Geochemical Problems Research Articles

Secondary Ion Mass Spectrometry in Geochemistry and Cosmochemistry: Determination and Distribution of Carbon and Hydrogen in Silicate Samples

Based on a review of recent domestic and international literature, examples of using secondary ion mass spectrometry (SIMS) for the determination of carbon and hydrogen in solving particular problems of geochemistry and space chemistry are presented. Special attention is paid to problems arising in calibration procedures for the quantitative determination of carbon and hydrogen by SIMS. A summary of equipment currently used for SIMS analysis is given. Mass spectral imaging method based on mathematical processing of the recorded secondary ion currents of carbon and hydrogen for visualizing 3D distributions of elements is considered in detail.

Combined assessment of the ecological and geochemical state of anthropogenically impacted areas

Based on the theoretical principles of biogeochemistry and evolutionary ecology, the geochemical structure of the modern noosphere was evaluated, and a method was developed for the combined assessment of the ecological and geochemical state of large anthropogenically impacted areas. It was demonstrated that persistent geochemically-induced endemic diseases are direct consequences of the development of human civilization. It was shown by the example of the iodine natural–anthropogenic province that the risk map of geochemically-induced endemic diseases constructed by overlaying map surfaces adequately reflects the modern ecological and geochemical state in any point of the region of interest. The proposed approach is valid for the solution of a wide range of environmental geochemical problems.

Classification of geochemical data based on multivariate statistical analyses: Complementary roles of cluster, principal component, and independent component analyses

AbstractIdentifying the data structure including trends and groups/clusters in geochemical problems is essential to discuss the origin of sources and processes from the observed variability of data. An increasing number and high dimensionality of recent geochemical data require efficient and accurate multivariate statistical analysis methods. In this paper, we show the relationship and complementary roles of k‐means cluster analysis (KCA), principal component analysis (PCA), and independent component analysis (ICA) to capture the true data structure. When the data are preprocessed by primary standardization (i.e., with the zero mean and normalized by the standard deviation), KCA and PCA provide essentially the same results, although the former returns the solution in a discretized space. When the data are preprocessed by whitening (i.e., normalized by eigenvalues along the principal components), KCA and ICA may identify a set of independent trends and groups, irrespective of the amplitude (power) of variance. As an example, basalt isotopic compositions have been analyzed with KCA on the whitened data, demonstrating clear rock type/tectonic occurrence/mantle end‐member discrimination. Therefore, the combination of these methods, particularly KCA on whitened data, is useful to capture and discuss the data structure of various geochemical systems, for which an Excel program is provided.

Application of Pb-Zn tailings for surface paste disposal: geotechnical and geochemical observations

Surface paste disposal (SPD) technology has been investigated recently to solve the geotechnical (tailings dam failure) and geochemical (acid mine drainage formation) problems relating to tailings disposal. The tailings dam accidents occurred in the last few years have expedited the researches to search for safer tailings disposal methods in mining industry. The aim of this study is to investigate which parameters affect the geotechnical and geochemical stability of sulphidic paste tailings as SPD. The pH, EC and crack intensity of paste tailings placed in layers were measured to observe how the parameters affect their stability. In this study, it can be seen that solid concentration of the paste material increases above ~80 wt.%, and its shear strength is above 20 kPa. In addition, the pH values reduced from 7.4 to 6.6 and the EC values increased from 2.9 to 3.3 mS/cm in seepage water of the paste layers. According to these values, it can be said that there is a very low environmental risk using the SPD. Results showed the applicability of the SPD method by obtaining geochemical and geotechnical stability.

Combined membrane–oxythermographic method in the solution of the geochemical problems of migration of material of natural waters

Two methods for obtaining information on the fractional composition of organic matter in natural waters (membrane filtration and oxythermography) are combined in this study. The method has a number of indisputable advantages, which distinguish it among the currently available methods of analytical chemistry. In earth science, the fractional composition of organic materials in natural waters is estimated by the concentration of organic carbon (Corg) in fractions. In our opinion, an indicator of chemical consumption of oxygen (CCO) for ecological estimation of water reservoir state is more informative, because this indicator carries specific ecological information on the necessary oxygen consumption for oxidation of pollutants coming into the natural water environment. Therefore, estimation of the CCO parameter in fractions provides real information on the availability of organic matter and the probable danger from its content in water. This is the principal novelty of the information obtained and our study. The method was tested in the study of variation of the fractional composition of water matter during passage of Volga water through the waterworks (upon removal of water from the storage reservoir through the dam of the Ivan’kovskaya hydro power plant in the Dubna area). Analogous results are almost absent in earth science literature. There is a lack of data on the influence of water release through the dam even with respect to the major-component chemical composition. Variation of the fractional composition of matter (both organic and inorganic) upon water release through a waterworks is not discussed in literature. Thus, this study is of fundamental character.

