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Ryo Matsumoto - One of the best experts on this subject based on the ideXlab platform.
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The effect of H2O2 treatment on stable isotope analysis (δ13C, δ18O and Δ47) of various Carbonate Minerals
Chemical Geology, 2020Co-Authors: Naizhong Zhang, Akihiro Kano, Mang Lin, Keita Yamada, Qi Liu, Naohiro Yoshida, Ryo MatsumotoAbstract:Abstract In Carbonate isotopic measurements, H2O2 treatment is one of the most often used methods to remove organic matter contaminants from Carbonate Minerals for accurate analysis, but the interaction between H2O2 solution and Carbonate Minerals may also lead to analytical bias. In this study, we quantitatively tested the effect of H2O2 treatment for 7 types of Carbonate Minerals, and the influences on Δ47 values of calcium Carbonate are systematically discussed for the first time. Most samples presented Δ47 offsets within the 2-SD of our analytical precision, except the methane derived authigenic Carbonate (MDAC). The shift of Δ47 values in MDACs is attributed to the mixing effect of two types of Carbonate Minerals: original one and isotopically altered one, and the magnitude is determined by the differences of both δ13C and δ18O values between two endmembers. Regarding biogenic Carbonate tested here, the analytical bias of H2O2 treatment is relative small in δ13C and δ18O values, and therefore the shift of Δ47 values is statistically neglectable. The δ13C and δ18O values for most samples tested in this study became positive (up to +1.7‰) after H2O2 treatment. Apart from previously well discussed mechanisms, such as removal of organic contamination, isotopic fractionation during the partial dissolution and dissolution of isotopic distinct Carbonate compositions in the heterogeneous Minerals, we experimentally demonstrated carbon and oxygen isotopic exchanges between Carbonate Minerals and H2O2 solution for the first time. The δ13C and δ18O values of Carbonate were influenced by isotopic exchanges with atmospheric CO2 in the CO2-HCO3−-CO32− system and H2O in H2O2 solution, respectively. Rich transition metals in the authigenic Carbonate Minerals (e.g. MDAC, travertine), which catalyze H2O2 decomposition, can enlarge this effect by altering H2O isotopic compositions. Though the small shift of δ13C and δ18O in biogenic Carbonate observed here (up to 0.6‰) would not change scientific interpretations and conclusions in most of previous studies, cautions should be taken in the future. Based upon our new experimental results, we suggest using a buffered H2O2 solution (pH≈8) isolated from atmospheric CO2 to remove potential organic contaminations in biogenic Carbonate. For authigenic Carbonate, H2O2 treatment is not recommended. If necessary, decreasing the H2O2 concentration, shortening the reaction time, leaving the solution in a CO2-free environment, and adjusting the solution to a basic condition will improve the accuracy in isotopic analysis of these Minerals.
John Webb - One of the best experts on this subject based on the ideXlab platform.
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distribution of trace elements between Carbonate Minerals and aqueous solutions
Geochimica et Cosmochimica Acta, 1998Co-Authors: Donald J Rimstidt, Anna Balog, John WebbAbstract:Abstract The experimental distribution coefficients, K′d, for trace elements in Carbonate Minerals show a systematic pattern of behavior that differs from that expected if the distribution were controlled by equilibrium thermodynamics. Regression of experimental distribution coefficients, K′d, from the literature shows that they correlate well with the quotient of the solubility products of the trace element and host Carbonate. However, the slope of the correlation line differs from that predicted by equilibrium theory in a way that suggests that the experiments are affected by a kinetic process, whereby the trace element is incorporated into the growing Carbonate crystal at a rate that is either faster or slower than the incorporation of Ca. The correlations predict that the K′d for elements that form rhombdohedral Carbonates (e.g., Cd, Zn, Cu, Mn, etc.) is expressed by K ′ d =1.6 K MCO 3 K TrCO 3 0.57 for calcite and K ′ d =4.1 K MCO 3 K TrCO 3 0.57 for siderite. These correlations can be used to estimate the K′d values for cases where no experimental data are available, including for other phases and other temperatures. Thus, the experimental K′d values can be used to understand general trends in trace element behavior. Analysis of K′d for calcite shows that this mineral can effectively sequester a variety of toxic cations (e.g., Pb, Cd, Cu, etc.) from solution, so precipitation of calcite from contaminated solutions may provide an effective method of environmental remediation. On the other hand, values of K′d should be used with caution when interpreting ancient geochemical environments for Carbonates, because K′d values are strongly rate-dependent and the rates of mineral precipitation are seldom known.
Rolf S. Arvidson - One of the best experts on this subject based on the ideXlab platform.
