Carbonate mineralization

Figure 5.12 Relative chemical stability of carbonate minerals...

The carbonate minerals that comprise limestone ate calcite [13397-26-7] (calcium carbonate), which is easily the most abundant mineral type aragonite [14791-73-2] (calcium carbonate) dolomite [17069-72-6] (double carbonate of calcium and magnesium) andmagnesite [13717-31 -5] (magnesium carbonate). Individual limstone types ate further described by many common names (1). Some of this nomenclature is repetitious and overlapping. The following terms ate in common use in Europe and the United States. 

None of the natural sulfides of manganese are of any commercial importance. Some siUcates have been mined. Rhodonite and braunite are of iaterest because these are frequendy associated with the oxide and carbonate minerals. The chemical composition of some common manganese minerals are given ia Table 3. 

Carbonate Decomposition. The carbonate content of Green River oil shale is high (see Table 4). In addition, the northern portion of the Piceance Creek basin contains significant quantities of the carbonate minerals nahcoUte and dawsonite. The decomposition of these minerals is endothermic and occurs at ca 600—750°C for dolomite, 600—900°C for calcite, 350—400°C for dawsonite, and 100—120°C for nahcohte. Kinetics of these reactions have been studied (19). Carbon dioxide, a product of decomposition, dilutes the off-gases produced from retorting processes at the above decomposition temperatures. 

It has been shown (20,21) that siUcate weathering is more important than carbonate mineral weathering as a longterm control on atmospheric CO2. The HCO3 and ions produced by weathering of CaCO precipitate in the... 

The choice of selected raw materials is very wide, but they must provide calcium oxide (lime), iron oxide [1309-37-1/, siHca, and aluminum oxide (alumina). Examples of the calcereous (calcium oxide) sources are calcium carbonate minerals (aragonite [14791-73-2] calcite [13397-26-7] limestone [1317-65-3] or mad), seasheUs, or shale. Examples of argillaceous (siHca and alumina) sources are clays, fly ash, mad, shale, and sand. The iron oxide commonly comes from iron ore, clays, or mill scale. Some raw matedals supply more than one ingredient, and the mixture of raw matedals is a function of their chemical composition, as deterrnined by cost and availabiHty. 

Almost all the Earth s carbon is found in the lithosphere as carbonate sediments that have precipitated from the oceans. Shells of aquatic animals also contribute CaC03 to the lithosphere. Carbon returns to the hydrosphere as carbonate minerals dissolve in water percolating through the Earth s crust. This process is limited by the solubility products for carbonate salts, so lithospheric carbonates represent a relatively inaccessible storehouse of carbon. 

Keywords. Calcium carbonate. Mineralization, Hyperbranched polymer, Supramolecular assembly. Anionic dendrimer... 

Figure 1.107 shows the frequency of 8 C of carbonates from epithermal Au-Ag vein-type deposits and that from base-metal vein-type deposits. The carbonates are divided into two types type A and type B. Type A is characterized by (1) abundant occurrence in each deposit (2) coexistence with sulfide minerals and (3) large grain size. Main carbonate minerals are rhodochrosite and Mn calcite, whereas calcite is the main carbonate mineral for type B. Mn-carbonates of type A occur in Pb-Zn-Mn vein-type deposits. Type B is characterized by (1) poor amounts in each deposit (2) coexistence... 

The veins are composed mostly of quartz and a small amount of sulfide minerals (pyrite, pyrrhotite, arsenopyrite, chalcopyrite, sphalerite, and galena), carbonate minerals (calcite, dolomite) and gold, and include breccias of the host rocks with carbonaceous matters. Layering by carbonaceous matters has been occasionally observed in the veins. Banding structure, wall rock alteration and an evidence of boiling of fluids that are commonly observed in epithermal veins have not been usually found. 

Kaufman A, Broecker W (1965) Comparison of " C and °Th ages for carbonate minerals from Lakes Lahontan and Boimeville. J Geophys Res 70 4039-4054 Ludwig KR, Titterington DM (1994) Calculation of Th/U Isochrons, ages, and errors Geochim Cosmochim Acta 58 5031-5042... 

