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Red clay as a special soil has a high liquid-plastic limit, water swelling and water loss shrinkage. To solve the problems red clay was modified by calcium carbonate produced in Hezhou, Guangxi. The Liquid-plastic limit, water loss shrinkage, nuclear magnetic resonance (NMR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and consolidated drained (CD) triaxial shear test were carried out on the modified soils. The results show that when the calcium carbonate content is 20%, the plastic limit is 24.38 and the liquid limit is 38.67, which are reduced by 35.04% and 22.16%, respectively. The Montmorillonite content in the modified soil is reduced by 27.7%. The shrinkage coefficient decreased from 0.325 to 0.102. The NMR test shows that the content is 5% and 10% would lead to a decrease in the macropores and an increase in the micropores pores. The phenomenon is the opposite (15% and 20%). All contents led to the porosity increase. The calcium carbonate content of 5% was selected for triaxial shear tests to obtain the stress-strain curves. The Duncan-Zhang was used to predict the modified soil. The model has a large error in the prediction of the peak of the principal stress difference, but the overall trend is relatively consistent. Therefore, the correction coefficient related to the confining pressure was introduced. The corrected model fits the triaxial shear test well. The research provides a method for the liquid-plastic limits and shrinkage properties of modified red clay, explores the influence of calcium carbonate content on microscopic pores, and the correction of the model provides a theoretical basis for practical application. [ABSTRACT FROM AUTHOR]

Red clay soil in Guilin, characterized by a large pore ratio, high liquid-plastic limit, and high shrinkage, necessitates effective stabilization methods due to the region's seasonal flooding. This study employed enzyme-induced carbonate precipitation technology in conjunction with MgO and lignin fiber to stabilize the soil. The study aimed to elucidate the solidification mechanism of red clay and assess the effects of admixture dosage and curing age on unconfined compressive strength, carbonate formation, liquid-plastic limit, and fine particle content. The findings indicated that MgO significantly enhanced the unconfined compressive strength through a synergistic effect. The mineralization process of EICP technology facilitated CO2 production, promoting the carbonation of MgO, which, in turn, established an alkaline environment that further increased carbonate formation. The damage to the specimen was in the form of brittle damage. Conversely, conversely, the inclusion of lignin fibers enhanced the ductility of the soil matrix. The fibers interlaced within the soil matrix, preventing contraction and cracking under external forces and inhibiting the propagation of small fissures into larger ones, leading to plastic deformation. The dosage of MgO played a crucial role in the strength of stabilized red clay. At lower dosages, strength gains were primarily due to increased carbonate content, while higher dosages reduced water content, increasing inter-particle friction and soil densification. As strength increased, clay content decreased, and specific gravity rose. [ABSTRACT FROM AUTHOR]

Red clay exhibits characteristics such as softening owing to water absorption and cracking because of water loss, which can lead to slope instability, road cracking, and compromised structural integrity when used directly in roadbed filling. Although the addition of industrial materials such as cement is a common engineering treatment, it severely impairs soil renewability. Lignosulfonate (LS) extracted from paper plant waste fluids is a natural bio-based polymer with promising applications as a soil improver. In this study, the boundary moisture content and mechanical properties of LS-treated red clay were investigated using Atterberg, unconfined compressive strength, and direct shear strength tests. Additionally, the LS-treated red clay modification mechanism was explored at multiple scales using zeta potential analysis, X-ray diffraction, scanning electron microscopy coupled with energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The results indicated that the LS dosage significantly affected both the water content and mechanical strength of the red clay boundaries. The optimal dosage of LS for red clay was 3 wt. %, at which the liquid limit was reduced by 32.97%, the plastic limit by 19.33%, and the plasticity index by 48.37%. The 28-day compressive strength of LS-treated red clay was increased by 378.4%, and the direct shear strength was increased by 136%. Analysis of the microstructure and mineral composition revealed that the LS-treated red clay did not form new minerals, but primarily filled pores and connected soil particles. Through the combined effects of hydrogen bonds, electrostatic interactions, and cation exchange, the LS-treated red clay reduced the size of the mineral particles and the thickness of the mineral double electric layer, resulting in increased structural densification. These results are of great scientific significance for the ecological modification of soils. [ABSTRACT FROM AUTHOR]

Reflectance spectroscopy is rapid, inexpensive, and non-destructive and can provide important information about the mineralogy of rocks and sediments. We measured the reflectance spectroscopy of Miocene red clay deposits on the northeastern margin of the Tibetan Plateau, with the aim of developing a rapid methodology for detecting paleoclimatic changes. We obtained visible/near-infrared (VNIR) and short-wave infrared (SWIR) spectroscopy data from the red clay in the Jianzha Basin, and analyzed their relationship with independent paleoclimatic records, including mineral contents and environmental magnetic parameters. The results show that the VNIR parameters, including D500, D900, R500, and R900 (where D and R represent the depth and reflectance of the absorption peaks around 500 and 900 nm, respectively) are temperature-sensitive and correlated with the magnetic susceptibility, frequency-dependent magnetic susceptibility, and the marine δ18O record. The results of frequency-domain analysis of the VNIR parameters show that they reflect climate change on orbital timescales. SWIR parameters, such as AS1400, D1400/D1900 and D1900 (where AS represents the asymmetry of the absorption peaks around 1400 nm), are correlated with the illite and montmorillonite content, and they are sensitive to the weathering intensity. The spectral parameters of the eolian red clay in the Jianzha Basin reflect regional climatic changes caused by the uplift of the Tibetan Plateau at ∼8.5 Ma and global climatic cooling at ∼7.2 Ma, and thus they are applicable as both regional and global paleoenvironmental indicators. [ABSTRACT FROM AUTHOR]

