Phosphates solubility

The calcium phosphate solubility constant [KCa3(P04)2] is extremely small and phosphate quickly reacts with calcium when present in warm to hot, alkaline BW in the ortho- form. This reaction is complete and superior to the soda ash precipitation reaction. In addition, calcium phosphate is stable and does not decompose. 

The chosen coordinates defining minimum/maximum pH levels and minimum/maximum phosphate (as ppm P04) led to the production of various coordinated phosphate program control charts for different pressure ratings (maximum phosphate solubility is a function of pressure). The area within the coordinates providies a simple control box for BW testing purposes. 

The Food and Drug Administration (FDA) published a safety alert in 1994 in response to two deaths associated with calcium-phosphate precipitation in PN.16 Autopsy reports from these patients revealed diffuse micro vascular pulmonary emboli containing calcium-phosphate precipitates. Because calcium and phosphate can bind and precipitate in solution, caution must be exercised when mixing these two electrolytes in PN admixtures. Several factors can affect calcium-phosphate solubility, including... 

Calcium and magnesium are the major cations (co-)precipitating trace elements as carbonate. Trace elements are also precipitated as sulfate or phosphate. Solubility and reactions of carbonates, sulfates and phosphates of selected major and trace elements are in Table 3.9. 

The methods of analysis for phosphate solubility are not absolute, but empirical that is, they are based on practical experience. For example, the neutral ammonium citrate method is favoured in the USA because it has received over 100 years of study and experimentation, and provides an index correlating the laboratory results with the fertilizing value of water-insoluble phosphates under the conditions prevailing in the principal farming regions of the country. The particular solvent is therefore not an attempt to accurately reproduce the properties of the soil solution in the immediate vicinity of the... 

Superphosphate contains a mixture of monocalcium phosphate (soluble in water), plus dicalcium phosphate and calcium sulphate (both with low solubility in water) together with other mineral residues. Thus the solubility in water gives the monocalcium phosphate (sometimes abbreviated to monophosphate) content, and extraction of the residue with neutral ammonium citrate gives the dicalcium phosphate component. 

Sauve, S., McBride, M. Hendershot, W. 1998. Lead phosphate solubility in water and soil suspensions. Environmental Science Technology, 32, 388-393. 

Total phosphorus includes colloidal inorganic phosphate, casein (organic) phosphate, soluble inorganic phosphate, ester phosphate and phospholipids. 

Analysis of Guano.—Guano is a very complex mixture, containing urate, oxalate, and phosphate of ammonia, earthy phosphates, soluble alkaline salts, and organic matter, The analysis of such a compound is attended with some labor. As the value of guanos, however, depends on the quantify of ammonia, phosphates, soluble and insoluble, and alkaline 6alts which they contain, a very simple analysis is quite sufficient for agricultural purposes.. 

J. N. Ryan, Enhanced Dissolution of Cinnabar (Mercuric Sulfide) by Dissolved Organic Malta Isolated from the Florida Everglades, Environ. Sci Technol 1998, 32, 3305 S. Sauvd, M. McBride, and W. Hendershot, Lead Phosphate Solubility in Water and Soil Suspensions, Environ. Sci Technol 1998,32, 388. 

Liu, X. and Byrne, R.H. (1997) Rare earth and yttrium phosphate solubilities in aqueous solution. Geochim. Cosmochim. Acta, 61, 1625-1633. 

Barium chloride White precipitate of barium hydrogen phosphate soluble in dilute mineral acids and acetic acid... 

Magnesium nitrate reagent or magnesia mixture White crystalline precipitate of magnesium ammonium phosphate soluble in acetic acid and mineral acids practically insoluble in 2.5% ammonia solution... 

Iron (III) chloride Yellowish white precipitate of iron (III) phosphate soluble in mineral acids insoluble in dilute acidic acid... 

White precipitate of zinc phosphate soluble in dilute acids... 

