Ammonium Phosphate Precipitation

The conditional solubility product of magnesium ammonium phosphate, struvite (MgNH4P04[s)) illustrates a situation where more than one of the dissolving species is affected by solution pH. These species are the ammonium ion NH4+) and the phosphate ion (P04 ). Because an increase in pH will decrease the ammonium ion concentration and increase the phosphate ion concentration, it follows that there should be a pH value where the solubility of MgNH4p04(s) is a minimum, that is, the pH where the product [Mg +][NH4 ][P04 ] is a minimum. Where is this point  

We can attack this problem by writing equations for the pH-dependent reactions involving each of the species in the precipitate. Thus 

Then is a function of pH and its minimum value will occur when the product Mg3+) X (q nh4+) x (0 043-) is a maximum. The values of these ionization fractions are presented in Appendix 1 is plotted as a function of pH in Fig. 6-19, assuming in one case that fju = Q and in the other that fx = 0.1. Activity coefficients were obtained from Fig. 3-4. We can see from this figure that the minimum solubility occurs at about pH 10.7. 

With the concentrations indicated in Table 6-6 we can compute the product Cr.Mg X Ct.nhj X Ct.po and if this significantly exceeds the conditional solubility product, Pj, then struvite should precipitate. 

Constituent mg/liter moles/liter mg/liter moles/liter mg/liter moles/liter 

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Calculate the number of micromoles of Pi and 7-min phosphate in the entire volume of filtered solution. If the inorganic phosphate (in the unhydrolyzed sample) in the filtrate is less than 15% of the phosphate found after 7-min hydrolysis, you may proceed with the rest of the experiment. (NOTE When students are working in pairs, some instructors prefer to have one student proceed directly with steps 12 through 14 while the other student conducts the assays of steps 5 through 9. This assumes that the magnesium ammonium phosphate precipitation effectively removes most of the inorganic phosphate from your preparation, as occurs in most (but not all) cases. Consult your instructor.)... 

Dawson and Heaton (DIO) determined magnesium in plasma and urine. A water-cooled burner was used with an air-acetylene flame. Good agreement was found with an ammonium phosphate precipitation method when allowance was made for the loss of magnesium during precipitation. 

Phosphorus species. Ammonium phosphate precipitates Be from neutral or slightly acidic solutions as BeNH4P04. 

Orthophosphate Hquid mixtures are ineffective as micronuttient carriers because of the formation of metal ammonium phosphates such as ZnNH PO. However, micronutrients are much more soluble in ammonium phosphate solutions in which a substantial proportion of the phosphoms is polyphosphate. The greater solubiHty results from the sequestering action of the polyphosphate. The amounts of Zn, Mn, Cu, and Fe soluble in base solution with 70% of its P as polyphosphate are 10 to 60 times their solubiHties in ammonium orthophosphate solution. When a mixture of several micronutrients is added to the same solution, the solubiHty of the individual metals is lowered significantly. In such mixtures the total micronuttient content should not exceed 3% and the storage time before precipitates appear may be much shorter than when only one micronuttient is present. 

Localized pre-boiler scale and corrosion debris deposits. Combination of New phosphate, iron, copper, and silica deposition Old re-deposited debris Transport of Fe, Cu, Ni, Zn, Cr oxides to HP boiler section, leading to deposition, fouling, and possible tube failures Transport of minerals and debris including malachite, ammonium carbamate, basic ferric ammonium carbonate Precipitation in FW line of phosphates, iron, and silicates... 

Figure 2. Gel filtration. The dry residue obtained after ammonium sulfate precipitation was redissolved in 50 mM phosphate buffer, pH 7.4 0.15 M NaCl 0.013 % sodium azide, which was loaded on a Superdex 75HR1030 column equilibrated with the same buffer. Elution was downward flow (0.15 ml/min) and 0.25 ml fractions were collected. The fractions were assayed for protein content (— ) and PNL activity (- - ).

Magnesium may be precipitated from solution as MgNH4P04.6H20, a compound which has been widely used as a basis for the gravimetric determination of the element over many years. An examination of its use will serve to illustrate some of the problems associated with inorganic precipitations. The initial precipitation is made from a solution at pH = 11-12 by the addition of ammonium phosphate in excess. 

For a precipitate used in gravimetric analysis magnesium ammonium phosphate has a rather high solubility (0.1 g dm 3 in water at 20°C). Hence solution volumes should be kept as low as possible and the precipitate must be filtered from cold solution. Furthermore, the solution composition must be carefully controlled to ensure the maintenance of conditions of... 