Red clay is widely distributed globally and is closely related to human production and life. The middle reaches of the Yellow River basin in China are characterized by complex geological structures, concentrated rainfall periods. The soluble salts such as sodium sulfate enter the red clay particles along with the infiltrating water, forming a red clay-like saline soil. In order to study the effects of water and salt on red clay soils, this paper uses red clay in the Heyang of Weinan with different ratios of distilled water (10–20%) and Na2SO4 (0–4%), and obtains the resistivity of red clay soils at different frequencies (100 Hz–100 kHz) using an inductance, capacitance and resistance digital bridge tester. The results show that the resistivity of red clay is negatively correlated with water and salt content. With the increase of water content, the increase of conductive paths in the pore water improved the electrical conductivity of the red clay; while when the concentration of Na2SO4 increased, the free moving anions and cations in the pore water increased, the electrical conduction efficiency increased and the resistivity decreased. The high frequency increased the conductivity of red clay by contributing to electrical double layer deformation, whereas the electrode polarization led to inhibition of conductivity under low frequency. A negative power exponential relationship exists between the resistivity of red clay and the test frequency. This study may provide a valuable reference for the rapid identification of the physical properties of red clay and its internal structure. [ABSTRACT FROM AUTHOR]

This study investigates the modification of red clay with calcium carbonate. The pore distribution was obtained using a combination of mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) techniques. The influence of calcium carbonate content, density, confining pressure, and shear strain on the pores was studied. Introducing pore classification to assess the extent of the damage under different conditions and the relationship between different types of pores. The results show that the content of added calcium carbonate has little effect on pore distribution when the density is low (1.4 and 1.5 g/cm3). The content of calcium carbonate has an influence on pore distribution when the density is high (1.6 g/cm3). With the density increases, the number of macropores and mesopores between soil particles decreases, while the small pores increase. The confining pressure results in the preferential drainage of free water from macropores. The porosity decreases as the confining pressure increases. Under the same confining pressure, as the shear strain increases, the large pores decrease while the small pores increase. Based on the analysis of damage degree, the shear strain is positively linearly related to the damage degree of intragranular mesopores, which forms a convex function relationship with intragranular macropores and intergranular mesopores (except under a confining pressure of 100 kPa). [ABSTRACT FROM AUTHOR]

This research was undertaken to optimize the phenolic compound removal from Olive Mill Wastewater (OMW) by sawdust and red clay as natural adsorbents. Fractional factorial experimental design at 25−1 was used in order to optimize the experimental conditions for high removal efficiency. Statistics ANOVA analysis, Fisher's test, and Student's test suggested that the adsorbent dose has the most significant influence on polyphenol removal for both adsorbents. The maximum removal of polyphenols by sawdust reached 49.6% at 60 °C by using 60 g/L of adsorbent dose, pH 2, reaction time of 24 h, and agitation speed of 80 rpm. Whereas, for red clay, 48.08% of polyphenols removal was observed under the same conditions for sawdust except the temperature of 25 °C instead of 60 °C. In addition, the thermodynamic parameters suggested spontaneous process for both adsorbents, endothermic for the sawdust and exothermic for red clay. Furthermore, the phytotoxicity effect of OMW on durum wheat (Triticum turgidum L. var. durum) and white bean (Phaseolus vulgaris L.) seed germination was investigated. The obtained results showed that the untreated OMW inhibited the seed germination of T. turgidum and P. vulgaris seeds. OMW treatment with red clay followed by dilution (95% water) resulted in 87 and 30% germination of P. vulgaris and T. turgidum, respectively. While, the treatment of OMW with sawdust and dilution at 95% resulted in 51 and 26% germination of P. vulgaris and T. turgidum, respectively. [ABSTRACT FROM AUTHOR]

Desiccation cracking is a common problem of red clay under wet and dry conditions. The presence of cracks could reduce soil strength properties, which is the major reason for shallow failure of red clay slopes. This study aims to propose some additives to improve the crack resistance as well as the strength of red clay. To this end, three natural fibers and three natural gels were primarily selected to modify red clay. Desiccation crack tests were conducted to identify the best fiber and gel in terms of crack resistance. Then, direct shear tests and uniaxial tensile tests were performed on the soil specimens modified by the best fiber and gel to determine the optimal dosages regarding strength improvements. The results demonstrated that natural gels reduced the crack resistance of red clay, while natural fibers could enhance the crack resistance. Lignocellulose was the best additive in improving the crack resistance of red clay, and the modified effect was positively correlated with the fiber dosage. Adding 1.5% lignocellulose into red clay could reduce the crack rate from 2.19% to 0.30%, with a reduction of 0.86 times. The tensile strength, shear strength and its parameters of lignocellulose-modified red clay showed a trend of increasing first and then decreasing with increasing lignocellulose dosage. At the optimal lignocellulose dosage of 0.75%, the shear strength and tensile strength were increased by 44.63% and 18.21%, respectively. The strength of red clay modified by both lignocellulose and guar gum was positively correlated with the dosage of guar gum, and the desirable dosage of guar gum was 1.0%. In engineering practice, the wet red clay mixed with 0.75% lignocellulose and grass seeds can be employed as planting soil and is sprayed uniformly onto the slope surface after excavation using a spraying planting machine. To further improve the strength of the planting soil, 1.0% guar gum solution can be sprayed on the soil surface. The findings could provide useful guidance for the protection of red clay slopes. [ABSTRACT FROM AUTHOR]