Barium chloride solution yellow precipitate of barium vanadate (distinction from arsenate and phosphate), soluble in dilute hydrochloric acid. 

Markich S. J., Brown P. L., and Jeffree R. A. (2001) Divalent metal accumulation in freshwater bivalves an inverse relationship with metal phosphate solubility. Sci. Tot. Environ. 275, 27-41. 

K. A. Fitzgerald and M. W. MacKay. Calcium and phosphate solubility in neonatal parenteral nutrient solutions containing TrophAmine. Am. J. Hasp. Pharm., 43, 88-93 (1986)... 

Properties Pink powder, contains some tribasic phosphate. Soluble in acids slightly soluble in water. 

PN solutions therefore may need to be modified by clinicians to provide supplemental amounts of CEAAs. Cysteine is a CEAA in preterm and term infants that may be added to PN solutions at the time of compounding. An additional benefit of including cysteine is that it enhances calcium and phosphate solubility in PN solutions by decreasing the solution s pH. Carnitine is a qnarternary amine required for transport of free fatty acids into the mitochondria for beta-oxidation and energy prodnction. Newborns are at risk for carnitine deficiency becanse of their immature synthetic and conservation mechanisms. Decreased plasma carnitine concentrations are associated with impaired lipid metabolism in patients receiving intravenous lipid emulsion (TVLE). ... 

Strongly retained anions such as phosphate tend to adsorb on soil minerals according to this function, where the saturation of sorption sites is interpreted to mean that 0a = 1, The success of equation 4.41 for many soils means that phosphate solubility is often controlled by the degree of saturation of sorption sites. Furthermore, adherence to the Langmuir function by anions that chemisorb strongly means that, as the adsorption capacity of a soil is approached, solubility increases abruptly. Consequently, as soils approach their saturation limit for adsorption, they are much more likely to allow anions to leach. 

Consider now the case of A1P04-2H20 (variscite) precipitation in soil as a model system. This example is of interest because of the potential control of AP solubility in acid mineral soils by phosphate fertilizer additions, and because of the observation that phosphate solubility in these soils tends to be limited by the known solubility of variscite. 

The concentration of A1 hydroxide in soils is usually high enough that Eq. 3.45 is adequate and Eq. 3.46 is unnecessary. That is probably not true for ions in trace concentrations in soils. The mole fraction concentrations of phosphate and transition metal ions in soils are <3C0.01. So soil phosphate solubility at equilibrium can be orders of magnitude less than the solubility of pure A1 phosphate, as many soil measurements show. We can call it equilibrium because the solubility changes slowly to imperceptibly with time. If anything, the aqueous phosphate concentration decreases with time as the surface A1 ions slowly diffuse into the weathered surface, mix further with other ions, and further increase their entropy. Simple AIPO4 solubility product equivalent to Eq. 3.45, on the other hand, predicts that the phosphate concentration will increase with time. 

Although simplistic, this approach emphasizes a very important point phosphate solubility is a function not only of phosphate activity, but the activity of Ca, LREEs, or Y + HREEs as well. Therefore, factors that change the activities of any of these species in the melt will affect the total solubility of the solid. 

Kinetic considerations. Studies of phosphate solubility reveal kinetic limitations to dissolution rates. Harrison and Watson (1984) and Rapp and Watson (1986) measured the dissolution rates of apatite and monazite, respectively, and found that the dissolution rate is limited by diffusion of P or LREEs away from the dissolving apatite or monazite. Furthermore, the diffusivity, and hence dissolution rate, is strongly dependent on the H2O content of the melt. In dry melts, dissolution is so slow that complete dissolution of even small crystals of apatite or monazite is unlikely. In melts produced by dehydration melting of muscovite or biotite, where the H2O content is in the range of 4-8 wt % H2O, apatite crystals on the order of 500 pm diameter will dissolve in 100-1000 years. 

Additional studies on the melting of phosphates will help quantify phosphate solubility and will aid greatly in the interpretation of these minerals from migmatites. 

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