The behavior of mineral mixtures can be significantly different from the behavior of the individual components of the mixture due to differences between the mechanical and chemical properties of the individual minerals, and their ensuing effects on interparticle interactions and fabric formation. This study examines mixtures of kaolinite and calcium carbonate at different mass fractions using sedimentation, viscosity, and liquid-limit tests. These macroscale tests represent a wide range of solid-volume fractions and strain levels, with emphasis on high water-content conditions to magnify the effects of electrical forces. The results demonstrate that interparticle interactions depend on mineral surface-fluid effects, particle geometry, relative particle size, and solids content. With small solids contents, the kaolinite/calcium carbonate mixture behavior is a function of electrostatic interactions between oppositely charged mineral particles that promote flocculation; however, with large solids contents, the specific surface area of the minerals is the controlling factor. These results are relevant to many natural soil environments and to the possible development of engineered mineral mixtures for industrial applications.

The oceans store a substantial fraction of carbon as calcium carbonate (CaCO3) and organic carbon (Corg) and constitute a significant component of the global carbon cycle. The Corg and CaCO3 flux depends on productivity and is strongly modulated by the Asian monsoon in the tropics. Anthropogenic activities are likely to influence the monsoon and thus it is imperative to understand its implications on carbon burial in the oceans. We have reconstructed multi-decadal CaCO3 and Corg burial changes and associated processes during the last 4.9 ky, including the Meghalayan Age, from the Gulf of Mannar. The influence of monsoon on carbon burial is reconstructed from the absolute abundance of planktic foraminifera and relative abundance of Globigerina bulloides. Both Corg and CaCO3 increased throughout the Meghalayan Age, except between 3.0–3.5 ka and the last millennium. The increase in Corg burial during the Meghalayan Age was observed throughout the eastern Arabian Sea. The concomitant decrease in the Corg to nitrogen ratio suggests increased contribution of marine organic matter. Although the upwelling was intense until 1.5 ka, the lack of a definite increasing trend suggests that the persistent increase in Corg and CaCO3 during the early Meghalayan Age was mainly driven by higher productivity during the winter season coupled with better preservation in the sediments. Both the intervals (3.0–3.5 ka and the last millennium) of nearly constant carbon burial coincide with a steady sea-level. The low carbon burial during the last millennium is attributed to the weaker-upwelling-induced lower productivity.

The effect of freshwater sources on wintertime sea-ice CO2 processes was studied from the glacier front to the outer Tempelfjorden, Svalbard, in sea ice, glacier ice, brine and snow. March–April 2012 was mild, and the fjord was mainly covered with drift ice, in contrast to the observed thicker fast ice in the colder April 2013. This resulted in different physical and chemical properties of the sea ice and under-ice water. Data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in April 2012 contained on average 54% of frozen-in glacial meltwater. This was five times higher than in April 2013, where the ice was frozen seawater. In April 2012, the largest excess of sea-ice total alkalinity (AT), carbonate ion ([CO32−]) and bicarbonate ion concentrations ([HCO3−]) relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral-enriched glacial water. In April 2013, the excess of these variables was mainly due to ikaite dissolution as a result of sea-ice processes. Dolomite dissolution increased sea-ice AT twice as much as ikaite and calcite dissolution, implying different buffering capacity and potential for ocean CO2 uptake in a changing climate.

Accurate radiocarbon (14C) dating of lime mortars requires a thorough mineralogical characterization of binders in order to verify the presence of carbon-bearing contaminants. In the last 20 years, cathodoluminescence (CL) has been widely used for the identification of geologic calcium carbonate (CaCO3) aggregates and unreacted lime lumps within the particle size fraction selected for carbon recovery. These components are major sources of older and younger carbon, respectively, and should be removed to obtain accurate age determinations. More recently, laser-induced fluorescence (LIF) has provided another means of investigating the preservation state and composition of CaCO3 binders. Considered the growing interest of the mortar dating community in the latest advancements of these analytical methods, here we review the principles of CL and LIF of CaCO3, their instrument setup, and their application to the characterization of ancient lime mortars used for 14C dating. In addition, we provide examples of SEM-CL and LIF analyses using high-resolution instrumentation, we discuss current issues and propose future lines of research.

Chagas disease is a public health problem, affecting about 7 million people worldwide. Benznidazole (BZN) is the main treatment option, but it has limited effectiveness and can cause severe adverse effects. Drug delivery through nanoparticles has attracted the interest of the scientific community aiming to improve therapeutic options. The aim of this study was to evaluate the cytotoxicity of benznidazole-loaded calcium carbonate nanoparticles (BZN@CaCO3) on Trypanosoma cruzi strain Y. It was observed that BZN@CaCO3 was able to reduce the viability of epimastigote, trypomastigote and amastigote forms of T. cruzi with greater potency when compared with BZN. The amount of BZN necessary to obtain the same effect was up to 25 times smaller when loaded with CaCO3 nanoparticles. Also, it was observed that BZN@CaCO3 enhanced the selectivity index. Furthermore, the cell-death mechanism induced by both BZN and BZN@CaCO3 was evaluated, indicating that both substances caused necrosis and changed mitochondrial membrane potential.