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Due to the peculiarity of the spring domain strata in Jinan, the phenomenon of serious water seepage appears in the process of excavation. The macro permeability of soil is closely correlated with its microstructure. In this study, using the X-ray micro-tomography (micro-CT) system and a self-designed soil seepage device, the internal pore structure of Jinan red clay and the water flow inside the sample under different seepage stages were observed. The microstructure of water phase and air phase in the sample was segmented by the watershed algorithm. Calculation and comparison of pore and throat size distributions and coordination number (CN) at different seepage stages were conducted by establishing pore network model (PNM). Meanwhile, the seepage experiment simulations were conducted based on the 3D pore structure of red clay. The results show that the preferentially flow of Jinan red clay is obvious due to the existence of the vertically developed macropore channel. The fine particles (mainly silt particles) are washed away during seepage, thereby expanding the pore channels. The maximum pore radius and pore connectivity have important influence on seepage characteristics of Jinan red clay, but the correlation between porosity is small. [ABSTRACT FROM AUTHOR]

The primary goal of this research is to determine the mechanical properties of opaque glazed ceramic tiles containing fly ash, tincal waste, and recycled red clay, including to assess if the results meet international requirements. Opaque glaze and tincal waste were the main components of all glaze compositions of four groups, which were named OG (original), FA, RC, and FC (mixture) according to the additive. The ceramic tiles were prepared by dipping the biscuits in the glaze composition and firing them at 1150°C. The water absorption of the FA, RC, and FC tiles was less than that of the OG tiles (< 0.52%) and the scratch hardness values were between 6 and 7. All the experimental groups were also resistant to thermal shock, chemicals, and staining showing high opacity (L* > 92) and having a light yellow–red color. The micro- and crystallographic structure of some selected tiles were determined by scanning electron microscopy and x-ray diffraction techniques. Zircon, diopside and augite phases were recognized. [ABSTRACT FROM AUTHOR]

As a sustainable green and efficient foundation treatment technology, reactive magnesia (MgO) and carbon dioxide (CO2) carbonation–stabilization methods are applied innovatively to improve the engineering properties of red clay. The effect of initial water content, carbonation time on the mechanical, electrical and microstructural properties of carbonated solidified MgO-mixed red clay is analyzed systematically through unconfined compressive strength–electrical resistivity synchronous test, X-ray diffraction and scanning electron microscopy test. The test results demonstrated that the stress–strain–resistivity curves of MgO carbonated red clay present good regulation, in which the stress–strain curves first increase sharply and then drop under the loading process, while the resistivity–strain curves display an opposite trend. The unconfined compressive strength (UCS) of carbonated samples, which is affected significantly by the increase in the water content and carbonation time is increasing apparently compared with no-binder parent soil. The process of carbonation exerts a perceptible effect on the relationship of UCS-E50, and the strength gain of carbonated specimens is contacted closely with the uptake amount of CO2 under the same initial parameters. Compared with carbonation duration, the initial water content has larger influence on the electrical resistivity of carbonated specimens, and the fitting equations combined with the strength and resistivity of carbonated samples were proposed. A series of mineralogical and microscopic tests, including XRD and SEM, demonstrated that nesquehonite and dypingite or hydromagnesite play an important role in improving the strength. The crystalline nesquehonite can make the structure of soil tighter because of the better cementation capacity and reduce effectively the influence of the swell of carbonation process. [ABSTRACT FROM AUTHOR]

Tensile strength is an important soil parameter that affects the stability of structures built on clayey soils. This paper presents an experimental study of the change of tensile properties of red clay during wet-dry cycles. Cyclic wet-dry tests were performed on compacted red clay specimens with different initial water contents and dry densities. Direct tensile tests and Brazilian split tests were then conducted on these specimens to determine the soil strengths. The effects of initial water content, initial dry density, number of wet-dry cycles, and crack rate on the tensile properties of red clay were investigated. The results demonstrate that the tensile strength of red clay is generally 1.566 times the splitting strength. Both the tensile strength and splitting strength are negatively correlated with the initial water content but are positively correlated with the initial dry density. Because of the presence of desiccation cracks, the tensile strength goes on reducing under wet-dry cycles. The tensile strength can be expressed by a power function of the initial water content, initial dry density, and crack rate. The proposed equation is useful to evaluate the tensile strength of cracked soils subjected to wet-dry cycles. [ABSTRACT FROM AUTHOR]

Red clay has the characteristics of high water content, high porosity ratio, and complex inverse profile, which can hardly meet the requirement strength and is of most importance in the prevision of foundation or landslides which are mainly controlled by the red clay of geotechnical properties. Hence, the X-ray diffraction test, oedometer test, triaxial un-drained (CU) test, and scanning electronic microscope test are conducted to study the geotechnical properties of intact red clay. In this paper, firstly, the effect of depth on the properties of intact specimens is investigated, including mineral component, dry density, free swell ratio, water content, void ratio, and grain size distribution. Then, the characteristics of compression behavior and its development with depth are investigated. A normalization method is carried, considering the effect of structure. Secondly, CU test is performed to analyze the mechanical behavior and strength parameters of intact, reconstructed, and slurry specimens. In addition, the classification of intact red clay is used to characterize the compression behavior. The intact specimens can be classed as structural un-compacted and structural over-consolidation soil. Moreover, an attempt is made to explain the mechanism of structural strength enhancement in intact red clay, involving interlocking strength, bonding strength, and compaction strength. [ABSTRACT FROM AUTHOR]

