Phosphorus dissolution

Onken and Matheson (1982) studied kinetics of phosphorus dissolution in EDTA (ethylenediamine tetraacetic acid) solution for several soils. They examined eight kinetic models (Table 2.2) and found that phosphorus dissolution in EDTA solution was best described using the two-constant rate, Elovich, and differential rate equations as indicated by high r2 and low SE values. None of the models best described the dissolution for all soils. 

TABLE 2.2 Summary of r2 and SE of Eight Kinetic Models for Phosphorus Dissolution in EDTA Solution from Six Test Locations Varying in Plant Response to Applied Phosphorus"... 

As can be seen in Fig. 3.67, the corrosion resistance of amorphous alloys changes with the addition of metalloids, and the beneficial effect of a metaU loid in enhancing corrosion resistance based on passivation decreases in the order phosphorus, carbon, silicon, boron (Fig. 3.72). This is attributed partly to the difference in the speed of accumulation of passivating elements due to active dissolution prior to passivation... 

The method can be applied to the determination of phosphorus in a wide variety of materials, e.g. phosphate rock, phosphatic fertilisers and metals, and is suitable for use in conjunction with the oxygen-flask procedure (Section 3.31). In all cases it is essential to ensure that the material is so treated that the phosphorus is converted to orthophosphate this may usually be done by dissolution in an oxidising medium such as concentrated nitric acid or in 60 per cent perchloric acid. 

Inorganic reactions in the soil interstitial waters also influence dissolved P concentrations. These reactions include the dissolution or precipitation of P-containing minerals or the adsorption and desorption of P onto and from mineral surfaces. As discussed above, the inorganic reactivity of phosphate is strongly dependent on pH. In alkaline systems, apatite solubility should limit groundwater phosphate whereas in acidic soils, aluminum phosphates should dominate. Adsorption of phosphate onto mineral surfaces, such as iron or aluminum oxyhydroxides and clays, is favored by low solution pH and may influence soil interstitial water concentrations. Phosphorus will be exchanged between organic materials, soil inter-... 

The problem is to calculate the steady-state concentration of dissolved phosphate in the five oceanic reservoirs, assuming that 95 percent of all the phosphate carried into each surface reservoir is consumed by plankton and carried downward in particulate form into the underlying deep reservoir (Figure 3-2). The remaining 5 percent of the incoming phosphate is carried out of the surface reservoir still in solution. Nearly all of the phosphorus carried into the deep sea in particles is restored to dissolved form by consumer organisms. A small fraction—equal to 1 percent of the original flux of dissolved phosphate into the surface reservoir—escapes dissolution and is removed from the ocean into seafloor sediments. This permanent removal of phosphorus is balanced by a flux of dissolved phosphate in river water, with a concentration of 10 3 mole P/m3. 

To a flame-dried, three-neck, 1-1 flask were added, in order, p-xylene (107 g, 1.0 mol), phosphorus trichloride (412 g, 3.0 mol), and anhydrous aluminum chloride (160 g, 1.2 mol). The reaction mixture was slowly heated to reflux with stirring. After 2.5 h at reflux, the reaction was allowed to cool to room temperature and the volatile components distilled at reduced pressure. The residual oil was slowly added to cold water (1 1) with stirring, and a white solid formed. The solid was removed by filtration, washed with water, and air dried. The solid was suspended in water (1 1) to which was added 50% sodium hydroxide solution (90 ml) to cause dissolution. The solution was saturated with carbon dioxide and filtered through Celite . The basic solution was washed with methylene chloride (200 ml) and acidified with concentrated hydrochloric acid (200 ml). The white solid that separated was isolated by extraction with methylene chloride (3 x 250 ml). The extracts were dried over magnesium sulfate, filtered, and evaporated under reduced pressure to give the pure 2,5-dimethylbenzenephosphinic acid (99 g, 60%) as an oil, which slowly crystallized to a solid of mp 77-79°C. 

While stirred, 1-heptene (9.8 g, 0.1 mol) was added at 20°C to a suspension of phosphorus pentachloride (41.7 g, 0.2 mol) in dimethyl-dicholorsilane (100 ml). The reaction mixture was stirred at 20°C for 3 h and cooled to -10°C. Sulfur dioxide dried over phosphorus pen-toxide was bubbled into the reaction mixture until complete dissolution of the intermediate complex was observed. After evaporation of solvent, the residue was vacuum distilled to give pure 2-chlorohept-l-ylphosphonic dichloride (22.1 g, 88%). 

