Chemical Controls on the Dissolution Kinetics of Calcite in Seawater

Inorganic carbon dynamics in coastal marine systems

Storage of carbon dioxide (CO2) by precipitation of carbon-bearing minerals in geological formations is, on the long run, more stable and therefore much safer than direct storage or solution trapping. Among available options for CO2 sequestration that are particularly attractive are those that offer additional economic benefits apart from the primary positive effect for the atmosphere (e.g., enhanced gas or oil recovery), such as the novel approach of storing dissolved CO2 as calcite in managed geothermal aquifers. Hydrogeothermal energy in Germany is mainly provided from deep sandstone aquifers by a so-called doublet installation consisting of one well for hot water production and one well for injection of the cooled water. When cold brines are enriched with CO2 and injected into an anhydrite-bearing reservoir, this mineral dissolves. As a result, the water becomes enriched in calcium ions. Numerical simulations demonstrate that dissolved Ca and CO2 react to form and precipitate calcium carbonate provided that alkaline buffering capacity is supplied from plagioclase in the reservoir rock or by surface water treatment with fly ashes. We show that anhydrite dissolution with the concurrent pore-space increase is important to balance pore-space reduction by precipitation of calcite and secondary silicates. Laboratory experiments prove the feasibility of transforming anhydrite into calcite and provide necessary kinetic input data for the modeling. Suitable geothermal reservoirs exist, which contain sufficient anhydrite as matrix mineral and plagioclase for supplying alkalinity. Mass balance calculations performed with respect to the anhydrite and feldspar content show that, for an assumed operation time of 30 yr, the theoretical storage capacity is significant: millions of tons of CO2 can be trapped as calcite in geological formations used by geothermal heating plants.

The effect of pCO2 on carbon acquisition and intracellular assimilation was investigated in the three bloom-forming diatom species, Eucampia zodiacus (Ehrenberg), Skeletonema costatum (Greville) Cleve, Thalassionema nitzschioides (Grunow) Mereschkowsky and the non-bloom-forming Thalassiosira pseudonana (Hust.) Hasle and Heimdal. In vivo activities of carbonic anhydrase (CA), photosynthetic O2 evolution, CO2 and HCO3? uptake rates were measured by membrane-inlet mass spectrometry (MIMS) in cells acclimated to pCO2 levels of 370 and 800 ?atm. To investigate whether the cells operate a C4-like pathway, activities of ribulose-1,5-bisphosphate carboxylase (RubisCO) and phosphoenolpyruvate carboxylase (PEPC) were measured at the mentioned pCO2 levels and a lower pCO2 level of 50 ?atm. In the bloom-forming species, extracellular CA activities strongly increased with decreasing CO2 supply while constantly low activities were obtained for T. pseudonana. Half-saturation concentrations (K1/2) for photosynthetic O2 evolution decreased with decreasing CO2 supply in the two bloom-forming species S. costatum and T. nitzschioides, but not in T. pseudonana and E. zodiacus. With the exception of S. costatum, maximum rates (Vmax) of photosynthesis remained constant in all investigated diatom species. Independent of the pCO2 level, PEPC activities were significantly lower than those for RubisCO, averaging generally less than 3%. All examined diatom species operate highly efficient CCMs under ambient and high pCO2, but differ strongly in the degree of regulation of individual components of the CCM such as Ci uptake kinetics and extracellular CA activities. The present data do not suggest C4 metabolism in the investigated species.

Carbonic anhydrase catalyzed bio-sequestration of CO2 to form HCO3-, followed by trapping as solid CaCO3 is one of the most promising technologies for CO2 capturing. The effects of reaction condition on the CO2 hydration using free carbonic anhydrase were systematically investigated. In order to improve the stability of the enzyme and facility its recycling, the carbonic anhydrase was in situ encapsulated inside hollow fibers via a novel co-axial electrospinning technology. Compared with the free enzyme, the immobilized carbonic anhydrase showed much improved thermal stability and suffered much reduced inhibitory effects from cation ions, such as Cu2+ and Fe3+. After 11 reuses, the immobilized enzyme retained about 81.9% of its original activity by comparing the amount of formed CaCO3 precipitation. In the presence of immobilized carbonic anhydrase, both calcite and vaterite CaCO3 solid were formed; while in the absence of enzyme or with free carbonic anhydrase, only calcite CaCO3 was observed.