Iron sulfide sails through the Grand Tack

Geochemistry A long-standing problem in geochemistry is the sequestration of iron-loving elements into the core of early Earth. Rather than causing the observed depletion of these elements in the mantle, Rubie et al. contend that metal segregation during the formation of Earth's core should have increased mantle concentrations. This is because of the high-pressure conditions of core formation that prevailed for Earth when Jupiter was executing its “Grand Tack” through the solar system. The sulfur concentrations in the magma oceans of early Earth became very high during accretion and, as Earth cooled, liquid iron sulfide stripped the mantle of the iron-loving elements, explaining the observed depletion. Science , this issue p. [1141][1] [1]: /lookup/doi/10.1126/science.aaf6919

Modeling of Coupled Processes: Flow, Transport and Geochemistry, Application to the Dissolution of Salt Dome

One of the most recognized hydro geochemical problems is the one of salt dome (case 5, level 1 of the international HYDROCOIN ground water flow benchmark). Several teams simulated this problem with different calculation codes. The rock salt dome is characterized by a very low permeability (10-20 m2). The hydrogeologists usually consider this rock as impervious. In reality, this value of permeability allows the circulation of the water inside the rock. In this paper we use the code GEODENS for the calculation of the flow and the transport with variable density. The problem of the dome is characterized by high concentrations (density), we thus used a chemistry code that we coupled with GEODENS for the calculation of the density and the concentrations in the presence of precipitated salts. Moreover we study the influence of this low permeability on the variations of the porosity of the rock of the dome as well as the quantities of salt dissolved (lost). We showed that the porosity of the top band of the dome has increased by a factor of 4.5 after a simulation of 10000 years. For the same duration, the top layer of the dome lost 50% of the quantity of salt initially stored in these pores. The acceleration of the dissolution process, even if it is rather slow, cannot be neglected when long duration occurs.

Omic Approaches to Microbial Geochemistry

The past two decades have witnessed an explosion of DNA sequencing technologies that provide unprecedented insights into genome sequences—the blueprints of life on Earth. Although initially driven by biomedical research, this revolution offers exciting opportunities in Earth sciences. Analyzing genomes and other biomolecules (“omic” methods) within environmental samples provides new vistas of microbial geochemistry. However, the massive amount of data produced can be hard to decipher, and the resources and infrastructure to train and support geoscientists in omics approaches are lacking. This article summarizes some of the opportunities and challenges in the applications of omic approaches to geochemical problems.

Effect of iron content on the structure and disorder of iron-bearing sodium silicate glasses: A high-resolution 29Si and 17O solid-state NMR study

Despite its geochemical importance and implications for the properties of natural magmatic melts, understanding the detailed structure of iron-bearing silicate glasses remains among the outstanding problems in geochemistry. This is mainly because solid-state NMR techniques, one of the most versatile experimental methods to probe the structure of oxide glasses, cannot be fully utilized for exploring the structural details of iron-bearing glasses as the unpaired electrons in Fe induce strong local magnetic fields that mask the original spectroscopic features (i.e., paramagnetic effect). Here, we report high-resolution 29Si and 17O solid-state NMR spectra of iron-bearing sodium silicate glasses (Na2O–Fe2O3–SiO2, Fe3+/ΣFe=0.89±0.04, thus containing both ferric and ferrous iron) with varying XFe2O3 [=Fe2O3/(Na2O+Fe2O3)], containing up to 22.9wt% Fe2O3. This compositional series involves Fe–Na substitution at constant SiO2 contents of 66.7mol% in the glasses. For both nuclides, the NMR spectra exhibit a decrease in the signal intensities and an increase in the peak widths with increasing iron concentration partly because of the paramagnetic effect. Despite the intrinsic difficulties that result from the pronounced paramagnetic effect, the 29Si and 17O NMR results yield structural details regarding the effect of iron content on Q speciation, spatial distribution of iron, and the extent of polymerization in the iron-bearing silicate glasses. The 29Si NMR spectra show an apparent increase in highly polymerized Q species with increasing XFe2O3, suggesting an increase in the degree of melt polymerization. The 17O 3QMAS NMR spectra exhibit well-resolved non-bridging oxygen (NBO, Na–O–Si) and bridging oxygen (BO, Si–O–Si) peaks with varying iron concentration. By replacing Na2O with Fe2O3 (and thus with increasing iron content), the fraction of Na–O–Si decreases. Quantitative consideration of this effect confirms that the degree of polymerization is likely to increase with iron content and that Fe3+ is predominantly a network-former. The 17O NMR spectra suggest a moderate degree of preferential partitioning of iron between NBO and BO clusters. The present results bear strong promise for studying iron-bearing silicate glasses using solid-state NMR techniques, constraining the effect of iron content on the degree of polymerization. The observed changes in atomic structures of iron-bearing sodium silicate glasses will be helpful for unraveling atomic origins of the properties of natural silicate melts.

