Hydration and precipitation

Hydraulic cements. These cements are formed from two constituents one of which is water. Setting comprises a hydration and precipitation process. Into this category fall Portland cement and plaster of Paris. 

N. Carroll, S.A. (2000) X-ray absorption spectroscopy of strontium coordination. I Static and thermal disorder in crysystalline, hydrated and precipitated solids and in aqueous solution. J. Coll. Interf. Sci. 222 184-198... 

To prevent hydration and precipitation of phosphatides during storage and shipping, the phosphorous content of crude soybean oil must be reduced to less than 0.02 percent (200 ppm) before entering the trade. This usually is accomplished by water degumming. 

O Day PA, Newville M, Neuhoff PS, Sahai N, Carroll SA (2000b) X-ray absorption spectroscopy of strontium(II) coordination I. Static and thermal disorder in crystalline, hydrated, and precipitated solids and in aqueous solution. J Colloid Interface Sci 222 184-197 O Day PA, Parks GA, Brown GE Jr (1994c) Molecular structure and binding sites of cobalt (II) surface complexes onkaolinite from X-ray absorption spectroscopy. Clays Clay Minerals 42 337-355 O Day PA, Rehr JJ, Zabinsky SI, Brown GE Jr (1994a) Extended X-ray Absorption Fine Structure (EXAFS) analysis of disorder and multiple-scattering in complex crystalline solids. J Am Chem Soc 116 2938-2949... 

Anhydrous cupric sulphate is white but forms a blue hydrate and a blue aqueous solution. The solution turns yellow when treated with concentrated hydrochloric acid, dark blue with ammonia, and gives a white precipitate and brown solution when treated with potassium iodide. A yellow-brown aqueous solution of ferric chloride becomes paler on acidification with sulphuric or nitric... 

Calcium. Calcium is the fifth most abundant element in the earth s cmst. There is no foreseeable lack of this resource as it is virtually unlimited. Primary sources of calcium are lime materials and gypsum, generally classified as soil amendments (see Calcium compounds). Among the more important calcium amendments are blast furnace slag, calcitic limestone, gypsum, hydrated lime, and precipitated lime. Fertilizers that carry calcium are calcium cyanamide, calcium nitrate, phosphate rock, and superphosphates. In addition, there are several organic carriers of calcium. Calcium is widely distributed in nature as calcium carbonate, chalk, marble, gypsum, fluorspar, phosphate rock, and other rocks and minerals. 

Causticization, the reaction of hydrated lime [1305-62-0], Ca(OH)2, with sodium carbonate to regenerate sodium hydroxide and precipitate calcium carbonate, is an important part of the Bayer process chemistry. 

Soluble sodium sibcate glass sobd and bquid (anhydrous). Excludes quantities consumed in the manufacture of meta-, ortho-, and sesquisibcates. Includes quantities consumed in the manufacture of glass powder, hydrated glasses, and precipitated products. Shipment figures include unspecified amounts shipped to other plants for the manufacture of meta-, ortho-, or sesquisibcates. 

With Acyl Halides, Hydrogen Halides, and Metallic Halides. Ethylene oxide reacts with acetyl chloride at slightly elevated temperatures in the presence of hydrogen chloride to give the acetate of ethylene chlorohydrin (70). Hydrogen haUdes react to form the corresponding halohydrins (71). Aqueous solutions of ethylene oxide and a metallic haUde can result in the precipitation of the metal hydroxide (72,73). The haUdes of aluminum, chromium, iron, thorium, and zinc in dilute solution react with ethylene oxide to form sols or gels of the metal oxide hydrates and ethylene halohydrin (74). 

Titanium oxide (Ti02). This is produced from dmenite ore by mixing ore with carbon and heating in a rotary kiln. Also, the rotary lain is used in the process of recovery of titanium oxide from hydrated titanium precipitate at about 1250 K. 

The spectra of 1,3,5-, 1,3,7-, and 1,3,8-triazanaphthalerie cations revealed that they were predominantly hydrated, and mild oxidation to the corresponding 4-oxo compounds indicated that hydroxylation took place on C-4. Ring-chain tautomerism in the cation was excluded, at least during the first 45 min after mixing, because negative aldehyde tests were obtained with p-nitrophenylhydrazine. 1,3,6-Triazanaphthalene, under the same conditions, gave a yellow precipit-... 

A mixture of 59.5 g of that oily product, 1.B5 liters of benzene and 1 kg of potassium bisulfite in 200 liters of water is stirred at room temperature for two hours. The precipitated bisulfite addition product of the ketone is isolated by filtration and washed with isopropanol and then with ether. Five hundred grams of the adduct is mixed with 119.5 g of potassium cyanide, 292 ml of B5% hydrazine hydrate and 910 ml of water. The mixture is stirred overnight at room temperature after which the product is isolated by filtration. The product is washed 3 times with 250 ml portions of water and then 3 times with 230 ml portions of ether. It is then air dried and vacuum dried at room temperature. The intermediate so produced has the following formula ... 

To 1,400 ml of an approximately 50% water/triglycol solution of the potassium salt of cheno-deoxycholic acid, obtained by the Wolff-Kishner reduction (using hydrazine hydrate and potassium hydroxide) from 50 g of 7-acetyl-12-ketochenodeoxycholic acid, 220 ml of dilute hydrochloric acid is added to bring the pH to 2. The solution is stirred and the crude cheno-deoxycholic acid precipitates. The precipitate is recovered and dried to constant weight at about 60°C. About 36 g of the crude chenodeoxycholic acid, melting in the range of 126°-129°C, is obtained. 

