Alkaline chlorination

Alkaline cell Alkaline chlorination Alkaline coupling Alkakne-earth metals Alkaline earths... 

Cyanide destmction by alkaline chlorination is a widely used process. With alkaline chlorination, cyanide is first converted to cyanate with hypochlorite [7681-52-9] at a pH greater than 10. A high pH is required to prevent the formation of cyanogen chloride [506-77-4] which is toxic and may evolve in gaseous form at a lower pH. With additional hypochlorite, cyanate is then oxidized to bicarbonate, nitrogen gas, and chloride. The pH for this second stage is 7—9.5 (6). 

Ozone can be used to completely oxidize low concentrations of organics in aqueous streams or partially degrade compounds that are refractory or difficult to treat by other methods. Compounds that can be treated with ozone include alkanes, alcohols, ketones, aldehydes, phenols, benzene and its derivatives, and cyanide. Ozone readHy oxidizes cyanide to cyanate, however, further oxidation of the cyanate by ozone proceeds rather slowly and may require other oxidation treatment like alkaline chlorination to complete the degradation process. 

C41 Cyanide Oxidation -- Alkaline Chlorination R09 Reuse as Fuel - Other... 

Corrective Action Application At a hazardous waste treatment storage and disposal facility in Washington State, a cyanide-bearing waste required treatment. The influent waste stream contained 15 percent cyanide. Electrolytic oxidation was used to reduce the cyanide concentration to less than 5 percent. Alkaline chlorination was used to further reduce the cyanide concentration to 50 mg/1 (the cleanup objective). The electrolytic process was used as a first stage treatment because the heat of reaction, using alkaline chlorination to treat the concentrated cyanide waste, would be so great that it would melt the reactor tank. 

Ozonation treatment can be used to oxidize cyanide, thereby reducing the concentration of cyanide in wastewater. Ozone, with an electrode potential of +1.24 V in alkaline solutions, is one of the most powerful oxidizing agents known. Cyanide oxidation with ozone is a two-step reaction similar to alkaline chlorination.22 Cyanide is oxidized to cyanate, with ozone reduced to oxygen as per the following equation ... 

FIGURE 9.5 Cyanide reduction via alkaline chlorination. (Adapted from U.S. EPA, Meeting Hazardous Waste Requirements for Metal Finishers, Report EPA/625/4-87/018, U.S. Environmental Protection Agency, Cincinnati, OH, 1987.)... 

The term A, as in Cyanide A, shall mean amenable to alkaline chlorination. 

Chemical/physical treatment processes are those in which a chemical reaction is used to alter or destroy a hazardous waste component. Chemical treatment techniques can be applied to both organic and inorganic wastes, and may be formulated to address specific target compounds in a mixed waste. Typical chemical treatment processes include oxidation-reduction reactions such as ozonation, alkaline chlorination, electrolytic oxidation and chemical dechlorination. Physical treatment processes separate waste component by either applying physical force or changing the physical form of the waste. Various physical processes include adsorption, distillation, or filtration. Physical treatment is applicable to a wide variety of waste streams but further treatment is usually required. 

Chemical Oxidation Design Considerations 2.4.1. Cyanide Alkaline Chlorination Process Design... 

Introduce the cyanide alkaline chlorination, excess chlorination (superchlorination), and acid hydrolysis processes, which treat industrial effluents containing cyanide. 

The cyanide alkaline chlorination process uses chlorine and caustic to oxidize cyanides to cyanates and ultimately to carbon dioxide and nitrogen. The oxidation reaction between chlorine and cyanide is believed to proceed in two steps as follows, according to Eqs. (11) and (12) ... 

A typical reaction condition for the alkaline chlorination of 1 kg (2.2 lb) of cyanide to cyanate requires 6 kg (13.2 lb) each of sodium hydroxide and chlorine. The reaction is carried out at pH 10, and at least 15 min contact time is required to drive the reaction to completion. If metal cyanide complexes are present, extended chlorination for longer periods may be necessary. Complete destruction of cyanate requires a second oxidation stage with approx 45 min retention at a pH below 8.5. The theoretical reagent requirement for this second stage is 4.1 kg (9.0 lb) of chlorine and 1.1 kg (2.4 lb) of caustic per kg (2.2 lb) of cyanide. 

The formation of CBPs is influenced by pH, temperature, ammonia, carbonate alkalinity, chlorine dose, contact time, removal of natural organic matter before chlorine application, etc. Moreover, the composition of these mixtures may change seasonally resulting... 

Industrial cyanide-bearing waste is to be treated in a batch process using alkaline chlorination. In this process, cyanide is reacted with chlorine under alkaline conditions to produce carbon dioxide and nitrogen as end products. 

Cyanide may be detoxified to cyanate by oxidation with chlorine or hypochlorite (Chap. 15). Or the oxidation may be conducted by air in the presence of sulfur dioxide and copper ion at pH 9 or 10 [44]. Einally BOD reduction to 80-90% of the original values will be achieved via either biological waste treatment or alkaline chlorination methods before discharge. 

A phenol derivative, phenolphthalein is prepared by the reaction of phenol with phthalic anhydride in the presence of sulphuric acid and used as an indicator for acidity or alkalinity. Chlorinated phenol is much safer than phenol. Chlorine gas reacts with phenol to add one, two or three chlorine atoms and to form, respectively, chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol . The chlorination of phenol proceeds by electrophilic aromatic substitution. The latter two molecules are less soluble in water than phenol and appear to be a stronger antiseptic than phenol. Interestingly, in the first half of the past century, a bottle of antiseptic chlorophenols was a common attribute as a medicine in many homes. Its solution was used for bathing cuts, cleaning grazes, rinsing the mouth and gargling to cure sore throats. Nevertheless, it was revealed that its solution likely contains dioxins. 

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