Coprecipitation is a partitioning process whereby toxic heavy metals precipitate from the aqueous phase even if the equilibrium solubility has not been exceeded. This process occurs when heavy metals are incorporated into the structure of silicon, aluminum, and iron oxides when these latter compounds precipitate out of solution. Iron hydroxide collects more toxic heavy metals (chromium, nickel, arsenic, selenium, cadmium, and thorium) during precipitation than aluminum hydroxide.38 Coprecipitation is considered to effectively remove trace amounts of lead and chromium from solution in injected wastes at New Johnsonville, Tennessee.39 Coprecipitation with carbonate minerals may be an important mechanism for dealing with cobalt, lead, zinc, and cadmium. 

The waste organic acids dissolved carbonate minerals, alumino-silicate minerals, and iron/manganese-oxide coatings on the primary minerals in the injection zone. 

Mechanical intrusion is the penetration of the matter to be dated by carbon of a different age from that of the sample itself if not taken into account, mechanical intrusion, too, leads to erroneous ages. The penetration of rootlets from growing plants into buried specimens, the infiltration of windblown organic matter, and the accidental insertion of fibers from brushes or other instruments used to clean a sample are examples of likely modern carbon intrusions into prospective samples, which lead to assigning to a sample later dates than the true ones old carbon intrusions, such as those caused by the penetration of carbonate minerals from groundwater, or of petrol or oil from excavating tools, on the other hand, are conducive to assigning earlier dates than the true ones. 

Mineral acids include hydrochloric acid and blends of hydrochloric and hydrofluoric acid (usually 12% HCl/3% HF). Hydrochloric acid is used to acidize carbonate formations. Its advantages are relatively low cost, high carbonate mineral dissolving power, and the formation of soluble reaction products (which minimizes formation damage). The primary disadvantage of hydrochloric acid is its corrosive nature. 

The protocol involving NaOAc-HOAc at pH 5 was first proposed and used by Jackson (1958) to remove carbonates from calcareous soils to analyze soil cation exchange characteristics (Grossman and Millet, 1961). Other researchers used HOAc for the extraction of metals from sediments and soils (Nissenbaum, 1972 Mclaren and Crawford, 1973). Tessier et al. (1979) first used the NaOAc-HOAc solution at pH 5 to dissolve the carbonate fraction from sediments. Since then, the NaOAc-HOAc buffer has been widely used as a specific extractant for the carbonate phase in various media (Tessier et al., 1979 Hickey and Kittrick, 1984 Rapin et al., 1986 Mahan et al., 1987 Han et al., 1992 Clevenger, 1990 Banin et al., 1990). Despite its widespread use, this step is not free from difficulties, and further optimization is required in its application. Questions arise with regard to this step in the elemental extraction from noncalcareous soils, the dissolution capacity and dissolution rates imposed by the buffer at various pHs, and the possibility that different carbonate minerals may require different extraction protocols (Grossman and Millet, 1961 Tessier et al., 1979). 

The following sections summarize the studies on the dissolution technique for the carbonate fraction from arid and semi-arid soils with different amounts and types of carbonate minerals. In addition, the selectivity and effectivity of the NaOAc-HOAc extraction technique at varying pHs to extract the carbonate phase, and only the carbonate phase, from soils is examined (Han and Banin, 1995). 

Pascual J.A., Hernandez T., Garcia C., Ayuso M. Carbon mineralization in an arid soil amended with organic wastes of varying degrees of stability. Commun Soil Sci Plant Anal 1998 29 835-846. 

Balesdent J, Mariotti A, Boisgontier D (1990) Effect of tillage on soil organic carbon mineralization estimated from 13C abundance in maize fields. J Soil Sci 41 587-596... 

Lackner, K.S. et al., Carbon dioxide disposal in carbonate minerals, Energy, 20(11), 1153-1170,1995. 

Despite the vast amount of work on 14C dating which has already been accomplished and despite the fact that it is the best developed method available today, numerous difficulties still exist with its application. First, carbonate geochemistry which helped control 14C concentrations in the past is not simple to reconstruct. Carbonate minerals are commonly in a state of near equilibrium with groundwater, and only slight changes in water temperature or chemistry will promote either dissolution or precipitation of carbonate ions. In this way, the proportion of modern carbon in the water can be changed and some isotope... 

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