This paper summarizes the results of an investigation on carbon dioxide (CO2) sequestration in concrete. Carbon dioxide (CO 2 ) is the predominant greenhouse gas resulting from human industrial Activities. A significant fraction of CO 2 discharged into the atmosphere comes from Industry point sources. Cement production alone contributes approximately 5% of global CO 2 emissions. This emitted carbon dioxide, however, can be partially recycled into concretes through early age curing to form thermodynamically stable calcium carbonates. The carbonation reaction between carbon dioxide and appropriate calcium Compounds results in permanent fixation of the carbon dioxide in a thermodynamically stable calcium carbonate. Carbon dioxide and water can be found in almost every environment and thus all concretes will be subjected to carbonation. This paper summarizes a recent study on optimization of concrete and the flue gas carbon dioxide collected from cement kiln can be beneficially utilized in concrete production to reduce carbon emission, accelerate early strength, and improve durability of the products. Cement industry contributes to 5% of global CO2 emissions. To mitigate pollution, there is a need of CO2 sequestration into stable forms. Present research focusses on CO2 being channelized towards an important construction practice. This paper summarizes the potential of CO2 absorption in concrete. In reference to cement content, carbon uptake in 4-hour carbonation reaches 28 days strength achieved by conventional curing method.

Controls on the Sulfur Isotopic Composition of Carbonate-Associated Sulfate

The CaCO3 content in Quaternary deep-sea sediments from Pacific and Atlantic oceans have been suggested to respond differently to glacial/interglacial cycles; CaCO3 contents are highest during glacials in the Pacific but highest during interglacials in the Atlantic Ocean. It is not yet clear as to whether a Pacific or an Atlantic pattern of CaCO3 fluctuations dominates the Indian Ocean. We have analyzed the Ocean Drilling Program (ODP) Site 709A from the western equatorial Indian Ocean for the last 1370 ka to determine the relationships between percentages and fluxes of CaCO3 and Quaternary paleoclimatic changes. We also analyzed the coarse (>25 µm) and fine (<25 µm) fractions of CaCO3 in an attempt at estimating the influence of differences in productivity of foraminifera and calcareous nannofossils in shaping the CaCO3 record. Carbon isotopes and Ba/Al ratios were used as indices of productivity. Percentages and fluxes of CaCO3 in the total sediment and <25 µm fraction do not show any clear relationships to glacial/interglacial cycles derived from d18O of the planktonic foraminifera Globigerinoides ruber. This indicates that CaCO3 fluctuations at this site do not show either a Pacific or an Atlantic pattern of CaCO3 fluctuations. Fluxes of CaCO3 (0.38 to 2.46 g/cm**2/ ka) in total sediment and Ba/Al ratios (0.58 to 3.93 g/cm**2/ka) show six-fold variability through the last 1370 ka, which points out that productivity changes are significant at this site. Fluxes of the fine CaCO3 component demonstrate a 26-fold change (0.02 to 0.52 g/cm**2/ka), whereas the coarse CaCO3 component exhibit eight-fold change (0.13 to 1.07 g/cm**2/ka). This suggests that productivity variations of calcareous nannofossils are greater in comparison with the foraminifera. On the other hand, mean values of coarse CaCO3 fluxes are higher compared to those of fine CaCO3, which reveals that the foraminifera contribute more to the bulk CaCO3 flux than the calcareous nannofossils in the equatorial Indian Ocean.

