Mineral Crystal Lattice Research Articles

Incongruent dissolution of silicates and its impact on the environment: an example of a talc mine

The paper analyzes the process of incongruent dissolution of silicates taking place in close proximity to a talc mine. The chemical and phase composition as well as the concentrations and mobility of potentially toxic elements (PTE) in research material with varying levels of weathering were determined using instrumental (XRF, XRD) and chemical methods (extractions: BCR, aqua regia, water leaching, 0.05 M EDTA). It was demonstrated that the predominant minerals in the weathering crust include weathering-resistant minerals (i.e. quartz and muscovite) and secondary minerals (kaolinite, illite and interstratified minerals, vermiculite/chlorite) and that the predominant processes are hydrolysis and oxidation. The weathering process has an impact on the complexity of the chemical and mineral composition and the diverse structure of the weathering crust. A layer of Fe and Al oxides and hydroxides forms in the upper part of the weathering crust, while the amount of silica decreases. Low-mobility elements (i.e. Si, Al and Fe) react on the phase separation surface, causing the formation of clay minerals (i.e. vermiculite, montmorillonite) or Al and Fe hydroxides (e.g. goethite). The duration of weathering causes an increase in the content of PTEs in solid materials: multifold in the case of Cr (15), Ba (9), Pb (7), Zn (6) and considerably lower in the case of V (1.3), Sr (0.8) and Co (0.4). It was demonstrated that PTEs co-occur in several chemical fractions in the weathering crust and that the highest share of their total concentration are cations incorporated in the crystal lattice of minerals and bound by strong crystalline bonds (F4 46%). The lowest share was observed for the reducible fraction (9%) and the share of the oxidizable fraction was 29% The most mobile cations connected by the weakest bonds comprised only 16% of the total concentration. Based on the content of the readily soluble fraction of PTEs, it was concluded that the degree of weathering does not increase the environmental risk, but actually reduces it for Cr, Cr and Pb. The obtained Ecological Risk Index (ERI) values indicate that the ecological risk associated with the elements tested is low for the entire area, which means that natural weathering processes do not have any impact on environmental pollution.

Magnesium Silicate Binding Materials Formed from Heat-Treated Serpentine-Group Minerals and Aqueous Solutions: Structural Features, Acid-Neutralizing Capacity, and Strength Properties.

The influence of structural features of three serpentine-group minerals (antigorite, chrysotile, and lizardite) on the hydration of heat-treated materials and the formation of magnesium silicate binder has been studied. Initial serpentine samples have been fired in the interval 550-800 °C with a step of 50 °C; acid neutralization capacity (ANC) values have been determined for all samples. Antigorite samples (SAP) have exhibited a maximum reactivity at a temperature of 700 °C (ANC 7.7 meq/g). We have established that the acid-neutralizing capacity of chrysotile and lizardite samples in the temperature range of 650-700 °C differ slightly; the capacity varied in the interval of 19.6-19.7 meq/g and 19.6-19.7 meq/g, respectively. The samples obtained at optimal temperatures (antigorite-700 °C, lizardite, and chrysotile-650 °C) have been studied. Heat-treated serpentines have interacted with water vapor for a year; serpentine hydration has been investigated. The strength characteristics of the resulting binder agents were studied after 7, 28, 180, and 360 days. Upon hardening within 7 days, the strengths of the SAP and SCH samples have been almost the same (2.2 MPa), whereas this indicator for the SLH and SLK samples has been significantly lower (0.5 MPa). After hardening for over a year, the chrysotile sample SCH had the highest strength (about 8 MPa), whereas the strength of antigorite SAP was 3 MPa. The samples of initial, heat-treated, and hydrated heat-treated serpentines have been studied using XRD, differential scanning calorimetry, and surface texture analysis. The serpentine structure is crucial in destroying the mineral crystal lattice during heat treatment. In contrast to heat-treated chrysotile and lizardite, antigorite did not adsorb water. Structural features of chrysotile provided the highest compressive strength of the binding agent compared with antigorite and lizardite. The acid-neutralizing ability of lizardite was noticeably higher than antigorite, whereas its compressive strength was lower due to the layered mineral structure and impurities. We have established that the minerals' structural features are crucial for the hydration of heat-treated serpentines; the structure determines material utilization in various environmental technologies.

