Chemical pulping pollution from

A high yield chemical pulp, eg, 52—53% bleached yield from softwoods, can be obtained, but strength properties ate inferior to those obtained from the kraft process. If a protector, eg, potassium iodide, is added, an additional 2—3% yield is obtained, as is an improvement in all strength properties. The gas penetration problem can be minimized if ftbetization is accompHshed before treatment with oxygen. Oxygen treatment of virtually all types of semichemical and mechanical pulps has been explored (55). Caustic, sodium bicarbonate, and sodium carbonate have been used as the source of base (56,57). In all cases, the replacement of the kraft by these other processes has not been justified over the alternative of pollution abatement procedures. 

When chlorine dioxide is used for pulp bleaching in conjunction with the Kraft (sulfide) process for chemical pulping, by-product sodium sulfate can be used as a source of makeup sulfur and sodium consumed in the chemical cycle. The demand for sodium and sulfur in pulp bleaching is related to the loss of these chemicals through carryover in unbleached pulp. As process improvements have sought to reduce pollution from pulp mills, less sodium sulfate makeup is required. The trends in pulp bleaching to increase substitution of chlorine with chlorine dioxide have caused an oversupply of sodium sulfate, so that this by-product is often regarded as waste (81). 

The most important industrial alkalis are the weak alkali ammonia (Section 9.3), caustic soda (sodium hydroxide), and lime (calcium oxide).1-6 For many industrial and agricultural purposes, the most economical source of alkali is lime, which is used in steelmaking and other metallurgical operations ( 45% of U.S. production of lime), in control of air pollution from smokestack gases (Chapter 8), in water and sewage treatment (Sections 9.6 and 14.5), in pulp and paper production (Section 10.4), in reduction of soil acidity, in cement and concrete manufacture (indirectly, as discussed later), and in many chemical processes such as paper making (Section 10.4). In short, lime is one of the most important of all chemical commodities. 

Sulfur dioxide is a colorless, nonflammable gas formed by the burning of materials that contain sulfur. It is a major air pollutant from automobiles, smelters, and plants burning soft coal or oils high in sulfur content. It is soluble in water to form sulfurous acid, which may be oxidized to sulfuric acid both are components of acid rain. Occupational exposures to sulfur dioxide occur in ore and metal refining, chemical manufacturing, and wood pulp treatment and in Its use as a disinfectant, refrigerant, and dried-food preservative. 

Bleaching — When the desired quality of the final product requires bleaching of pulp recovered from wood, it is usually done by the addition of oxidizing chemicals, such as chlorine, chlorine compounds, peroxides, and hydrosulfites. The oxidizing chemicals react with the non-cellulose porticm of the pulp, rendering it soluble in water or in alkaline solutions. As a result, the bleaching step adds to the wastewater volume and pollutant loading. 

The development of the different types of glass fibre has been in response to demand from specific markets, and the latest call is for improvement in long-term resistance to chemicals. The whole sector termed anti-corrosion is now one of the most important applications for glass fibre-reinforced materials, embracing the industries of marine products, chemicals, pulp and paper, and food manufacture as well as water treatment, anti-pollution, power plant desulphurisation, and many other important sectors dealing with environmental protection. 

Properties Commercial grades Uses Manufacture White to grayish-white solid. Reacts with water to form calcium hydroxide. Commercial lime is available in lump, pebble, ground, and pulverized forms. One of the oldest commercial chemicals. Used in hundreds of applications. The most important uses are for making steel and chemicals, water treatment, pollution control, pulp and paper, and construction. Limestone (calcium carbonate, CaCOj) from mines or quarries is heated in a kiln (calcined). 

Making paper without pollution requires that each part of the process be nonpolluting. The chemicals most commonly used in the production of pulp are NaOH and Na2 S. In modem paper mills, sulfur-containing by-products are scmbbed from the plant exhaust, and the aqueous sodium hydroxide is reclaimed and recycled. The fillers used to make paper opaque—titanium dioxide, calcium carbonate, and kaolin (a clay)—are natural, nonpolluting minerals. The polymer binders and sizers are relatively easy to recapture from the aqueous waste stream. 

Power boilers at pulp and paper mills are sources of particulate emissions, S02, and NOx. Pollutants emitted from chemical recovery boilers include S02 and total reduced sulfur compounds (TRS). 

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