Salts calcium phosphates

Calcium Phosphates. The alkaline-earth phosphates are generally much less soluble than those of the alkaH metals. Calcium phosphates include the most abundant natural form of phosphoms, ie, apatites, Ca2Q(P0 3X2, where X = OH, F, Cl, etc. Apatite ores are the predominant basic raw material for the production of phosphoms and its derivatives. Calcium phosphates are the main component of bones and teeth. After sodium phosphates, the calcium salts are the next largest volume technical- and food-grade phosphates. Many commercial appHcations of the calcium phosphates depend on thek low solubiHties. 

Several compounds of the CaO—P2O3—H2O system are given in Table 8. The common names for the mono-, di-, and tricalcium phosphates arise from the traditional double-oxide formulas, CaO 2i5p T2O3, 2CaO H2O +205, and 3CaO +205, respectively. These terms are routinely used in industry. With the exception of the monocalcium salt, the calcium phosphates are all sparingly soluble. 

Both monocalcium phosphate and dicalcium phosphate dissolve incongmently in water, disproportionating to more basic calcium phosphate and phosphoric acid. The extent of these reactions varies with the temperature and the amount of water. If water is added gradually to anhydrous monocalcium phosphate, equiUbrium conditions first correspond to a mixture of the anhydrous salt and its monohydrate. After conversion to the monohydrate, further reaction affords dicalcium phosphate plus free phosphoric acid. Dicalcium phosphate decomposes in aqueous solution to the more basic hydroxyapatite and phosphoric acid via intermediate octacalcium phosphate. The compHcated stepwise conversion of the acidic mono- and dicalcium phosphates to hydroxyapatite is summarized in equations 6—9. The kinetics are quite complex. 

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. 

In addition to the requirement to conform to steam purity needs, there are concerns that the boiler water not corrode the boiler tubes nor produce deposits, known as scale, on these tubes. Three important components of boiler tube scale are iron oxides, copper oxides, and calcium salts, particularly calcium carbonate [471-34-1]. Calcium carbonate in the feedwater tends to produce a hard, tenacious deposit. Sodium phosphate is often added to the water of recirculating boilers to change the precipitate from calcium carbonate to calcium phosphate (see also Water, industrial water treatment). 

Charcoal is generally satisfactorily activated by heating gently to red heat in a crucible or quartz beaker in a muffle furnace, finally allowing to cool under an inert atmosphere in a desiccator. Good commercial activated charcoal is made from wood, e.g. Norit (from Birch wood), Darco and Nuchar. If the cost is important then the cheaper animal charcoal (bone charcoal) can be used. However, this charcoal contains calcium phosphate and other calcium salts and cannot be used with acidic materials. In this case the charcoal is boiled with dilute hydrochloric acid (1 1 by volume) for 2-3h, diluted with distilled water and filtered through a fine grade paper on a Buchner flask, washed with distilled water until the filtrate is almost neutral, and dried first in air then in a vacuum, and activated as above. To improve the porosity, charcoal columns are usually prepared in admixture with diatomaceous earth. 

Kalk. m. lime (equivalent, in old names of salts, to calcium as, phosphorsauerer Kalk, phosphate of lime, calcium phosphate) limestone (Old Chem.) cabc. —. tzender —, caustic lime, quicklime. — gelfischter —, slaked lime. — gebraonter —, quicklime. 

Crucibles fitted with permanent porous plates are cleaned by shaking out as much of the solid as possible, and then dissolving out the remainder of the solid with a suitable solvent. A hot 0.1 M solution of the tetrasodium salt of the ethylenediaminetetra-acetic acid is an excellent solvent for many of the precipitates [except metallic sulphides and hexacyanoferrates(III)] encountered in analysis. These include barium sulphate, calcium oxalate, calcium phosphate, calcium oxide, lead carbonate, lead iodate, lead oxalate, and ammonium magnesium phosphate. The crucible may either be completely immersed in the hot reagent or the latter may be drawn by suction through the crucible. 

The precipitation of anhydrite (anhydrous calcium sulfate, CaS04) may also occur. Under ambient temperatures, anhydrite is much more soluble than calcium carbonate, but because calcium sulfate, in common with other calcium salts such as calcium phosphate (also known as tricalcium phosphate [Ca3(P04)2]), has an inverse-temperature solubility, it deposits more rapidly on the hottest heat transfer surfaces. 

Most salts absorb heat when they go into solution, and their solubility increases with a rise in temperature however, calcium carbonate (CaC03), in common with several other anhydrous salts such as calcium sulfate (CaS04) and calcium phosphate [Ca3(P04)2], has an inverse temperature solubility and thus readily precipitates to form deposits in hot water areas (FW tanks, FW lines, and boiler heat exchange surfaces). 

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. 

C04-0025. Design a synthesis of 1.5 kg of calcium phosphate that starts with soluble salts. 

C04-0146. The largest single use of sulfuric acid is for the production of phosphate fertilizers. The acid reacts with calcium phosphate in a 2 1 mole ratio to give calcium sulfate and calcium dihydrogen phosphate. The mixture is crushed and spread on fields, where the salts dissolve in rain water. (Calcium phosphate, commonly found in phosphate rock, is too insoluble to be a direct source of phosphate for plants.) (a) Write a balanced equation for the reaction of sulfuric acid with calcium phosphate, (b) How many kilograms each of sulliiric acid and calcium phosphate are required to produce 50.0 kg of the calcium sulfate-dihydrogen phosphate mixture (c) How many moles of phosphate ion will this mixture provide ... 

C18-0073. For the following salts, write a balanced equation showing the solubility equilibrium and write the solubility product expression for each (a) silver chloride (b) barium sulfate (c) iron(H) hydroxide and (d) calcium phosphate. 

Mineral acids these are acids derived from mineral substances, such as, for example, hydrochloric acid which is obtained from common salt, nitric acid from sodium or potassium nitrate, sulfuric acid from sulfur, phosphoric acid from calcium phosphate, etc. 

Calcium salt. Calcium gluconate is the preferred salt in PN because it is has a low dissociation in solution with lesser free calcium available at a given time to bind phosphate (as opposed to calcium chloride, which dissociates rapidly in solution). 

A number of mineral-based substances display an adjuvant effect. Although calcium phosphate, calcium chloride and salts of various metals (e.g. zinc sulfate and cerium nitrate) display some effect, aluminium-based substances are by far the most potent. Most commonly employed are aluminium hydroxide and aluminium phosphate (Table 13.13). Their adjuvanticity, coupled to their proven safety, render them particularly valuable in the preparation of vaccines for young children. They have been incorporated into millions of doses of such vaccine products so far. 

Inorganic salts that contain halogens are usually soluble. They commonly occur as simple, single, negatively charged anions in soil. There are two common exceptions to this generalization. First, fluorine is commonly found bonded to phosphate in insoluble minerals called apatites, which are calcium phosphate fluorides. 

---