Calcitic Materials Research Articles

Site-specific interactions enhanced dissolution of natural aragonite (110) surfaces in succinic acid (SUC) solutions: Implications for the oceanic aragonite dissolution fluxes

Aragonite, one of the most common biological calcium carbonate minerals, is widespread in marine plankton and neritic sediments (e.g., accounting for 89% of pelagic calcification of CaCO3 in the surface ocean). Its dissolution directly affects the export fluxes of CaCO3 in seawater. The aragonite dissolution in the ocean correlates with the increase of partial pressure of carbon dioxide and is pertinent to acidic biomolecules. However, aragonite dissolution in seawater with acidic biomolecules has been overlooked, and the interaction mechanism is unclear. In-situ atomic force microscopy (AFM) was employed to observe the dissolution features of aragonite (110) growth surfaces in succinic acid (SUC, HOOC-CH2-CH2-COOH) solutions. The results demonstrate that (1) both the morphologies and spreading rates of the etch pits formed on aragonite (110) surfaces are altered by the interactions between SUC molecules and the surfaces; (2) the [11‾1] and [1‾11] steps of the etch pits on aragonite (110) surfaces in SUC solutions are kinetically controlled; (3) dissolution rates of aragonite (110) surfaces are proportional to SUC concentrations, which is attributed to the strong complexation between SUC molecules and surface-bounded Ca atoms (≡Ca+); (4) etch pits morphologies of aragonite (110) and calcite (10.4) surfaces are different in SUC solutions, and the spreading rates of the etch pits of the former are one to two orders of magnitude lower than those of the latter. Furthermore, aragonite is found to be more sensitive to SUC molecules than calcite, suggesting that dissolving aragonitic materials could be more easily affected by circumambient biomolecules than dissolving calcitic materials. In seawater that contains organic molecules, the dissolution fluxes of aragonite could be much slower than those of calcite. These findings not only reveal the site-specific interactions between SUC molecules and the ≡Ca+ on aragonite (110) surfaces but also emphasize its implication for the oceanic aragonite dissolution fluxes.

The Protection of Building Materials of Historical Monuments with Nanoparticle Suspensions

Marble and limestone have been extensively used as building materials in historical monuments. Environmental, physical, chemical and biological factors contribute to stone deterioration. The rehabilitation of stone damage and the delay of further deterioration is of utmost importance. Inorganic nanoparticles having chemical and crystallographic affinity with building materials is very important for the formation of protective coatings or overlayers. In the present work, we have tested the possibility of treating calcitic materials with suspensions of amorphous calcium carbonate (am-CaCO3, ACC) and amorphous silica (AmSiO2). Pentelic marble (PM) was selected as the test material to validate the efficiency of the nanoparticle suspension treatment towards dissolution in undersaturated solutions and slightly acidic pH (6.50). Suspensions of ACC and AnSiO2 nanoparticles were prepared by spontaneous precipitation from supersaturated solutions and by tetraethyl orthosilicate (TEOS) hydrolysis, respectively. The suspensions were quite stable (nine days for ACC and months for AmSiO2). ACC and Am SiO2 particles were deposited on the surface of powdered PM. The rates of dissolution of PM were measured in solutions undersaturated with respect to calcite at a constant pH of 6.50. For specimens treated with ACC and AmSiO2 suspensions, the measured dissolution rates were significantly lower. The extent of the rate of dissolution reduction was higher for AmSiO2 particles on PM. Moreover, application of the nanoparticles on the substrate during their precipitation was most efficient method.