This research conducted a triaxial test on lime-treated clay with different contents to analyze the effect of mechanical properties. Scanning electron microscope (SEM) and low-field nuclear magnetic resonance (NMR) analysis were used to analyze the effect. X-ray diffraction (XRD) was used to analyze the chemical changes of calcium oxide on red clay. The results show that with the increase of calcium oxide content, the strength increases, and it can be increased by 282% at 200 kPa confining pressure. The calcium oxide in the red clay reacted with the water in the soil to form calcium hydroxide. The alkaline environment will erode the edge of the soil particles and cause pores to become larger. SEM observed that the addition of calcium oxide caused the agglomeration of soil particles and changed the pore structure of red clay. Low-field NMR showed that calcium oxide had a significant effect on the pore structure of red clay. Calcium oxide increased the total pore volume of the soil sample. Calcium oxide had a substantial influence on the three pore distribution ranges, I (1.1–11 µm), II (15–137 µm), and III (137–512 µm). The porosity fitted with shear strength, it negatively correlated with I and III, and positively correlated with II. [ABSTRACT FROM AUTHOR]

Red clay is the main geometrical as the foundation of buildings, dam, and excavation which are usually designed and constructed without concern of its structure with depth, leading to a design which is not reasonable and a massive waste of resources. The research reports investigations carried out on red clay to study its compressibility, strength and stress path, and their variation with depth. The effect of structure with depth on red clay has been discussed and the mechanics were investigated by undrained consolidated triaxial tests, X-ray diffraction, and one-dimensional compression tests. This research determined a gradual destructuration process by a new normalized method. The change of structure with depth has been analyzed which is different from saprolitic soil caused by its special weathering process. Higher strength parameters were consistent with regular clay content. The compressibility and strength were shown to strongly depend on the depth, and hardening phenomenon has been observed for all specimens at the laboratory scale. In addition, triaxial tests with a varying number of consolidations were conducted to assess the influence of the consolidation. The results revealed a marked type of ultimate steady state (USS). The strength increases by 12.7%, 33.8%, and 2.67% for axial strain (20%) under the confining pressures of 200, 300, and 400 kPa, respectively. [ABSTRACT FROM AUTHOR]

Results of the investigation of the tribotechnical properties of solid lubricant coatings obtained on VK6 hard alloy (94% WC + 6% Co) as a result of the thermohydrochemical treatment (THCT) in an aqueous disperse medium based on red clay are presented. Multidimensional optimization of the composition of the medium and temperature–time parameters of the process of THCT with respect to the friction coefficient of the obtained solid lubricant coatings is performed. By using mathematical models, process parameters–property diagrams are constructed. Processing using the optimum THCT mode makes it possible to decrease the friction coefficient of a hard-alloy surface 3.4-fold in comparison with the untreated surface under the conditions of the absence of a lubricant. [ABSTRACT FROM AUTHOR]

Accurately evaluated the bearing capacity characteristic value of red clay is of great important to make use of high strength. Based on analyzing current specifications methods to determine the bearing capacity eigenvalue of red clay foundation, it is found that deficiencies are the limitation of application, the disturbance of determining indexes such as water content, liquid limit, plastic limit and compression modulus, and even lack of reflecting effects of the stress level, the shape and failure mode of subgrade. To deal with these shortcomings, a method for determining the bearing capacity of red clay foundation in view of the stress level was proposed. This method adopts tangent modulus that can reflect different depth of stress levels instead of compression modulus to calculate the curve of load and settlement under the size of plate, and utilizes the modified Vesic formula to consider the influence of the shape and failure mode of ground to calculate the ultimate bearing capacity as major parameter of different depth of stress level calculation. The indoor shear strength index can be used to calculate the ultimate bearing capacity if there is no plate load test. According to the characteristic of the settlement and load curve, the intrinsic value of subgrade bearing capacity is achieved using the plate load test method. Verified through an engineering cases, the characteristic value of the bearing capacity obtained using this method is more consistent with that obtained by the plate load test, meanwhile more flexible in the actual application. It also can be used for reference to determine the characteristic value of bearing capacity in other red clay area. [ABSTRACT FROM AUTHOR]

Red clay is widely distributed in Zhejiang Province, China. Rain-induced shallow landslides easily occur on red clay slopes due to the reduction in shear strength caused by rainwater infiltration. The aim of this paper was to study the soil–water characteristic of red clay and its application on analyzing the stability of red clay slope. A series of field tests at different depths of red clay slope were carried out to monitor the variations of water content and matric suction under typical climate conditions. The results showed that the distribution of water content in red clay slope is complex because of long-term wetting–drying cycles. The water content within shallow layer is sensitive to external environment, and the response time of the water content is related to rainfall intensity. It is also observed that the soil water characteristic curve (SWCC) varies at different depths. The SWCCs of red clay can be fitted by linear function. The SWCCs from laboratory tests illustrated that saturated water content is more than 40%. Most of the SWCCs obtained at the depth of 90 cm are within the hysteresis loops of the SWCCs from laboratory test. The short-term rainfall has less effect on the stability of the slope, but the stability continuously decreases after the rain stops. The SWCCs obtained from laboratory were applied to analyze slope stability. Considering the influence of cracks, the computed results are close to field data. The study has a certain directive significance to the design of red clay slopes. [ABSTRACT FROM AUTHOR]

