Leaching Of Cations Research Articles

IMPACT OF LONG‐TERM FRESHWATER IRRIGATION ON SOIL FERTILITY

AbstractIrrigation increases agricultural productivity and inevitably affects soil properties. When irrigation water is of a good quality and does not cause soil salinity or sodicity or contamination, and when there is no soil erosion, a gradual increase in soil fertility under irrigation conditions is, as a rule, expected. However, studies in various countries present examples of a gradual decline in soil fertility under long‐term freshwater irrigation due to leaching of organic matter and exchangeable cations. It is known that ploughing and agricultural activities modify natural soil formation processes and soil fertility. Irrigation enhances soil formation processes but also causes soil leaching. This paper presents data on the impact of long‐term freshwater irrigation on soil fertility for different climatic zones of Mexico, assessed by comparing some agrochemical properties of irrigated and non‐irrigated soils. This comparison shows that irrigation generally has a positive effect on soil fertility in arid conditions and a negative effect in semi‐arid, semi‐humid and humid tropical zones. Therefore, when planning and applying irrigation to crops, it is necessary to take into account not only crop water requirements, but also the need to preserve and improve soil fertility. © 2019 John Wiley & Sons, Ltd.

Effect of cement incorporation on the leaching characteristics of elements from fly ash and slag treated soils

Inclusion of cement in fly ash and slag mixed soils could potentially alter the leaching behavior of elements. This study investigated the leaching characteristics of calcium (Ca), magnesium (Mg), sulfur (S), manganese (Mn), barium (Ba) and chromium (Cr) from cement activated soil-fly ash, soil-slag mixtures and soil, fly ash, steel slag and cement alone. Batch water leach tests, acid neutralization capacity and pH-dependent leach tests were performed. Test results indicated that, effluent concentrations of Ca and Ba increased, while Mg concentrations decreased with cement additions. No consistent trend was observed between S concentrations and cement content. The leaching of Cr and Mn remained unaffected by cement incorporation. Results of this study showed that the solution pH had the greatest influence on the leaching behaviors of the elements. Ca, Mg, S and Mn followed cationic leaching patterns, whereas Ba showed both cationic and amphoteric leaching patterns. The highest concentrations of Cr were observed at extreme acidic conditions, followed by a concentration plateau at the pH range of 5.5–10, and subsequent decrease and increase in concentrations at pH of 11.5 and 13, respectively. Geochemical modeling results suggested that except for Cr, the leaching mechanisms of the elements were controlled by their sulfate and (hydr)oxide minerals. The leaching of Cr was possibly controlled by BaCrO4 and CaCrO4. It was observed that the presence of carbonate minerals did not play a significant role on the leaching mechanisms of the elements, when cement was used as an activator.

Intensified vegetation water use under acid deposition.

Despite the important role vegetation plays in the global water cycle, the exact controls of vegetation water use, especially the role of soil biogeochemistry, remain elusive. In this study, we reveal a new mechanism of soil biogeochemical control of large-scale vegetation water use. Nitrate and sulfate deposition from fossil fuel burning have caused substantial soil acidification, leading to the leaching of soil base cations. Of these, calcium has a unique role in plant cells by regulating stomatal aperture, thus affecting vegetation water use. We hypothesized that the leaching of the soil calcium supply, induced by acid deposition, would increase large-scale vegetation water use. We present evidence from a long-term whole watershed acidification experiment demonstrating that the alteration of the soil calcium supply by acid deposition can significantly intensify vegetation water use (~10% increase in evapotranspiration) and deplete available soil water. These results are critical to understanding future water availability, biogeochemical cycles, and surface energy flux and to help reduce uncertainties in terrestrial biosphere models.