THE PROCESS OF SOLONETZIZATION OF SOILS UNDER THE INFLUENCE OF MINERALIZED WATERS

In the soils studied by us, changes in the composition of the soil absorption complex (SAC) occur mainly between three cations, such as Ca++, Mg++, Na+, the radii of which differ from each other within 20%. According to A.E., Fersman [11], when the ion radii differ by up to 20%, cations are considered interchangeable, in other words, isomorphic in the crystal lattices of minerals, which is why when irrigating with mineralized water, sodium ions replace Mg++ and Ca++ ions. This substitution occurs gradually and over a long period the influence of mineralized waters and at a certain stage quantitatively stabilizes. In order to predict the probability of the sodium cation entering the SAC, and therefore the potential danger of soil alkalinization during irrigation with mineralized waters, a special indicator SAR (Sodium adsorption ratio) is used, which, based on Ca ++, Mg ++, Na data, makes it possible to assess the quality of irrigation water. Our waters, both river and mineralized, had a low risk of salinization and alkalinization according to this indicator, and therefore, when they were used as irrigation water, they did not render the soil unusable for a short period of 3-10 years, i.e. in terms of solonetzization, there were no significant changes, the soils were not solonetzic and remained so. But the process of solonetzization took place.

Residual properties of conventional concrete repetitively exposed to high thermal shocks and hydrocarbon fluids

The rapid degradation of traditional concrete at aprons in army airbases is a major problem for the operation of jet aircraft safely. Aprons are often saturated by rainfall water and hydrocarbon fluids (HFs) and are frequently subjected to heat shocks from jet exhaust. The current study investigates the causes of rapid degradation of airbase concrete and the effects of that on concrete properties. Standard sized concrete cylinders (w/c ratio = 0.35, 0.45 and 0.55) using Australian general-purpose cement were prepared and repeatedly exposed to both high thermal shocks and HFs, separately and combined until degradation becomes obvious in term of surface scaling. Surface scaling was developed when cylinders were subjected to the coupled effects of high thermal shocks and HFs, cylinders did not form scaling when subjected to high thermal shocks and HFs individually. However, significant changes in residual properties were identified for all exposure types. The considered cylinders showed 40% of decrease in the compressive strength and more than 27% of decrease in the splitting tensile strength. In addition, the elasticity of concrete was reduced by more than 63% after the formation of scaling on the surface. The crystal lattices of minerals in cylinders, such as alite, belite, quartz, ettringite, portlandite, and mullite were significantly decomposed owing to the repetitive actions of both thermal shocks and HFs combined, which resulted in the deterioration of mechanical properties. Deterioration of mechanical properties of cylinders highly depended on w/c ratio. Cylinders with a lower w/c ratio retained the higher percentage of residual strength when subjected to the coupled effects of high thermal shocks and HFs. This study also reports the influence of w/c ratio on mass loss characteristics and microstructures of conventional concrete subjected to both thermal shocks and HFs simultaneously.

Improving processes of gold-silver refractory ores treatment at the complex deposit of precious metals

The paper considers the results obtained in the study of the prospective gold-silver complex deposit at the Eriksky ore cluster (Khabarovsk Territory) with refractory pofycomponent ores. Energy dispersive, atomic emission, grain size and dispersive analysis of rock samples were carried out. Samples contained microelements of a wide range including gold, silver, bismuth, cobalt, chromium, manganese, molybdenum, nickel, lead, vanadium, tungsten, zinc, copper, etc. It was found that pofycomponent and dispersed composition of mineral raw materials at the deposit defines it as a complex object to extract valuable components. It was proposed to use systems based on methods that reduce consumption of reagents to address the issue of precious metal extraction with more environmentally and technologically efficient tools. It is achieved by creating conditions for a sustainable process of preparation for leaching of mineral components containing gold and platinum through destruction of the mineral component of refractory polycomponent ores by increasing micro disintegration fields using ultrasound. Providing sustainability of mineral crystal lattice destruction by regrinding the solid phase formed during cavitation is a fundamental factor when preparing for the extraction of microparticles of valuable components.