Synthetic hydroxyapatite prepared by mixing stoichiometric amounts of aqueous solutions of calcium nitrate and ammonium phosphate was used in this study. The pH of the boiling suspension was maintained at about 10 by flowing a mixture of NH and throughout the precipitation process. The precipitate was repeatedly washed until the conductivity of the supernatant liquid was observed to be constant. The washed sample was freeze-dried and analyzed. An elemental analysis of the batch preparation showed the Ca/P molar to be ratio 1.64, with the predominant impurity being 2... 

Dibasic ammonium phosphate is used as a fertilizer as a fire extinguisher a flame retardant for plywood, papers, and fabrics to prevent afterglow in matches in purifying sugar as a flux for soldering tin, copper, zinc and brass and to control precipitation of alkah-soluble or acid-insoluble coUoidal dyes on wool. 

Fluorhydroxyapatite can be synthesised by the traditional double-decomposition method generally used for apatite precipitation. An ammonium phosphate and fluoride solution (solution B) is added, dropwise, into a hot (generally at boiling temperature) calcium solution (solution A) at a basic pH level as previously published [122,123]. Fluorapatites close to stoichiometry are obtained (a = 2, see the following reaction equation) however, a very small residual amount of OH always seems to be present. Filtration and several washing operations are necessary to remove the counter-ions. The reaction is almost total due to the very low solubility of fluorhydroxyapatites. 

Alkalies. — The solution of 2 gm. of ammonium phosphate in 100 cc. of water is treated with lead acetate solution in slight excess to precipitate the phosphoric acid, and is then filtered. The excess of lead in the filtrate is then precipitated with hydrogen sulphide, the liquid filtered, the filtrate evaporated to dryness, and the residue ignited. The residue should not be soluble in water, nor should it have an alkaline reaction. 

Carbonates and Sulphates. — On adding hydrochloric acid to a solution of 1 gm. of ammonium phosphate in 20 cc. of water, no effervescence should take place and on adding barium chloride solution, no precipitate of barium sulphate should form on standing twelve hours. 

Magnesium. I lisNolve 3 gm. of sodium chloride in 10 cc. uf wiilcr. nod add ft cc. of ammonia water and ammonium phosphate solution. No precipitate should form within three hours. 

Magnesium, formerly determined by precipitation as magnesium ammonium phosphate and determining P in the latter, can be analyzed readily by EDTA titrations. It can be obtained either as the difference between titrations for (Ca and Mg) and Ca alone or by titrating the supernatant after Ca is precipitated as oxalate (White and Davies 1962). 

A precipitate may be formed as a result of chemical reaction between separately soluble gases or liquids. Commercial examples are productions of sodium sulfate, ammonium sulfate, and ammonium phosphate. 

Magnesium Ammonium Phosphate. MgNH(POr. white precipitate. K,t, 2.5 x 0 1 -. by reaction of soluble salt solution and sodium phosphate in the presence of excess ammonium hydroxide, upon igniting yields magnesium pyrophosphate. MgyPsOz. while solid. 

Salts therefore, are prepared (1) from solutions of acids and bases by neutralization and separation by evaporation and crystallization (2) from solutions of two salts by precipitation where the solubility of the salt formed is slight (e.g., silver nitrate solution plus sodium chloride solution yields silver chloride precipitate [almost all as sulid], and sodium nitrate present in solution as sodium cations and nitrate anions [recoverable as sodium nitrate, solid by separation of silver chlondc and subsequent evaporation of the solution]) (3) from fusion of a basic oxide (or its suitable compound—sodium carbonate above) and an acidic oxide (or its suitable compound—ammonium phosphate), since ammonium and hydroxyl are volatilized as ammonia and water. Thus, sodium ammonium hydrogen phosphate... 

Figure B3.1.1 A 15% SDS-polyacrylamide gel stained with Coomassie brilliant blue. Protein samples were assayed for the purification of a proteinase, cathepsin L, from fish muscle according to the method of Seymour et al. (1994). Lane 1, purified cathepsin L after butyl-Sepharose chromatography. Lane 2, cathepsin L complex with a cystatin-like proteinase inhibitor after butyl-Sepharose chromatography. Lane 3, sarcoplasmic fish muscle extract after heat treatment and ammonium sulfate precipitation. Lane 4, sarcoplasmic fish muscle extract. Lanes M, low-molecular-weight standards aprotinin (Mr 6,500), a-lactalbumin (Mr 14,200), trypsin inhibitor (Mr 20,000), trypsinogen (Mr 24,000), carbonic anhydrase (Mr 29,000), gylceraldehyde-3-phosphate dehydrogenase (Mr 36,000), ovalbumin (Mr 45,000), and albumin (Mr 66,000) in order shown from bottom of gel. Lane 1 contains 4 pg protein lanes 2 to 4 each contain 7 pg protein.

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