Kaolinitic Soils Research Articles

Thermal stability of artificial radiation-induced defects in kaolinite: Enhancing EPR dating protocol

Kaolinite naturally contains radiation-induced electron defects in its structure induced by ionizing radiations and can be analyzed with electron paramagnetic resonance spectroscopy (EPR). They include the so-called A-center, which is crucial for geochronological applications due to its stability at the scale of geological periods. Indeed, previous studies have substantiated the thermal stability of naturally occurring A-centers in kaolinite through annealing experiments. However, the stability of artificially created A-centers, which are used to determine paleodose through calibration via irradiation experiments and subsequent dating of kaolinite formation, still needs to be more adequately specified to confirm their relevance. Therefore, this research probed the thermal stability of A-centers produced by ionizing 1.5 MeV He+ beams in two samples, i.e., the reference KGa-2 and a very disordered lateritic soil kaolinite. Heating experiments showed that the annealing of irradiated samples at 250 °C was relevant to determining A-center concentration. Second, the annealing of artificial A-centers at higher temperatures was found to be a second-order process, as for natural A-centers. Annealing parameters such as activation energy (2–2.6 eV) were determined with estimates of half-life at 300 K, which was found to be >1012 years for natural and artificial A-centers. Thus, the parameters for artificial A-centers are consistent with the thermal annealing behavior of their natural counterparts. These new findings affirm that artificially generated A-centers mimic natural ones in terms of EPR spectra and thermal stability, enhancing the reliability and precision of the EPR dating methodology used in kaolinite dating.

Effect of nanoparticle-enhanced biocementation in kaolinite clay by microbially induced calcium carbonate precipitation

Microbially induced calcium carbonate precipitation (MICP) is a nature-based technique that has been developed over the past two decades for soil stabilization. However, the use of MICP for clay stabilization has received limited attention in the literature. On the other hand, the utilization of nanomaterials, such as nano-silica (nano-SiO2), for soil stabilization has been explored in numerous studies in the literature. This paper investigates the effect of nano-CaCO3 and nano-SiO2 on MICP stabilization in kaolinite clay. Nanoparticle-enhanced bio-cementation is introduced to effectively improve the strength of kaolinite clay at high water contents. Unconfined compressive strength (UCS) tests were conducted to evaluate the impact of the nano-bio-treatment (mixture of nano-additives and MICP) on soil strength. Additionally, the microstructure of the treated soils was examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, and X-ray diffraction (XRD) analyses. The results indicate that the MICP stabilization method is effective in enhancing the strength of kaolinite soil through a mixing approach. The study of UCS in the treated samples revealed that the use of nano-CaCO3 and nano-SiO2 can have either detrimental or beneficial effects on the MICP method, depending on the degree of saturation of the treated samples. The highest UCS observed for the MICP method at a target water content of 0.25 was more than three times that of untreated soil at the same moisture content. Furthermore, the increase in UCS for the samples treated with MICP was 2.5 times that of the untreated soil at a 30% target water content. The most significant finding, however, is that, at a 30% target water content, the samples improved with MICP+ 1.5% nano − SiO2 exhibited UCS values that were six and fifteen times greater than those of the untreated and MIC-treated samples, respectively. SEM images illustrated that the addition of nano-SiO2 with the MICP method led to an agglomerated soil texture, and the formation of calcium carbonate attached to the clay minerals. This results in an increase in soil strength.

Effects of rainfall intensity and slope gradient on soil sealing and crusting, erosion, and phosphorus solubilizing bacteria