EVALUATION OF BOUND WATER FORMS IN CLAYS

Clays during lithogenesis change the composition, structure and properties, including physicochemical. The result of the thermal analysis was thermograms, on which four peaks of loss of bound water mass were established. These peaks in the author's interpretation are presented as different types of bound water in clays. The obtained experimental data, from the position of the size of the structural elements, allowed to distinguish the following types of water: loosely bound and strongly bound water of the surface of colloids, water surface of crystallites (minerals) and the crystal lattice of minerals. It has been revealed that when the montmorillonite and kaolinite clays are heated, endo-effects are observed in the temperature range up to 900°C caused by the release of H2O and OH-, the source of which is adsorption water and crystal lattice water of minerals. For montmorillonite in the high-temperature range, endo-effects due to the release of CO and CO2 were also noted, which is due to the presence of calcite in its composition. The energy activity of the surfaces of the particles of montmorillonite and kaolinite clays is distributed in the following sequence: the crystallite surface > of the surface of the colloid > of the surface of the strongly bound water of the colloid, which does not contradict the physical nature of the formation of the clay particle. It has been revealed that in montmorillonite clay, the water of the surface of crystallites has the greatest strength of bonds between molecules, the smaller is the strongly bound water of the colloid and the least is loosely bound water of the colloid. In kaolinite clay, the greatest strength of the bonds between molecules is the water of the surface of crystallites, the smaller is the loosely bound water of the colloid and the least strongly bound water of the colloid. In kaolinite and montmorillonite clays, the temperature of the effect and the heat of dehydration of the studied forms of bound water determine the change in the loss of bound water mass in different directions. The results of the studies allowed to quantify various forms of water in clay minerals.

Quasielastic neutron scattering of brucite to analyse hydrogen transport on the atomic scale.

It is demonstrated that quasielastic neutron scattering is a novel and effective method to analyse atomic scale hydrogen transport processes occurring within a mineral crystal lattice. The method was previously characterized as sensitive for analysing the transport frequency and distance of highly diffusive hydrogen atoms or water molecules in condensed matter. Here are shown the results of its application to analyse the transport of much slower hydrogen atoms which are bonded into a crystal lattice as hydroxyls. Two types of hydrogen transport process were observed in brucite, Mg(OH)2: a jump within a single two-dimensional layer of the hydrogen lattice and a jump into the next nearest layer of it. These transport processes observed within the prototypical structure of brucite have direct implications for hydrogen transport phenomena occurring within various types of oxides and minerals having layered structures.

Helium and Argon Isotopes in the Fe-Mn Polymetallic Crusts and Nodules from the South China Sea: Constraints on Their Genetic Sources and Origins

In this study, the He and Ar isotope compositions were measured for the Fe-Mn polymetallic crusts and nodules from the South China Sea (SCS), using the high temperature bulk melting method and noble gases isotope mass spectrometry. The He and Ar of the SCS crusts/nodules exist mainly in the Fe-Mn mineral crystal lattice and terrigenous clastic mineral particles. The results show that the 3He concentrations and R/RA values of the SCS crusts are generally higher than those of the SCS nodules, while 4He and 40Ar concentrations of the SCS crusts are lower than those of the SCS nodules. Comparison with the Pacific crusts and nodules, the SCS Fe-Mn crusts/nodules have lower 3He concentrations and 3He/4He ratios (R/RA, 0.19 to 1.08) than those of the Pacific Fe-Mn crusts/nodules, while the 40Ar/36Ar ratios of the SCS samples are significantly higher than those of the Pacific counterparts. The relatively low 3He/4He ratios and high 40Ar concentrations in the SCS samples are likely caused by terrigenous detrital input with high radiogenic 4He and 40Ar contents. The SCS crusts and nodules have shorter growth periods, implying that in situ post-formation radiogenic 3He, 4He and 40Ar produced by decay of U, Th and K have no effect on their isotope compositions. Thus, the SCS crusts/nodules inherited the noble gases characteristics of their sources. Helium and Ar isotope compositions in the SCS Fe-Mn crusts and nodules reflect the product of an equilibrium mixture between air-saturated seawater and radiogenic components during their growth, while the partial 3He excess in some SCS samples may represent a little mantle-derived origin. The different He and Ar isotope compositions of the Fe-Mn crusts and nodules between the South China Sea and the Pacific Ocean are due to their different sources and genetic processes. The characteristics of He and Ar isotope compositions in the SCS polymetallic crusts and nodules are similar to the properties of hydrogenetic Fe-Mn oxide/hydroxide precipitates, which reflects mainly the product of an equilibrium mixture between air-saturated seawater and radiogenic components.