Removal and Recovery of Phosphonate Antiscalants

Antacids have been widely used in the treatment of various gastric and duodenal disorders such as heartburn, reflux esophagitis, gastritis, irritable stomach, gastric and duodenal ulcers. A pH-responsive of bi-polymer of sodium alginate and pectin have been studied as raft-forming polymers using sodium bicarbonate and calcium carbonate as gas-generating and calcium ion sources. The aim of study was to formulate and evaluate mono and bilayer tablets of floating and sustained release antacid delivery systems using sodium carboxy methyl cellulose as a gel forming substance, calcium and magnesium carbonate as sources of acid neutralizing and carbon dioxide gas generators agents upon contact with acidic solution. The effect of the formulation contents on the buoyancy has been investigated. In addition to, the antacid activities of intact and pulverized tablets have been studied. The result obtained showed that the buoyance is remarkably affected by the percentages of sodium carboxy methyl cellulose and carbonates salts. All formulas of mono and bilayer tablets revealed sustained action of acid neutralization and raft formation. Besides, bilayer tablets showed a significant and higher level of acid neutralizing capacity than monolayer tablets. Moreover, the pulverized of bilayer tablets exhibited significant and higher acid neutralizing capacity at raft than that at bulk of artificial gastric juice medium. Keywords: Raft forming agent, Antacid, floating drug delivery, Acid neutralizing capacity, Sodium carboxy methyl cellulose.

Microalgal biomass cultivated in wastewater has the potential for refining to energy products such as biodiesel and biohydrogen with the additional benefit of also treating the wastewater. As many species of microalgae can employ both Heterotrophic and Autotrophic modes of carbon synthesis, low-carbon waters benefit from the addition of inorganic carbon to the water. Capital and operational costs are a deterrent to using CO2 and other alternatives may be more attractive. NaHCO3 is a popular alternative but as a result of its solubility and alkalinity quickly raises the pH of the water which inhibits algal growth due the presence of free ammonia at high pH values. In this experiment, the growth of a South African strain of Desmodesmus multivariabilis was studied in the presence of solid calcium carbonate. Calcium carbonate was chosen for its low solubility, which would potentially allow for its dissolution to be driven by the inorganic carbon uptake in the media. The performance was compared to that of aerated wastewater and wastewater with solid CaSO4 as a non-carbon-containing substitute. It was found that there were significant differences in the growth and metabolism of all three experiments. Growth in the presence of solid calcium carbonate and calcium sulphate showed a preference for attached growth in the vicinity of solids, while suspended growth was preferred when just air was supplied. Furthermore, the experiment with air showed the highest growth rate, nitrogen uptake and a biomass yield that was more than an order of magnitude higher than with CaCO3. The experiment with CaSO4 showed low yields and growth rates, possibility indicating and inhibitory effect of the CaSO4. In the presence of CaCO3, a very high yield of extracellular organic metabolites was observed. The presence of these metabolites, as well as the stability of the pH and low growth, is a possible indication that the organism was controlling the pH as a defence mechanism. Despite not being a favourable substrate for growing D. multivariabilis, the high yield of extracellular metabolites may have a commercial potential, and the nature and use these metabolites deserve further investigation.

Strontium/calcium (Sr/Ca) ratios in bulk and foraminiferal calcite have been used to constrain the history of Sr/Ca in the oceans and to evaluate calcite diagenetic alteration. However bulk Sr/Ca records also may be influenced by differences in Sr uptake and/or in the diagenetic susceptibility of different calcium carbonate sedimentary components. We present data on the sediment size fraction and calcium carbonate distribution in bulk samples, Sr/Ca in a range of sedimentary size components, and Sr/Ca in bulk sediments. Ocean Drilling Program samples from sites on Ontong Java Plateau and Ceara Rise (in the western equatorial Pacific and Atlantic, respectively) and from sites in the eastern equatorial Pacific were selected to represent progressive stages in the diagenetic pathway from the sea floor through a range of burial depths equivalent to sediment ages of ~5.6, ~9.4, and ~37.1 Ma. Samples were subdivided by size to produce a unique data set of size-specific Sr/Ca ratios. Fine fraction (<45 ?m) Sr/Ca ratios are higher than those of all corresponding coarse fractions, indicating that fine nannofossil-dominated calcite has a Sr partition coefficient 1.3-1.5 times greater than that of coarse foraminifera-dominated calcite. Thus, absolute values of bulk Sr/Ca in contemporaneous samples reflect, in part, the ratio of fine to coarse calcite sedimentary components. Sr/Ca values in fine and coarse components also behave differently in their response to pre-burial dissolution and to recrystallization at depth. Coarse size components are sensitive to bottom water carbonate ion undersaturation, and they lose original Sr/Ca differences among contemporary samples over not, vert, similar10 my. In contrast, fine components recrystallize faster in more deeply buried samples. Interpretation of the historical Sr/Ca record is complicated by post-depositional diagenetic artifacts, and thus our data do not provide clear evidence of specific temporal changes in oceanic Sr/Ca ratios over the past 10 million years. This paper represents the first systematic attempt to examine trends in calcite Sr/Ca as a function of sediment size fraction and age.