Indicators of lime reactivity in soil: particle size, carbon dioxide evolution, and citric acid titration

ABSTRACT Accurate predictions of the short-term reactivity of liming products are needed for situations where rapid soil pH adjustment is desired. Lime efficiency (LE) describes the capacity of a liming material to neutralize soil acidity in comparison with a finely ground CaCO3 standard (LE = 100%). Our objectives were to evaluate LE for calcitic liming materials varying in particle size at 1–12 months after soil incorporation using pH change (LEpH) and CO2 evolution (LECO2) as response indicators, and to evaluate a 15-min citric acid (CA) test as a predictor of LE. We evaluated LE for lime particle size separates from 10 to 200 USA mesh (< 2000 µm to 75 µm) and for three commercial liming products (65, 25 and 11 µm average particle size) in a sandy loam soil. In field microplots, it took 6 months to achieve LE of > 80% with lime particles of <60 mesh (< 250 µm). LEpH was linearly related to LECO2 at one month following lime incorporation into soil. Both LEpH and LECO2 increased as a function of CA test values, as described by logarithmic equations. Lime particle size, CO2 evolution, and CA test values were all useful indicators of short-term LE.

Short-term effect of forest liming on eastern red-backed salamander (Plethodon cinereus)

Liming, the application of calcitic materials to soil, is increasingly used in acidic, base-poor sugar maple stands of eastern North America to restore nutritional status and vigor of sugar maple trees. However, few studies have evaluated the effect of base cation addition on other components of these ecosystems. The eastern red-backed salamander (Plethodon cinereus) is one of the most abundant vertebrates in forests of eastern North America, and is commonly used as an indicator of forest disturbances. So, it is important to know how it might be affected by soil liming. This is the first study dealing with the potential direct and short-term effect of liming on amphibians of North America.Lime, in the form of CaCO3 (3Mgha−1), was added at the surface of microcosms containing a low buffered soil and forest floor from a sugar maple stand to evaluate the short-term effect of this treatment on this amphibian species. Two grades of lime were used in this study: finely ground and sandy CaCO3. Finely powdered lime was included to verify if it could clog salamander skin pores, since this could negatively affect health and growth, and consequently induce mortality. The results suggest that, even when applied in finely ground form, direct contact with lime had no short-term effect on the species’ health and survival rate. Given this, and the fact that it can be found in a wide range of soil pH conditions, the red-backed salamander is thus unlikely to be affected by the use of liming to restore acidic, base-poor sugar maple bushes. Some old liming trials carried out in forests of eastern North America could be used in the next years to verify the long-term effects of liming on this species. This should help foresters decide whether or not liming treatments are compatible with conservation, ecological and management objectives.

Distinguishing between calcites formed by different mechanisms using infrared spectrometry: archaeological applications

Infrared spectrometry is a well-established method for the identification of minerals. Due to its simplicity and the short time required to obtain a result, it can be practiced on-site during excavation using portable infrared spectrometers. However, the identification of a mineral may not be sufficient. For example, a lime plaster floor and a crushed chalk surface have a similar appearance and are composed of the same mineral – calcite. Here we exploit differences in the infrared spectra of geogenic, biogenic and pyrogenic calcites for the identification of each calcite type. The infrared calcite spectrum has three characteristic peaks in the region of 400–4000 cm −1, designated ν 2, ν 3, and ν 4. When a calcite sample is ground, as part of the measurement preparation procedure, some grinding dependent changes will be revealed in the infrared spectrum. With additional grinding, the ν 3 peak narrows and the heights of the ν 2 and ν 4 peaks decrease, when both are normalized to the ν 3 height. By plotting the normalized heights of the ν 2 versus the ν 4 of several grindings of the same sample, a characteristic trend line is formed for each calcite type. The trend lines of geogenic calcites have the shallowest slopes and highest ν 4 values when compared to pyrogenic calcites, which can be further divided to ash and plaster/mortar samples. This method can assist in distinguishing between the various calcites, and provide insights into homogeneity and preservation state of the calcitic materials in question.

