Salt waste streams

Improvements to the methanol reductant processes may be found in the patent Hterature. These include methods of operation to reduce acidity in the crystallisation 2one of the generator to promote crystallisation of sodium sulfate and to reduce sulfuric acid consumption (48). Other improvements sought are the elimination of formic acid and chlorine impurities from the chlorine dioxide, as weU as methods of recovering acid and sodium hydroxide, or acid and neutral sodium sulfate from the soHd sodium sesquisulfate salt waste stream (48—52). 

No catalyst neutralization step hence, no salt waste streams are being produced. 

Cs, Sr, and Ba are mostly found in salt waste streams as chlorides, nitrates, and sulfates and hence are soluble in water. Even Cs oxide is very soluble. Therefore, they readily react during phosphate stabilization and are chemically immobilized. We shall see in the case studies later in this chapter that such stabilization is very effective in a CBPC matrix. 

Leaching of salts Simulated salt waste streams (both supernatant and sludge)... 

Details of Salt Waste Streams and their Waste Forms. 

An enzymatic procedure for amine resolution, employing acylation by C. antarctica lipase B and deacylation by penicillin G acylase, has been demonstrated by Ismail et al. (Figure 14.14) [20]. The acylase catalyzed deacylation provides a greener process than the standard chemical deacylation as a result of the elimination of the salt waste stream typically generated by deacylating under strongly alkaline condi tions. It is also more amenable to sensitive functional groups that are not stable under basic conditions. A drawback of this approach is that the amide hydrolysis step is... 

Alternative Methods of Curing. The presence of salt in hides and skins has been a problem for taimers. Moreover, the quantity of salt, usually 10—20% by weight in cured hides, is an environmental problem. In the discharge of the water from the rewet and washing, the soluble soHds are normally greater than 20, 000 mg/L. This amounted to 2000 4000 mg/L in the combined waste stream of the taimery. 

Hydroxjiamine is used as a substitute for the ferrous sulfamate (26). These systems are called salt-free flow sheets. The main purpose is to ease the problems associated with the processing and storage of the Hquid waste streams (27). Another approach is to use an electropulse column to electrolyticaHy produce to reduce Pu to Pu on a continuous basis (28,29). The half reactions for the flow sheets are... 

Residuals Produced The resulting effluent may contain dissolved inorganic salts at concentrations which may be unacceptable for discharge. Based on the chemical composition of the waste stream, a precipitate may be formed which may require removal and disposal. 

We should also compare the scope of the technologies for different waste streams. With the exception of Brocat which only handles HBr, the systems can be used with HBr or metal salt streams. However, H2O2 has an advantage in terms of handling impurities in the steam such as low levels of organics. Chlorine and chlorate will suffer from reduced efficiency due to side reactions Brocat has potential problems with catalyst poisoning. H2O2 suffers no major drawbacks in this respect. 

An American Salt Company plant and the Dow Chemical Company s Midland plant also benefit directly from each other s presence. Dow found that after recovering bromine from brine it had more salt left than it desired. American Salt needed salt. By locating next to Dow s plant it was able to buy this salt stream for less than it would cost to mine it or pump it from natural underground reservoirs. In turn, Dow was able to sell an unwanted stream that it would otherwise have had to pump back into the ground. The American Salt plant is typical of many satellite plants. These are plants that either use a by-product or a waste stream from another plant or are built mainly to supply a needed chemical to an adjacent plant. The nearby presence of another plant determines their location. 

The chlorine liquefaction plant comprises a bromine-removal column, a compression-condensation unit and a Tetra absorption/distillation unit (Fig. 14.2). Waste streams of chlorine are absorbed in diluted cell-liquor in the chlorine destruction area. As a result, the destruction liquid contains sodium chloride and less sodium hydroxide than is usual. Bromine from the bromine-removal column is also added to the chlorine destruction unit. The hypochlorite solution that is formed contains a reasonable amount of bromine and salts. However, it is a hypochlorite of non-marketable quality. 

The workup for such reactions involves neutralization and concomitant generation of salts such as NaCl, Na2S04, and (NH4)2S04. The ehmination of such waste streams and a reduction in the dependence on the use of hazardous chemicals, such as phosgene, dimethyl sulfate, peracids, sodium azide, halogens, and HF, are primary goals in green chemistry. 

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