Insight into unresolved complex mixtures of aromatic hydrocarbons in heavy oil via two-dimensional gas chromatography coupled with time-of-flight mass spectrometry analysis

The aromatic hydrocarbon fractions of five crude oils representing a natural sequence of increasing degree of biodegradation from the Liaohe Basin, NE, China, were analyzed using conventional gas chromatography–mass spectrometry (GC–MS) and comprehensive two-dimensional gas chromatography (GC×GC). Because of the limited peak capability and low resolution, compounds in the aromatic fraction of a heavily biodegraded crude oil that were analyzed by GC–MS appeared as unresolved complex mixtures (UCMs) or GC “humps”. They could be separated based on their polarity by GC×GC. UCMs are composed mainly of aromatic biomarkers and aromatic hydrocarbons with branched alkanes or cycloalkanes substituents. The quantitative results achieved by GC×GC-FID were shown that monoaromatic hydrocarbons account for the largest number and mass of UCMs in the aromatic hydrocarbon fraction of heavily biodegraded crude oil, at 45% by mass. The number and mass of diaromatic hydrocarbons ranks second at 33% by mass, followed by the aromatic biomarker compounds, triaromatic, tetraaromatic, and pentaaromatic hydrocarbons, that account for 10%, 6%, 1.5%, and 0.01% of all aromatic compounds by mass, respectively. In the heavily biodegraded oil, compounds with monocyclic cycloalkane substituents account for the largest proportion of mono- and diaromatic hydrocarbons, respectively. The C4-substituted compounds account for the largest proportion of naphthalenes and the C3-substituted compounds account for the largest proportion of phenanthrenes, which is very different from non-biodegraded, slightly biodegraded, and moderately biodegraded crude oil. It is inferred that compounds of monoaromatic, diaromatic and triaromatic hydrocarbons are affected by biodegradation, that compounds with C1-, C2-substituents are affected by the increase in degree of biodegradation, and that their relative content decreased, whereas compounds with C3-substituents or more were affected slightly or unaffected, and their relative content also increased. The varying regularity of relative content of substituted compounds may be used to reflect the degree of degradation of heavy oil. Moreover, biomarkers for the aromatic hydrocarbons of heavily biodegraded crude oil are mainly aromatic steranes, aromatic secohopanes, aromatic pentacyclotriterpanes, and benzohopanes. According to resultant data, aromatic secohopanes could be used as a specific marker because of their relatively high concentration. This aromatic compound analysis of a series of biodegraded crude oil is useful for future research on the quantitative characterization of the degree of biodegradation of heavy oil, unconventional oil maturity evaluation, oil source correlation, depositional environment, and any other geochemical problems.

The control volume radial basis function method CV-RBF with Richardson extrapolation in geochemical problems

The aim of this paper is to present how to implement a control volume approach improved by Hermite radial basis functions (CV-RBF) for geochemical problems. A multi-step strategy based on Richardson extrapolation is proposed as an alternative to the conventional dual step sequential non-iterative approach (SNIA) for coupling the transport equations with the chemical model. Additionally, this paper illustrates how to use PHREEQC to add geochemical reaction capabilities to CV-RBF transport methods. Several problems with different degrees of complexity were solved including cases of cation exchange, dissolution, dissociation, equilibrium and kinetics at different rates for mineral species. The results show that the solution and strategies presented here are effective and in good agreement with other methods presented in the literature for the same cases.

