Hypochlorites wastes

Chlorine scrubber waste solutions are a special case here. The controlled reaction of chlorine and caustic soda produces commercial bleach solutions. A loss of strict control of the reaction conditions allows the hypochlorite produced by the primary reaction to degrade (Section 9.1.10.3A). In an emergency scrubber, total capture of chlorine that is released unpredictably and at highly variable rates is a more urgent goal than is the preservation of the hypochlorite. The liquor may then become a waste product. It should be considered a hypochlorite waste and treated as in Section 16.5.2.6. 

ElectrolyticaHy generated hypochlorite may be used for the oxidative destmction of cyanides (qv) or the sterilization of domestic wastes. Several on-site systems for swimming pool sterilization and municipal waste treatment works have been developed. One of these systems is described in Reference 124. On-site production and immediate use of chlorine is considered safer than the transportation of chlorine. 

There are several available terminal oxidants for the transition metal-catalyzed epoxidation of olefins (Table 6.1). Typical oxidants compatible with most metal-based epoxidation systems are various alkyl hydroperoxides, hypochlorite, or iodo-sylbenzene. A problem associated with these oxidants is their low active oxygen content (Table 6.1), while there are further drawbacks with these oxidants from the point of view of the nature of the waste produced. Thus, from an environmental and economical perspective, molecular oxygen should be the preferred oxidant, because of its high active oxygen content and since no waste (or only water) is formed as a byproduct. One of the major limitations of the use of molecular oxygen as terminal oxidant for the formation of epoxides, however, is the poor product selectivity obtained in these processes [6]. Aerobic oxidations are often difficult to control and can sometimes result in combustion or in substrate overoxidation. In... 

Use hypochlorite solutions in excess scattered over spillage of cyanide solutions and wearing respirator and gloves, mop up and collect in buckets. Allow to stand for 24 hours before diluting greatly and running to waste... 

A jug containing calcium hypochlorite (probably as moist solid) was used as a disposal receptacle for cyanide wastes from student preparations of benzoin. When a little acetic acid residue was inadvertently added, an explosion occurred, attributed to a cyanide-chlorine redox reaction. 

Removal of formic acid from industrial waste streams with sodium hypochlorite solution becomes explosive at 55°C. 

Anon., Environment, Safety Health Bull., 1993, 93(2), 1 As part of an analytical procedure prior to silver recovery, 10 ml commercial hypochlorite solution (15% available chlorine ) was added to highly alkaline waste developer solution. The redox reaction was violent enough to spray the worker, causing alkali bums. 

The pungent and irritating odor of chloramines is often mistaken for the chlorine odor of swimming pools. Chloramines form from the combination of sodium hypochlorite (added to sterilize the water) and nitrogen-containing compounds that are human waste by-products. 

The reduction in the numbers of incinerators and the limitations of autoclaves have created the need for alternative medical waste treatment systems. Currently, there are over 40 such technologies available from greater than 70 manufacturers within the United States, Europe, the Middle East, and Australia. While these systems vary in their treatment capacity, the extent of automation, and overall volume reduction, all alternative technologies utilize one or more of the following methods (1) heating the waste to a minimum of 90 to 95°C by means of microwaves, radio waves, hot oil, hot water, steam, or superheated gases (2) exposing the waste to chemicals such as sodium hypochlorite (household bleach) or... 

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. 

In the electrolysis plant of Akzo Nobel in Rotterdam a hypochlorite production unit is in operation. This unit has two functions handling chlorine-containing waste gases from the plant and production of hypochlorite. The reaction is carried out in a two-step apparatus in which a liquid jet-loop reactor and a packed column are in series. In this way chlorine is converted to hypochlorite and emissions of chlorine to the atmosphere are avoided. 

The abatement of chlorine vents and the subsequent destruction of the resulting sodium hypochlorite has been the subject of many studies. There are a variety of approaches to the waste hypochlorite destruction including chemical dosing, homogeneous and slurry catalysis as well as fixed-bed catalysis. For the most part these processes treat the hypochlorite at its natural strength the stoichiometric equivalent strength of the caustic soda fed to the scrubber. 

While hypochlorite in pure solutions is an industrially and commercially useful product, notably in water treatment and disinfection, incidental production exceeds demand. If discharged as a waste stream it can act as a powerful bio-toxin owing to its high oxidation potential, can form chlorinated organics when mixed with other streams and can release chlorine if the stream becomes acidic. There is thus a need to treat these waste hypochlorite streams. 

The destruction of the resulting sodium hypochlorite has been the subject of many studies. There are a variety of approaches to waste hypochlorite destruction. 

The process is dependent upon temperature, pH and hypochlorite concentration, and must be carefully controlled to avoid thermal runaway reactions. The reaction itself, combined with settling times for the catalyst slurry, can take three to four days, and the end-product - heavy metal salts - must be handled as hazardous waste. 

Traditionally, processes have used a single destruction technique, and this has historically been the case also for HYDECAT . Thus, nearly all installed processes treat the waste hypochlorite at the concentration it exits the scrubbing system down to concentrations suitable for discharge (Fig. 26.2). The key aspect in the re-evaluation described herein is to question the practices of firstly single technology and secondly end-of-pipe treatment the destruction of the hypochlorite exclusively in the blowdown stream from the scrubber. That is, it is questioned whether installation of a single treatment technique solely to process the effluent at its natural concentration from the scrubber loop is necessarily the best process option. This chapter will consider the two parts of the question paraphrased above sequentially. 

King, F. Hancock, F.E. (1996) Catalysis and pollution abatement the removal of hypochlorite from waste chlorine/caustic effluent. Catalysis Today, 27, 203-207. 

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