Silica calcitization

Homopolymers. Polymers such as poly(methacrylamido-4,4,8,8-tetra-methyl-4,8-diaza-6-hydroxynonamethylene dichloride), abbreviated poly(MDTHD), and a triaza analog, abbreviated poly(MTHHDT), have been shown to be effective stabilizers of silica, calcite, and hematite (14,15) as indicated by the data summarized in Table V. 

Copolymers of MDTHD and DMAPMA appeared to be the most effective silica, calcite, and hematite mineral fines stabilizers. Increasing the copolymer MDTHD content had little effect on polymer performance. Similar results were observed for a series of MDTHD -DMAEMA copolymers and a series of DMAEMA CH-C1 salt - DMAEMA copolymers (Table VI). In contrast, increasing the MDTHD content of MDTHD - NNDMAm copolymers from 67% to 90% improved copolymer performance as a silica fines and hematite fines stabilizer. 

In the calculation results (Fig. 24.1), amorphous silica, calcite (CaCCF), and sepiolite precipitate as water is removed from the system. The fluid s pH and ionic strength increase with evaporation as the water evolves toward an Na-C03 brine (Fig. 24.2). The concentrations of the components Na+, K+, Cl-, and SO4- rise monotonically (Fig. 24.2), since they are not consumed by mineral precipitation. The HCO3 and Si02(aq) concentrations increase sharply but less regularly, since they are taken up in forming the minerals. The components Ca++ and Mg++ are largely consumed by the precipitation of calcite and sepiolite. Their concentrations, after a small initial rise, decrease with evaporation. 

Fig. 24.1. Volumes of minerals (amorphous silica, calcite, and sepiolite) precipitated during a reaction model simulating at 25 °C the evaporation of Sierra Nevada spring water in equilibrium with atmospheric C02, plotted against the concentration factor. For example, a concentration factor of x 100 means that of the original 1 kg of water, 10 grams remain.

Much stronger kinetic stabilization can be expected for processes leading to the inclusion of radionuclide ions into the colloid structure (Fig. 7, lower part). Spectroscopic indications for such processes have indeed been found again by TRLFS for the Cm(III) interaction with colloidal and particulate amorphous silica, calcite and CSH phases (Chung et al. 1998 Stumpf Fanghanel 2002 Tits et al. 2003). The incorporation of actinide ions into colloidal precursor clay phases has been recently investigated as a possible mechanism in natural... 

The surface-sediment P concentration at our station is actually higher than the mass-weighted mean concentration in the primary depositional flux (1.135 versus 0.950 mg of P/g), a result of less efficient recycling of P than of major components of the depositional flux (biogenic silica, calcite, and organic matter). In total, 63% of the primary mass flux is recycled annually at the sediment surface. This change would result in a hypothetical recycling-corrected P concentration in the primary flux of 2.57 mg/g. A comparison... 

The endotherm that peaked at 868°C with a corresponding DTG peak at 870°C coincides with a significant dissolution of CaO as indicated by XRD relative peak heights. It is speculated that the reaction peaked at 816°C for the coarse batch (seen in the soda ash-silica-calcite mixture) was suppressed in the fine particle sizes because of the silicacious nature of the liquid phase. The endotherm that peaked at 868°C would then represent a shift to higher temperature for this reaction, with corresponding reduction in solid CaO. The weight loss associated with this endotherm would correspond to decreased CO2 solubility in a liquid phase enriched in calcia. 

Carbonates Phosphates Silica Calcite Aragonite Vaterite Monohydrocalcite Amorphous Dahllite Francolite Amorphous calcium phosphate hydrogel Amorphous ferric phosphate hydrogel Opal Iron oxides Sulfates Halides Oxalates Magnetite Goethite Lepidocrocite Amorphous hydrates Celestite Barite Gypsum Fluorite Weddellite Whewellite... 

Opaline silica (+) Calcite (+++) Vaterite High magnesian Phosphates... 

Model predictions, followed by analyses of in-situ sidewall core samples, showed that amorphous silica, calcite and lesser amounts of gypsum are the dominant phases expected to precipitate in the... 

