Phosphates leaching

Limits the potential for nitrate and phosphate leaching into surface and groundwaters. 

Yang, J., Mosby, D. E., Casteel, S. W. Blanchar, R. W. 2002. In vitro lead bioaccessibility and phosphate leaching as affected by surface application of phosphoric acid in lead-contaminated soil. Archives of Environmental Contamination and Toxicology, 43, 399-405. 

Although adding excessive amounts of phosphates to the environment could result in excessive, unwanted plant and algal growth in aquatic environments, so much of the excess amount of phosphate in fertilizers is locked into the soil that relatively little phosphate leaches into ponds and streams adjacent to farmlands. Excess phosphate from detergents is potentially a much greater problem for the environment. 

Experimental variables of the zinc phosphate pigments may differ. One example is distribution of particle diameter smaller diameter means increased surface area, which increases the amount of phosphate leaching from the pigment. The more phosphate anion in a solution, the better the... 

Next, assume that the rate of phosphate leached from surfaces is a function of surface area leached. As surfaces of a mass increase, rates of leaching increase by a factor k ... 

Uranium is present in small (50—200 ppm) amounts in phosphate rock and it can be economically feasible to separate the uranium as a by-product from the cmde black acid (30% phosphoric acid) obtained from the leaching of phosphate for fertilizers (qv). The development and design of processes to produce 500 t U Og per year at Ereeport, Louisiana have been detailed (272). 

For extraction of uranium from sulfate leach Hquors, alkyl phosphoric acids, alkyl phosphates, and secondary and tertiary alkyl amines are used in an inert diluent such as kerosene. The formation of a third phase is suppressed by addition of modifiers such as long-chain alcohols or neutral phosphate esters. Such compounds also increase the solubihty of the amine salt in the diluent and improve phase separation. 

For solvent extraction of a tetravalent vanadium oxyvanadium cation, the leach solution is acidified to ca pH 1.6—2.0 by addition of sulfuric acid, and the redox potential is adjusted to —250 mV by heating and reaction with iron powder. Vanadium is extracted from the blue solution in ca six countercurrent mixer—settler stages by a kerosene solution of 5—6 wt % di-2-ethyIhexyl phosphoric acid (EHPA) and 3 wt % tributyl phosphate (TBP). The organic solvent is stripped by a 15 wt % sulfuric acid solution. The rich strip Hquor containing ca 50—65 g V20 /L is oxidized batchwise initially at pH 0.3 by addition of sodium chlorate then it is heated to 70°C and agitated during the addition of NH to raise the pH to 0.6. Vanadium pentoxide of 98—99% grade precipitates, is removed by filtration, and then is fused and flaked. 

Most U.S. production (20 x 10 lbs ia 1996) of primary vanadium compounds has been as by-products or coproducts of uranium and of ferrophosphoms derived from smelting Idaho phosphates. Most of this processiag was from leaching acids, residues, and spent catalysts. The only domestic commercially mined ore, for its sole production of vanadium, is Arkansas brookite. It has contributed significantly to domestic supply siace ca 1969, however, it has not been mined siace 1992 (25). 

This dissociated zircon is amenable to hot aqueous caustic leaching to remove the siHca in the form of soluble sodium siHcate. The remaining skeletal stmcture of zirconia is readily washed to remove residual caustic. Purity of this zirconia is direcdy related to the purity of the starting zircon since only siHca, phosphate, and trace alkaHes and alkaline earth are removed during the leach. This zirconia, and the untreated dissociated zircon, are both proposed for use in ceramic color glazes (36) (see Colorants for ceramics). 

A beryUium concentrate is produced from the leach solution by the counter-current solvent extraction process (10). Kerosene [8008-20-6] containing di(2-ethylhexyl)phosphate [298-07-7] is the water-immiscible beryUium extractant. The slow extraction of beryUium at room temperature is accelerated by warming. The raffinate from the solvent extraction contains most of the aluminum and aU of the magnesium contained in the leach solution. 

The paper-impregnation drying oven exhausts contain high concentrations (10—20% LEL) of alcohols and some resin monomer. Vinyl resins and melamine resins, which sometimes also contain organic phosphate fire retardants, may be used for air filters. The organic phosphates could shorten catalyst life depending on the mechanism of reduction of catalyst activity. Mild acid leaching removes iron and phosphoms from partially deactivated catalyst and has restored activity in at least one known case. 

Another example of a cost-effective liquid-liquid extraction process is the one used for recoveiw of uranium from ore leach liquors (Fig. 15-3). In this case the solvents, alkyl phosphates in kerosine, are recovered by liquid-liquid extraclion using a strip solution, and the... 

Ryon, Daley, and Lowrie [Chem. Eng. Ftog., 55(10), 70, (1959), U.S. AFC ORNL-2951, I960]. Continuous extraction of uranium from sulfate-ore-leach liquors and kerosine -t- trihiityl phosphate and di(2-ethylhexyl)-phosphoric acid baffled vessels, turbine agitated. There is strong evidence of the influence of a slow chemical reaction. 

TABLE 15-6 Settling of Aqueous Uranium Leach Liquors with Kerosine-Alkyl Phosphate Solvent ... 

Polyphosphoric acid supported on diatomaceous earth (p. 342) is a petrochemicals catalyst for the polymerization, alkylation, dehydrogenation, and low-temperature isomerization of hydrocarbons. Phosphoric acid is also used in the production of activated carbon (p. 274). In addition to its massive use in the fertilizer industry (p. 524) free phosphoric acid can be used as a stabilizer for clay soils small additions of H3PO4 under moist conditions gradually leach out A1 and Fe from the clay and these form polymeric phosphates which bind the clay particles together. An allied though more refined use is in the setting of dental cements. 

Zinc (76ppm of the earth s crust) is about as abundant as rubidium (78 ppm) and slightly more abundant than copper (68 ppm). Cadmium (0.16 ppm) is similar to antimony (0.2 ppm) it is twice as abundant as mercury (0.08 ppm), which is itself as abundant as silver (0.08 ppm) and close to selenium (0.05 ppm). These elements are chalcophiles (p. 648) and so, in the reducing atmosphere prevailing when the earth s crust solidified, they separated out in the sulfide phase, and their most important ores are therefore sulfides. Subsequently, as rocks were weathered, zinc was leached out to be precipitated as carbonate, silicate or phosphate. 

The separation of basic precipitates of hydrous Th02 from the lanthanides in monazite sands has been outlined in Fig. 30.1 (p. 1230). These precipitates may then be dissolved in nitric acid and the thorium extracted into tributyl phosphate, (Bu"0)3PO, diluted with kerosene. In the case of Canadian production, the uranium ores are leached with sulfuric acid and the anionic sulfato complex of U preferentially absorbed onto an anion exchange resin. The Th is separated from Fe, A1 and other metals in the liquor by solvent extraction. 

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