Amine grafting of acid-activated bentonite for carbon dioxide capture

A low-cost bentonite (ZBent) and acid-activated derived samples have been employed as clay adsorbents to assess their performance for pure CO2 adsorption in a thermogravemetric system. The raw bentonite reached a CO2 uptake of only 6.2 mg/g ads due to its low specific surface area and pore volume. After acid modification, an increase in its specific surface area and pore volume was observed, due to the leaching of octahedral cations and the generation of an amorphous silica phase. However, the degradation of the clay structure only improved slightly the adsorption of CO2. In a next step, raw and acid-treated clay minerals were functionalized with two different amine species (aminopropyl-trimethoxysilane; AP, and diethylene-triamine-trimethoxysilane; DT) by grafting. Unlike the case of DT species, the incorporation of AP moieties favored the chemical interaction between the amines species and the CO2 molecules in all cases. Functionalization with AP molecules increased the adsorption capacity of CO2 up to 29.2 mg/g ads at 30 °C for ZBent-24 h-AP, the material obtained after longer acid treatment time and functionalized with AP. AP-functionalized samples also had good stability and reusability during eight cyclic adsorption/desorption tests.

Leaching of elements from cement activated fly ash and slag amended soils

Very few studies have investigated the leaching characteristics of cement activated fly ash and slag treated soils, although the inclusion of cement significantly enhances the material pH and may alter the leachability of elements. In this study the leaching behavior and mechanisms of chromium (Cr), copper (Cu), iron (Fe) and sulfur (S) from cement activated fly ash and slag stabilized soils were evaluated. An array of synthetic precipitation leaching procedure (SPLP), batch water leach test (WLT), toxicity characteristic leaching procedure (TCLP) and pH-Static leach tests were conducted. A geochemical equilibrium model Visual MINTEQ was implemented to identify the leaching controlling mechanisms of the metals. Results indicated that, the leached concentrations of Cr, Cu, Fe and S in SPLP, WLT and TCLP effluents were in the range of 0.016–0.74 mg/L, 0.013–0.17 mg/L, 0.019–0.27 mg/L and 1.78–234 mg/L, respectively. Quantitative comparisons between the standard test procedures suggested the necessity of multiple test methods for a comprehensive leaching assessment. Cr and Cu showed amphoteric leaching behaviors, whereas Fe and S followed cationic leaching patterns. According to the geochemical analyses, amorphous Cr(OH)3; tenorite and Cu(OH)2; ferrihydrite and goethite; gypsum and anhydrite; could control the leaching of Cr, Cu, Fe and S, respectively. The effluent Cr concentrations frequently exceeding the U.S. EPA specified maximum contaminant level of 0.1 mg/L. Yet, the use of cement activated fly ash and slag mixed soils could be beneficial, since less toxic trivalent Cr (III) was identified through geochemical modeling.

Leaching behavior of aluminum, copper, iron and zinc from cement activated fly ash and slag stabilized soils

The use of industrial by-products such as fly ash and slag have become very prevalent in soil stabilization owing to its suitable physical and mechanical properties, and economical advantages. However, fly ash and slag have been identified as the potential source of toxic substances, and may pose environmental risk by leaching heavy and trace metals into soil, surface and groundwater. Toxicity characteristic leaching procedure (TCLP) tests were conducted to investigate the environmental hazards associated with the leaching of aluminum (Al), copper (Cu), iron (Fe) and zinc (Zn) from fly ashes, slag, type I/II cement and cement activated fly ash and slag stabilized soils. Sulfate (SO4), dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations were also quantified to evaluate their influence on metal leaching. To understand the effect of pH on the leaching behavior, pH-dependent leach tests were conducted at the pH ranges of 2–14. Results indicated that an increase in fly ash or slag content may not necessarily increase the effluent metal concentrations. Al, Cu, Zn and DOC followed an amphoteric leaching pattern where concentrations increased in both acidic and basic conditions. In contrast, maximum DIC concentrations occurred at neutral or near neutral pH values. Fe and SO4 showed cationic leaching behavior where concentrations decreased with an increase in effluent pH. Additionally, the leaching controlling mechanisms of the metals were identified by implementing geochemical modeling program Visual MINTEQ. The geochemical analyses indicated that the solubility of Al3+ and Fe3+ were controlled by precipitation/dissolution reactions of oxide/hydroxide minerals at all pH values. Leaching of Cu2+ was only solubility controlled at pH higher than 7, whereas Zn2+ leaching was solubility controlled in the pH range of 8–12.