Initial stages of carbonate weathering: climate chamber studies under realistic pollution conditions

Climate chamber studies how to be a reasonable tool for the investigation of alteration processes of natural stones, especially of carbonates. Even though the concentration of SO2 in the atmosphere is decreasing since years, until today, most of the studies focused on the role of S-compounds which had to be considered the major damaging immission component. Contrary to SO2 the concentrations of NOx and especially ozone, primarily due to traffic exhaust, is still increasing today. The role of ozone as an oxidant of NO to NO2 and SO2 to SO3 as well as its role at the formation of sulphate on calcitic materials has already been subject of some studies. Typically these experiments were performed at accelerating testing conditions by using gas concentration considerably above realistic immission values. In this study we pursued a different experimental strategy. The concentrations of NO2, SO2 and O3 employed have been oriented on realistic average values (corresponding to the max. mean half hour value in Austria measured in 2003): 0.150 to 0.200 ppm for NOx and SO2 and about 0.120 ppm for ozone. The major aim of this contribution is answering the following questions:

Inorganic coatings for the protection of marble surfaces from deterioration

The dissolution of marble, a calcitic natural stone is an important cause contributing to the weathering process of the building materials of monuments, statues and other artefacts of cultural heritage. Protection against dissolution may be effected either through the use of water soluble additives or by the development of coatings of sparingly soluble salts of inhibitors of dissolution with calcium. In the present study coatings were prepared by the reaction of anions known to protect marble against dissolution: phosphate, phosphonate and oxalate anions were used in acidic media for the development of the respective calcium salts. The present study is a contribution both to understanding the presence of coatings found on ancient monuments and to the development of novel methods for the protection of calcitic materials. For the phosphoric acid treatment, the increase of the calcium concentration resulted in the re-precipitation of the calcium phosphate dehydrate phase forming coatings of 100 ?m converting to the less acidic octa-calcium phosphate. The efficiency towards dissolution was demonstrated with dissolution kinetic experiments at constant undersaturation, which showed partial dissolution of the calcium phosphate coating. The use of (1-hydroxyethylidene)- 1,1 diphosphonic acid (HEDP) both in solution and in the form of coatings also resulted in reduced rates of dissolution for Pentelic marble slabs. Two different calcium-diphosphonate salts were formed depending on the appliced pH. Finally, oxalic acid treatment resulted in the formation of a layer of calcium oxalate monohydrate. The independence of the solubility of this salt on pH makes it a good candidate for the protection of marble against dissolution in polluted environment.

Low-loss Electron Energy-loss Spectroscopy and Dielectric Function of Biological and Geological Polymorphs of CaCO(3).

: Previous work on microstructural characterization has shown variations in terms of defects and organization of nanostructures in the two polymorphs of calcium carbonate, calcite, and aragonite in mollusc shells. Large variations in mechanical properties are observed between these sections which have been attributed to variations in composite microstructure as well as intrinsic properties of the inorganic phases. Here we present local low-loss electron energy-loss spectroscopic (EELS) study of calcitic and aragonitic regions of abalone shell that were compared to geological (single-crystal) counterpart polymorphs to reveal intrinsic differences that could be related to organismal effects in biomineralization. In both sets of samples, local dielectric function is computed using Kramer-Kronig analysis. The electronic structures of biogenic and geological calcitic materials are not significantly different. On the other hand, electronic structure of biogenic aragonite is remarkably different from that of geological aragonite. This difference is attributed to the increased contribution from single electron excitations in biogenic aragonite as compared to that of geological aragonite. Furthermore, an apparent bound characteristic of the Re(1/epsilon) is observed for biological samples which suggests a "quasi-plasmon"-like nature of the collective excitations. Implications of these changes are discussed in the context of macromolecular involvement in the making of the microstructures and properties in biogenic phases.

Fracture Toughness and Interfacial Design of a Biological Fiber‐Matrix Ceramic Composite in Sea Urchin Teeth

The working zone of a sea urchin tooth is a ceramic‐fiber‐reinforced ceramic‐matrix composite. It is composed of reinforcing calcitic fibers, a matrix of high‐magnesium‐containing calcite crystals, and organic material. It is much harder and tougher than most other calcitic materials. Fracture toughness and microhardness have been studied using microindentation. A comparison of fracture morphologies between intact teeth and teeth from which the organic component has been removed reveals that the thin organic sheath at the fiber/matrix boundary has an important contribution to the fiber pull‐out fracture behavior and, hence, to the toughness of the teeth.

