Hydroxyapatite precipitation

Eanes, E.D. and Posner, A.S. 1970 A note on the crystal growth of hydroxyapatite precipitated from aqueous solutions. Materials Research Bulletin 5 377-384. 

Arends, J., J. Christoffersen, M. R. Christoffersen, H. Eckert, B. O. Fowler, J. C. Heughebaert, G. H. Nancollas, J. P. Yesinowski, and S. J. Zawacki (1987), "A Calcium Hydroxyapatite Precipitated from an Aqueous Solution An International Multimethod Analysis", J. Crystal Growths4, 515-532. 

Inskeep WP and Silvertooth JC (1988) Inhibition of hydroxyapatite precipitation in the presence of fulvic, humic, and tannic acids. Soil Sci Soc Am J 52, 941-946. 

Odutuga, A. A., Prout, R. E. S., Hoare, R. J. Hydroxyapatite precipitation in vitro by lipids extraced from mammalian hard and soft tissues. Arch, oral Biol. 20, 311 (1975)... 

Several chemical reactions, including calcium carbonate and hydroxyapatite precipitation, have been studied to determine their relationship to observed water column and sediment phosphorus contents in hard water regions of New York State. Three separate techniques have been used to Identify reactions important in the distribution of phosphorus between the water column and sediments 1) sediment sample analysis employing a variety of selective extraction procedures 2) chemical equilibrium calculations to determine ion activity products for mineral phases involved in phosphorus transport and 3) seeded calcium carbonate crystallization measurements in the presence and absence of phosphate ion. 

Arends J, Ghristoffersen J, Ghristoffersen MR, Eckert H, Fowler BO, Heughebaert JG, Nan-collas GH,Yesinowski JP,Zawacki SJ (1987) A calcium hydroxyapatite precipitated from an aqueous solution. J Gryst Growth 84 515-532... 

Table 6.5) that quickly drives up the pH of the solution, thus providing OH- ions for precipitation of hydroxyapatite. On exceedingthe solubility product of hydroxyapatite, precipitation of secondary hydroxyapatite occurs according to... 

FIG. 2 Mass spectrometer temperature-programmed dehydration (MSTPD) spectra showing the evolution of water as a function of temperature from (1) hydroxyapatite precipitated from an aqueous solution via an amorphous precursor phase, (2) hydroxyapatite prepared in a hydrothermal bomb, and (3) apatite from a mineral source. (After Ref. 28.)... 

Lazic, S., Zee, S., Miljevic, N. and Milonjic, S. (2001) The effed of temperature on the properties of hydroxyapatite precipitated from caldum hydroxide and phosphoric add. Thermochimica Acta, 374, 13-22. 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

Hydroxyapatite, Ca2Q(PO (OH)2, may be regarded as the parent member of a whole series of stmcturaHy related calcium phosphates that can be represented by the formula M2q(ZO X2, where M is a metal or H O" Z is P, As, Si, Ga, S, or Cr and X is OH, F, Cl, Br, 1/2 CO, etc. The apatite compounds all exhibit the same type of hexagonal crystal stmcture. Included are a series of naturally occurring minerals, synthetic salts, and precipitated hydroxyapatites. Highly substituted apatites such as FrancoHte, Ca2Q(PO (C02) (F,0H)2, are the principal component of phosphate rock used for the production of both wet-process and furnace-process phosphoric acid. 

Tricalcium Phosphate. Commercial tricalcium phosphate (TCP) is actually an amorphous basic calcium phosphate close to hydroxyapatite in composition. Because of its extremely low solubiUty in water, TCP is precipitated almost quantitatively from dilute phosphate solutions with a slurry of hydrated lime. TCP is separated by dmm-, spray-, or flash-drying the TCP slurry, with or without intermediate sedimentation or filtration steps. It is used as an industrial-grade flow conditioner and parting agent. 

A wide variety of precipitates form in cooling water systems carbonates, silicates, sulfates, and phosphates are common. Below and slightly above 212°F (100°C), calcite, aragonite, gypsum, hydroxyapatite, magnesium phosphate, anhydrite, and serpentine are commonly encountered (see Table 4.1). 

Where precipitating phosphate programs are used, residual calcium forms a sludge of the basic salt hydroxyapatite [Ca10(PO4)6(OH)2]. 

NOTE Depending on operating conditions, alkalinity, pH level, point of feed, and so forth, when phosphate is present in the BW, calcium salts precipitate primarily as either insoluble tricalcium phosphate [Ca3(P04)2] or hydroxyapatite [Ca]0(0H)2(P04)6J. 

Some phosphate-cycle reactions are shown below, and, although for the sake of simplicity only calcium phosphate is shown as a precipitant, depending on the operational circumstances, the reaction produces either tricalcium phosphate, hydroxyapatite, or a combination of both salts. 

The BW pH level should be above 10.2 to ensure that hydroxyapatite preferentially precipitates. Also, where magnesium is present, the pH level should be above 10.5 so that magnesium hydroxide [brucite, Mg(OH)2] precipitates, rather than the stickier and more adherent magnesium phosphate [Mg3(P04)2]. In any event, where possible, it is... 

NOTE If the BW contains phosphate, the preferred reaction is for calcium to precipitate as hydroxyapatite, rather than to chelate with EDTA or NTA (a further competing anion effect). Consequently, there would seem to be no valid reason to produce combined phosphate-chelant programs, with the chelant acting as a reserve against unforeseen hardness incursions caused by a softener leakage, or other source. In practice, the chelant acts to solubilize existing deposits, producing a very clean boiler. 

Sodium carboxymethyl chitin and phosphoryl chitin had most evident influences on the crystallization of calcium phosphate from supersaturated solutions. They potently inhibited the growth of hydroxyapatite and retarded the rate of spontaneous calcium phosphate precipitation. These chitin derivatives were incorporated into the precipitate and influenced both the phase and morphology of the calcium phosphate formed (flaky precipitate resembling octacalcium phosphate instead of spherical clusters in the absence of polysaccharide) [175]. 

Chitosan scaffolds were reinforced with beta-tricalciiun phosphate and calcium phosphate invert glass [177]. Along the same line, composites of Loligo beta-chitin with octacalcium phosphate or hydroxyapatite were prepared by precipitation of the mineral into a chitin scaffold by means of a double diffusion system. The octacalciiun phosphate crystals with the usual form of 001 blades grew inside chitin layers preferentially oriented with the 100 faces parallel to the surface of the squid pen and were more stable to hy-... 

Final alcohol precipitation not only allows for removal of the phenol and any remaining non-covalently bound hydrocarbon but also concentrates the DNA. Ribonuclease treatment removes any contaminating RNA. Additional purification by cesium chloride centrifugation (35) is also often performed. This is particularly suited to small quantities of DNA. Hydroxyapatite chromatography is also effective in separating RNA, proteins, and DNA (36.37). 

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