PH-Dependent Leaching Characteristics of Major and Toxic Elements from Red Mud

This study analyzes the leaching behavior of elements from red mud (bauxite residue) at pH values ranging from 2 to 13. The leaching characteristics of metals and contaminated anions in five red mud samples produced by Bayer and combined processes were analyzed using the batch leaching technique following the US Environmental Protection Agency (USEPA) Method 1313. In addition, the geochemical model of MINTEQ 3.1 was used to identify the leaching mechanisms of metals. The results showed that Ca, Mg, and Ba follow the cationic leaching pattern. Al, As, and Cr show an amphoteric leaching pattern. The leaching of Cl− is unaffected by the pH. The maximum leaching concentration of the proprietary elements occurs under extremely acidic conditions (pH = 2), except for As. The leaching concentration of F− reaches 1.4–27.0 mg/L in natural pH conditions (i.e., no acid or base addition). At the same pH level, the leaching concentrations of Pb, As, Cr, and Cu are generally higher from red mud produced by the combined process than that those of red mud from the Bayer process. The leaching concentration of these elements is not strongly related to the total elemental concentration in the red mud. Geochemical modeling analysis indicates that the leaching of metal elements, including Al, Ca, Fe, Cr, Cu, Pb, Mg, Ba, and Mn, in red mud are controlled by solubility. The leaching of these elements depended on the dissolution/precipitation of their (hydr)oxides, carbonate, or sulfate solids.

Controlled Hydrolysis of Metal-Organic Frameworks: Hierarchical Ni/Co-Layered Double Hydroxide Microspheres for High-Performance Supercapacitors.

Pseudomorphic conversion of metal-organic frameworks (MOFs) enables the fabrication of nanomaterials with well-defined porosities and morphologies for enhanced performances. However, the commonly reported calcination strategy usually requires high temperature to pyrolyze MOF particles and often results in uncontrolled growth of nanomaterials. Herein, we report the controlled alkaline hydrolysis of MOFs to produce layered double hydroxide (LDH) while maintaining the porosity and morphology of MOF particles. The preformed trinuclear M3(μ3-OH) (M = Ni2+ and Co2+) clusters in MOFs were demonstrated to be critical for the pseudomorphic transformation process. An isotopic tracing experiment revealed that the 18O-labeled M3(μ3-18OH) participated in the structural assembly of LDH, which avoided the leaching of metal cations and the subsequent uncontrolled growth of hydroxides. The resulting LDHs maintain the spherical morphology of MOF templates and possess a hierarchical porous structure with high surface area (BET surface area up to 201 m2·g-1), which is suitable for supercapacitor applications. As supercapacitor electrodes, the optimized LDH with the Ni:Co molar ratio of 7:3 shows a high specific capacitance (1652 F·g-1 at 1 A·g-1) and decent cycling performance, retaining almost 100% after 2000 cycles. Furthermore, the hydrolysis method allows the recycling of organic ligands and large-scale synthesis of LDH materials.

Effect of natural organic acids on mobilization of macro- and microelements from rocks

Experimental study of leaching of the main cations (Na, K, Mg, and Ca), alkaline and alkaliearth microelements (Li, Rb, Cs, Be, Sr, and Ba), heavy metals (Mn, Fe, Co, Ni, Cu, Zn, Cd, Tl, and Pb), hydrolyzate elements (Y, RZ, Ti, Th, and U), and anionic elements (F, Si, P, and V) from rocks of different acidity with distilled water and a multicomponent solution of organic acids, having the distribution of dissociation constants corresponding to natural dissolved organic matter was carried out. It has been shown that carboxylic acids, which are part of the dissolved organic matter contained in surface waters, cause a sharp increase in the mobilization of both the main cations and trace elements from silicate rocks. The chemical properties of the elements are of secondary importance, as was shown by the general correlation between the parameter related to the mobility of the elements at the initial stage of the leaching and their content in the rocks.

An Amorphous Nickel-Iron-Based Electrocatalyst with Unusual Local Structures for Ultrafast Oxygen Evolution Reaction.