By carbon dioxide mineralization, CO2 can be stored safely and leakage-free for very long times. Owing to their high calcium content, steelmaking slags are suitable for mineral carbonation. In a country like Finland, where no suitable geological formations for CO2 storage seem to exist, steelmaking slag carbonation offers an important CO2 emissions reduction option for steel plants. If calcium could be extracted selectively from the slags prior to carbonation, a pure, and possibly marketable, calcium carbonate may be produced. This could replace some of the natural and synthetic CaCO3 used in industry, combining savings in natural resources with CO2 emissions reduction. Development work on the production of pure calcium carbonate from steelmaking slags by carbonation is presented in this study. Selective extraction of calcium from steelmaking slags was investigated using various solvents. Precipitation of CaCO3 from dissolved calcium at atmospheric pressure was also investigated. Amongst the various tested solvents ammonium salt solutions (NH4Cl, CH3COONH4, NH4NO3) were found to be the most promising for selectively extracting calcium from steel converter slag. These solvents dissolved calcium efficiently also from desulphurization slag, while extraction of calcium from two other types of slag was poor. CaCO3 was successfully precipitated from the solution containing ammonium salt and dissolved steel converter slag.

The equatorial Pacific is an important part of the global carbon cycle and has been affected by climate change through the Cenozoic (65 Ma to present). We present a Miocene (12-24 Ma) biogenic sediment record from Deep Sea Drilling Project (DSDP) Site 574 and show that a CaCO3 minimum at 17 Ma was caused by elevated CaCO3 dissolution. When Pacific Plate motion carried Site 574 under the equator at about 16.2 Ma, there is a minor increase in biogenic deposition associated with passing under the equatorial upwelling zone. The burial rates of the primary productivity proxies biogenic silica (bio-SiO2) and biogenic barium (bio-Ba) increase, but biogenic CaCO3 decreases. The carbonate minimum is at ~17 Ma coincident with the beginning of the Miocene climate optimum; the transient lasts from 18 to 15 Ma. Bio-SiO2 and bio-Ba are positively correlated and increase as the equator was approached. Corg is poorly preserved, and is strongly affected by changing carbonate burial. Terrestrial 232Th deposition, a proxy for aeolian dust, increases only after the Site 574 equator crossing. Since surface production of bio-SiO2, bio-Ba, and CaCO3 correlate in the modern equatorial Pacific, the decreased CaCO3 burial rate during the Site 574 equator crossing is driven by elevated CaCO3 dissolution, representing elevated ocean carbon storage and elevated atmospheric CO2. The length of the 17 Ma CaCO3 dissolution transient requires interaction with a 'slow' part of the carbon cycle, perhaps elevated mantle degassing associated with the early stages of Columbia River Basalt emplacement.

