Removal of toxic gases

As noted earlier, the phenomenon of adsorption is encountered in such diverse applications as the separation of components in chromatography, die removal of toxic gases by activated charcoal, heterogeneous catalytic reactions and die dyeing of fabrics. The surface area of solids is most... 

The present study aims at increasing the surface area of raw OFA through physicochemical treatment. The produced treated OFA is used for the adsorption of H2S. The success of such physicochemical activation in H2S removal is expected to lead to the utilization of OFA as low cost activated carbon for removal of toxic gases such as H2S. 

Toxic or malodorous pollutants can be removed from industrial gas streams by reaction with hydrogen peroxide (174,175). Many Hquid-phase methods have been patented for the removal of NO gases (138,142,174,176—178), sulfur dioxide, reduced sulfur compounds, amines (154,171,172), and phenols (169). Other effluent treatments include the reduction of biological oxygen demand (BOD) and COD, color, odor (142,179,180), and chlorine concentration. 

Sodium chlorite has also been used for treatment and removal of toxic and odorous gases such as hydrogen sulfide and mercaptans. Chlorine dioxide from chlorite is also useful for microbial and slime control in paper mills and alkaline paper machine systems (164,165). The use of sodium chlorite in textile bleaching and stripping is well known. Cotton is not degraded by sodium chlorite because the oxidation reactions are specific for the hemiceUulose and lignin components of the fibers. 

More than 80% of all sodium chlorite produced is used for the generation of chlorine dioxide. Sodium chlorite is also used in disinfectant formulations and sterilization. Like chlorine dioxide, it must be registered with EPA under FIFRA for each specific application use as a disinfection. Sodium chlorite is used in other industrial settings in NO and SO combustion flue gas scrubber systems in the treatment and removal of toxic and odorous gases such as hydrogen sulfide and mercaptans and as a solution formulation to oxidize copper surfaces in multilayer circuit boards (Kaczur and Cawlfield 1993). 

Similarly, in RA, reactions occur simultaneously with the component transport and absorptive separation, in the same column zone. These processes are used predominantly for the production of basic chemicals, e.g., sulphuric or nitric acids, and for the removal of components from gas and liquid streams. This can be either the cleanup of process gas streams or the removal of toxic or harmful substances in flue gases. Absorbers or scrubbers where RA is performed are often considered gas-liquid reactors (10). If more attention is paid to the mass transport, these apparatuses are instead treated as absorption units. 

An another industrial use of activated carbon is in hazardous gases adsorption. Activated carbon filters, combined in series with ventilation units are commonly used for the removal of toxic contaminants such as SO2, CS2, H2S from effluent air. 

The second class of harmful gases are inorganic toxic gases that include SO NO H2S, and NH3 These gases can be toxic to humans, animals, and plants that are present in various gas streams.Therefore, it is important to remove these toxic gases to minimize release to the environment. 

Precautions have to be taken during the dissolution of cadmium precipitates or the galvanic precipitation of cadmium with 2inc to remove possible mist and toxic gases such as arsine. Suitable exhaust hoods and scmbbers must be provided. The fume that may be formed during cathode melting must be removed similarly. 

Wet and dry scrubbers Dry scrubbers are generally preferred today. Scrubbers can be used for the removal of both particulate matter and toxic sulfur gases (dry scrubber or spray dryer desulfurizers). 

Ash particles produced in coal combustion are controlled by passing the flue gases through electrostatic precipitators. Since most of the mass of particulate matter is removed by these devices, ash received relatively little attention as an air pollutant until it was shown that the concentrations of many toxic species in the ash particles increase as particle size decreases. Particle removal techniques become less efiective as particle size decreases to the 0.1-0.5 pm range, so that particles in this size range that escape contain disproportionately high concentrations of toxic substances. 

Liquid household bleach is generally a 5% solution of sodium hypochlorite (NaOCl). Ammonia cleansers—including general household cleansers, wax removers, glass and window cleaners, and oven cleaners — are aqueous solutions of 5-10% ammonia, NH3. Mixing bleach with cleansers containing ammonia leads to the formation of a family of potentially toxic compounds known as chloramines. These toxic gases have acrid fumes that can bum mucous membranes. Scented bleaches can mask one s natural ability to detect these harmful fumes. 

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