Кинетика сорбции ионов меди, никеля и кобальта при совместном присутствии из водных растворов цеолитами

Экспериментально исследовано взаимное влияние на кинетику сорбции ионов меди (II), никеля (II) и кобальта (II) при совместном присутствии цеолитом Ягоднинского месторождения Камчатского края. Показано, что лимитирующей стадией сорбции является внутридиффузионный механизм. Для каждого иона рассчитаны величина сорбционной емкости, коэффициент внутренней диффузии, константа скорости реакции обмена по моделям псевдо-первого и псевдо-второго порядков.

Methods and Equipment for Breaking Down Gold-Containing Concentrates from Lean Ores and Mining Industry Waste

Exhaustion of rich or readily enriched precious metal ores leads to involvement in operation of stubborn ores from which effective extraction of precious metals by traditional methods is impossible. Within stubborn ores, a considerable part of gold is finely associated with sulphide minerals, generally with arsenopyrite and pyrite, and remains inaccessible for leaching even with fi ne comminution. Presence of an active carbonaceous agent occluding cyanide complexes of gold from solutions is another reason for stubbornness of gold-bearing ores. The joint negative effect of both factors on enrichment gives rise to doubly stubborn ores. A reduction in gold extraction indicators during hydrometallurgical processing for ores and concentrates with sorption and active organic carbon is overcome in most cases by using ion-exchange resins and activated carbon, whereas recovery of gold bonded in sulfides requires breakdown of the mineral crystal lattice. For this purpose, oxidizing roasting, and autoclave or bacterial oxidation of sulfides in a pulp are usually applied. The last two methods are now the most widespread. At the same time, roasting gold ores and concentrates is applied at a number of the overseas enterprises. This shows that hightemperature processes remain the main methods for preparing gold-bearing ores and concentrates for leaching. On the basis of results of calculations, research, and design and engineering development, and industrial tests the authors conclude that it is possible to increase extraction of gold and silver in products from the Mai and Badran fields after pyrolysis in a rotary drum furnace. Compared with oxidizing roasting environmental protection issues are resolved. Procedures and production equipment schemes are developed.

КРИСТАЛЛОХИМИЧЕСКИЕ АСПЕКТЫ ОЦЕНКИ ЭНЕРГИИ ВЗАИМОДЕЙСТВИЯ ЧАСТИЦ ГЛИНИСТЫХ МИНЕРАЛОВ

The goal of the paper is to analyze the changes in mineral crystal lattice under acid activation. Methods. Clay from the Slyudyanka deposit is the material under investigation. The methods used in the study include x-ray phase analysis using Bruker D8 Advance diffractometer. The diffractogram is recorded using the EVA program installed on a PC in combination with the diffractometer. The quantitative composition is calculated using the Topas 3.0 program. The study also uses the methods of scanning microscopy of the oriented sample, titrimetric analysis methods (the methods of neutralization and complexometry 0; conductivity measurement (determination of solution electrical conductivity); potentiometric measurements (determination of electrokinetic potential at electrophoresis); sedimentation analysis in gravitational and centrifugal fields. Modern databases and Excel are used for thermodynamic calculations. Results. Crystallochemical analysis of mineral structure and thermodynamic assessment of process spontaneous flow conditions allowed to explain the nature of the potential curve after acid activation of the clay from the Slyudyanka deposit. The extreme nature of this dependence is associated with the changes in the field of force on the surface of particles as a result of the flow of the complex of physico-chemical interactions, the most important of which are interactions of backbone ions with the components of environment. In its turn, the changes in the interaction energy of clay particle weight calculated by the results of colloid-chemical studies allow to analyze the processes occurring in the crystal lattice of clay under acid activation. Experimental data confirm the similarity of some patterns of acid activation of clay minerals associated to the fact that the process is accompanied by the washout of ions from the crystal lattice skeleton and formation of structure defects. The defects of crystal lattice causing the disturbance of its regularity, the transition of surface silica in amorphous state provide the change in both system dispersion and porosity of clay samples. Conclusions. It is more preferable to use the acid activation for the production of mineral sorbents with developed porosity when minerals with an expanding structural cell are used as a source material.