Soil erosion significantly affects various soil properties and processes, yet its impacts on soil microbial populations remains unclear. Understanding the effects of soil erosion on soil microbial properties enables the formulation of recommendations to protect soils and reduce their vulnerability. This study aimed to determine the effects of rainfall intensity and slope on soil crusting, erosion and bacterial communities in soils with various texture and mineralogy. Three kaolinitic soils with low to medium clay content (K1, K2, and K3) and three smectitic soils with high clay content (S1, S2, and S3) were subjected to simulated rainfall at three intensities (45, 70 and 100 mm/h) and two slopes (5° and 8°). Infiltration rate was measured using a graduated cylinder in 2-minute rotations of the simulator. Runoff and sediment yield were collected in a beaker. Crust strength was measured using a cone penetrometer, and its thickness was determined with a vernier caliper. Bacterial isolates were obtained by plating serial dilutions in nutrient agar and incubating them at 25°C for 24–48 h48 hous. The phosphate solubilising bacteria were then identified. The smectitic soils formed the strongest crusts with S2 exhibiting significantly (p < 0.05) higher crust strength (18.54 Kpa) at an intensity of 45 mm/h and slope of 8° On the other hand, soil K3 (kaolinitic) had the lowest crust strength (5.4 Kpa) at an intensity of 100 mm/h and slope of 8° Soil loss increased with higher rainfall intensity and steeper slopes for the kaolinitic soils with K1 being most erodible (468.2 kg/ha) at an intensity of 100 mm/h and slope of 8° The number of phosphate solubilising bacteria decreased with increasing rainfall intensity. Furthermore, this study revealed that soil properties played a more significant role in shaping bacterial composition and phosphate solubilisation than rainfall intensity alone. These findings highlight the complex interactions between soil erosion, bacterial communities, and soil properties, which are crucial for devising effective soil conservation strategies.

Laboratory study of a kaolinitic soil and sodium hydroxide interaction mechanisms and resulting swelling stresses

The study of prolonged exposure of natural soils to alkaline solutions has been conducted to analyze and control the local soil swelling behavior observed in industrial sites. The occurrence of foundation heave in a Brazilian industrial site prompted a laboratory investigation aimed at understanding the mechanism of interaction between soil and alkali that induced swelling behavior. The study was extended to determine the corresponding swelling stress to be used in reinforcement design, and to investigate the soil response to chemical stabilization with 5% ferric chloride solution. Previously, a comprehensive mineralogical and physical-chemical investigation was accomplished using industrial caustic liquor and four natural soils from local stratigraphy. All soils are mainly constituted by kaolinite and quartz, and one also presents some montmorillonite. Both kaolinite and montmorillonite were degraded by NaOH liquor, and newly formed minerals were identified. The expansion is related to the mechanism of the silica-NaOH reaction. In the study reported here, the local soil with the highest volume change in sedimentation tests with NaOH solutions was subjected to quasi-constant volume oedometer tests with water and with 4N NaOH solution to determine the swelling stresses resulting from the reactions until stabilization. The alternative of chemical treatment with 5% ferric chloride solution was investigated through the same testing procedure. X-Ray diffraction analyses were applied to evaluate the changes in mineralogy. The swelling vertical stress reached 40 kPa under confined conditions, and stabilization took up to 40 days. The chemical treatment was effective in controlling ongoing reactions, but not effective in prevention.

Transport Behavior of Cd2+ in Highly Weathered Acidic Soils and Shaping in Soil Microbial Community Structure.

The mining and smelting site soils in South China present excessive Cd pollution. However, the transport behavior of Cd in the highly weathered acidic soil layer at the lead-zinc smelting site remains unclear. Here, under different conditions of simulated infiltration, the migration behavior of Cd2+ in acid smelting site soils at different depths was examined. The remodeling effect of Cd2+ migration behavior on microbial community structure and the dominant microorganisms in lead-zinc sites soils was analyzed using high-throughput sequencing of 16S rRNA gene amplicons. The results revealed a specific flow rate in the range of 0.3-0.5mL/min that the convection and dispersion have no obvious effect on Cd2+ migration. The variation of packing porosity could only influence the migration behavior by changing the average pore velocity, but cannot change the adsorption efficiency of soil particles. The Cd has stronger migration capacity under the reactivation of acidic seepage fluid. However, in the alkaline solution, the physical properties of soil, especially pores, intercept the Cd compounds, further affecting their migration capacity. The acid-site soil with high content of SOM, amorphous Fe oxides, crystalline Fe/Mn/Al oxides, goethite, and hematite has stronger ability to adsorb and retain Cd2+. However, higher content of kaolinite in acidic soil will increase the potential migration of Cd2+. Besides, the migration behavior of Cd2+ results in simplified soil microbial communities. Under Cd stress, Cd-tolerant genera (Bacteroides, Sphingomonas, Bradyrhizobium, and Corynebacterium) and bacteria with both acid-Cd tolerance (WCHB 1-84) were distinguished. The Ralstonia showed a high enrichment degree in alkaline Cd2+ infiltration solution (pH 10.0). Compared to the influence of Cd2+ stress, soil pH had a stronger ability to shape the microbial community in the soil during the process of Cd2+ migration.