Products of sorption of uranyl ions on HDTMA-red clay in the presence of phosphates were characterized by thermal analysis. It was established on the basis of DTG curves of the sorption products and FTIR spectra of the gaseous phase of sorption products decomposition that the thermal stability of the mineral increased when P(V) ions were sorbed along with U(VI) ions, i.e., the temperature of defragmentation/oxidation of surfactant increased when going from U(VI)–HDTMA-clay to U(VI)–P(V)–HDTMA-clay to P(V)–HDTMA-clay. The DSC curves of the sorption products showed that defragmentation/oxidation was an exothermic process and dehydration and dehydroxylation had an endothermic character. The investigated sorption system has practical importance, since an evident increase in U(VI) sorption over the entire pH range is observed when going from U(VI)–HDTMA-clay to U(VI)–P(V)–HDTMA-clay. [ABSTRACT FROM AUTHOR]

Red clay has obvious nonlinear dynamic characteristics during dynamic compaction. In this paper, based on equal energy level, the dynamic compaction model tests on red clay under different testing programs were conducted. Dynamic stress, duration of dynamic compaction and crater depth were measured. During dynamic compaction, the distribution and the variation of dynamic stress and the reinforcement effect were analyzed. The best fitting equation of crater depth was established. Test results show that during dynamic compaction, the peak dynamic stress decreased with the depth. In addition, dynamic stress at each point had obvious time lag. By increasing drop numbers, the peak dynamic stress in soil also increased. Until the peak dynamic stress variation fluctuated within a certain range and also the depth, the optimum number of the drop was achieved. When single tamping energy was the same, the peak dynamic stress with heavier tamper was larger than that with lighter tamper at same point. Dimensional analysis was applied to obtain the fitting equation of crater depth. The parameters of fitting equation demonstrated that the influence of the weight of tamper on crater depth was greater than that of the drop height under the identical tamping energy. Consequently, the utilization efficiency and reinforcement effects of heavier tamper with lower drop height are greater than that of lighter tamper with higher drop height at an identical energy level. [ABSTRACT FROM AUTHOR]

Geochemical characteristics of sediments are responses to physical and chemical alteration in landslides. However, consequences of in situ interactions associated with landslides are difficult to distinguish from those related to long-term weathering in young soft sediments such as loess. In this study, geochemical characteristics of the Kulcs landslide in Hungary are studied to identify the provenance of the loess-paleosol-red clay sequence and geochemical signatures that can potentially be attributed to the effects of landsliding. Results indicate that sliding is largely initiated by the lithological changes within the landslide body. Sediments above the sliding zone closely resemble the non-slipped Pleistocene old loess deposits from Hungary. It is also confirmed that the sliding zone develops in old paleosols in the loess sequence and red clays at its base which are all characterized by the enrichment of Al, K, Na, HO and considerable depletion in Ca and Mg associated with carbonates. Altogether, these geochemical characteristics indicate that chemical weathering trend of unconsolidated landslide sediments is slightly modified by the redistribution of carbonates and decomposition of plagioclase. It is assumed that the distribution of Mn and Ba is modified by the water-sediment interaction in the landslide. [ABSTRACT FROM AUTHOR]

Red clay was previously used to enhance bioremediation of diesel-contaminated soil. It was speculated that the enhanced degradation of diesel was due to increased bacterial growth. In this study, we selected Acinetobacter oleivorans DR1, a soil-borne degrader of diesel and alkanes, as a model bacterium and performed transcriptional analysis using RNA sequencing to investigate the cellular response during hexadecane utilization and the mechanism by which red clay promotes hexadecane degradation. We confirmed that red clay promotes the growth of A. oleivorans DR1 on hexadecane, a major component of diesel, as a sole carbon source. Addition of red clay to hexadecane-utilizing DR1 cells highly upregulated β-oxidation, while genes related to alkane oxidation were highly expressed with and without red clay. Red clay also upregulated genes related to oxidative stress defense, such as superoxide dismutase, catalase, and glutaredoxin genes, suggesting that red clay supports the response of DR1 cells to oxidative stress generated during hexadecane utilization. Increased membrane fluidity in the presence of red clay was confirmed by fatty acid methyl ester analysis at different growth phases, suggesting that enhanced growth on hexadecane could be due to increased uptake of hexadecane coupled with upregulation of downstream metabolism and oxidative stress defense. The monitoring of the bacterial community in soil with red clay for a year revealed that red clay stabilized the community structure. [ABSTRACT FROM AUTHOR]

Loess and red clay on the Chinese Loess Plateau provides a detailed history of the East Asian monsoon in the Neogene. Based on grain-size analysis of a Shilou red clay section in Shanxi, China, the eolian origin of Shilou red clay was demonstrated; then the evolution of the East Asian winter monsoon was explored. The results showed that most of the particles were fine-grained, with a median size of 5-9 µm. The sand fraction (>63 µm) in most samples was less than 5 %. The particle-size distribution shows a unimodal pattern with a modal size of 2-30 µm. The grain-size content agreed with the decreasing north-southward trend of eolian deposits on the Chinese Loess Plateau, implying that the red clay particles were carried mainly by northerly low-level winds. All the evidences point to an eolian origin for the Shilou red clay sediments. According to the variation of 10-70 µm, coarse content (>43 µm) and the U-ratio of the Shilou grain-size record, the Neogene evolution of the East Asian winter monsoon was divided into five stages: 11.0-7.5, 7.5-5.6, 5.6-4.8, 4.8-3.1 and 3.1-2.6 Ma. During the period of 11.0-7.5 Ma, the grain-size varied more frequently and with larger amplitude, implying large fluctuations in the winter monsoon. After 7.5 Ma, the grain sizes decreased slightly, indicating that the winter monsoon gradually weakened. Between 5.6 and 4.8 Ma, the grain sizes showed extreme variation with the highest and lowest values across the whole section, indicating large changes in the winter monsoon. From 4.8 Ma, the grain sizes increased slightly then changed dramatically after 3.1 Ma, which is evidence that the winter monsoon strengthened gradually and intensified later. This new finding indicates that the evolution of winter monsoon is closely related to Tibetan Plateau uplift and global paleoclimate change. [ABSTRACT FROM AUTHOR]

