Carbonate and precipitation

Dapex [Di-alkylphosphoric acid extraction] A process for the solvent extraction of uranium from sulfuric acid solutions using di-(2-ethylhexyl) phosphoric acid (HDEHP). The HDEHP is dissolved in kerosene containing 4 percent of tributyl phosphate. The uranium is stripped from the organic phase by aqueous sodium carbonate and precipitated as uranyl peroxide (yellow cake). The process was no longer in use in 1988. See also Amex. 

As noted before, many conventional methods rely on hydrolysis/precipi-tation chemistry to deposit Pt and other metals onto carbon, followed by chemical or gas-phase reduction. One common method is the use of metal sulfito chemistry. This method involves the preparation of metal sulfito complexes (e.g., Na3[Pt(S03)2(0H)2]) in water, the addition of carbon, and precipitation of metal by oxidation to deposit metal oxide particles. The route has advantages in that alkali metals and halides are excluded from the preparation. The method has been extended to bimetallics such as PtRu. 

Theis Richter (1979) showed that adsorption onto hydrous Fe-oxide was the major solubility control for Cd, Ni, and Zn in soils surrounding two ash disposal ponds, and stated that certain fly ashes are capable of causing the deposition of secondary Fe-oxides. The ash pond leachate conditions favoured the precipitation of Pb and Cr hydroxides, Pb carbonate, and precipitation of Cu as malachite. The leaching of As (as arsenate) and Se (as selenite) was found to be controlled by adsorption onto amorphous Fe-oxide by van der Hoek Comans (1994). 

In the reduction stripping process uranium(IV) in the raw wet process acid is oxidized to uranium(Vl) by treatment with sodium chlorate, hydrogen peroxide or air at 60 to 70°C, the uranium(VI) formed being extracted with trioctylphosphine oxide/di-(2-ethylhexyl)phosphate in kerosene and the resulting solution finally reductively stripped repeatedly with aqueous iron(II) solutions. This results in an enrichment by a factor of 40. After oxidation of the stripped solution with sodium chlorate or ambient oxygen and renewed extraction of the uranium(VI) formed with trioctylphosphine oxide/di-(2-ethylhexyl)phosphate, the phosphoric acid is removed from the organic phase by washing. The uranium(Vl) is then stripped with ammonium carbonate and precipitated as the ammonium diuranyl-tricarbonato-complex. This is filtered off, washed and calcined. 

At the surface, the ocean waters throughout most of the world are 200-500 % supersaturated in calcium carbonates and precipitation of these carbonate scales will influence the corrosion reaction occurring at the metal surface [6]. The buildup of protective calcareous deposits by cathodic protection can lower the subsequent current demand in natural seawater [22-24]. 

Miscellaneous Fillers - Although kaolin clay, calcium carbonate, and precipitated silica accoimt for most of the non-black fillers used in rubber today, there are a munber of other fillers routinely used for their low cost or imique fimtionality. 

NH4. HCO3. CU and Na and the least soluble salt sodium hydrogen carbonate, is precipitated when ionic concentrations increase, and is removed by vacuum filtration. 

If the hydrogencarbonate is in solution and the cation is Ca or Mg. the insoluble carbonate is precipitated this reaction may be used, therefore, to remove hardness in water by precipitation of Ca or Mg ions.) The ease of decomposition of hydrogencar-bonates affords a test to distinguish between a hydrogencarbonate and a carbonate carbon dioxide is evolved by a hydrogencarbonate, but not by a carbonate, if it is heated, either as the solid or in solution, on a boiling water bath. 

Prepare a mixture of 30 ml, of aniline, 8 g. of o-chloro-benzoic acid, 8 g. of anhydrous potassium carbonate and 0 4 g. of copper oxide in a 500 ml. round-bottomed flask fitted with an air-condenser, and then boil the mixture under reflux for 1 5 hours the mixture tends to foam during the earlier part of the heating owing to the evolution of carbon dioxide, and hence the large flask is used. When the heating has been completed, fit the flask with a steam-distillation head, and stcam-distil the crude product until all the excess of aniline has been removed. The residual solution now contains the potassium. V-phenylanthrani-late add ca. 2 g. of animal charcoal to this solution, boil for about 5 minutes, and filter hot. Add dilute hydrochloric acid (1 1 by volume) to the filtrate until no further precipitation occurs, and then cool in ice-water with stirring. Filter otT the. V-phcnylanthranilic acid at the pump, wash with water, drain and dry. Yield, 9-9 5 g. I he acid may be recrystallised from aqueous ethanol, or methylated spirit, with addition of charcoal if necessary, and is obtained as colourless crystals, m.p. 185-186°. 

Mix 1 g. of the nitro compound with 4 g, of sodium dichromate and 10 ml. of water in a 50 ml. flask, then attach a reflux condenser to the flask. Add slowly and with shaking 7 ml. of concentrated sulphuric acid. The reaction usually starts at once if it does not, heat the flask gently to initiate the reaction. When the heat of reaction subsides, boil the mixture, cautiously at first, under reflux for 20-30 minutes. Allow to cool, dilute with 30 ml. of water, and filter oflF the precipitated acid. Purify the crude acid by extraction with sodium carbonate solution, precipitation with dUute mineral acid, and recrystaUisation from hot water, benzene, etc. 

Tl>e base is only slightly soluble in ether, thus rendering its use uneconomical. It may be extracted with chloroform and precipitated from the dried chloroform solution with carbon tetrachloride. 

In a 1 litre round-bottomed flask, equipped with an air condenser, place a mixture of 44 g. of o-chlorobenzoic acid (Section IV,157) (1), 156 g. (153 ml.) of redistilled aniline, 41 g. of anhydrous potassium carbonate and 1 g. of cupric oxide. Reflux the mixture in an oil bath for 2 hours. Allow to cool. Remove the excess of aniline by steam distillation and add 20 g. of decolourising carbon to the brown residual solution. Boil the mixture for 15 minutes, and filter at the pump. Add the filtrate with stirring to a mixture of 30 ml. of concentrated hydrochloric acid and 60 ml. of water, and allow to cool. Filter off the precipitated acid with suction, and dry to constant weight upon filter paper in the air. The yield of iV-phenylanthranilic acid, m.p. 181-182° (capillary tube placed in preheated bath at 170°), is 50 g. This acid is pure enough for most purposes. It may be recrystaUised as follows dissolve 5 g. of the acid in either 25 ml. of alcohol or in 10 ml. of acetic acid, and add 5 ml. of hot water m.p. 182-183°. 

A mixture of 0.10 mol of freshly distilled 3-methyl-3-chloro-l-butyne (see Chapter VIII-3, Exp. 5) and 170 ml of dry diethyl ether was cooled to -100°C and 0.10 mol of butyllithium in about 70 ml of hexane was added at this temperature in 10 min. Five minutes later 0.10 mol of dimethyl disulfide was introduced within 1 min with cooling betv/een -100 and -90°C. The cooling bath vjas subsequently removed and the temperature was allowed to rise. Above -25°C the clear light--brown solution became turbid and later a white precipitate was formed. When the temperature had reached lO C, the reaction mixture was hydrolyzed by addition of 200 ml of water. The organic layer and one ethereal extract were dried over potassium carbonate and subsequently concentrated in a water-pump vacuum (bath... 

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