The Effect of K-Fertilization and Irrigation on the Composition of Cultivated Soils: Examples from Israel

Evaluation of soil sustainability should take into account chemical and mineralogical changes due to cultivation. Potassium (K) application is a key farming practice that may potentially affect phyllosilicate composition and soil properties. Irrigation is another agent that affects soil composition. This study aims to evaluate the imprints of cultivation on the chemical and mineralogical compositions of lowland soils under semi-arid and Mediterranean climate regimes and to assess them with the natural pedogenesis. The sites examined include two permanent plot experiments with crop rotation, and three single-plant plots. Cultivated, control, and fallow soils were analyzed for their chemical and mineralogical composition. The X-ray diffraction patterns of the clay fraction were decomposed to achieve quantitative detection of changes among the illite–smectite (IS) phases and in kaolinite amounts. In loamy and clayey soils dominated by IS phases, cultivation caused minor changes and diverse behavior of the IS phases. Yet, the K balance was negative under high fertilization levels and higher plant mass production. Fertilization enhanced the natural process of transforming IS into kaolinite and illite in the sandy soil, leading to a positive K balance. This study emphasizes the importance of IS minerals as a dynamic K pool that responds to plant needs.

Soil carbon turnover and balance in the priming effects of basalt, montmorillonite, and kaolinite in a Luvisol soil

Soil carbon turnover and balance in the priming effects of basalt, montmorillonite, and kaolinite in a Luvisol soil

Effect of biosolid-derived dissolved organic matter on orthophosphate sorption to soils depends on clay mineralogy and solution composition.

Dissolved organic matter (DOM) from biosolids can alter the sorption of orthophosphate (inorganic phosphorus (IP)) to soils and, therefore, affect the bioavailability of IP. It is not clear how clay mineralogy and solution composition interfere with DOM effects on IP sorption by soils. Hence, we studied the effect of DOM on IP sorption to five semi-arid soils dominated by either illite/smectite (I/S) or kaolinite clays. IP sorption isotherms were constructed in either NaCl or CaCl2 background solution, with and without the addition of DOM. The IP sorption capacity maxima (SMAX, Langmuir model) of the I/S soils were 33-102% higher in the presence of CaCl2, as compared to NaCl. Although DOM had no effect on the IP-SMAX in the presence of CaCl2, it increased the IP-SMAX by 35-59% in the presence of the NaCl solution. Surprisingly, DOM sorption to the I/S soils was 30-90% greater in the presence of a Na+-dominated solution, as compared to a Ca2+-dominated solution. In contrast to the I/S soils, the SMAX of the kaolinitic soil was not affected by the background electrolyte (Na+, Ca2+) or the addition of DOM. Furthermore, the addition of IP reduced the sorption of DOM to the kaolinitic soil (by up to 50%) in both background electrolyte solutions. These results highlight the contrasting roles of divalent and monovalent cations in conjunction with DOM in IP sorption to semi-arid I/S soils. We propose a new approach based on two conceptual mechanisms to explain the DOM's enhancement of IP sorption to I/S soils. (1) Under dispersion conditions in the Na+-dominated solutions, Ca2+-mediated DOM-IP complexes bind to the clay's negative planar surfaces. (2) Under flocculation conditions in the Ca+-dominated solutions, the distance between adjacent platelets decreases, reducing both the electronegative charge spillover and Ca2+ bridge-mediated DOM sorption. In contrast, the addition of DOM to kaolinite, a multi-platelet clay with a low isomorphic negative charge, reduces IP sorption due to competitive sorption on the clay's broken edges.