Echinoderms are vulnerable to ocean acidification because of their high magnesium calcite skeletons. Here, skeletal Mg/Ca ratios were examined within and between individuals of 20 Antarctic echinoderms representative of the asteroids, ophiuroids and echinoids. The highest mean Mg/Ca ratios occurred in the discs and arms (0.111 and 0.110, respectively) of brittle-stars and the lowest in the spines (0.010) of cidaroid sea urchins. Many taxa (11 of 14 species) from the collection sites showed no intraspecific differences in Mg/Ca ratios between given skeletal components. Exceptions were the spines of two regular sea urchins and the skeletal ossicles of the combined arms and disc of a brittle-star. The relationship between skeletal magnesium content and latitude was further evaluated and an inverse correlation was found between Antarctic echinoderm taxa skeletal magnesium content and latitude across 62° to 76°, indicating that the relationship occurs over relatively narrow latitudes. Upon examination of an even narrower range (70–76° latitude), a region where the mineralogy of echinoderm skeletons has not been investigated, the predicted inverse relationship between Mg/Ca ratio and latitude was still observed in sea-stars, but not in brittle-stars or sea urchins.

The present paper investigates standing stock variations of Halimeda opuntia on a sandstone reef of the South-west Atlantic Ocean, in order to better understand the role of this seaweed as a CaCO3 producer. The study was conducted over two 3-month periods, using photo quadrats to analyse the coverage area, and destructive sampling to quantify area-specific biomass and CaCO3 percentage. The alga occupied 2.4% of the substrate (4464 m2), growing as clumps with an average biomass of 1.59 kg m−2, resulting in a standing stock of 7097.8 kg of alga. This standing stock varied with environmental conditions, particularly wind speed. Assuming an exponential model for these variations, H. opuntia produced at least 13,050.14 kg (54.37 g m−2 day−1) of carbonate sediments. There was a positive correlation between changes in standing stock and coverage, but not with area-specific biomass. This suggests that net algal growth results in the occupation of new spaces, with minimal increases in height or segment density. Therefore monitoring coverage should complement traditional individual-based methods for estimating Halimeda growth and production. Combined, these approaches should result in more accurate models of the role of this alga on marine carbonate budgets.

Electron Rutherford backscattering (ERBS) is a new technique that could be developed into a tool for materials analysis. Here we try to establish a methodology for the use of ERBS for materials analysis of more complex samples using bone minerals as a test case. For this purpose, we also studied several reference samples containing Ca: calcium carbonate (CaCO3) and hydroxyapatite and mouse bone powder. A very good understanding of the spectra of CaCO3 and hydroxyapatite was obtained. Quantitative interpretation of the bone spectrum is more challenging. A good fit of these spectra is only obtained with the same peak widths as used for the hydroxyapatite sample, if one allows for the presence of impurity atoms with a mass close to that of Na and Mg. Our conclusion is that a meaningful interpretation of spectra of more complex samples in terms of composition is indeed possible, but only if widths of the peaks contributing to the spectra are known. Knowledge of the peak widths can either be developed by the study of reference samples (as was done here) or potentially be derived from theory.

Calcium carbonate crystals were prepared via a simple precipitation reaction of sodium carbonate with calcium chloride from mixed solutions of various amphiphilic organic solvents and water in the presence of cetyltrimethylammonium bromide at 25 and 60 °C. Our analysis shows that amphiphilic organic solvents and temperature have large influences on the structure and morphology of CaCO3. X-ray diffraction patterns show that single-phase hexahedral calcite was formed at 25 °C, and orthorhombic aragonite was obtained at 60 °C. Mixtures of major amounts of long aragonite crystals and minor amounts of calcite particles were also obtained at 60 °C in the methanol and the acetone solutions. Scanning electron microscopy images show that CaCO3 particles and aggregates with various morphologies, such as large solid and hollow hexahedral crystals and small round granules of calcite as well as glass-like and wheat-like aggregates of aragonite, were obtained depending on the experimental conditions. Based on the experimental results, a conclusion on the effects of temperature and amphiphilic organic solvents on the crystal structure and morphology are made.

Although bone metabolism is largely under genetic control, the role of nutrition is considerable. The present study evaluates the effects of chicken eggshell powder, a new source of dietary Ca, and purified CaCO3 on bone mineral density (BMD) of the lumbar spine and hip. Besides BMD we also looked at biochemical markers of bone and Ca metabolism. Both Ca sources were provided in combination with minerals and vitamins including Mg, cholecalciferol and phylloquinone. We designed a randomised, double-blind, placebo-controlled study to take place over 12 months. Healthy Caucasian women (n 85), selected by age (≥50 and <70 years), from the databases of general practitioners were recruited by telephone calls. They had to be at least 5 years post-menopausal, with lumbar spine T-score being >-2·5. At baseline, their mean habitual daily Ca intake was adequate. The women were randomly allocated to: eggshell powder-enriched (group A; n 24), purified CaCO3-enriched (group B; n 22), or a placebo product (group C; n 27). BMD was measured at baseline and then after 6 and 12 months of supplementation as were the biochemical markers bone-specific alkaline phosphatase, amino-terminal propeptide extension of type I collagen, deoxypyridinoline, calcitonin, intact parathyroid hormone, calcidiol, and urinary Ca. After 12 months of supplementation, only mean BMD of the femoral neck in group A was significantly increased (P=0·014) by 1·75 % (95 % CI 0·18, 3·32) compared with a decrease of -0·60 % (95 % CI -1·92, 0·72) in group C. This increase coincided with significant decreases in markers of bone resorption and formation. No significant changes were seen in BMD at other sites, including lumbar spine, nor in groups B and C. No differences were found between groups A and B, or B and C. The present study indicates that healthy late post-menopausal women with an adequate Ca intake at baseline may increase BMD of the hip within 12 months following supplementation with the chicken eggshell powder-enriched supplement.