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. 

Triazones form ammonium ions much more slowly than urea. Slow-release potassium is also being developed. A coating of sulfur seems to delay its release. For phosphorus Mg(NH4)P04 is becoming popular because it has a slower dissolution rate in the soil. Despite the simple chemicals used in most fertilizers, some interesting research and formulation work will keep chemists involved in the industry for some time to come. 

Galvez et al. (1999) demonstrated that phosphorus up to a P/Fe mol ratio of 0.03 mol mol , can be incorporated into the hematite structure by heating P-con-taining 2-line ferrihydrite. Support for structural incorporation comes from a higher unit cell c (1.3776 => 1.3824 nm), IR-stretching bands of P-OH, a lowered intensity ratio of the XRD 104/113 lines and congruent release of Fe and P upon dissolution. 

A.J.G. Blesa, M.A. (1988) The dissolution of magnetite by nitrilotriacetatoferrate(II). J. Chem. Soc. Earaday Trans. I. 84 9-18 Delgado, A. Torrent, J. (2000) Phosphorus forms and desorption patterns in heavily fertilized calcareous and limed acid soils. Soil Sci. Soc. Am. J. 64 2031-2037 Delgado, A.V. Gonzalez-Caballero, F. (1998) Inorganic particles as colloidal models. Effects of size and shape on the electrokinetics of hematite (a-Fe203). Croatica Chemica Acta 71 1087-1104... 

Phosphoric acid also can be made by many different methods. Dissolution of phosphorus pentoxide in water and boiling yields phosphoric acid. Pure phosphoric acid can be obtained by burning phosphorus in a mixture of air and steam ... 

Dissolution of phosphorus sesquioxide in water also forms phosphorus acid. When shaken with ice water, phosphorus acid is the only product... 

In a 1-L three-necked round-bottomed flask and under an atmosphere of nitrogen, a suspension of Os3(CO)12 (0.5 g, 0.55 mmol)4 is prepared in acetonitrile (750 mL), freshly distilled from a slurry of phosphorus pentoxide under nitrogen. To ensure dissolution of the maximum amount of Os3(CO)12, the suspension is heated under reflux for 1 h. The solution is then allowed to cool to room temperature, and under a nitrogen atmosphere, a solution of freshly sublimed, dry trimethylamine oxide (42 mg, 0.55 mmol) in acetonitrile (200 mL) is added to the stirred suspension over a period of 4h using a pressure-equalized dropping funnel. 

Kanobo, I.A.K. and Gilkes, R.J. 1988. The effect of particle size in North Carolina phosphate rock on it dissolution in soil and on levels of bicarbonate-soluble phosphorus. Fertilizer Research 15 137-145. 

Concentrated hydrochloric acid also dissolves the trichloride, about 100 g. of the latter dissolving in 1 litre of acid at 100° C.7 Dissolution in hydriodic acid is accompanied by evolution of heat and the triiodide is formed.8 Ethyl iodide reacts similarly.9 Double decomposition reactions occur w hen arsenic trichloride is heated with phosphorus triiodide, stannic iodide or germanium iodide, the reactions being complete.10 Similarly, potassium iodide heated with arsenic trichloride in a sealed tube at 210° C., and potassium bromide at 180° to 200° C., form respectively arsenic triiodide and tribromide.11 Stannous chloride, added to the solution in hydrochloric acid, causes reduction to arsenic (see p. 29). Arsenic trichloride may be completely separated from germanium chloride by extraction with concentrated hydrochloric acid.12 Ammonium, sodium and cobaltic chlorides react with arsenic trichloride to form additive compounds with magnesium, zinc and chromic chlorides there is no reaction.13... 

The time-sequence pattern of P deposition to the sediment surface differed markedly from that observed with silicon (25). Biogenic silicon underwent relatively little dissolution in the water column as compared with phosphorus, which resulted in a bell-shaped deposition pattern (Figure 11). Rapid regeneration of P during sedimentation resulted in a slower net settling rate for P than for biogenic silicon. 

---