Rationally designing active and durable catalysts for the oxygen evolution reaction (OER) is of primary importance in water splitting. Perovskite oxides (ABO3 ) with versatile structures and multiple physicochemical properties have triggered considerable interest in the OER. The leaching of A site cations can create nanostructures and amorphous motifs on the perovskite matrix, thus facilitating the OER process. However, selectively dissolving A site cations and simultaneously obtaining more active amorphous motifs derived from the B site cations remains a great challenge. Herein, a top-down strategy is proposed to transform bulk crystalline perovskite (LaNiO3 ) into a nanostructured amorphous hydroxide by FeCl3 post-treatment, resulting in an extremely low overpotential of 189 mV at 10 mA cm-2 . The top-down-constructed amorphous catalyst with a large surface area has dual NiFe active sites, where high-valence Ni3+ -based edge-sharing octahedral frameworks are surrounded by interstitial distorted Fe octahedra and contribute to the superior OER performance. This top-down strategy provides a valid way to design novel perovskite-derived catalysts.

Reconstructing a high paleolatitude Mesozoic paleoenvironment from a truncated and deeply buried regolith, Norwegian North Sea

The paleoregolith in this study was unconformably overlain by lower Cretaceous (Valanginian) marine deposits of the Åsgard Formation and buried below two kilometers of sediments, on the Utsira High, Norwegian North Sea. The upwards intensification of chemical alteration, manifested in the replacement of feldspars by clays, leaching of base cations and reduced mechanical rock strength, in addition to the presence of terrestrial biotitic features, suggested weathering during subaerial exposure of the Utsira High during the Mesozoic. The paleoregolith can be divided into three weathering facies: altered coherent rock, saprock and saprolite, whereas the absence of true soil horizons suggested erosional truncation of the regolith before burial. Possible remnants of the eroded soil were identified as pedogenic mud aggregates in the overlying Åsgard Formation, bearing similar compositional characteristics as the saprolite.Clay mineralogy, bulk geochemical composition, micromorphology and depth of biotic features were used to reconstruct the paleoenvironmental conditions that prevailed during the formation of the regolith in the Mesozoic North Sea. Our results point to a regolith formation under periodically water-restricted conditions, promoting the co-existence of interstratified illite-smectite (beidellite) and kaolinite, deep presence of endomycorrhizae (the fungal extension of the root structure) and precipitation of iron oxide nodules. Application of recently developed geochemical climofunctions indicated that the regolith formed in a mesic (10–12 °C) and subhumid (1157–1406 mm/yr) environment, and under strongly acidic soil conditions (pH 5.2–5.6).

Influence of Α-Site Cations on Performance of Α2Ir2O7 Pyrochlore Oxygen Evolution Catalysts in Acidic Condition

The acidic nature of proton exchange membrane (PEM) electrolysis coupled with the highly oxidizing conditions of the oxygen evolution reaction (OER) greatly limits viable options for catalysts that are both active and stable. Precious metal catalysts, such as IrOx, are high performing OER materials, but scarcity and high cost may limit widespread implementation. Pyrochlore catalysts of the form A2B2O7 (where A is typically a rare-earth or alkaline-earth metal and B is a transition metal) have emerged as promising active candidates with reduced precious metal content and intriguing stability. For example, Y2Ir2O7 has demonstrated excellent activity and stability under acidic OER conditions despite some leaching of the Y cation, potentially leading to the in situ formation of a new active phase during catalysis1. In this work, the influence of the A-site cation on the activity and stability of Ir-based pyrochlore materials (A2Ir2O7) was systematically explored. Using a series of rare-earth metals, activity and stability were experimentally correlated with changes in the physical, chemical, and electronic properties to better understand the origin of the enhanced performance. This experimental work was supported by density functional theory (DFT) calculations. The fundamental insight gained will help to design OER catalysts with improved activity and reduced precious metal content, all without compromising stability. Cyclic voltammetry, chronoamperometry, chronopotentiometry, and double layer capacitance were used to determine the electrochemical performance of the catalysts. Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify leaching of the A-site cations and Ir under acidic OER conditions and establish a relationship between the loss of material and the change in catalytic performance. This relationship was further investigated with DFT calculations. Additionally, the crystal structure, surface composition, and morphology of the catalysts before and after electrochemical testing were probed using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM).