Adsorption of La, Eu, and Lu on red clay was studied in an initial concentration range of 10-10 mol/dm and a pH range of 2-10. Among the different forms of red clay: T-clay (thermally modified), R-clay (raw, unmodified), Na-clay (sodium form), H-clay (acid form), and HDTMA-clay (surfactant-modified form), T-clay was found to be the most effective adsorbent of the lanthanides studied. The adsorption/desorption isotherms, i.e. log K versus log c dependencies, had a linear character. Among the investigated lanthanides, Eu was most strongly bound by the clay surface and, therefore, parameters a (slopes of the lines log K = alog c + b) of Eu were the highest compared to those for La and Lu. Desorption isotherms were located above adsorption isotherms, which resulted from chemiadsorption of the investigated lanthanides. Changes in lanthanide adsorption with pH were successfully modelled based on the molar fractions of Ln, LnOH, LnCO, and Ln(CO) species in the aqueous phase [Ln-lanthanide(III)]. [ABSTRACT FROM AUTHOR]

Uranium is a very toxic and radioactive element. Removal of uranium from wastewaters requires remediation technologies. Actual methods are costly and ineffective when uranium concentration is very low. Little is known about the enhancement of sorption of uranyl ions by phosphate ions on aluminosilicates. Here, we studied sorption of uranyl acetate on red clay in the presence of phosphates. The concentration of U(VI) ranged 0.0001-0.001 mol/L, whereas the concentration of PO was constant at 0.0001 mol/L. We designed a new method for the analysis of ternary surface complexes. We observed for the first time a remarkable improvement of U(VI) sorption on red clay under the influence of phosphates. We also found that at least two different ternary surface complexes U(VI)-phosphate-clay are formed in the sorbent phase. The complexation of UO cations by phosphate ligands in the sorbent phase was confirmed by the X-ray photoelectron spectra of U 4f electrons. [ABSTRACT FROM AUTHOR]

Loess and red clay on the Chinese Loess Plateau have produced a detailed history of the East Asia monsoon for the past eight million years. Recently, a well-conserved red clay sequence was discovered at Shilou on the eastern edge of Chinese Loess Plateau, extending the monsoon history back to approximately 11 Ma. By comparing lithologic features, particle size distribution, magnetic susceptibility and deposition rate of Shilou red clay sequence, the paleomonsoon evolution from 11 to 2.6 Ma can be divided into four stages: largely fluctuated stage (11.0-8.0 Ma), relatively strengthened period (8.0-6.5 Ma), extremely changed stage (6.5-4.9 Ma) and further intensified period (4.9-2.6 Ma). The new evidence indicates that variation of paleomonsoon has close relationship with uplifting of the Tibetan Plateau and ongoing global cooling and the consequent expansion of ice sheets during 11.0-2.6 Ma. [ABSTRACT FROM AUTHOR]

The Wulanhua Fauna (~7 Ma) derives from the basal part of Late Miocene red clays in Siziwang Banner, Inner Mongolia. Chinese red clay deposits are rich in fossils of the Hipparion fauna, and are relatively widely distributed across Shanxi, Shaanxi, Henan, and Gansu provinces. The Mongolian Plateau also contains well-developed Neogene deposits, especially in central Inner Mongolia, where a sequence of mammalian faunas has been identified. The discovery of the Wulanhua Fauna provides an important indicator of the paleogeographical distribution of the Hipparion fauna, and this study also contributes to a better understanding of the climatic and environmental significance of red clays. Most forms of the Wulanhua Fauna are the same as or close to taxa within the Baode Fauna. However, some forms are slightly more derived than those of the Baode Fauna, which may indicate a slightly younger geological age of about 7 Ma. The components of the Wulanhua Fauna suggest that the habitat was a typical steppe and therefore yield direct evidence to delineate the boundary between the east and west subregions of the Late Miocene Hipparion fauna in North China. [ABSTRACT FROM AUTHOR]

The change in the thickness of water films of special clay particles such as sliding clay, red clay, and expansive clay is an important factor in producing geological disasters and geological environmental damage. In order to reduce the thickness of water films, ionic soil stabilizer (ISS) is used to treat sliding clay, red clay, and expansive clay. Direct shear test of sliding clay and shrinkage, free swell rate, zeta potential, and cation-exchange capacity of red clay and expansive clay are carried out. The results show that as the plastic indexes of special clay soil decrease, the shear strength of sliding clay increases, the shrinkage and free swell rate of red clay and expansive clay decrease, and the thickness of the water film thins after treatment with the ionic soil stabilizer. Therefore, the geological engineering disasters caused by changes in the thickness of water films of special clay can be effectively inhibited. [ABSTRACT FROM AUTHOR]