Methane seeps are globally distributed geologic features in which reduced fluid from below the seafloor is advected upward and meets the oxidized bottom waters of Earth’s oceans. This redox gradient fuels chemosynthetic communities anchored by the microbially-mediated anaerobic oxidation of methane (AOM). Both today and in Earth’s past, methane seeps have supported diverse biological communities extending from microorgansisms to macrofauna and adding to the diversity of life on Earth. Simultaneously, the carbon cycling associated with methane seeps may have played a significant role in modulating ancient Earth’s climate, particularly by acting as a control on methane emissions. The AOM metabolism generates alkalinity and dissolved inorganic carbon (DIC) and at a 2:1 ratio, promoting the abiogenic, or authigenic, precipitation of carbonate minerals. Over time, these precipitates can grow into pavements covering hundreds of square meters on the seafloor and dominating the volumetric habitat space available in seep ecosystems. Importantly, carbonates are incorporated into the geologic record and therefore preserve an inorganic (i.e., d13C) and organic (i.e., lipid biomarker) history of methane seepage. However, the extent to which preserved biomarkers represent a snapshot of microorganisms present at the time of primary precipitation, a time-integrated history of microbial assemblages across the life cycle of a methane seep, or a view of the final microorganisms inhabiting a carbonate prior to incorporation in the sedimentary record is unresolved. This thesis addresses the ecology of carbonate-associated seep microorganisms. Chapters One and Two contextualize the extant microbial diversity on seep carbonates versus within seep sediments, as determined through 16S rRNA gene biomarkers. Small, protolithic carbonate “nodules” recovered from within seep sediments are observed to be capable of capturing surrounding sediment-hosted microbial diversity, but in some cases also diverge from sediments. Meanwhile, lithified carbonate blocks recovered from the seafloor host microbial assemblages demonstrably distinct from seep sediments (and seep nodules). Microbial 16S rRNA gene diversity within carbonate samples is well-differentiated by the extent of contemporary seepage. In situ seafloor transplantation experiments further demonstrated the microbial assemblages associated with seep carbonates to be sensitive to seep quiescence and activation on short (13-month) timescales. This was particularly true for organisms whose 16S rRNA genes imply physiologies dependent on methane or sulfur oxidation. With an improved understanding of the modern ecology of carbonate-associated microorganisms, Chapter Three applies intact polar lipid (IPL) and core lipid analyses to begin describing whether, and to what extent, geologically relevant biomarkers mimic short-term dynamics observed in 16S rRNA gene profiles versus archive a record of historic microbial diversity. Biomarker longevity is determined to increase from 16S rRNA genes to IPLs to core lipids, with IPLs preserving microbial diversity history on timescales more similar to 16S rRNA genes than core lipids. Ultimately, individual IPL biomarkers are identified which may be robust proxies for determining whether the biomarker profile recorded in a seep carbonate represents vestiges of active seepage processes, or the profile of a microbial community persisting after seep quiescence.

The concentration of CO2 in global surface ocean waters is increasing due to rising atmospheric CO2 emissions, resulting in lower pH and a lower saturation state of carbonate ions. Such changes in seawater chemistry are expected to impact calcification in calcifying marine organisms. However, other physiological processes related to calcification might also be affected, including enzyme activity. In a mesocosm experiment, macroalgal communities were exposed to three CO2 concentrations (380, 665, and 1486 µatm) to determine how the activity of two enzymes related to inorganic carbon uptake and nutrient assimilation in Corallina officinalis, an abundant calcifying rhodophyte, will be affected by elevated CO2 concentrations. The activity of external carbonic anhydrase, an important enzyme functioning in macroalgal carbon-concentrating mechanisms, was inversely related to CO2 concentration after long-term exposure (12 weeks). Nitrate reductase, the enzyme responsible for reduction of nitrate to nitrite, was stimulated by CO2 and was highest in algae grown at 665 µatm CO2. Nitrate and phosphate uptake rates were inversely related to CO2, while ammonium uptake was unaffected, and the percentage of inorganic carbon in the algal skeleton decreased with increasing CO2. The results indicate that the processes of inorganic carbon and nutrient uptake and assimilation are affected by elevated CO2 due to changes in enzyme activity, which change the energy balance and physiological status of C. officinalis, therefore affecting its competitive interactions with other macroalgae. The ecological implications of the physiological changes in C. officinalis in response to elevated CO2 are discussed.