Isotopic Composition and Diagenetic Alteration of Lower Carboniferous Brachiopod Shells: Constraints from Proton Microprobe (PIXE) Trace Element Analysis

The chemical and isotopic evolution of ocean water mirrors the dynamics of the earth system. Information concerning seawater isotopic composition and its chemistry is derived from rock components that have precipitated in equilibrium with ambient seawater. For a correct interpretation of isotope data, samples that have suffered a l tera t ion by diagenetic processes must be avoided. Trace element analysis is frequently utilized as a diagnostic tool. Unfortunately, conventional techniques, such as AAS or ICP, frequently require more sample than is available or yield only a bulk mean composition (Veizer et aL, 1987). Furthermore, for most ancient calcitic materials, the concentrations for the elements of interest (e.g. Mn, Fe, Sr) are generally below the detection limit of standard electron microprobes (cf. Riciputti et al., 1994). A microanalytical tool is therefore required that combines low detection limits with high lateral resolution. In this study, t r a c e e l e m e n t c o m p o s i t i o n s o f L o w e r Carboniferous brachiopod shell fragments were analysed using the Bochum proton microprobe. The data are compared to the ICP 'bulk' analyses and the 8180 data of a number of fragments prepared from the same shells.

A pH‐Stat Procedure for Evaluating Reactivity of Agricultural Limestone

AbstractLimestone dissolution occurs as a surface reaction; therefore, the particle‐size distribution of the material influences its reactivity. Particle‐size distribution alone, however, may not provide a good comparative index of reactivity because of differences in mineralogy, surface composition, and morphology. A pH‐stat titration procedure was previously developed to determine the “effective” reactivity of soil carbonate. The objective of this study was to evaluate the pH‐stat procedure as a method for comparing the reactivities of liming materials. Eighteen liming materials, representing a wide range of physical and chemical properties, were analyzed. The relative reactivities of the materials are expressed as Iceland‐spar reactivity equivalent (ISRE), and reported as particle‐size distribution (ISRE‐PSD) or surface area (ISRE‐SA) of a standard Iceland‐spar calcite that has the equivalent quantity and reactivity as the sample. The ISRE‐PSD of the calcitic materials gave higher proportions of fine‐clay‐size particles than were obtained by sieving and sedimentation, indicating that the calcitic liming materials had greater surface reactivities than the Iceland‐spar calcite standard. The dolomitic materials, being less reactive than the calcitic materials, exhibited large proportions of ISRE fine‐sand‐size particles and small proportions of ISRE clay‐size particles. Calculations of surface area using ISRE‐PSD data provide a more explicit index of reactivity than the ISRE‐PSD. The ISRE‐SA values of the calcitic and dolomitic materials were not highly correlated with surface areas determined by the Brunauer‐Emmett‐Teller (BET) or sedimentation procedures, indicating the pH‐stat procedure provides a method for comparing the reactivities of liming materials not possible by BET, sieving, or sedimentation methods.

Control of SOx emissions by in‐furnace sorbent injection: Carbonates vs. hydrates

AbstractHigh temperature, isothermal data on SO2 capture by calcium based sorbents were obtained in a dispersed‐phase reactor for limestons, dolomites, hydrated calcitic limes, and hydrated dolomitic limes as a function of Ca/S molar ratio, temperature, and SO2 partial pressure. The experimental results indicate that SO2 capture is approximately linearly dependent on Ca/S molar ratio and relatively insensitive to SO2 partial pressure above 2000 ppm. SO2 capture is a strong function of general sorbent class; dolomitic sorbents are better than calcitic materials on an equivalent calcium basis and hydrated materials are more reactive than carbonates. Computer model predictions based on a grain formulation, available fundamental rate data, and measured surface areas accurately predict limestone performance; however, predicted capture for the hydrated sorbents is significantly below that measured experimentally. The measured capture results do, however, generally correlate with the BET surface areas measured when the sorbents were calcined in a muffle furnace at 980 K for 20 minutes with an inert environment.