minerals separated from lithic fragments included chlorite, chloritic intergrades, mica, smectites, and possibly vermiculite. The inherited origin of these crystalline clays corrects previous suggestions of origin which involved weathering of ash.For volcanic ash soils in forested areas located at distances farther than 100 km from the source at Crater Lake, 2:1 type clay minerals separated from ash horizons were shown to be relics from underlying paleosols. Crystalline clay suites in different ashy profiles exhibited greater similarity to their respective palesol clay fraction than to other profiles in the same ash deposit. Once incorporated into ashy horizons, palesol clay high in montmorillonite exhibited partial chloritization and samples high in mica exhibited some loss of interlayer K. Uprooting of trees is believed to be the major mechanism involved in mixing ash soils with palesols in forested areas where the Mazama deposit is relatively thin (&lt; 100 cm).

EFFECT OF HYDROLYSIS OF ALUMINUM ON COMPETITIVE ADSORPTION OF POTASSIUM AND ALUMINUM BY EXPANSIBLE PHYLLOSILICATES

ABSTRACT The competitive adsorption of K and Al on montmorillonite and vermiculite as influenced by the degree of hydrolysis and polymerization of solution Al was examined. The Na-saturated minerals (0.2–2μ) were suspended in the hydroxy-Al solutions of basicites (OH/Al molar ratios) of 0, 0.5, 1.0, 1.5, 2.0, and 2.5 in the presence of a fixed concentration of K, and the suspensions were then equilibrated at 25 ± 0.2°C. Compared to Al, K became more competitive for the exchange sites in vermiculite with the increase in initial basicity of solution Al, and the reverse trend was true for montmorillonite. The more unrestricted Z-axis expansibility of montmorillonite favors the diffusion of a given size polymer in the interlayer space; thus the hydroxy-Al ions with higher charge are more competitive than K. In the case of vermiculite, the limited expansibility, the presence of wedge zones, the charge and size of the hydroxy-Al ions, and the presence of strongly competing K ions greatly hinder the adsorption of Al over K as the degree of hydrolysis of Al increases. The products of adsorption were found to vary significantly with the mineral and initial basicity. With the increase in the initial basicity, an increasingly ordered micalike mineral was formed from vermiculite. It is evident that the degree of hydrolysis and polymerization of solution Al greatly affects the adsorption of K and Al by 2:1 expansible phyllosilicates, and would thus affect the competitive formation of micalike minerals and Al interlayers of expansible phyllosilicates in soils and sediments.