Magnetic susceptibility (MS) is one of the most important indicators of the East- Asia summer monsoon. Presented in this study is a high resolution magnetic susceptibility record from the Xifeng section, which consists of Quaternary loess-paleosol sequence and Pliocene red clay. Variations in magnetic susceptibility are well correlated with the δ18O record in deep-sea sediments and the eolian flux of Greenland. The climatic evolution in the Xifeng section shows that since the Late Tertiary, the driving force of the East-Asia paleo-monsoon is correlated with solar radiation on a 10-ka time scale. [ABSTRACT FROM AUTHOR]

Background, Goal and Scope. The ceramic tile industry is one of the most important industries in Spain, with the highest concentration of firms to be found in the province of Castellón on the Mediterranean coast. The basic input material for this industry is red clay. The aim of this study was to carry out an LCA of the process of mining, treating and marketing this clay in order to identify the stages and unit processes that have the greatest impact on the environment. This LCA examines all the stages of the red clay from cradle to the customers gate, including the process of mining and treating the clay in the mining facilities and its later distribution to end users. Methods. Life cycle inventory (LCI): An exhaustive LCI was performed by collecting data from the mine run by Watts Blake Bearne Spain, S.A. (WBB-Spain) in Castellón. Inputs and out- puts were collected for all the unit processes involved in the mining, treatment and marketing of the clay: - Mining the clay, which embraces the unit processes of removing the layer of vegetation covering the chosen area, preparing the area to allow access for the firms vehicles, and boring or blasting the place the clay is to be extracted from. - Treating the clay that is mined to make the finished product, which entails all unit processes required to separate out the waste material and transport it to the tip (which will later be reconditioned), excavating and transporting the clay to the crushing plant and later storing it in heaps before delivery to customers. All the internal transport that takes place between each unit process has also considered. - Distribution of the final product, where the clay is loaded onto dumper trucks and delivered to the customer. Life cycle impact assessment (LCIA): According to ISO 1404X standards, the LCIA is performed at two levels. Firstly, the emissions accounted for in the inventory stage are sorted into impact categories to obtain an indicator for each category (mandatory elements). Secondly, the weighting of environmental data to a single unit is applied (optional elements). In compliance with ISO 14042, a sensitivity analysis is performed and three different impact assessment methods (Eco-Indicator95, Eco- Indicator'99 and EPS'2000) are applied in order to analyse their influence on the results. Results. The processes that involve the movement of clay within the mine (excavation and loading and transport to the crushing facilities and heaps) are the ones that make the greatest contribution to impact categories for pollutant emissions. As weighting methods in LCA remain a controversial issue, a recommendation when robust results are required, can be to use several methods to examine the sensitivity of the results to different values and worldviews. In our application case, in spite of the differences between the three impact assessment methods applied (Eco-Indicator95, Eco-Indicator'99 and EPS'2000), the same conclusions can be established from the environmental point of view and we can conclude that the ultimate results are not sensitive in the transformation of mid-points to end-points. Discussion. Taking into account the characteristics of the product being analysed, in addition to the impact categories for pollutant emissions that are traditionally considered in LCA studies, environmental parameters related to resource use (fuel, electricity and water consumption), waste generation (dangerous and non-dangerous wastes) and land use (natural resource appreciation and land use efficiency) and its later rehabilitation (degree of rehabilitation) have been defined. These parameters can be used as additional criteria for an environmental product declaration or criteria for a future eco-labelling of red clay. Conclusion.… [ABSTRACT FROM AUTHOR]

The Late Miocene and Pliocene are the key periods for understanding the origin and development of the present Asian monsoon circulations and ecologic environments. Here we present a pollen record from Chaona Red Clay section located in the central Loess Plateau in attempt to establish the histories of vegetation and associated climate changes between 8.10 and 2.60 Ma. Our results show that Gramineae-dominated woodland-grasslands developed in this region with Cedrus- and Pinus-characterized montane coniferous forests distributing in higher elevations from 8.10 to 6.73 Ma, probably suggesting a semi-humid climate in a warm-temperate zone. A subsequent expansion of Ulmus-dominated deciduous forests and a synchronous increase of Gramineae-dominated grassland reflect a warmer and more humid climate between 6.73 and 5.67 Ma. The vegetation changed to an Artemisia. and Gramineae-characterized steppe in lower elevations and to a coniferous forest in higher elevations from 5.67 to 3.71 Ma, implying probably a warm and semiarid climate in lowland and hill, and a colder and moister climate in mountain. During this period, a considerable warmer and more humid climate occurred between 4.61 and 4.07 Ma as indicated by pollen assemblages. The period between 3.71 and 2.58 Ma was characterized by the disappearance of Cedrus and Tsuga and also by an abrupt expansion of Cupressaceae, reflecting a drastic enhancement of monsoon-related climatic seasonality. [ABSTRACT FROM AUTHOR]

Detailed rock magnetism investigation of the Jiaxian red clay sequences indicated that there are common magnetic mineralogy properties in red clay and loess-paleosol sequences from the Chinese Loess Plateau as well as the marked properties of themselves, magnetic minerals mainly with magnetite, maghemite, hematite, and possibly limonite/goethite contributing to the magnetic behavior. Meanwhile, it is found that the strong paleosol in red clay sequences has a lower coercivity and higher content of ultra-fine ferrimagnetic grains than that of the weak paleosol, which is similar to loess and paleosol in upper Wucheng Loess sequences, and indicates that humid conditions and relatively strong pedogenesis play a significant role in the increase of ultra-fine magnetic minerals and transformation of the magnetic minerals. This suggests that, like Quaternary loess-paleosols, the change of characteristics of paleoclimatic conditions of the late Tertiary red clay deposits is fluctuant. In addition, the results of magnetic hysteresis properties show that the applied saturated field for samples from the Jiaxian red clay sequences is higher than that of the samples from eastern and southern Chinese Loess Plateau. It is obviously shown that there exist more hard magnetic minerals and relatively weak biochemical processes in the Jiaxian red clay sequences on northern Chinese Loess Plateau. We conclude that the paleoclimatic environment is different between northern and eastern/southern Chinese Loess Plateau, and it should be more arid in northern Chinese Loess Plateau. [ABSTRACT FROM AUTHOR]