Based on the strong dilution trends of non-reactive species, such as chloride and sulfate, the extent of interaction of fracture condensate water with matrix pore water must have been very limited. However, reactive species, such as silica, show increasing concentrations owing to reaction with predominantly fracture-lining silica polymorphs and feldspars at higher temperatures. A precipitation zone of secondary mineral phases such as amorphous silica, calcite, and gypsum in... 

Cement is the natural or synthetic material which binds rock particles together. In sedimentary rocks, the cementing substanees include silica, calcite, clay and iron oxide. See also ordinary Portland cement. 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

Other minerals beside water-swelling clays have been found to undergo fines migration. The permeability damage caused by essentially non-swelling clays such as kaolinite and chlorite is a well-known phenomenon. Silica fines have been identified as a potential source of permeability damage in various poorly consolidated U.S. Gulf Coast formations (1). Other minerals identified as constituents of mobile fine particles include feldspar, calcite, dolomite, and siderite (4,5). 

Silica before 15% HC1 infection Silica after 15% HC1 injection Calcite Hematite... 

Limited silica fines stabilization data indicated that increasing copolymer molecular weight from 100,000 to 1,000,000 daltons had, if anything, a negative effect on silica fines stabilization. At a molecular weight of 1,000,000 daltons, this copolymer appeared to be more effective in stabilizing silica fines than silica/kaolinite, calcite, or hematite fines. However, the results may be due in part to the larger particle size and lower surface area of the silica fines (see Table II). 

When the DMAEMA content of NVP - DMAEMA copolymers was reduced from 20% to 8%, the silica fines stabilization effectiveness appeared to improve slightly. When the 80/20 NVP - DMAEMA copolymer was converted to a terpolymer containing 8% DMAEMA (CH SO, silica fines stabilization was substantially unaffected. However, stabilization of silica/kaolinite fines was greatly improved. This suggested that the interaction of polymer quaternary nitrogen atoms with anionic sites on mineral surfaces was important for the stabilization of migrating clays but a different interaction was important for the stabilization of silica fines. Calcite fines stabilization improved while hematite fines stabilization effectiveness decreased. This also indicated the nature of the adsorbed polymer - fine particle complex varied for different minerals. 

Depressants are used to make materials less floatable, and again have been used for some time.4,18 A recent example is the use of phosphoric acid to depress the flotation of a sedimentary phosphate ore, enhancing the selectivity of recovery of calcite and silica.24 Natural and synthetic polymers have also been used as depressants.20... 

Gangue minerals are composed of calcite, dolomite and silica and often contains clay minerals (i.e. kaoline, montmorillanite)... 

Cementation by calcite, dolomite, anhydrite, pyrobitumen and silica... 

Major structural components of hard parts Ca, C, SI, 0, P, F, Sr, S Calcite, aragonite, opaline silica, celestite, apatite, fluoroapatite Components of frustules and tests, bone, teeth... 

The clay minerals of aeolian origin comprise 25 to 75% of the mass of pelagic sediments. The large range in composition reflects the latitudinal nature of the dust belt as well as dilution by other locally important particle types such as clay minerals of volcanogenic origin and biogenic hard parts (calcite and opaline silica). 

As with the calcareous tests, BSi dissolution rates depend on (1) the susceptibility of a particular shell type to dissolution and (2) the degree to which a water mass is undersaturated with respect to opaline silica. Susceptibility to dissolution is related to chemical and physical factors. For example, various trace metals lower the solubility of BSi. (See Table 11.6 for the trace metal composition of siliceous shells.) From the physical perspective, denser shells sink fester. They also tend to have thicker walls and lower surface-area-to-volume ratios, all of which contribute to slower dissolution rates. As with calcivun carbonate, the degree of saturation of seawater with respect to BSi decreases with depth. The greater the thermodynamic driving force for dissolution, the fester the dissolution rate. As shown in Table 16.1, vertical and horizontal segregation of DSi does not significantly coimter the effect of pressure in increasing the saturation concentration DSi. Thus, unlike calcite, there is no deep water that is more thermodynamically favorable for BSi preservation they are all corrosive to BSi. 

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