Phosphatic clay

B. J. Schemer and A. G. SmeUey, Dewatering of Thickened Phosphate Clay Wastefrom Disposal Ponds, Paper A81-6, The Metallurgical Society of AIME, Warrendale, Pa., 1981 J. R. Pederson, ed., U.S. Bureau of Mines Research 81, U.S. Government Printing Office, Washington, D.C., 1981, p. 83. 

Nriagu, J. O. (1976). Phosphate-clay mineral relations in soils and sediments. Can.. Earth Sci. 13,717-736. 

G. Graf, and G. Lagally, Interaction of clay minerals with adenosine-5-phosphates. Clays Clay Min. 25 12 (1980). 

Ostwald s step rule holds that a thermodynamically unstable mineral reacts over time to form a sequence of progressively more stable minerals (e.g., Morse and Casey, 1988 Steefel and Van Cappellen, 1990 Nordeng and Sibley, 1994). The step rule is observed to operate, especially at low temperature, in a number of min-eralogic systems, including the carbonates, silica polymorphs, iron and manganese oxides, iron sulfides, phosphates, clay minerals, and zeolites. 

A drum dryer (Fig. 6.4) consists of one or more heated metal rolls on which solutions, slurries or pastes are dried in a thin film. The thin film dries in less than one revolution of the slowly revolving rolls and is scraped off by a doctor blade to form a product in flake, chip or granular form. Drum dryers are widely used in chemical processing frequently to dry hydrates, carbonates, arsenates, acetates, phosphates, clays and food products [11]. 

United States.—The principal deposits are in South Carolina, Florida, Tennessee, Arkansas, Utah and Wyoming. The South Carolina deposits are of Miocene age and occur both as land and river rock. They contain 25 to 28 per cent, of phosphoric oxide and 35 to 42 per cent, of lime. They were the earliest to be exploited, namely, from 1868 onwards, and in 1893 they furnished about one-fifth of the world s supply. Since this date the production has declined, while that of Florida has greatly increased. In 1913 Florida and Tennessee together produced some 96 per cent, of the total output from the United States of America. The hard-rock deposits of Florida are of Tertiary age, and they run parallel to the coast for 144 miles. After concentration by mechanical means they contain usually from 77 to 79 per cent, of calcium phosphate (more rarely up to 82 per cent.) with 3 per cent, of oxides of iron and alumina, some calcium fluoride and other constituents, and 3 per cent, of moisture. The best grades of Tennessee rock were guaranteed to contain 72 per cent, of calcium phosphate, and 65 per cent, is common. The soft rock is a phosphatic clay. The river pebbles are dark grey to black and are very cheaply obtained by dredging. 

The studies by Eighmy and Eusden [10] are limited to stabilization of Pb, Cd, and Zn, which are sole contaminants of the MSW ash. By extension, it is believed that similar minerals are formed during phosphate treatment of other waste streams. For example, Singh et al. [50] have studied the interaction of Pb, Cd, and Zn with phosphatic clay and reported their investigations on the sorption and desorption of these metals. They report precipitation of Pb as fluoropyromorphite. In the case of Cd and Zn, their studies are not as conclusive, but Singh et al. suspect sorption and coprecipitation of phosphates are still the main mechanisms of stabilization. 

S. Singh, L. Ma, and W. Harris, Heavy metal interactions with phosphatic clay sorption and desorption behavior, J. Environ. QuaL, 30 (2001) 1961 — 1968. 

Graf, G. and Lagaly, G., 1980. Interaction of clayminerals with adenosine-5-phosphates. Clay Clay Min., 28 12-18. 

Under conditions near the surface of the earth, a wide spectrum of secondary minerals can form that may be common to both igneous and sedimentary phosphate rocks. These minerals include iron and aluminum phosphates, clays, and iron oxides. 

Deason, D.M. and Onoda, GY. (1984). Controlled dispersion of clays and its effects on phosphate clay dewatering. Min. Metall. Proc., 1(2) 149-152. 

Inorganic paint for asbestos board can be made with silica as a binder. Hard, weather-resistant paint is made with a combination of colloidal silica, lithium hydroxide and potassium silicate or alkali metal phosphate, clay, and pigment, and baked on in the presence of steam (629). Collidal silica stabilized with tetraethanol ammonium silicate was used as a binder for iron oxide and clay pigments (630). A heatproof coating for asbestos or metals consisted of colloidal silica and magnesium hydrogen phosphate (631) and was hardened at 200 C. 

Most uraniferous phosphates are classified as syngenetic types because they acquired their uranium at the time of deposition. One exception appears to be the occurrence at Baukoma, Zaire, where uranium occurs in an Eocene phosphatic clay beneath a shallow lake. The phosphatic clay, with an average content of 3000ppm uranium, rests on a limestone and in places on a sandstone that overlies the limestone. ... 

SeUgrem et al. (2000) conducted tests on sand as well as sand-clay mixtures pumped by centrifuged pumps. The phosphate clays had a diameter d Q between 1 p-m and 50 p,m. The sands were much coarser with of 0.64 mm (0.025 in), 1.27 mm (0.05 in), and 2.2 mm (0.09 in). The presence of clay and other particles finer than 75 p,m and a concentration smaller than 20% had a beneficial effect by reducing the head loss and efficiency derating factor. The data recorded by SeUgrem et al. (2000) should not be applied to a higher concentration of clays because the viscosity effect introduces a new component to the equation. 

Preferred clays include sodium or calcium montmoriUonite or phosphatic clays, including phosphatic waste clay, or mixtures thereof. Optionally, the concrete composite can include a dispersion agent that helps keep the clay in a dispersed state when stored as an additive to prevent, or at least limit, clumping of the clay. 

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