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Mineral forms, precipitation

Polyphenols are ubiquitous in all plant organs where they are found as monomers or in polymerised forms (Schofield et al, 2001). In addition to the beneficial effect of poljq)henols, they also bind minerals and precipitate proteins and carbohydrates, in effect reducing the nutritive value of foods. Polyphenols have been classified for nutritional purposes into extractable and non-extractable types (Bravo, 1998). Extractable polyphenols are low-and intermediate-weight phenolics while non-extractable polyphenols have high molecular weight and are insoluble in normal solvents. [Pg.338]

Uncertainties aside, it is interesting to pursue the question of whether the brine has the potential to precipitate sulfide minerals. In the second step of the calculation, where the model allows precipitation reactions to progress to the system s equilibrium state, three minerals form in small quantities ... [Pg.102]

In Chapter 16, we wrote rate laws for simple dissolution and precipitation reactions, such as those for the silica minerals forming from SiC>2(aq). Rewriting Equation 16.22 in terms of volumetric concentration C , assuming the activity coefficient Yi does not vary over the reaction, gives the rate law,... [Pg.305]

In the reaction path we calculated (Fig. 24.2), the precipitation of calcite consumes nearly all of the calcium originally in solution so that no further calciumbearing minerals form. Calcite precipitation, on the other hand, does not deplete... [Pg.361]

The Amethyst fluid is richer in strontium and calcium than the other fluids, but nearly depleted in barium. Celestite becomes saturated first, and more of this mineral forms from this fluid than from the Forties fluid. Anhydrite becomes saturated later in the mixing process and precipitates,... [Pg.441]

Sulfate, halide, and carbonate minerals form in mine waste as a result of chemical weathering reactions and as a by-product of mineral processing. The formation of carbonate minerals is of particular interest for its potential in offsetting greenhouse gas emissions associated with mining. We have documented secondary carbonate mineral precipitation at the Mount Keith Nickel Mine (Western Australia) and the... [Pg.143]

The weathering of minerals forms particles with a size continuum from ions to grains. Mineral dissolution and precipitation occur more or less continuously as a function of ambient conditions. Particles of the clay textural fraction may be suspended in solution as colloids as well as occurring as part of the stationary solids. [Pg.113]

Remineralisation occurs when partly dissolved crystals are induced to grow by precipitation of the mineral-forming ions Ca + and POl". This is a natural process that occurs as a result of the concentration of these ions in saliva [23] and it serves to oppose the demineralising effects of caries. The processes involved are complex [24] and involve dynamic activity at the interface between the tooth, the saliva, the pellicle and the plaque. Fluoride plays a role in enhancing these processes, and though this is not the only contribution that fluoride makes to protect the tooth from caries, it is nonetheless an important one. [Pg.338]

Sevenson Environmental Services, Inc. (Sevenson), is the owner of the MAECTITE chemical treatment process for the precipitation and stabilization of toxic heavy metals. Chemical treatment by the MAECTITE process converts teachable lead, hexavalent chromium, or other heavy metals into insoluble minerals and mixed mineral forms within the material or waste matrix. The technology can be used as an in situ or an ex situ method and does not use pozzolanic or siliceous binders to stabilize the treated material. [Pg.965]

C. Extraction. The major sources ofSi are the many mineral forms of Si02 which range all the way from highly pure quartz to quartz with numerous impurities to silicates. The insolubility and non-reactivity of Si02 lead to its ready separation from many of its mineral forms. Purification of Si02 may be carried out in numerous ways such as the fusion of the mineral with Na2C03, then dissolution in water, then acidification with concentrated acid to precipitate the Si02. [Pg.185]

The mobility of metals in soil solutions is controlled by several processes (1) desorption or dissolution (rate depends on the solubility of metal-mineral form) (2) diffusion (depends on speciation of metal, soil oxidation/reduction potential, and pH) (3) sorption or precipitation (depends on soil solution concentration and rhi-zosphere effects) and (4) translocation in the plants (depends on plant species, soil solution concentration, and competing ions) (McBride... [Pg.241]

In weathering situations, saturation of fluids with SiC relative to any species of pure silica is probably only rarely achieved. In continental and shallow sea deposits, silica is precipitated in some initially amorphous form, opaline or chert when lithified or extracted by living organisms. Authigenically formed silicates are probably not in equilibrium with quartz when they are formed. As compaction increases in sediments, silica concentrations in solution are again above those of quartz saturation (15 ppm) and again it must be assumed that the diagenetic minerals formed are not in equilibrium with a silica polymorph except where amorphous silica is present. It is possible that burial depths of one or two kilometers are necessary to effectively stabilize that quartz form. It must be anticipated that the minerals formed under conditions of silica saturation near the earth s surface will be a minority of the examples found in natural rock systems. [Pg.29]

The insoluble Ca(II) salts of weak acids, such as calcium phosphate, carbonate, and oxalate, serve as the hard structural material in bone, dentine, enamel, shells, etc. About 99% of the calcium found in the human body appears in mineral form in the bones and teeth. Calcium accounts for approximately 2% of body weight (18,19). The mineral in bones and teeth is mosdy hydroxyapatite [1306-06-5] having unit cell composition Ca10(PO4)6(OH)2. The mineralization process in bone follows prior protein matrix formation. A calcium pumping mechanism raises the concentrations of Ca(II) and phosphate within bone cells to the level of supersaturation. Granules of amorphous calcium phosphate precipitate and are released to the outside of the bone cell. There the amorphous calcium phosphate, which may make up as much as 30—40% of the mineral in adult bone, is recrystallized to crystallites of hydroxyapatite preferentially at bone collagen sites. These small crystallites do not exceed 10 nm in diameter (20). [Pg.408]

These observations clearly preclude the possibility that the solution from which mineral forms is essentially that of blood or other body fluids, or even sea water. Analyses of fluid extracted from the space in mollusks between the mantle, the organ that forms the shell, and the shell surface, show that it is different from sea water or the blood [86]. It is not, however, clear that this is the actual fluid from which the mineral precipitates. The trace element compositions of the mollusk shell minerals, as well as the shells of many other organisms, are also incompatible with crystallization from a medium similar to sea water [87], indicating that mineral deposition occurs from a specialized medium. [Pg.23]

Another means of assessing the nature of the medium/solution from which the mineral forms is to analyse the very first mineral deposits precipitated. These must reflect the chemistry of the medium in which they formed. In most chiton teeth a poorly crystalline ferrihydrite is the first mineral deposited and it subsequently transforms into magnetite. In the anterior layer, amorphous calcium phosphate is first deposited, and only after several weeks does it begin... [Pg.23]


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See also in sourсe #XX -- [ Pg.23 ]




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Mineral precipitation

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