Transformation of the montmorillonite structure and its adsorption properties due to the thermochemical treatment

Complex studies revealed changes in the composition, structure, and properties of bentonite clays from the Taganskoye (Kazakhstan) and Dashkovskoe (Moscow region) deposits due to the thermochemical treatment. The leaching of cations from the interlayer and octahedral positions, protonation of the interlayer and OH-groups, leads to modification of the interlayer and 2:1 layer composition, which in turn contributes to significant changes in properties:-a decrease in the cation exchange capacity due to a decrease in the layer charge and increase in the specific surface due to destruction and partial amorphization. Bentonites from the Dashkovskoye deposit demonstrated higher resistance to thermochemical treatment than the bentonites from the Taganskoye deposit due to the protecting effect of the organic matter. Results of the work showed that even after quite intensive thermochemical treatment (13M HNO3, 90 °C, 5 hours), bentonite clays retain a significant part of the adsorption capacity.

Genesis of poikilotopic zeolite in aeolianites: An example from the Parnaíba Basin, NE Brazil

Zeolite cement is one of the main components of the Jurassic to Lower Cretaceous fluvial-aeolian succession in the Parnaiba Basin, northeastern Brazil. Core and outcrop-based stratigraphic analyses permitted the paleo-environmental and diagenetic interpretation of aeolian sandstone and showed the influence of the volcanic substrate in the origin of the zeolite cement. The substrate is represented by an extensive volcanic plain developed in the last stages of the Central Atlantic Magmatic Province (CAMP) in West Gondwana. The siliciclastic deposits consist of dune field, sand sheet and wadi deposit facies associations. The zeolite cement of the aeolian succession forms poikilotopic crystals with anomalous up to 50% modal content. X-ray diffraction and SEM/EDS/CL analyses showed laumontite and Ca-stilbite exhibiting, respectively, massive and radial textures. During eodiagenesis, the main processes included clay infiltration linked to water table fluctuations and flash flood events, producing clay coatings and displacive stilbite cementation. Massive laumontite cementation and smectite-chlorite conversion occurred in the mesodiagenesis, while in the final stages, the zeolite was partially replaced by calcite cement. Telodiagenesis is recorded by iron exsudation and the corrosion of clay films. Several processes can be inferred to explain the origin of the zeolite cement in the Jurassic-Lower Cretaceous sandstone of the Parnaiba Basin. After the first magmatic pulse (Triassic magmatism), the zeolite-bearing basalts were submitted to chemical weathering, causing cation leaching. Afterwards, the deposition of aeolian sands related to a wet desert system occurred above this weathered substrate. Fractured basaltic substrate favored the release of ions to the surface, with fluids enriched in sodium and calcium that percolated the permeable aeolian sandstone beds during the diagenesis. Furthermore, zeolite cement is geographically associated with the volcanic substrate in the western Parnaíba Basin. However, it is absent in the eastern part, where the aeolianites overlie sedimentary rocks. We suggest that the system was thermally reactivated by the last thermal CAMP phase, with basalt emplacement in the eastern Parnaiba Basin linked to the opening of the Equatorial Atlantic Ocean (Cretaceous magmatism). The progressive heating towards the western part of the basin triggered fluids convection, and the enrichment in ions such as Ca2+, Si4+, Na+, Al3+, HCO−3 and SO42−, promoting optimal conditions for zeolite crystal growth (100 °C–300 °C). Sandstone textural aspects, as well as extensional faults and fractures allowed fluids migration resulting in the massive poikilotopic zeolite cementation, characterizing one of the most singular features of the diagenetic history of the West Gondwana record.