Hydrogen and oxygen stable isotope signatures of goethite hydration waters by thermogravimetry-enabled laser spectroscopy

The hydrogen and oxygen stable isotope composition (δ2H and δ18O values) of mineral hydration waters can give information on the environment of mineral formation. Here we present and validate an approach for the stable isotope analysis of mineral hydration waters based on coupling a thermogravimetric analyzer with a laser-based isotope ratio infrared spectroscopy instrument (Picarro L-2130i), which we abbreviate as TGA-IRIS. TGA-IRIS generates δ2H and δ18O values of liquid water samples with precision for δ2H of ±1.2‰, and for δ18O of ±0.17‰. For hydration waters in goethite, precision for δ2H ranges from ±0.3‰ to 1.6‰, and for δ18O ranges from ±0.17‰ to 0.27‰. The ability of TGA-IRIS to generate detailed water yield data and δ2H and δ18O values of water at varying temperatures allows for the differentiation of water in varying states of binding on mineral surfaces and within the mineral matrix. TGA-IRIS analyses of hydrogen isotopes in goethite yields δ2H values that reflect the hydrogen of the OH− phase in the mineral and are comparable to that made by IRMS and found in the literature. In contrast, δ18O values on goethite reflect the oxygen in OH− groups bound to Fe (Fe-OH group), and not the oxygen bound only to Fe (Fe-O group) in the mineral crystal lattice, and may not be comparable to literature δ18O values made by IRMS that reflect the total O in the mineral. TGA-IRIS presents the possibility to isotopically differentiate the various oxygen reservoirs in goethite, which may allow the mineral to be used as a single mineral geothermometer. TGA-IRIS measurements of hydration waters are likely to open new avenues and possibilities for research on hydrated minerals.

Aluminum fractionation in acidic soils and river sediments in the Upper Mero basin (Galicia, NW Spain).

This study aims to determine aluminum fractions in the fine earth of acidic soils under different land uses (forest, pasture and cultivation) and in the river bed sediments of the headwater of the Mero River in order to identify and quantify Al-bearing phases to assess Al mobility and potential bioavailability (environmental availability) in the monitoring area. Sequential extraction is used to evaluate the Al partitioning into six fractions operationally defined: soluble/exchangeable/specifically adsorbed, bound to manganese oxides, associated with amorphous compounds, aluminum bound to oxidizable organic matter, associated with crystalline iron oxides, and residual fraction (aluminum within the crystal lattices of minerals). The mean concentration of total aluminum (24.01gkg-1) was similar for the three considered uses. The mean percentage of the aluminum fractions, both in soils and sediments, showed the following order: residual fraction≫amorphous compounds≈crystalline iron oxides>water-soluble/exchangeable/specifically adsorbed>bound to oxidizable organic matter≈Mn oxides. However, in the soils, the amorphous compounds and water-soluble/exchangeable/specifically adsorbed fraction showed considerable differences between some types of uses, the percentage of aluminum linked to amorphous compounds being higher in forest soils (16% of total Al) compared to other uses (mean about 8% of total Al). The highest values of water-soluble/exchangeable/specifically adsorbed Al were also found in forest soils (mean 8.6% of the total Al versus about 4% of pasture and cultivation), which is consistent with the lower pH and higher organic matter content in forest soils. Nevertheless, the potentially bioavailable fraction (sum of the first three fractions) is low, suggesting very low geoavailability of this element in both soils and sediments; hence, the possibility to affect the crops and water quality is minimal.