Behavior of lanthanides during the formation of the Iul’tin deposit, Chukchi Peninsula

† The determination of the factors of ore formation and sources and evolution of hydrothermal solutions is an important geochemical problem. Recent studies of tin and tungsten deposits have employed new methods and approaches to elucidate, on the one hand, the rea� sons for the formation of large and very large deposits and, on the other hand, the physicochemical parameters of formation of these deposits. These studies resulted in the extension or even revision of existing genetic models. The rare earth elements (REEs), which include La and lanthanides, are traditionally used as indicators of fractionation in magmatic systems and exogenic pro� cesses. The elements whose contents are specific for solutions of particular compositions and that preserve the respective signatures during solution–rock exchange reactions and infiltration toward mineralized zones can be used as geochemical tracers of the nature of hydro� thermal fluids. The contents and ratios of REE in miner� als can be used as indicators of the nature and evolution of hydrothermal solutions, because mixing of waters from different sources and an increase in the fraction of exo�

Simulation of surface dynamics during dissolution as a function of the surface orientation: Implications for non-constant dissolution rates

An important problem in geochemistry is the understanding of how changes occurring on a surface during dissolution affect the variability of measured dissolution rates. In this study a new approach to study the effect of surface dynamics on dissolution rates is tested by coupling experimental data with a numerical model that simulates the retreat of surface profiles during dissolution. We present specific results from the simulation of dissolution of fluorite surfaces. The equations that determine the retreat of a surface are based on experimentally obtained equations that relate the retreat rate of a surface to a single variable, the crystallographic orientation of the surface.Our results show that depending on the starting orientation, different types of topography are developed, similar to those observed experimentally. During the initial dissolution phase, changes of topography are rapid and associated with fast dissolution rates. The progressively slower dissolution rates are coupled with the development of surface segments with orientations that dissolve at a slower rate. Consequently, the overall retreat rate of a profile decreases during the simulation, and tends to a near-constant value. The results show a close relationship between dissolution rates, surface orientation and surface dynamics, which suggests that the dissolution rate of a specific mineral phase is not constant but varies with dissolution time and surface structure. This variability needs to be considered in the evaluation of experimentally derived dissolution rates, future dissolution experiments, and predictive kinetic models of dissolution.

A chemical kinetics algorithm for geochemical modelling

A chemical kinetics algorithm is presented for geochemical applications. The algorithm is capable of handling both equilibrium- and kinetically-controlled reactions in multiphase systems. The ordinary differential equations (ODEs) are solved using an implicit multistep backward differentiation formula (BDF) algorithm to ensure efficiency and stability when integrating stiff ODEs. An adaptive control scheme of the time step is adopted to guarantee small steps in steeper regions and large steps in smoother regions of the integration. Analytical derivatives of the reaction rates and species activities are used to permit the use of larger time steps, and to increase the robustness of the calculations. The chemical equilibrium calculations are performed using a Gibbs free energy minimisation algorithm, which is based on a trust-region interior-point method adapted with a watchdog strategy that yields quadratic rates of convergence near the solution. The chemical kinetics algorithm is applied to geochemical problems relevant to carbon storage in saline aquifers. The calculations assume aqueous, gaseous and mineral phases, where the kinetics of the water–gas–rock interactions are investigated. The results allow us to estimate the time frames at which brine of different salinities and supercritical CO2 attains equilibrium with a carbonate rock, as well as the amount of carbon dioxide trapped by solubility and mineralisation mechanisms.

Decomposition and Preconcentration Methods for the Determination of Pt, Pd, Re in Mineral Raw Materials

Nowadays the actual problem of geochemistry is a deep and complex processing of mineral raw materials. Data on the quantitative content of precious and rare metals in various types of ores and rocks are necessary. It stimulates the development and improvement of chemical analytical methods for determination of these elements. Such methods are not applicable without sample preparation stage. Preparation of samples for analysis is the decomposition and preconcentration of rare and precious metals from matrix of mineral raw materials. The sample preparation schemes of platinum, palladium and rhenium are described in this paper.

Geochemical problems of the behavior of phosphorus: A basis for the biogenic hypothesis of phosphorite formation

The most important problems of the phosphorite formation are considered. It is shown that phosphorus is a typical biogenic component, which is concentrated in the course of biogenic sulfate reduction at the mud stage of transformation of rocks highly enriched in organic matter due to acidification of solutions, while precipitation is stimulated by alkalinization of the interstitial and rock solutions by carbonates. The role of terrestrial source in the formation of phosphorite deposits is emphasized.

