Precipitation treatment

Chemical treatment precipitation (for example, of heavy metals), neutralisation. 

Figure 2.6 Photochromic glass (a) glass melt containing dissolved CuCl and AgCl (b) melt is cast into a homogeneous glass blank (c) heat treatment precipitates crystallites (much exaggerated in size here) in the blank and (d) sodium chloride structure of AgCl containing copper impurities and Frenkel defects.

Electronic parts makers, platers and other metal finishers require clean water rinses to remove plating chemicals from parts prior to the next process. The rinse water is sometimes expensive or in short supply. Furthermore, if the water is of poor quality, it must be pre-treated prior to use. The water is discarded after one use with conventional waste treatment, precipitation and clarification and a hazardous mixed metal sludge is generated which must be shipped to a hazardous waste landfill. 

The nitrile is refluxed for 45 minutes with a mixture of 350 ml. of sulfuric acid and 350 ml. of water and then is poured into 3 1. of cold water with stirring. The precipitated acid is removed, dissolved in hot 50 ethanol-water mixture, and treated with activated carbon. The addition of water to the filtrate from the carbon treatment precipitates a-naphthylacetic acid melting at 131.5°. The yield of acid is 131.5 g, (56 based on chloromethylnaphthalene). 

Solid-phase-bound reagents have also been used for precipitating excess reagents so that they may be removed by simple filtration. As an example, a combination of a resin-bound calcium sulfonate and a sulfonic acid resin is able to remove excess TBAF from silyl deprotection reactions. This treatment precipitates the fluoride as CaF2 whereas the tetrabutylammonium remains bound to the sulfonic acid resin [139]. 

Medium-active waste also can be treated by floe precipitation processes similar in character to those widely used in water treatment. Precipitants are required which will remove the unwanted radioactive species from the waste solution and quickly settle, carrying the radioactivity into a small bulk of sludge. The supemate can be treated as a low-active waste and discharged locally to the environment. Typical precipitants for common cations are as follows. 

Some hydrolysis may occur in stage 1 it is recognizable by the appearance of heavy turbidity or precipitation in the aqueous layer, and may necessitate an intermediate treatment (precipitation with ammonia, followed by solution of the precipitate with H2SO4). 

Method Precipitation Sulfur Treatment Precipitation Sulfur treabrnnl... 

Sieving and milling of active materiai Packaging in protective atmosphere Environmental processes (e.g. biowastewater treatment, precipitation of metal)... 

Opatowski Process. A process for the extraction of BeO from siliceous ores. The ground ore is mixed with NH4HSO4 and water and heated to 95 C to dissolve metal salts. Mn is oxidised using NH4S2O8, and ammonia treatment precipitates the metals as hydroxides. After separation, treatment with NaOH dissolves the beryllia as Na2Be02, which is hydrolized to Be(OH), which on heating to 250 C, decomposes to beryllia, BeO. The process is effective for concentrations of BeO in the ore of 51%, and the (NH4)2S04 formed is recycleable. (J. Opatowski, Canadian Pat. 663 776 1962). 

Reduction of L-aspartyl /3-semialdehyde to L-homoserine is catalyzed by homoserine dehydrogenase (Fig. 3, reaction 3). Both DPNH and TPNH can serve as hydrogen donors. However, DPNH is about three times as effective as TPNH. This dehydrogenase has also been purified from yeast extracts about a hundredfold by heat treatment, precipitation at pH 4.6 with ammonium sulfate, followed by chromatography on a calcium phosphate gel column. 

FIGURE 3.60 YBCO coils after heat treatment. Precipitates of YjBaCuOs are dispersed in a matrix of... 

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