Effects of Industrial and Agricultural Recycled Waste Enhanced with Lime Utilisation in Stabilising Kaolinitic Soil

Soft kaolin clay is a problematic soils encountered in various construction projects that lead to the implementation of soil stabilisation. On the other side, the massive production of industrial and agricultural waste currently presents a critical problem for the environment. However, the utilisation of industrial and agricultural wastes in altering the characteristics of kaolinitic soil can be considered as an ideal solution to enhance the characterisation of problematic soils in the field of construction. Therefore, this study examines the alterations of the engineering properties of soft kaolin clay by utilising silica fume as the industrial by-product and eggshell ash as the agricultural by-product enhanced with lime use. To assess the impact of silica fume, eggshell ash, and lime on the various characteristics of kaolinitic soil, a series of laboratory experiments containing Atterberg limits, specific gravity, compaction test, unconfined compression test, X-ray fluorescence, X-ray diffraction, sieve analysis, and field emission scanning electron microscope is carried out. In this study, 2%, 4% and 6% of silica fume, 3%, 6% and 9% of eggshell ash and lime and the optimal combination of SF, ESA with 3%, 6% and 9% of lime are usedand were cured for 1, 7, 14 and 30 days. The results present that the optimal utilization of silica fume, eggshell ash, and lime can alter the engineering characteristics of the soft kaolin clay by reducing the specific gravity, consistency limits, linearshrinkage, and maximum dry density, while increasing the value of shrinkage limit, and optimum moisture content. In terms of strength improvement, the highest unconfined compression strength was recorded when soft kaolin clay was treated with 6% silica fume, 6% eggshell ash and 9% of lime for four (4) different days of curing with a strength improvement of 81.03%, 82.46%, 88.49% and 88.74%. Therefore, this study concludes that optimal use of silica fume, eggshell ash, and lime can persistently alter the characteristics of kaolinitic soil and open the way to economical and sustainable materials in improving the problem soil.

Sorption of oxytetracycline to microsized colloids under concentrated salt solution: A perspective on terrestrial-to-ocean transfer of antibiotics

The sorption of antibiotics on soil minerals and their cotransport have been widely studied for the past few years; however, these processes in concentrated salt solutions (estuary-like conditions) are not fully understood. This study aims to determine the possible sorption of oxytetracycline (OTC) on various natural and synthesized microsized minerals (including haematite, goethite, kaolinite, bentonite, lateritic, kaolinitic and illitic soil clays) under conditions mimicking pure, fresh, brackish and sea waters. The sorption of OTC was found to decrease in surface charge (herein zeta potential), hence altering the colloidal properties of the materials used. The sorption capacities of soil clays for OTC follow the inequality illitic soil clay > kaolinitic soil clay > lateritic soil clay, and the sorption capacities were found to decrease at higher salt concentrations. Seawater can intensify the release of the sorbed OTC from soil clay surfaces while favouring the coaggregation of the remaining OTC with soil clays. This implies that the long-range transport of OTC or other similar antibiotics can be governed by the mineralogical composition/properties of the suspended particles. More importantly, increasing salt concentrations in estuaries may form a chemical barrier at which limited amounts of OTC/antibiotics can pass through, while the remaining OTC/antibiotics can be favoured to aggregate simultaneously with suspended mineral particles.

The Influence of Electrokinetic Remediation Process on the Removal of Cationic and Anionic Dyes from Kaolinitic Soils

Low permeability soils possess specific mineralogical properties such as particle size, high buffer capacity, and high sorption capacity, which make them difficult to remediate and so pose serious environmental problems when polluted. The grain pores of these low permeability so ils trap in pollutants tightly, which are inaccessible and non-responsive to traditional technologies during remediation. Traditional technologies, some of which are ex-situ remediation techniques further compound these environmental problems through logistics and economic infeasibility. Electrokinetic Remediation (EKR) can offer certain advantages for treatment of various contaminants which include organic compounds, heavy metals, radionuclides, organic waste and some mixed inorganic species from a matrix with high salinity, low permeability and high buffering capacity. In addition, (EKR) is a clean and novel technique which accesses the grain pores of low permeability soils such as clays and silts, which have proven non-responsive to other soil remediation technologies such as soil flushing and soil washing. Among these fine soils, it has been proven that (EKR) is more effective on clay soil with particle size &lt;2mm, moderate plasticity, lower cation exchange capacity (CEC) and lower buffering capacity which can be found in this order: kaolinite&gt;illinite &gt;bentonite.

Exploring the Influence of Chemical Conditions on Nanoparticle Graphene Oxide Adsorption onto Clay Minerals.

