Paper pulp, chemical bleaching

Sodium Tetrahydroborate, Na[BH ]. This air-stable white powder, commonly referred to as sodium borohydride, is the most widely commercialized boron hydride material. It is used in a variety of industrial processes including bleaching of paper pulp and clays, preparation and purification of organic chemicals and pharmaceuticals, textile dye reduction, recovery of valuable metals, wastewater treatment, and production of dithionite compounds. Sodium borohydride is produced in the United States by Morton International, Inc., the Alfa Division of Johnson Matthey, Inc., and Covan Limited, with Morton International supplying about 75% of market. More than six million pounds of this material suppHed as powder, pellets, and aqueous solution, were produced in 1990. 

Nearly 95% of the sodium chlorate produced ia North America is used to produce chlorine dioxide [10049-04-4] CIO2, for pulp (qv) bleaching (see Bleaching AGENTS, pulp and paper) (37). Minor amounts are used to produce other chemicals such as KCIO, NaC102, NaClO, etc, to recover uranium [7440-61-17, U (see Uraniumand uranium compounds) and for agricultural uses as a defoHant or herbicide (see Herbicides). 

World production expressed as 100% H2O2 approached 1.9 million tonnes in 1994 of which half was in Europe and one-fifth in the USA. The earliest and still the largest industrial use for H2O2 is as a bleach for textiles, paper pulp, straw, leather, oils and fats, etc. Domestic use as a hair bleach and a mild disinfectant has diminished somewhat. Hydrogen peroxide is also extensively used to manufacture chemicals, notably sodium perborate (p. 206) and percarbonate, which are major constituents of most domestic detergents at least in the UK and Europe. Normal formulations include 15-25% of such peroxoacid salts, though the practice is much less widespread in the USA, and the concentrations, when included at all, are usually less than 10%. 

Pulp mills. These separate the fibers of wood or other materials, such as rags, Enters, waste-paper, and straw, in order to create pulp. Mills may use chemical, semichemical, or mechanical processes, and may create coproducts such as turpentine and tall oil. Most pulp mills bleach the pulp they produce, and, when wastepaper is converted into secondary fiber, it is deinked. The output of some pulp mills is not used to make paper, but to produce cellulose acetate or to be dissolved and regenerated in the form of viscose fibers or cellophane. 

Various technologies and chemicals are used to manufacture pulp, but most pulp manufacturing systems contain the process sequence shown in Table 21.4. Overall, most of the pollutant releases associated with pulp and paper mills occur at the pulping and bleaching stages where the majority of chemical inputs occur. 

Table 10. Common Chemicals used in Bleaching of Paper Pulps...

Hydrogen peroxide (HOOH) is sold in drugstores as a 3% aqueous solution for domestic use and is marketed as a 30% aqueous solution for industrial and laboratory use. Because of its oxidizing properties, hydrogen peroxide is used as a mild antiseptic and as a bleach for textiles, paper pulp, and hair. In the chemical industry, hydrogen peroxide is a starting material for the synthesis of other peroxide compounds, some of which are used in the manufacture of plastics. 

Additional sources of acid contamination include carboxyl group in the cellulose, acidic carbohydrate gums, bleach and pulping chemical residues, and some constituents of coating colors. Acids may be introduced after the paper is manufactured by atmospheric contamination, particularly sulfur dioxide which is absorbed by the paper and, in the presence of moisture, will generate sulfuric acid. 

Dioxins are some of the most toxic chemicals known to science. Dioxins are unwanted by products of a wide range of manufacturing processes including smelting, chlorine bleaching of paper pulp, and the manufacturing of some herbicides and pesticides. In terms of dioxin release into the environment, waste incinerators (solid waste and hospital waste) are often the worst culprits, due to incomplete burning [115]. One of the most toxic chemical in the class is 2,3,7,8-tetrachlorodibenzo-/ /Y/-dioxin (TCDD) and probably the most toxic compound ever synthesized by man. 

Use Bleaching paper pulp, textiles, etc. intermediate organic chemicals water purification medi-... 

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