Phosphate speciation

Calcium Phosphates—Speciation, Solubility, and Kinetic Considerations... 

Frarrz G, Andrehs G, Rhede D (1996) Crystal chemistry of morrazite and xenotime from Saxothrrringian-Moldanubian metapelites, NE Bavaria, Germany. Eur J Mineral 8 1097-1108 Gan H, Hess PC (1992) Phosphate speciation in potassium alrrminosilicate glass. Am Mineral 77 495-506 Gorz H, White EH (1970) Minor and trace elements in HF-soluble zircons. Contrib Mineral Petrol 29 180-182... 

Murray RW, Leinen M, Isem AR (1993) Biogenic flux of A1 in the central equatorial Pacific Ocean Evidence for increased productivity during glacial periods. Paleoceanogr 8 651-670 Murray RW, Knowlton C, Leinen M, Mix AC, Polski CH (2000) Export production and carbonate dissolution in the central equatorial Pacific Ocean over the past 1 Ma. Paleoceanogr 15 570-592 Nancollas GH, Amjad Z, Koutsoukas P (1979) Calcium phosphates-speciation, solubility, and kinetic considerations. Am Chem Soc Symp Ser 93 475-497... 

Lookman, R., Crobet, P., Merckx, R. and van Reims-dijk, W.H. (1997) Application of and Al MAS NMR for phosphate speciation studies in soil and aluminium hydroxides promises and constraints. Geoderma 80, 359-388. 

Several factors can influence metal uptake by stream autotrophic biofllms in fluvial systems. These include chemical factors (pH, saUnity, phosphate concentration) which affect metal bioavailabiHty by either altering the speciation of the metal or by complexing it at the biotilm s matrix and cell surfaces [18, 40], and also other biological and physical factors. 

Speciated Components Little information is available for RMs with respect to the chemical forms or species in which elements occur. In the first approximation, bioavaila-ble, extractable, or leachable levels of elements are of interest. Secondly, at a higher degree of sophistication, data on the levels of the actual species or inorganic moieties such as nitrate, ammonium, phosphate, bromide, bromate, iodide, iodate, and molecular species of which the elements are constituents would be of relevance to those conducting mechanistic and speciation research. Reference materials that are certified for extractable elemental concentrations are not available to monitor the usual procedures in soil science based on extraction. 

In arid and semi-arid soils with a pH range of 6-9, free calcium is the major Ca speciation form in soil solution. When pH > 9.2-9.5, CaP04 becomes a major calcium species in soil solution of neutral and calcareous soils, especially when the activity of H2P04 is > 10 5 M (Lindsay, 1979), such as after phosphate fertilizers are used. Lindsay (1979) further pointed out that CaS04° contributes significantly to the total calcium in solution when S042- is > 10 M. 

Figure 3.4. Effects of phosphate levels on Cd and Zn solution speciation in California soils that received sludge application (data extracted from Villarroel et al., 1993)...

Ma L.Q., Choate A.L., Rao G.N. Effects of incubation and phosphate rock on lead extractabihty and speciation in contaminated soils. J Environ Qual 1997a 26 801-807. 

Russell and Rabenstein [43] described a speciation and quantitation method for underivatized and derivatized penicillamine, and its disulfide, by capillary electrophoresis. Penicillamine and penicillamine disulfide were determined by capillary electrophoresis on a capillary (24 cm x 25 pm i.d. or 50 cm x 50 pm i.d. for underivatized thiols) with detection at 357 nm (200 nm for underivatized thiols). The run buffer solution was 0.1 M phosphate (pH 2.3). Detection limits were 20-90 pM without derivatization, and 5-50 pM after derivatization. Calibration graphs were linear from 1 pM to 5 mM thiols. 

In a final example of the use of a sliding activity path, we calculate a speciation diagram, plotted versus pH, for hexavalent uranium in the presence of dissolved phosphate at 25 °C. We take a 10 mmolal NaCl solution containing 1 mmolal each ofUO +, the basis species for U(VI), and HPO4... 

Fig. 14.12. Speciation diagram at 25 °C for a 1 mmolal solution of hexavalent uranium containing 1 mmolal dissolved phosphate, calculated as a sliding activity path.

Boron and arsenic are natural components of soil and are both present as oxyanions. Boron is present as boric acid or borate polymers, and arsenic is present as arsenate. While boron is weakly held by soil, arsenic is similar to phosphate in its interactions with soil constituents. Boron is an essential nutrient for plants however, it is also toxic to plants at relatively low levels. Arsenic is toxic. The laboratory chemistry of both of these elements is well understood, but their environmental chemistry, speciation and movement, is less well understood [23-27],... 

Speciation calculations can be performed for the weak acids and bases in a feshion similar to that presented earlier for Fe(III). The results of these calculations as a function of pH are shown in Figure 5.19. At the pH of seawater, the dominant species are carbonate, bicarbonate, ammonium, hydrogen phosphate, dihydrogen phosphate, and boric and silicic acid. In waters with low O2 concentrations, significant concentrations of HS can be present. 

As noted already for carbonate and sulfate, some conjugate bases are subject to a significant amount of ion pairing. This is also seen in phosphate, whose speciation is strongly influenced by ion pairing and acid-base reactions (Figure 5.20). 

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