Metal fractionation in topsoils and bed sediments in the Mero River rural basin: Bioavailability and relationship with soil and sediment properties

Comprehensive studies that examine the transfer of metals across soil-river bed sediment systems at the basin scale are scarce. An understanding of the distribution of metals among various fractions of soils and sediments within a basin is fundamental to understand their environmental behavior and, thus, to define watershed management plans. This study aims to determine the distribution of metals (Fe, Mn, Cu, and Zn) in topsoils under different land uses (cultivation, pastures, and forests) and river surface sediments in the upper Mero River basin (NW Spain) and to assess these metals' mobility and bioavailability in both environmental compartments to detect potential threats to crops and the water quality. Sequential extraction is used to fractionate the four metals into six fractions: soluble/exchangeable/specifically adsorbed, metals that are bound to Mn oxides, amorphous compounds, metals that are bound to organic matter, crystalline Al and Fe oxides, and residual metals (metals within the crystal lattices of minerals). The fractionation results for both soils and sediment indicate an abundance of metals in the residual fraction (except for Mn in soils) followed by relatively high percentages of oxide-bound fractions (mostly crystalline Fe oxides for both Fe and Zn, amorphous for Cu, and Mn oxides for Mn). On average, the Mn residual fraction in soils (30.2%) is only slightly exceeded by the Mn oxide fraction (34.7%). The land uses do not affect the sequence of metal-binding phases in soils, except for Mn, which is only slightly altered. The results also suggest that Fe, Mn, Cu and Zn in both soils and sediments are not readily mobile under current environmental condition and hence pose no threat to crops or the water quality. In overall terms, the mobility and bioavailability of the four metals (considering the sum of the three least mobile fractions, namely, organic matter, crystalline Al and Fe oxides, and residual) in the soils decrease in the following order: Mn>Cu>Fe>Zn. The same sequence occurs in the sediments, but the order between Fe and Zn is reversed. The soils and sediments that are studied cannot be considered polluted in terms of these metals because of their low levels and prevalence in the residual fraction, which is typical of contributions from natural sources and indicates the pedogenic/lithologic origin of these metals.

Applications of scanning electron microscopy in earth sciences

This paper expounds upon the basic principle of scanning electron microscopy (SEM), the main features of image types, and different signals, and the applications and prospects in earth sciences research are reviewed. High-resolution field emission SEM allows observation and investigation of a very fine micro area in situ. Using low-vacuum mode SEM, geological insulating samples can be analyzed directly without coating, demonstrating the wide application prospect. Combined with backscatter detector (BSE), energy dispersal X-ray spectroscopy (EDS), cathodoluminescence spectrometry (CL), and electron back-scattering diffraction (EBSD), SEM can yield multiple types of information about geological samples at the same time, such as superficial microstructure, CL analysis, BSE image, component analysis, and crystal structure features. In this paper, we use examples to discuss the geological application of SEM. We stress that we should not only focus on the CL image analysis, but strengthen CL spectrum analyses of minerals. These results will effectively reveal the mineral crystal lattice defects and trace element composition and can help to reconstruct mineral growth conditions precisely.

Study on the sulfidation behavior of smithsonite

Zinc extraction from low-grade mineral resources of oxidized zinc has recently become a focus of study. Sulfidation is an important process in oxidized ore flotation. In this study, the influence of sulfur ion adsorption on smithsonite surface was investigated with the use of zeta potential, inductively coupled plasma (ICP), scanning electron microscope (SEM), and X-ray photoelectron spectroscopic studies. Zeta potential measurements of sodium sulfide showed that sulfur ions were adsorbed onto the surface of pure smithsonite, as evidenced by the increased negative charge and the decrease in the pHIEP of smithsonite from 7.7 to 6 after sodium sulfide treatment. The ICP test revealed the gradual reduction in sulfur ion adsorption onto the surface of smithsonite in pulp sulfur. After 30min of absorption, CS in the solution declined from 1000×10−6mol/L to 1.4×10−6mol/L. SEM results showed that the mineral surface was partially changed to ZnS film after sodium sulfide treatment, whereas EDS analysis results showed that 2% S is contained on the smithsonite surface. X-ray photoelectron spectroscopy results indicated the presence of a characteristic signal peak of sulfur ions after sulfidation. Sulfur concentration increased to 11.89%, whereas oxygen concentration decreased from 42.31% to 13.74%. Sulfur ions were not only present during chemical adsorption, but were also incorporated into the crystal lattices of minerals by the exchange reaction between S2− and CO32− ions.