The origin and sedimentary environment of the Late Tertiary (Neogene) Red Clay Formation in northern China had long been controversial. A new mollusk record from the Xifeng red clay (red-earth) sequence in the central Loess Plateau provides the biological evidence for addressing questions of its origin and environmental implication. The study of composition and preservation condition of seventy mollusk fossil assemblages reveals the initial ecological condition of the red clay formation, avoiding the effect of post-deposited alteration. The result shows that all of identifiable mollusk species are composed of terrestrial taxa, most of them are the common species found in the overlying Quaternary loess-paleosol sequence. Most of fossil individuals preserved in the red clay strata are in living conditions based on the investigation of fieldwork, indicating the original population. Thus, the mollusk fossil assemblages can be used as an indicator of primary environment of the red clay formation. The mollusk record from the Xifeng red clay sequence supports the view that the red clay is an aeolian origin, similar to the overlying Quaternary loess deposits. Our data also reveal the history of environmental changes at Xifeng from 6.2-2.4 Ma, which is coupled in phase with the formation and development of the Arctic ice sheets and the process of the Tibetan Plateau uplift. Both may be the major cause and forcing mechanisms of the late Tertiary environmental changes in the Loess Plateau. [ABSTRACT FROM AUTHOR]

The study on magnetic properties of the red clay indicates that the red clay and loesspaleosol sequence have a common magnetic mineralogy, with magnetite, maghemite, hematite (and possibly goethite) contributing to the magnetic behavior. The red clay magnetic susceptibility is also found to have a positive relation with extrafine superparamagnetic grains. This suggests that, like the Quaternary loess-paleosols, an ultrafine ferrimagnetic component produced during pedogenesis in the red clay under humid conditions also plays an important role in susceptibility enhancement in the soil units. This is supported by the correlation between Rb/Sr ratio and magnetic susceptibility. This signifies that, like the above loess-paleosol sequence, the magnetic susceptibility of the red clay can be used as a general proxy paleoclimatic indicator, although whether its susceptibility in the red clay is comparable to pedogenesis intensity and requires further investigation. Magnetic susceptibility variation in the red clay thus also provides an eolian/pedogenic record of paleoclimatic evolution. Study of the background susceptibility indicates that, on average, the absolute scale of the paleoclimatic shift from red clay development to Quaternary loess deposition is similar to the climatic shift from stage 5 (S1) to stage 2–4 (L1). This may suggest that during the Quaternary there is an evident strengthening of the absolute wind intensity to bring more (about double) coarser and less weathered (non-SP fraction) eolian magnetic input from the source regions to the Loess Plateau than during the Pliocene. The presence of eolian red clay since 7.5 Ma BP in central-northern China implies an important environmental change from the underlying Cretaceous red sandstone. The red clay development was closely related to global drying and climate cooling since the Cretaceous and closely associated with the abrupt uplift of the Qinghai-Xizang Plateau at about that time. This uplift of the plateau intensified the East Asia monsoon system and started red clay deposition. [ABSTRACT FROM AUTHOR]

Red clay widely occupies the seafloor of pelagic environments in middle latitudes, and potentially preserves long paleoceanographic records. We conducted a rock-magnetic study of Pacific Ocean red clay to elucidate paleoenvironmental changes. Three piston cores from the western North Pacific Ocean and IODP Hole U1365A cores in the South Pacific Ocean were studied here. Principal component analyses applied to first-order reversal curve diagrams (FORC-PCA) reveals three magnetic components (endmembers EM1 through EM3) in a core of the western North Pacific. EM1, which represents the features of interacting single-domain (SD) and vortex states, is interpreted to be of terrigenous origin. EM2 and EM3 are carried by non-interacting SD grains with different coercivity distributions, which are interpreted to be of biogenic origin. The EM1 contribution suddenly increases upcore at a depth of ~ 2.7 m, which indicates increased eolian dust input. The age of this event is estimated to be around the Eocene–Oligocene (E/O) boundary. Transmission electron microscopy reveals that EM2 is dominated by magnetofossils with equant octahedral morphology, while EM3 has a higher proportion of bullet-shaped magnetofossils. An increased EM3 contribution from ~ 6.7 to 8.2 m suggests that the sediments were in the oxic–anoxic transition zone (OATZ), although the core is oxidized in its entire depth now. The chemical conditions of OATZ may have been caused by higher biogenic productivity near the equator. FORC-PCA of Hole U1365A cores identified two EMs, terrigenous (EM1) and biogenic (EM2). The coercivity distribution of the biogenic component at Hole U1365A is similar to that of the lower coercivity biogenic component in the western North Pacific. A sudden upcore terrigenous-component increase is also evident at Hole U1365A with an estimated age around the E/O boundary. The increased terrigenous component may have been caused by the gradual tectonic drift of the sites on the lee of arid continental regions in Asia and Australia, respectively. Alternatively, the eolian increase may have been coeval in the both hemispheres and associated with the global cooling at the E/O boundary. [ABSTRACT FROM AUTHOR]