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The dissolution kinetics of major sedimentary Carbonate Minerals
Earth-Science Reviews, 2001Co-Authors: John W. Morse, Rolf S. ArvidsonAbstract:Abstract Among the most important set of chemical reactions occurring under near Earth surface conditions are those involved in the dissolution of sedimentary Carbonate Minerals. These Minerals comprise about 20% of Phanerozoic sedimentary rocks. Calcite and, to a significantly lesser extent, dolomite are the major Carbonate Minerals in sedimentary rocks. In modern sediments, aragonite and high-magnesian calcites dominate in shallow water environments. However, calcite is by far the most abundant Carbonate mineral in deep sea sediments. An understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel CO 2 on climate, diagenesis of sediments and sedimentary rocks. It also has practical application for areas such as the behavior of Carbonates in petroleum and natural gas reservoirs, and the preservation of buildings and monuments constructed from limestone and marble. In this paper, we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century. Our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary Carbonate Minerals and solutions. We will not attempt to address the many applications of these results to such topics as mass transport of Carbonate components in the subsurface or the accumulation of calcium Carbonate in deep sea sediments. Such complex topics are clearly worthy of review papers on their own merits. Calcite has been by far the most studied mineral over a wide range of conditions and solution compositions. In recent years, there has been a substantial shift in emphasis from measuring changes in solution composition, to determine “batch” reaction rates, to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy (AFM). However, there remain major challenges in integrating these two very different approaches. A general theory of surface dissolution mechanisms, currently lacking (although see Lasaga and Luttge [Science 291 (2001) 2400]), is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components. Studies of aragonite, high-magnesian calcites, magnesite, and dolomite dissolution kinetics are much more limited in number and scope than those for calcite, and provide, at best, a rather rudimentary understanding of how these Minerals are likely to behave in natural systems. Although the influences of a limited number of reaction inhibitors have been studied, probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of “foreign” ions and organic matter on the near-equilibrium dissolution kinetics of Carbonate Minerals.
Randall T. Cygan - One of the best experts on this subject based on the ideXlab platform.
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A shell model for the simulation of rhombohedral Carbonate Minerals and their point defects
American Mineralogist, 2000Co-Authors: Diana K. Fisler, Julian D. Gale, Randall T. CyganAbstract:The electronic polarization of oxygen ions has been explicitly incorporated in a shell model to better simulate the structure of calcite and related rhombohedral Carbonate Minerals. Pair-potentials for Ca{sup 2+} ions and C and O comprising the Carbonate molecular ion were simultaneously fitted to experimental lattice, elastic, dielectric, and vibrational data for calcite, and the structure and elastic properties of aragonite. The resulting potential parameters for the CO{sub 3}{sup 2{minus}} group were then transferred to models for the structures and bulk moduli of the Carbonate Minerals incorporating Mn, Fe, Mg, Ni, Zn, Co, Cd, and thus a fully consistent set of interaction parameters for calculating the properties of the Carbonate Minerals was obtained. Defect energies for doping the divalent cations into the calcite structure, and for calcium and Carbonate ion vacancies were calculated. In addition, various disorder types for dolomite, including anti-site defects, stacking defects, stacking defects, and the energy related to increasing the Ca/Mg ration in the dolomite structure were simulated. The theoretical enthalpy for domomite ordering (34.4 kJ/mol) compares very well with experimental measurements.
Naizhong Zhang - One of the best experts on this subject based on the ideXlab platform.
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The effect of H2O2 treatment on stable isotope analysis (δ13C, δ18O and Δ47) of various Carbonate Minerals
Chemical Geology, 2020Co-Authors: Naizhong Zhang, Akihiro Kano, Mang Lin, Keita Yamada, Qi Liu, Naohiro Yoshida, Ryo MatsumotoAbstract:Abstract In Carbonate isotopic measurements, H2O2 treatment is one of the most often used methods to remove organic matter contaminants from Carbonate Minerals for accurate analysis, but the interaction between H2O2 solution and Carbonate Minerals may also lead to analytical bias. In this study, we quantitatively tested the effect of H2O2 treatment for 7 types of Carbonate Minerals, and the influences on Δ47 values of calcium Carbonate are systematically discussed for the first time. Most samples presented Δ47 offsets within the 2-SD of our analytical precision, except the methane derived authigenic Carbonate (MDAC). The shift of Δ47 values in MDACs is attributed to the mixing effect of two types of Carbonate Minerals: original one and isotopically altered one, and the magnitude is determined by the differences of both δ13C and δ18O values between two endmembers. Regarding biogenic Carbonate tested here, the analytical bias of H2O2 treatment is relative small in δ13C and δ18O values, and therefore the shift of Δ47 values is statistically neglectable. The δ13C and δ18O values for most samples tested in this study became positive (up to +1.7‰) after H2O2 treatment. Apart from previously well discussed mechanisms, such as removal of organic contamination, isotopic fractionation during the partial dissolution and dissolution of isotopic distinct Carbonate compositions in the heterogeneous Minerals, we experimentally demonstrated carbon and oxygen isotopic exchanges between Carbonate Minerals and H2O2 solution for the first time. The δ13C and δ18O values of Carbonate were influenced by isotopic exchanges with atmospheric CO2 in the CO2-HCO3−-CO32− system and H2O in H2O2 solution, respectively. Rich transition metals in the authigenic Carbonate Minerals (e.g. MDAC, travertine), which catalyze H2O2 decomposition, can enlarge this effect by altering H2O isotopic compositions. Though the small shift of δ13C and δ18O in biogenic Carbonate observed here (up to 0.6‰) would not change scientific interpretations and conclusions in most of previous studies, cautions should be taken in the future. Based upon our new experimental results, we suggest using a buffered H2O2 solution (pH≈8) isolated from atmospheric CO2 to remove potential organic contaminations in biogenic Carbonate. For authigenic Carbonate, H2O2 treatment is not recommended. If necessary, decreasing the H2O2 concentration, shortening the reaction time, leaving the solution in a CO2-free environment, and adjusting the solution to a basic condition will improve the accuracy in isotopic analysis of these Minerals.