Mineral solubility, effect

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. 

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

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. 

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). 

Temperature and pressure variations in natural systems exert major influences on carbonate mineral solubility and the distribution of carbonic acid chemical species. For example, the solubility of calcite decreases with increasing temperature, as does the solubility of CO2 gas in water. These two effects on solubilities can lead to precipitation of calcite as a cement in a marine sediment-pore water system that undergoes moderate burial. 

Several studies have been performed during the last two decades on CPPs which may function as carriers for different minerals, especially calcium. Published data on the effect of CPP/casein on mineral solubility and absorption are inconsistent, partly due to the diversity of the experimental approaches. Most of the findings in the literature that deal with the mineral absorption-stimulating effect of CPP are based on in vitro, in situ, cell culture or single meal studies. Majority of the studies have been done with rats and have provided considerable evidence for the potential effect of casein-derived phosphopeptides to improve mineral absorption. This potential is not limited to calcium but is also valid for zinc and iron, and possibly other elements that have not been investigated so far (FitzGerald, 1998). Furthermore, CPPs have been shown to have anticariogenic properties, based on their ability to localise amorphous phosphate in dental plaque (Reynolds, 1998). 

The divalent mineral-binding effect of CPPs can be put in use in applications where one wants to increase the availability for absorption of these minerals in the gut. Drinks with calcium and iron are examples for commercial uses of CPPs examples can be found especially in the Japanese market. Products for children that incorporate calcium or milk minerals and CPPs in sweets or cookies are found in the South Asian market. As mineral accretion is high during early childhood, incorporation of CPPs provides good solubility and availability for absorption of calcium or zinc and thus is worth considering for infant nutrition. Other possible uses are in calcium-enriched dairy products and natural calcium supplements. In addition, dental applications are obvious, since complexes of calcium, CPPs and phosphate may reduce caries in a dose-dependent fashion. 

Parentheses denote activity and brackets denote concentration of the species. The concentration of the Al(OH)3 species represents approximately the lowest possible solubility point of the mineral and it is the product of two constants (K -K ). Thus, its magnitude is not in any way related to pH. Mineral solubility increases as pH increases above the solution pH of zero net charge because of increasing complexa-tion effects, and mineral solubility also increases at pH values below the solution pH of zero net charge because of diminishing common-ion effects (Fig. 2A). All minerals are subject to the common-ion effect and many minerals are subject to the complexation or ion-pairing effect (Fig. 2B). 

The chemical oxidation of metal sulfides is controlled in part by the dissolution of sulfide minerals under acidic conditions and by the presence of oxidants (DO, Fe ) that lead to the disruption of sulfide chemical bonds. Bacteria can have a significant effect on the rate of oxidative dissolution of sulfide minerals by controlling mineral solubility and surface reactivity. Metal-enriched waters and solutions rich in sulfuric acid that form in association with mining can be directly linked to microbial activity. The majority of studies to date have focused on the reactivity and kinetics of sulfide minerals in the presence of A. ferrooxidans and L. ferrooxidans, and in some cases A. thiooxidans (Singer and Stumm, 1970 Tributsch and Bennett, 1981a,b Sand et al., 1992, 2001 Nordstrom and Southam, 1997 Sasaki et al., 1998 Edwards et al., 1998, 1999, 2000 Nordstrom and Alpers, 1999a Banfield and Welch, 2000 Tributsch, 2001). Additional studies have been conducted on other species of bacteria and archea (Edwards et al, 1998, 1999, 2000). 

It is useful to construct a graph relating carbonate mineral solubilities to CO2 pressure. This can be done for calcite starting with equilibrium constant expression (6.2) above. If done rigorously, the derivation accounts for the effects of ion activity coefficients and the presence of CaHCOI and CaCOf ion pairs and of CaOH. Considering all complexation, the exact charge-balance equation for a pure water in which calcite is dissolving is... 

The effectiveness of P in decreasing water-soluble Pb in aqueous solution as well as in soils has been well demonstrated (Ma et al., 1993, 1995 Ma and Rao, 1999). Consistent with the mechanism of dissolution of P minerals and subsequent or concurrent precipitation of pyromorphite minerals, the effectiveness of such a decrease depends on the solubility of the P mineral used. For example, at a rate of 4 g HA L HA effectively decreased aqueous Pb from 500 mg... 

For the above sparingly soluble minerals, the effect of dissolved species on interfacial properties can be marked. Results obtained for the zeta-potential of apatite and calcite in water and in 2 x 10 M KNO3 solutions are given in Fig. 3.7. It can be seen that the isoelectric points of calcite and apatite in both water and KNO3 solutions are about 10.5 and 7.4, respectively. The effect of the supernatant of calcite on the zeta-potential of apatite is also shown in Fig. 3.8. 

Past studies of solid-solution aqueous-solution (SSAS) systems have focused on measuring the partitioning of trace components between solid and aqueous phases. The effect of solid-solution formation on mineral solubilities was rarely studied. Recently however, Lippmann (1,2), Thorstenson and Plummer (3) and Plummer and Busenberg (4) have enriched our understanding of SSAS systems with their theoretical and experimental descriptions of solid-solution dissolution and component distribution reactions. The objectives of this paper are 1) to describe and to compare the concepts presented by the above authors, 2) to present some techniques which may help estimate the effect of SSAS reactions on the chemical evolution of natural waters. 

If the solubility product characterizes only the level at which the solution is saturated, the solubility is the equivalent amoimt of the mineral in the solution under the same conditions. The values of the solubility product do not depend on the water composition whereas the solubility does. That is why the latter are not constants and are practically not used in thermodynamic evaluations. Moreover, it is necessary to distinguish between the mineral solubility in pure water, which is usually listed in reference books, and solubility of minerals in the real natural water, which is called effective solubility. 

The reviewed solubility defines the properties of distilled deionized water, which is absent in nature. Its values may be found in any reference literatme. But it is not characteristic of properties of natural water. These properties of natural water solutions are defined by effective mineral solubility. 

Effective Solubility Effective solubility describes the solubility of minerals in water of natmal composition. It is associated with the presence in water of components of both own relative to the mineral and foreign, and also with the effect of temperature. Here, own means ions, which form at dissolution. 

Much greater effect on the value of r. has mineral solubility C,. 

Aluminum toxicity is particularly important on acidic tropical soils that may have low pH in their subsoils, which limits root development into these layers. Aluminum toxicities decrease the permeability of root cells and reduce root growth thus, the plant s ability to take jupjwateiLandjautrientsJs-decreased. This effect can be much more detrimental to the plant than P dcficiendes because of low pH d high A1 concentrations per se [41. In additim to nutrient availability due to solubility effects, mineralization of N from organic matter is decreased, arxl BNF by the rhizobia of legumes is decreased at low pHs. 

Most of the terminal electron acceptors used by bacteria for respiration, such as oxygen, nitrate, and sulfate, are soluble. This means they can make then-way to the cell to receive electrons from the membrane-bound molecules of the respiratory chain. The real question is how bacteria transfer electrons to solids like hematite (a FejOj) and goethite (a-FeOOH) (Figure 3). Because these minerals are effectively insoluble under environmentally relevant conditions, simple dissolution and diffusion of ferric iron to the cell cannot be the answer (ferric iron is the constituent of the mineral that receives electrons). Therefore, bacteria must have other strategies for transferring electrons to minerals during respiration. The question is, what are they ... 

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