To a solution of 39.5 g (0.0845 mol) of 2-(N-phthalimidoacetyl-N-cyclopropylmethyl)amino-5-chlorobenzophenone in a mixture of 423 ml of chloroform and 423 ml of ethanol Is added 9.52 g (0.1903 mol) of hydrazine hydrate and 9.52 ml of water. This solution is allowed to stand at room temperature. In 3 hours a precipitate begins to form in the solution. After standing 16 to 24 hours a voluminous pulpy white precipitate forms. The solvents are removed under vacuum while keeping the temperature under 40 0 and the residue is partitioned between dilute ammonia water and ether. 

Brown et al. [494] developed a method for the production of hydrated niobium or tantalum pentoxide from fluoride-containing solutions. The essence of the method is that the fluorotantalic or oxyfluoroniobic acid solution is mixed in stages with aqueous ammonia at controlled pH, temperature, and precipitation time. The above conditions enable to produce tantalum or niobium hydroxides with a narrow particle size distribution. The precipitated hydroxides are calcinated at temperatures above 790°C, yielding tantalum oxide powder that is characterized by a pack density of approximately 3 g/cm3. Niobium oxide is obtained by thermal treatment of niobium hydroxide at temperatures above 650°C. The product obtained has a pack density of approximately 1.8 g/cm3. The specific surface area of tantalum oxide and niobium oxide is nominally about 3 or 2 m2/g, respectively. 

The important oxides are black PdO and brown Pt02. The former can be made by heating palladium in oxygen other methods include heating PdCl2 in an NaN03 melt at 520°C. A hydrated form precipitates from aqueous solution, e.g. when Pd(N03)2 solution is boiled. It has 4-coordinate square planar palladium (Figure 3.8). 

A special technique was developed for rare-earth samples in which rapid hydration and carbonation occurred. The rare-earth oxalates were found to be more stable than the oxides and were used as sample material. In the rare-earth processing procedures that include an oxalate precipitate, the oxalate can be used as sample material. The advantages are that no diluent is required, weighing is eliminated, and recovery of the rare earths is simplified. 

The ratio of the two forms depends on the cation as well as on a. Ba has a greater tendency to make linkages of the COO-Me-OOC type than Mg and this difference is accentuated when the density of COO" in the polyanion is low. Thus, at a = 025 more Ba ions are in the COO-Ba-OOC form than in the COO-Ba form, while the reverse is true for Mg ions. Moreover, the structure COO-Mg is more stable and soluble than COO-Ba because Mg is more hydrophilic than Ba. For these reasons, Ba is precipitated at a = 0-25 while Mg is not. This interpretation is supported by titration experiments in the presence of divalent cations (Jacobsen, 1962). Magnesium forms very stable hydrates and would be expected to be more difficult to desolvate. 

It is well known that lyophilic sols are coagulated by the removal of a stabilizing hydration region. In this case, conversion of a sol to a gel occurs when bound cations destroy the hydration regions about the polyanion, and solvated ion-pairs are converted into contact ion-pairs. Desolvation depends on the degree of ionization, a, of the polyacid, and the nature of the cation. Ba ions form contact ion-pairs and precipitate PAA when a is low (0-25), whereas the strongly hydrated Mg + ion disrupts the hydration region only when a > 0-60. 

They considered that cement formation was the result of an acid-base reaction leading to the formation of hydrates by a through-solution mechanism, by nucleation and precipitation from pore fluids. Two phases were found in the matrix, one amorphous and the other crystalline. The crystalline phase was newberyite. Finch Sharp concluded that the amorphous phase was a hydrated form of aluminium orthophosphate, AIPO4, which almost certainly contained magnesiiun. They ruled out a pure AlP04.nH20, for they considered that the reaction could not be represented by the equation... 

Greater adsorption of trace metals is found at higher pH and C02(g) concentrations. Sites available for Zn2+ sorption are less than 10% of the Ca2+ sites on the calcite surface, and Zn adsorption is independent of surface charge. This indicates a surface complex with a covalent character (Zachara et al., 1991). Furthermore, the surface complex remains hydrated and labile because Zn2+ is rapidly exchangeable with Ca2+, Zn2+ and ZnOH. At the dolomite-solution interface, the carbonate(C03)-metal (Ca/Mg) complex dominates surface speciation at pH > 8, but at pH 4-8, hydroxide (OH) -metal (Ca/Mg) dominates surface speciation (Pokrovsky et al., 1999). Calcite has an observed selectivity sequence Cd > Zn > Mn > Co > Ni > Ba = Sr, but their sorption reversibility is correlated with the hydration energies of the metal sorbates. Cadmium and Mn dehydrate soon after adsorption to calcite and form a precipitate, while Zn, Co and Ni form surface complexes, remaining hydrated until the ions are incorporated into the structure by recystallization (Zachara et al., 1991). 

Excer A process for making uranium tetrafluoride by electrolytic reduction of a uranyl fluoride solution, precipitation of a uranium tetrafluoride hydrate, and ignition of this. 

The sulfur dioxide is recovered as sulfuric acid and reconverted to sodium sulfate. Alumina hydrate is precipitated from the sodium aluminate by carbon dioxide. The process has not become widely accepted because the product is contaminated by silica, but it was used in Belgium before and after World War I and in Germany in the 1920s and 1940s. 

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