Corrosion behaviour of low dielectric glass fibres in hydrochloric acid

Corrosion behaviour of the low dielectric glass fibres in hydrochloric acid with different time and concentrations was studied. Leaching of cations, surface morphologies and structure of the low dielectric glass fibres before and after corrosion were investigated by ICP, SEM and FTIR, respectively. Both the change of weight and tensile strength of the low dielectric glass fibres in hydrochloric acid was discussed. The results showed that the decrease of weight and tensile strength of the low dielectric glass fibres with the increasing time was attributed to the leaching of the metal cations from the fibres surface which can disrupt the continuity of glass network. The equilibrium was eventually reached which was attributed to the formation of intermediate product, silica acid gel adhered to the fibres surface and complex of iron. The loss of weight and tensile strength had a maximum value after 8 h in 2 M hydrochloric acid and cracks were only generated on the surface after immersed in 2 M hydrochloric acid for 24 h. It suggested that the corrosion was significantly affected by the concentration of hydrochloric acid. The corrosion mechanism was not only attributed to ions exchange, but the hydrolysis of aluminoborate complex species.

The influence of acid modification on the structure of montmorillonites and surface properties of bentonites

Bentonites are often used as components of engineered barrier systems (EBS) for the radioactive waste disposal and isolation of hazardous nuclear facilities. In this paper, we consider possible transformations of the composition, structure and properties of bentonites when they are used as EBS components during the decommissioning of open pools with liquid radioactive waste (LRW). Operating conditions were modeled by the treatment with nitric acid at different durations (from 1 to 6 h), concentrations (from 1 to 8 M) and temperatures (20and 90°C). Nitric acid was chosen because it is used in the preparation procedure of LRW for isolation. To assess the intensity of transformations, bentonites with a high content of Al- and Fe-rich montmorillonites were selected. The work revealed effects of interlayer modification, leaching of octahedral cations, changes of the grain size distribution, specific surface area and weakening of surface basicity. It was also shown that temperature has a stronger effect on the structural transformation of montmorillonite than acid concentration and treatment duration. Formation of Al hydroxy-interlayered (HI) layers was observed due to the treatment with the nitric acid of lower concentration (1 M). The effect of a higher concentration at the same treatment duration and temperature leads to a more intensive leaching of Al from the octahedral sheets and protonation of the interlayer, which prevents the formation of Al hydroxy-interlayered (HI) layers. CO2 desorption after the nitric acid treatment decreases significantly, maintaining a relatively high value only when the conditions allow the interlayer to be protonated. Modification of structural and adsorption characteristics due to the acid treatment can be used to simulate modification of the engineered barriers' properties for a long-term operation in the disposal of radioactive and toxic wastes.

Long-term effects of liming on the species composition of the herb layer in temperate Central-European forests

Upon the occurrence of acidic deposition-driven damage to forests at the beginning of the 1980s, large-scale liming has been applied to acidic forest sites in Germany. Due to possible negative consequences on soil chemistry and on (soil) fauna and flora, this measure was discussed highly controversially right from the beginning and is disputed until today. In investigations of liming effects on the forest understory vegetation, very few studies covered a time period of more than two decades with intermittent relevés. We analyzed relevés of the herbal understory on limed and control plots in one pine (Pinus sylvestris), one oak (Quercus robur), two European beech (Fagus sylvatica) and five Norway spruce (Picea abies) stands at permanent observation sites in south-western Germany. These relevés had been repeatedly conducted during approximately 25 years.The number of herbal plant species was generally low. An increase in the herb layer's plant cover with time was found at six out of the nine study sites and was mainly due to spreading of two grass species (Milium effusum, Deschampsia flexuosa) and of the subshrub Vaccinium myrtillus, which might have benefitted from continuous nitrogen deposition. Only two species (Agrostis stolonifera, Stellaria media) with a main distribution in open landscapes were found in the years of investigation and their occurrence was restricted to only four sites and some few years.Across all sites, the average Ellenberg indicator values of nutrient (nitrogen) supply (N-values) were significantly increased on the limed plots ten years after liming, and at Year 10, the N-values of the limed plots were significantly higher than that of the control, presumably due to increased decomposition rates after liming. At the spruce sites, the average Ellenberg indicator values of soil reaction (R-values) of the limed plots 10 years after liming were significantly higher than at the beginning (Year 0) and at the end of the investigation (2013). We found no significant differences among the Ellenberg indicator values of light condition (L-values).In conclusion, liming had a significant, but only transient effect on the composition of the understory species. Therefore, our results do not support arguments against liming of acidic forests that are based on long-term changes in the herbal flora. In managed forests for wood production on acidic soils, liming can continue contributing to buffer the soils against ongoing acidification and accompanying cation leaching caused by anthropogenic deposition of nitrogen.

