Gypsum, cement manufacture

Gypsum may be a potential source of sulfur and sulfuric acid. Some European plants make Portland cement and sulfuric acid from gypsum or anhydrite. In the Muller-Kuhne process, gypsum is mixed with clay and silica in quantities necessary to make cement, along with coke to reduce CaSC>4 to CaO. In equipment similar to that for portland-cement manufacture, the SOi is driven off and converted to sulfuric acid by the contact process,... 

In the portland cement manufacturing process, three steps occur. First, raw materials are crushed and mixed. The raw materials are powdered limestone, alumina, iron, and silica. Second, the raw materials are fed to an inclined rotary kiln in which they are heated to at least 2700 F. A rock-like substance called clinker is formed, which exits the kiln and is cooled. Third, the cooled clinker is finely crushed, and about 5 percent gypsum is added to produce finished cement. Details of the process are explained below. 

Use Reagent in analytical chemistry, medicine (cathartic), gypsum cements, fertilizer for chloride-sensitive crops such as tobacco and citrus, alum manufacture, glass manufacture, food additive. 

Arcanum duplicatum Caswell No. 702 Dipotassium sulfate EINECS 233-558-0 EPA Pesticide Chemical Code 005603 Glazier s salt HSDB 6047 Kalium sulphuricum Potassium sulfate Potassium sulphate Sal Polychrestum Sulfuric acid, dipotassium salt Sulphuric acid, potassium salt Tartarus vitriolatus. Analytical reagent, medicine (cathartic), gypsum cements, fertilizer, manufacture of alum and glass, food additive. Registered by EPA as a herbioide and insecticide. Colorless, hard crystals, mp = 1067° d = 2.66 soluble in H2O (12 g/100 ml at 25°, 25 g/100 ml at 100°),... 

As the last step in Portland cement manufacture, Portland clinker, in combination with limited amounts of gypsum and/or anhydrite, has to be ground to a fine powder. A ball mill is the standard equipment used for this purpose. It was reported recently (Goldstein, 1997) that the power consumption in the grinding process may be reduced if—in place of a single clinker—a blend of two clinkers is used, of which one has a higher and the other a lower lime saturation factor. 

Additional large-volume uses of lignosulfonates include animal feed pellet binders, dispersants for gypsum board manufacture, thinners/fluid loss control agents for drilling muds, dispersants/grinding aids for cement manufacture, and in dust control applications, particularly road dust abatement. 

We have finally assessed the environmental impact of the use of red gypsum in cement manufacturing. Table 12 shows the critical concenftation values that define the ecotoxicity threshold, i.e, if the concentration of a metal is lower than this limit, it does not generate significant environmental impact [26]. 

While making ammonium sulphate for APS fertilizer by reacting ammonium carbonate with gypsum, CaCOs is produced as a waste. This can be used for cement manufacturing. 

The use of g3 sum to control setting in Portland cement accounts for considerable quantities of the use of this material.1 Control of the reaction rate of tricalcium aluminate (C3A),the constituent of cement that reacts most rapidly with water, is most commonly achieved through the addition of gypsum (sometimes hemihydrate is also used) to commercial Portland cement. This material is normally added to the cement clinker (in amounts of approximately 2 to 3%) before grinding. The cement manufacturers usually specify a sulfurtrioxide content of about 36%. Excess sulfate in the form of hemihydrate can cause flash set in portland cement. 

Other fibrous and porous materials used for sound-absorbing treatments include wood, cellulose, and metal fibers foamed gypsum or Pordand cement combined with other materials and sintered metals. Wood fibers can be combined with binders and dame-retardent chemicals. Metal fibers and sintered metals can be manufactured with finely controlled physical properties. They usually are made for appHcations involving severe chemical or physical environments, although some sintered metal materials have found their way into architectural appHcations. Prior to concerns regarding its carcinogenic properties, asbestos fiber had been used extensively in spray-on acoustical treatments. 

Typical applications in the chemical field (Beaver, op. cit.) include detarring of manufactured gas, removal of acid mist and impurities in contact sulfuric acid plants, recovery of phosphoric acid mists, removal of dusts in gases from roasters, sintering machines, calciners, cement and lime Idlns, blast furnaces, carbon-black furnaces, regenerators on fluid-catalyst units, chemical-recoveiy furnaces in soda and sulfate pulp mills, and gypsum kettles. Figure 17-74 shows a vertical-flow steel-plate-type precipitator similar to a type used for catalyst-dust collection in certain fluid-catalyst plants. 

Salts of a-sulfo fatty acid esters can work as emulsifying agents for the preparation of asphalt emulsions and asphalt-latex emulsions. The ester sulfonates improve the storage stability of the emulsions [101,102]. In the manufacture of lightweight gypsum products air bubbles have to be mixed into the slurries. The use of salts of sulfonated C10 l8 fatty acid alkyl esters as foaming agents produces uniformly distributed fine bubbles [103]. Salts of C10 16 fatty acid alkyl ester sulfonates can also be added to cement mixtures to prevent slump loss of the mixtures [104]. 

Uses. The insoluble anhydrite is used in cement formulations and as a paper filler the soluble anhydrite is used as a drying agent the hemihydrate is used for wall plaster and wall-board gypsum is used in manufacture of plaster of paris and portland cement. 

The manufacture of Portland concrete consists of three basic steps—crushing, burning, and finish grinding. As noted earlier, Portland cement contains about 60% lime, 25% silicates, and 5% alumina with the remainder being iron oxides and gypsum. Most cement plants are located near limestone (CaCOs) quarries since this is the major source of lime. Lime may also come from oyster shells, chalk, and a type of clay called marl. The silicates and alumina are derived from clay, silicon sand, shale, and blast-furnace slag. 

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