High concentrations of graphene oxide (GO), a nanoparticle substance with rapid manufacturing development, have the ability to penetrate the soil surface down to the mineral-rich subsurface layers. The destiny and distribution of such an unusual sort of nanomaterial in the environment must therefore be fully understood. However, the way the chemistry of solutions impacts GO nanoparticle adsorption on clay minerals is still unclear. Here, the adsorption of GO on clay minerals (e.g., bentonite and kaolinite) was tested under various chemical conditions (e.g., GO concentration, soil pH, and cation valence). Non-linear Langmuir and Freundlich models have been applied to describe the adsorption isotherm by comparing the amount of adsorbed GO nanoparticle to the concentration at the equilibrium of the solution. Our results showed fondness for GO in bentonite and kaolinite under similar conditions, but the GO nanoparticle adsorption with bentonite was superior to kaolinite, mainly due to its higher surface area and surface charge. We also found that increasing the ionic strength and decreasing the pH increased the adsorption of GO nanoparticles to bentonite and kaolinite, mainly due to the interaction between these clay minerals and GO nanoparticles' surface oxygen functional groups. Experimental data fit well to the non-linear pseudo-second-order kinetic model of Freundlich. The model of the Freundlich isotherm was more fitting at a lower pH and higher ionic strength in the bentonite soil while the lowest R2 value of the Freundlich model was recorded at a higher pH and lower ionic strength in the kaolinite soil. These results improve our understanding of GO behavior in soils by revealing environmental factors influencing GO nanoparticle movement and transmission towards groundwater.

The formation and evolution of Al‐rich protoliths in the southern Ribeira belt, Brazil: Insights from remnants of a Precambrian paleoweathering surface

AbstractBauxitic clays, clayey bauxites and bauxites are residual products formed from the weathering of aluminosilicate‐rich parent rocks under wet and warm conditions. These deposits show a complex interplay between remobilisation of pre‐existing kaolinitic soils and depositional micro‐environments.In the southern Ribeira belt, Brazil, a paleoweathering surface developed on the continental shelf of the Capiru Group passive margin strata and on its basement/source rocks. This weathering cycle gave rise to a paleosol profile on the continental domain and a karstic paleotopography on the emerged carbonate shelf. The surface and karstic nets were later caped and filled with Al‐rich materials, typical of remobilised soils, bauxitic clays, clayey bauxites and pods of karst‐type bauxites.The age of the disconformity is Pre‐Brazilian/Pan‐African, implying a Neoproterozoic age for the weathering surface. In this study, we investigate the relationship among disconformities, paleosols and karst topography to better understand the stratigraphic control, chemical composition and mineralogy of the Al‐rich materials. We interpret this horizon as the remnants of a (meta‐)paleoweathering surface that can serve as a valuable key bed for stratigraphic correlation and paleogeographic reconstructions.We propose that the triggering process for the genesis of the paleosol profiles, bauxitic material and bauxite pods was a coupled mechanism between favourable climate and uplift along the northern margin of the Curitiba–Angola craton, creating a karstic topography that allowed the down‐plain transport of Al‐rich materials. In a later stage, these deposits were metamorphosed, developing a series of Al silicates in unusual paragenesis, typical of Al‐rich protoliths.The presence of these paragenesis, along with the recognition of the disconformity–paleoweathering surface pair, could be a useful tool to understand the paleoenvironmental and paleogeographic evolution of highly deformed terrains.

The Behavior of Rare Earth Elements during Green Clay Authigenesis on the Congo Continental Shelf