P and K additions enhance canopy N retention and accelerate the associated leaching

This study evaluated the interactive effects of combined phosphorus (P) and potassium (K) additions on canopy nitrogen (N) retention (CNR) and subsequent canopy leaching at a long-term N manipulation site on Whim bog in south Scotland. Ambient deposition is 8 kg N ha−1 year−1 and an additional 8, 24, and 56 kg N ha−1 year−1 of either ammonium (NH4+) or nitrate (NO3−) with or without P and K has been applied over 11 years. Throughfall N deposition below Calluna vulgaris and foliar N and P concentrations were assessed. Results showed that 60% for low dose and 53% for high dose of NO3− contrasting with 80% for low dose and 38% for high dose of NH4+ onto Calluna was retained by Calluna canopy. The CNR was enhanced by P and K addition in which 84% of NO3− and 83% of NH4+ for high dose were retained. CNR for NO3− increased the canopy leaching of dissolved organic N (DON) and associated organic anions. NH4+ retention increased canopy leaching of magnesium and calcium through ion exchange. Even over 11-years N exposure without P and K, foliage N:P ratio of Calluna did not increase, suggesting that N exposure did not lead to N saturation of Calluna at Whim bog. Our study concluded that increases in P and K availability enhance CNR of Calluna but accelerate the associated canopy leaching of DON and base cations, depending on foliar N status.

Understanding the Chemistry of Cation Leaching in Illite/Water Interfacial System Using Reactive Molecular Dynamics Simulations and Hydrothermal Experiments

Despite long standing pursuit, fundamental questions concerning the chemical pathways of leaching of ions in minerals, a phenomenon crucial to energy extraction, hydrometallurgy, metal recovery, and agriculture remain unanswered. Here we use large-scale ReaxFF reactive molecular dynamics (MD) simulations in combination with hydrothermal experiments to understand the chemistry of leaching in illite in contact with water. Our simulations under equilibrium conditions show that 12.58% of potassium cations leach out to the solution. On the other hand, aluminum and silicon, which form the structural network of illite, are far less leachable as only 0.51% and 2.86% respectively of Al and Si leach out. Upon analyzing the chemical pathway from the trajectory of MD simulations, water molecules supply protons near the illite surface that binds with the non-bridging oxygen (NBO) of the Al-O-Si linkage forming an [Al-O-Si]---H transition state that later converts to silanol group upon Al-O bond dissociation. Proton addition also weakens the interlayer K-O bonds, resulting in the diffusion of K+ ions to illite surface, where they combine with the hydroxyl group formed from water dissociation, to form KOH molecules. KOH molecules diffuse out reactively to bulk water via proton exchange mechanism. Furthermore, we also find that continued protonation results in the formation of Al(OH)3 and Si(OH)4 groups predominantly at the surface, which diffuse out into water resulting in the leaching of Al and Si cations. We observe excellent agreement in the equilibrium cation concentrations of ReaxFF simulations and hydrothermal experiments. Reactive MD methodology with reliable, ab-initio based forcefields is, therefore, a promising approach to understand chemistry of water dynamics and ion transport and can be extended to similar mineral/water interfacial systems.

Laboratory study of the effect of temperature difference on the disintegration of redbed softrock

ABSTRACTTo explore the impact of temperature difference (TD) on the disintegration of redbed softrock, three types of redbed rock, collected from Nanxiong Basin, were analyzed under three different treatments: TD, wetting and drying (WD), and TDWD-temperature difference and WD. To better understand the influence of different ranges of TD on disintegration during WD cycles, pH (hydrogen ion concentration) values, electrical conductivity (EC) values, and concentration of cations in leachate released during treatment were measured. The results show that no significant change can be observed under single TD treatment but that TD can increase the disintegration rate by accelerating the water–rock interaction. The effect of TD is more significant for rock with weak resistance to disintegration.