Minerals soluble

There are various parameters and assumptions defining radionuclide behavior that are frequently part of model descriptions that require constraints. While these must generally be determined for each particular site, laboratory experiments must also be conducted to further define the range of possibilities and the operation of particular mechanisms. These include the reversibility of adsorption, the relative rates of radionuclide leaching, the rates of irreversible incorporation of sorbed nuclides, and the rates of precipitation when concentrations are above Th or U mineral solubility limits. A key issue is whether the recoil rates of radionuclides can be clearly related to the release rates of Rn the models are most useful for providing precise values for parameters such as retardation factors, and many values rely on a reliable value for the recoil fluxes, and this is always obtained from Rn groundwater activities. These values are only as well constrained as this assumption, which therefore must be bolstered by clearer evidence. 

Are the equilibrium constants for the important reactions in the thermodynamic dataset sufficiently accurate The collection of thermodynamic data is subject to error in the experiment, chemical analysis, and interpretation of the experimental results. Error margins, however, are seldom reported and never seem to appear in data compilations. Compiled data, furthermore, have generally been extrapolated from the temperature of measurement to that of interest (e.g., Helgeson, 1969). The stabilities of many aqueous species have been determined only at room temperature, for example, and mineral solubilities many times are measured at high temperatures where reactions approach equilibrium most rapidly. Evaluating the stabilities and sometimes even the stoichiometries of complex species is especially difficult and prone to inaccuracy. 

Virial methods, the second type, employ coefficients that account for interactions among the individual components (rather than species) in solution. The virial methods are less general, rather complicated to apply, require considerable amounts of data, and allow little insight into the distribution of species in solution. They can, however, reliably predict mineral solubilities even in concentrated brines. 

Greenberg, J. P. and N. Mpller, 1989, The prediction of mineral solubilities in natural waters, a chemical equilibrium model for the Na-K-Ca-Cl-S04-H20 system to high concentration from 0 to 250 °C. Geochimica Cosmochimica Acta 53,2503-2518. 

Harvie, C. E., N. Mpller and J. H. Weare, 1984, The prediction of mineral solubilities in natural waters, the Na-K-Mg-Ca-H-Cl-S04-0H-HC03-C03-C02-H2O system to high ionic strengths at 25 °C. Geochimica et Cosmochimica Acta 48, 723-751. 

Hemley, J. J., G. L. Cygan and W. M. d Angelo, 1986, Effect of pressure on ore mineral solubilities under hydrothermal conditions. Geology 14, 377-379. 

Weare, J.H., 1987, Models of mineral solubility in concentrated brines with application to field observations. In I. S.E. Carmichael and H.P Eugster (eds.), Thermodynamic Modeling of Geological Materials Minerals, Fluids and Melts. Reviews in Mineralogy 17,143-176. 

We have developed an in vitro digestion procedure, not as a substitute for in vivo studies, but as a useful adjunct. Our initial objective was to develop an in vitro procedure for measuring exchangeability, the fraction of the food mineral which exchanges with an extrinsic isotope tracer added to the food. This was expected to facilitate the measurement of food mineral absorption in humans by the extrinsic tag method. Secondary objectives were to determine if in vitro mineral solubility could be used to estimate potential... 

The pancreatic digestion conditions studied included pH, the method of pH control, and bile salts mixture and concentration. In addition, experiments were run to determine if mineral solubility was affected by enzymatic activity, or only by pH-induced solubility changes. 

Table II. Effect of Peptic and Pancreatic Enzymes on Mineral Solubility After In Vitro Digestion...

Plummer, L. N., and F. T. Mackenzie (1974), "Predicting Mineral Solubility from Rate Data Application to the Dissolution of Magnesian Calcites", Amer. J. Sd. 274, 61 -83. 

To avoid the necessity of using activity coefficients, mineral solubility can be defined in terms of stoichiometric concentrations where... 

To return to our case study of iron, the equilibrium concentration of Fe(III) is ultimately controlled by its mineral solubility. Since atmospheric dust is a major source of new iron to the ocean, its solubility is a matter of hot debate. If the solubility is low, the particulate iron is likely to settle out of the euphotic zone before it can be assimilated by plankton. Iron is one of the most abundant elements in Earth s crust, so it is not surprising that concentrations in dust are high, ranging from 3 to 5% dry weight. 

Since [Fe(lll)]jojaj [Fe " ], the formation of ion pairs and complexes is greatly enhancing the equilibrium solubility of ferrihydrite. This is called the salting-in effect and illustrates why mineral solubility calculations in seawater must take ion speciation into consideration. 

Phosphate is remineralized during the oxidation of organic matter and dissolution of hard parts, such as bones and teeth, that are composed of the minerals hydroxyapatite and fluoroapatite. Unlike the other products of remineralization, pore-water phosphate concentrations are regulated only by mineral solubility, such as through vivianite (iron phosphate) and francolite (carbonate fluoroapatite). Redox reactions are not significant because phosphorus exists nearly entirely in the h-5 oxidation state. 

In acids soils, particularly those with kaolinite clay minerals, soluble Fe + concentrations tend to rise to high levels because of low CEC and because conditions do not favour precipitation of Fe(II) oxides or carbonates or synthesis of silicates. 

Eugster H. P. and Baumgartner L. (1987). Mineral solubilities and speciation in supercritical metamorphic fluids. In Reviews in Mineralogy, vol. 17, P. H. Ribbe (series ed.), Mineralogical Society of America. 

Advantages of the carbonate-exchange technique are (1) experiments up to 1,400°C, (2) no problems associated with mineral solubility and (3) ease of mineral separation (reaction of carbonate with acid). Mineral fractionations derived from hydrothermal and carbonate exchange techniques are generally in good agreement except for fractionations involving quartz and calcite. A possible explanation is a salt effect in the quartz-water system, but no salt effect has been observed in the calcite-water system (Hu and Clayton 2003). 

Interaction of phosphate solutions with goethite may lead to surface precipitation of phosphates if the concentration of P in solution exceeds the mineral solubility (Jo-nasson et al., 1988). A combined Auger, XPS, scanning SIMS and electron diffraction study showed that after 90 days at 60 °C, crystals of griphite (an Fe hydroxy phosphate) precipitated out of a phosphate solution onto crystals of goethite (Martin et al., 1988). 

Examination of Figure 1-12 provides some clue to qualitatively gauge the interface reaction rate for reactions in water. Figure 1-12 shows that, for mineral with low solubility and high bond strength (characterized by (z+z )max, where z+ and z are valences of ions to be dissociated), the overall dissolution rate is controlled by interface reaction otherwise, it is controlled by mass transport. Because diffusivities of common cations and anions in water do not differ much (by less than a factor of 10 Table l-3a), when the overall reaction rate is controlled by interface reaction, it means that interface reaction is slow when the overall reaction rate is controlled by mass transport, the interface reaction rate is rapid. Therefore, from Figure 1-12, we may conclude that the interface reaction rate increases with mineral solubility and decreases with bond strength (z+z )max to be dissociated. 

Table 3. Some phosphite mineral solubility prothtci anti Gibbs free energy of formation data... 

If the index is positive then the solution is supersaturated, whereas a negative value indicates understaturation. When modelling mineral solubility with other reactions involving protons it may be necessary to write the dissolution reaction of the solid phase as a dissolution reaction with protons. Consider the dissolution of gibbsite ... 

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