Clay mineral authigenesis at continental margins plays an important role in global marine element cycles. However, despite being increasingly used as tracers for both modern and past oceanographic conditions, the behavior of the rare earth elements (REEs) and their isotopes during marine clay authigenesis still remains poorly known. In this study, we report on a detailed geochemical investigation of glauconite from the West African continental shelf, near the mouth of the Congo River. Elemental, neodymium, and hafnium isotope analyses were conducted on both acid leachate and separated clay-size fractions of glauconite pellets, in order to investigate the behavior of REE during the formation of authigenic clays. Our data indicate that kaolinite dissolution and subsequent Fe-bearing clay authigenesis act as a net source of REEs to seawater. We show that enhanced glauconitization, as inferred from increasing Fe and K contents, is accompanied by significant decoupling of the REE toward markedly LREE-enriched shale-normalized patterns in neoformed clay separates. Using both Nd and Hf isotopes and SEM observations, we rule out any seawater influence and argue that this shift primarily reflects the progressively overwhelming presence of insoluble nanocrystals of detrital LREE-rich phosphates, which are known to occur in close association with kaolinite in tropical soils. Due to their marked insolubility in surface environments, such nanocrystals can be preserved during kaolinite dissolution and subsequently incorporated into the aggregates of authigenic green clays forming the peloids. Most strikingly, we show that the combined influence of net REE loss (due to kaolinite dissolution) and decoupling (due to subsequent entrapment of inherited LREE-bearing accessory phases into neoformed clay minerals) is accompanied by preferential release of a dissolved REE fraction characterized by seawater-like distribution patterns. These findings reinforce the emerging view that clay mineral dissolution and authigenesis at continental margins possibly play a major role in marine REE cycling.

Xanthan biopolymer-based soil treatment effect on kaolinite clay fabric and structure using XRD analysis

In this study, we evaluated the impact of xanthan gum biopolymer (XG) on kaolinite fabrics using X-ray diffraction (XRD) and the ensuing changes in the compaction behavior and shear resistance of kaolinite soils. The XRD peak analysis revealed that XG changed kaolinite fabrics into face-to-face associations. Moreover, environmental scanning electron microscopy showed the formation of XG-bridges between kaolinite particles, resulting in the change in fabrics and subsequently improving the resistance of kaolinite to external forces. Consequently, as XG content increased, the maximum dry density decreased, and the undrained shear strength increased. The viscous XG hydrogels produced a higher optimal moisture content and increased resistance to shear force. This study showed that XG affects the mechanical properties of kaolinite through changing kaolinite fabrics (up to 0.5% of the XG-to-kaolinite mass ratio) and absorbing pore-fluids (excess XG over 0.5% of the XG-to-kaolinite mass ratio).

Compression Curves and Compression Indices of Compacted Montmorillonitic and Kaolinitic Soils

Compression Curves and Compression Indices of Compacted Montmorillonitic and Kaolinitic Soils

Chemical weathering intensity controls the accumulation of nickel in rice (Oryza sativa L.) cultivated in basalt-derived paddy fields

Globally, a high concentration of nickel (Ni) in agricultural soil is closely related to basalt weathering. Rice grains readily accumulate Ni, however, the evolution of Ni distribution and mobility in paddy fields with basalt weathering remain unclear. This study investigated the distribution, geochemical fraction, and mobilization of Ni in basalt bedrock-paddy soil-rice plant continuums under contrasting climates through a combination of field surveys, chemical extractions, X-ray diffraction, and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses. Results show that the soils developed in tropical climates were more enriched in Ni than those in temperate climates. The concentration of Ni in rice grains from the studied temperate regions (3.71 ± 2.01 mg/kg) was higher than that in the tropical regions (0.57 ± 0.37 mg/kg). The concentration of Ni bound to Fe (hydro)oxides in paddy soils from temperate regions was five times higher than that in tropical regions. In contrast, the concentration of Ni found in phyllosilicate clays (mainly smectite/illite) in paddy soils from the temperate regions was only ∼1/4 of that of clay (mainly kaolinite) in the tropical paddy soils, and the ratio of Ni concentration in phyllosilicate clays to highly reactive Fe (hydro)oxides in paddy topsoil in temperate regions was one order of magnitude less than that in tropical regions, which contributes to the low bioavailability of Ni in tropical paddy soils. Furthermore, the accumulation of Ni in rice grains was insensitive to soil pH in tropical regions but showed significant negative correlations with the degree of chemical weathering (chemical index of alteration and index of laterisation) in temperate and tropical regions. These observations support the hypothesis that chemical weathering and the dissolution–recrystallization of Fe (hydro)oxides induced by frequent redox fluctuations in paddy soils cause Ni repartition between Fe (hydro)oxides and phyllosilicate minerals, which influence Ni geochemical cycling and bioavailability, and fundamentally regulate Ni accumulation in rice. This study elucidates the mechanism and controlling factors underlying Ni partition in the basalt-paddy soil-rice plant continuum under distinct climates, providing new insights into the understanding of geochemical behavior and environmental fate of Ni.