Electrical resistivity variation in uniaxial rock compression

This paper reports the relationship between electrical resistivity and rock failure during uniaxial compression. Experiments of rock samples on an electro-hydraulic servo-controlled testing machine show that the variation of electrical resistivity is closely related to rock deformation. Near to rock fracture, microcracks appear and change the microstructure of rock mass, causing the rupture of mineral crystal lattice, and the electrical resistivity has a rapid variation with the growth of cracks. The experimental result shows that rapid variation of electrical resistivity occurs at the critical point with stress level of approximately 75–85 % relative to the peak strength in uniaxial compression. This research may be useful to indirectly detecting the critical point of rock fracture.

Influence of afforestation on soil: The case of mineral weathering

Although concerns have been raised that increased nutrient demand by fast growing tree species could deplete soil nutrient pools, recent research suggests that some species are able to obtain nutrients via soil mineral weathering. Hybrid poplars, which are fast growing and nutrient demanding species, are increasingly used in intensive silvicultural settings. Understanding whether hybrid poplars have an effect on long term nutrient availability and can promote soil mineral weathering is therefore important. We investigated the levels of base cations (i.e. K, Ca, Mg, and Na) of surface soils (0–20cm) in 13 hybrid poplar plantations in Quebec, and compared the results with those of adjacent abandoned agricultural fields. To evaluate whether exchangeable base cation pools and non-exchangeable pools (i.e. those in the crystal lattice of minerals) were being depleted, we used a sequential leach with diluted salt (BaCl2 for exchangeable) and weak acid solutions (HCl and HNO3 for non-exchangeable). Levels of exchangeable and non-exchangeable cations were not statistically different between land use types. Exploratory analyses, however, revealed trends toward a greater depletion of Ca, Mg and Na in non-exchangeable forms following afforestation. The depletion of these non-exchangeable base cations due to afforestation occurred at sites where greater levels were initially present in soil. The results suggest increased soil mineral weathering due to greater amounts of minerals susceptible to dissolution and, in part, high clay content. Based on Ca, Mg and K concentrations of the different leaches and their molar ratios (Ca/ΣAl+Fe, Mg/ΣAl+Fe and K/ΣAl+Fe), we propose a lesser role of soil mineral weathering on Ca cycling than Mg and K, which could lead to faster depletion of exchangeable Ca pools of the surface soil due to fast growth and high Ca demand by the poplars.

QSPR Study Of Mineral Crystal Lattice Energy Based On Gene Expression Programming

In this study, gene expression programming (GEP), a novel genetic algorithm, is used to develop quantitative model as potential screening mechanism for mineral crystal lattice energy for the first time. Eight descriptors, including ionic radius, charges, effective nuclear charges and principal quantum number, are selected to establish this model. A nonlinear quantitative structure-property relationship (QSPR) model based on GEP has been built and its predicted coefficient (R) is 0.9912. This study has provided a new and effective method for the research of mineral crystal lattice energy.

QSPR modeling mineral crystal lattice energy by optimal descriptors of the graph of atomic orbitals

Models of the crystal lattice of minerals of general formula of A m C n : m, n = 1,2: A = Li, K, Na, Mg, Ca, Mn, Cu, Zn, Sr, Cd, Ba, Hg, Pb, Cs, and Rb ; C = Be, O, F, S, Cl, Br, and I; as a mathematical function of their structure have been constructed. Two elucidations of molecular structure have been used: molecular graph (vertexes are atoms, i.e., Li, Na, K, etc.) and graph of atomic orbitals, GAO (vertexes are atomic orbitals, i.e., 1s 2, 2p 5, 3d 10, etc). Statistical characteristics of the GAO-based models are better.