Efficient chemical equilibrium calculations for geochemical speciation and reactive transport modelling

Chemical equilibrium calculations are essential for many environmental problems. It is also a fundamental tool for chemical kinetics and reactive transport modelling, since these applications may require hundreds to billions equilibrium calculations in a single simulation. Therefore, an equilibrium method for such critical applications must be very efficient, robust and accurate. In this work we demonstrate the potential effectiveness of a novel Gibbs energy minimisation algorithm for reactive transport simulations. The algorithm includes strategies to converge from poor initial guesses; capabilities to specify non-linear equilibrium constraints such as pH of an aqueous solution and activity or fugacity of a species; a rigorous phase stability test to determine the unstable phases; and a strategy to boost the convergence speed of the calculations to quadratic rates, requiring only few iterations to converge. We use this equilibrium method to solve geochemical problems relevant to carbon storage in saline aquifers, where aqueous, gaseous and minerals phases are present. The problems are formulated to mimic the ones found in kinetics and transport simulations, where a sequence of equilibrium calculations are performed, each one using the previous solution as the initial guess. The efficiency and convergence rates of the calculations are presented, which require an average of 1–2 iterations. These results indicate that critical applications such as chemical kinetics and reactive transport modelling can potentially benefit by using this multiphase equilibrium algorithm.

NQR/NMR and Mössbauer spectroscopy of sulfides: potential and versatility

Nuclear quadrupole resonance (NQR), nuclear magnetic resonance (NMR) and nuclear gamma-resonance (NGR or Mossbauer Effect) methods are generally described as highly sensitive tools in studies of local electronic structure and symmetry in solid-state materials. This is due to high informativity in electronic structure investigations, high resolution in phase-structural diagnostics (down to nano-scale), possibility to study polycrystalline and complex compounds, and to the non-destructive character of these methods. As applied to Earth sciences, both NQR/NMR and Mossbauer spectroscopy methods contribute to mineralogical material science and mineral physics. Another important aspect is the fact that these methods, as demonstrated recently, belong to unique techniques suitable for on-line bulk mineralogical analysis. This includes remotely operated sensors used with conveyor systems in mining/materials handling and similar applications where real-time data collection/processing provides significant commercial benefits. These developments open new pathways for NQR/NMR and Mossbauer spectroscopy applications. Notably, NQR/NMR and Mossbauer effects are observed primarily on different nuclei-probes but provide similar information about the local properties of materials (hyperfine fields, electric field gradients and relaxation effects). This makes NQR/NMR and Mossbauer methods mutually complementary despite their significant technical differences. This paper includes examples of recent applications of NQR, NMR and Mossbauer spectroscopic tools to studies of copper-, antimony- and iron-containing sulfides, demonstrating how these methods can contribute to an improved understanding of geochemical problems.

Indirect uptake of atmospheric CO2 by the ocean

During the last ten years, the reasons for modern global climate warming have been actively discussed. Many scientists consider the strengthening of the greenhouse effect to be the result of СО 2 introduction into the atmosphere, which is formed by burning of fuel mineral. At the end of the twentieth century and beginning of the twentyfirst century, the volume of anthropogenic СО2 outburst reached 7 billion tons C per year, which corresponds to 1% of the total СО 2 in the Earth's atmosphere. Observations demonstrate a lower rate of СО2 concentration increase in the atmo� sphere, and it is considered that the ocean absorbs 30- 50% of the anthropogenic outbursts of carbon dioxide (8, 9). In addition, there are arguments supporting the opposite point of view, according to which the ocean does not absorb, but, on the contrary, releases СО2 into the atmosphere (2, 7). The solution of this contra� diction should determine the direction and intensity of СО 2 exchange between the atmosphere and the ocean, which also may be directly applied to one of the funda� mental problems of geochemistry related to the study of the geochemical cycle of carbon in the biosphere. As a rule, СО2 exchange between the ocean and the atmosphere is studied on the basis of measurements and calculations of flows at the water-air boundary, without account for one more onesided relationship, including the transport of atmospheric СО2 to the ocean through a number of processes occurring on land and in totality called land runoff in the broad sense of this term. In this study we make an attempt to consider the geochemical mechanism of this process and its quantitative characteristics. The estimations given below are based on calcula� tions of the geochemical carbon balance in the ocean (2) confirmed indirectly in (3). Although the character of geochemical information available does not allow us to apply the methods of mathematical statistics to determine the accuracy of estimations of carbon flows, their accuracy may be judged from comparison of the results of different works. Calculations of carbon flows (2) providing the most complete account of the terrig� enous carbon runoff are usually consistent with esti� mations of flow values obtained by other authors (10) within 30-50%, which may most likely be considered as their accuracy. The land runoff of dissolved and solid compounds is one of the main incoming positions of the carbon geochemical balance in the ocean, and various carbon forms have different geneses. Dissolved organic carbon and most of the sus� pended organic carbon are the products of photosyn� thesis of land plants using atmospheric СО2 trans� formed to one degree or another:

The 1st Conference on Contemporary Problems of Geochemistry

The 1st Conference on Contemporary Problems of Geochemistry