Bleached chemical wood pulp

A number of combustion and chemical production processes contribute to environmental concentrations of PCDD/F. Sources that have traditionally caused the greatest concern include municipal waste incinerators, hospital waste incinerators, bleached chemical wood pulp and paper mills, motor vehicles and wood combustion. We have attempted to represent the most recent data available on PCDD/F emissions from these sources. It should be remembered that the list presented here is by no means exhaustive. Potential sources of TCDD not discussed in the following paragraphs include discharges from metal processing and treatment plants, copper smelting plants and pentachlorophenol production. 

Bleached Chemical Wood Pulp and Paper Mills... 

Pulp and paper mills are a much smaller source of PCDD/Fs in the environment than in the past. In 1988, the EPA and the US pulp and paper industry collaborated on the 104-Mill Study to measure levels of dioxins in effluent, sludge and pulp from 104 bleached chemical wood pulp and paper mills in the US. The study estimated the total discharge from all US pulp and paper mills to be 1188 g TEQ yr 1.18 In response to these findings, the pulp and paper industry expended more than SI billion dollars to reduce TCDD and TCDF formation during bleaching operations.19 The 1993 estimated discharge from all US pulp and paper mills is 97.2 g TEQ (Table 2). 

Uses. The principal uses of NaBH are ia synthesis of pharmaceuticals (qv) and fine organic chemicals removal of trace impurities from bulk organic chemicals wood-pulp bleaching, clay leaching, and vat-dye reductions and removal and recovery of trace metals from plant effluents. 

It is interesting to note that ozone is the subject today of many discussions in relation with environmental concerns. However, this gas remains an important chemical reagent in industrial areas like the sterilization of water or the bleaching of wood pulp [1],... 

Simmons " has studied the carbohydrate composition of the alpha-, beta-, and gamma-fractions of bleached, coniferous, chemical wood-pulps. He concluded that the gamma fraction consists largely of mannan and xylan. The alpha and beta fractions may contain appreciable proportions of man-nan and xylan. However, the mannan and xylan in the beta fraction are occluded during precipitation of the beta-cellulose. These results " are in agreement with the ideas expressed above that alpha-cellulose and beta-cellulose are chemically similar, and differ only in D. P. 

Polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), often termed dioxins , consist of 210 different compounds which have similar chemical properties. This class of compounds is persistent, toxic, and bioaccumulative. They are generated as byproducts during incomplete combustion of chlorine containing wastes like municipal solid waste, sewage sludge, and hospital and hazardous wastes. Industrial processes such as bleaching of wood pulp in the manufacture of paper products, can also produce PCDDs and PCDFs [39]. 

A rather extensive review of chlorine dioxide has been published in French by Masschelein (155). This review includes the physical and chemical properties of chlorine dioxide, methods of synthesis, and different analytical methods for determining chlorine dioxide, as well as the industrial applications of chlorine dioxide. A review by Rapson (180) of the history of the application of chlorine dioxide to the bleaching of wood pulp covers the most important industrial use of chlorine dioxide and gives an indication of the economics of its use. 

Staining a surface, either chemically or optically, helps differentiate parts of a composite surface and identify the various phases. A variety of stains are available for diverse surfaces. Mineral sections can be etched with hydrofluoric acid then stained with Na3Co(N02)e to differentiate quartz (unetched), feldspars (etched but unstained), and potassium feldspars (etched and stained yellow). Paper surfaces can be stained with Harzberg stain (Calkin, 1934) to differentiate lignified cellulose e.g., straw, manilla, and mechanical wood pulp [yellow or yellow green]) from purified cellulose e.g., chemical wood pulp, bleached straw, or manilla [blue or blue violet]) or pure cellulose e.g., cotton or linen [wine red]). Isings (1961) selectively stains unsaturated elastomers with osmium tetroxide. 

Bleaching. The largest single use for hydrogen peroxide in the United States and North America is wood pulp bleaching, but consumption for the manufacture of chemicals, environmental appHcations, and for bleaching cotton (qv), wool (qv), and other textiles (qv) is significant. 

Alternatively cellulose is produced from wood via wood pulp. A number of processes are used in which the overall effect is the removal of the bulk of the non-cellulosic matter. The most widely used are the sulphite process, which uses a solution of calcium bisulphite and sulphur dioxide, the soda process using sodium hydroxide and the sulphate process using a solution of sodium hydroxide and sodium sulphide. (The term sulphate process is used since sodium sulphate is the source of the sulphide.) For chemical purposes the sulphite process is most commonly used. As normally prepared these pulps contain about 88-90% alpha-cellulose but this may be increased by alkaline purification and bleaching. 

As described in Section 4-1. one important class of chemical reactions involves transfers of protons between chemical species. An equally important class of chemical reactions involves transfers of electrons between chemical species. These are oxidation-reduction reactions. Commonplace examples of oxidation-reduction reactions include the msting of iron, the digestion of food, and the burning of gasoline. Paper manufacture, the subject of our Box, employs oxidation-reduction chemishy to bleach wood pulp. All metals used in the chemical industry and manufacturing are extracted and purified through oxidation-reduction chemistry, and many biochemical pathways involve the transfer of electrons from one substance to another. 

Dichlorophenol may be released to the environment in effluents from its manufacture and use as a chemical intermediate and from chlorination processes involving water treatment and wood-pulp bleaching. Releases can also occur from various incineration processes, from metabolism of various pesticides in soil or in the use of 2,4-D, in which it is an impurity. It has been detected at low levels in drinking-water, groundwater and ambient water samples (United States National Library of Medicine, 1997). 

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