Leaching Test Protocols to Evaluate Contaminant Response of Nano-Calcium Silicate–Treated Tropical Soils

The current study deals with the interaction of toxic metals with soils by conducting a series of leaching tests on four kaolinitic soils procured from locations with varying pollution levels, such as a pristine location, vicinity of steel mill works, battery works unit, and an abandoned municipal waste dump site. The procured soils were spiked with 3,000 mg/kg of toxic metals, lead (Pb), and nickel (Ni) to understand the contaminant transport. An innovative amendment, such as synthesized nano-calcium silicate (NCS), was also mixed with the soils for toxic metal immobilization. Leaching tests. such as the toxicity characteristic leaching procedure (TCLP), extended TCLP, and caged TCLP, were conducted on soil samples. These tests were successful in predicting the interactive behavior of the composite mix containing soil, NCS, and toxic metals, comprehensively. The vulnerability of soils based on TCLP can be expressed in the order of Soil C > Soil D > Soil B > Soil A. These results were concurrent with extended TCLP, wherein the response of these composites at various pH levels was presented. Caged TCLP quantified the leaching rate for different mixtures, and it was found that the leaching rate for virgin soils reduced from 1.3 to 0.075 cm/yr after the NCS amendment. The addition of NCS resulted in the agglomeration and aggregation of soil particles. This increased the density and reduced the void spaces of the soil–nano mix, thereby encapsulating the toxic metals permanently within its interstices. The highest attenuation was observed for Pb2+ compared with Ni2+ for all the mixtures considered. Thus, leaching tests can be considered a prospective short-term technique for monitoring polluted soil media compared with tedious and time-dependent column studies.

Self-alkali-activated self-cementation achievement and mechanism exploration for the synergistic treatment of the municipal solid waste incineration fly ashes and the arsenic-contaminated soils

The feasibility and potential mechanisms of the self-alkali activation brought by municipal solid waste incineration (MSWI) fly ashes to the self-cementation of arsenic-contaminated soils were quantitatively evaluated and comprehensively analyzed to avoid the additional application of the alkali activators and binder materials traditionally. The employment of the two kinds of precursor materials achieved the self-alkali-activated self-cementation (‘double self’) under ambient conditions. The largest compressive strength (MPa) of 25.64 and lowest leaching toxicities (mg/L) of 21.05, 2.86, 0.08, 0.02, 2.05, and 0.34 for Zn, Cu, Cr, Cd, Pb, and As were obtained in the solidified matrix. Geopolymerization kinetics of the ‘double self’ cementation can be mathematically fitted by the Johnson-Mehl-Avrami–Kolmogorov model. CaClOH and halite in the MSWI fly ashes set up the self-alkali activation by reacting with the kaolinite and quartz in soils contaminated with arsenic by forming layered hydration and three-dimensional geopolymerization products to push for self-cementation.

Consolidation and swelling behavior of kaolinite clay containing xanthan gum biopolymer

Recently, microbial biopolymer-based soil treatment (BPST) has gained attention for its application in environmentally friendly soil stabilization, particularly for enhancing the strength and stability of fine-grained soils. However, the effects of BPST on clay’s compressibility (consolidation) and expansion (swelling) behaviors remain unclear. This study used xanthan gum, a microbially produced polysaccharide with anionic charges, to stabilize kaolinite clay. The effect of xanthan gum BPST on the consolidation and swelling behavior of cohesive kaolinite clays was assessed through a series of experimental tests, including one-dimensional consolidation tests with elastic wave measurements, swelling tests, environmental scanning electron microscopy, and unconsolidated-undrained triaxial tests. The formation of xanthan gum hydrogels induces pore-clogging, resulting in a delay in the consolidation process, increased energy dissipation, and compressibility. Furthermore, the interaction between kaolinite and xanthan gum improved the undrained shear strength of kaolinite soils, thereby reducing the consolidation time required for a specific bearing capacity. This study demonstrates the possible application of controlling hydraulic conductivity, seismic stabilization, and rapid surface stabilization. However, additional drainage is necessary for in situ applications.