Soils phosphate stabilization

Soils contaminated with Pb may also be remediated by iron-based nanoparticles. Iron phosphate (vivianite) nanoparticles stabilized with CMC have been reported to reduce the toxicity-characteristic leaching procedure (TCLP) and physiologically based extraction test (PBET) bioaccessibility in calcareous, neutral, and acidic soils (84). While phosphate addition has been known since at least 1993 to immobilize Pb(II) in soils, phosphate addition can cause its own problems in that it easily leaches into surface and groundwaters, where it causes problems related to excessive nutrient input. CMC-vivianite nanoparticles release 50% less phosphate into the environment than more traditional phosphate soil amendments, partly because of the insolubility of vivianite. Unlike the PdNPs/S mixture, the Pb-sequestering reactions take place at ambient temperatures. At acidic pH values, the reaction sequence is as shown in Equations (20.5a) and (20.5b). 

Ethylene/VA copolymer SR, insulation Ethylene/VA copolymer SR, lacquers Ethylene/VA copolymer SR, lamp seals Ethylene/VA copolymer SR, moldings/extrudates Ethylene/VA copolymer SR, pressure-sensitive/hot-melt adhesives Ethylene/VA copolymer SR, sealants Ethylene/VA copolymer SR, waterproof sheeting Ethylene/VA copolymer stabilization, latex Sodium laureth-4 phosphate stabilization, soil Acrylamide stabilizer... 

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. 

Fowle et al. (2000) have measured the sorption by a soil bacterium (B. subtilis) of uranyl in 0.1 M NaC104 at 25°C as a function of pH, time, and solid solute ratio, using a batch technique. The stoichiometiy and thermodynamic stability of the important uranyl-surface complexes indicated that uranyl formed two different surface complexes, one involving neutral phosphate functional groups, and another with deprotonated carboxyl functional groups, on the bacterial cell wall ... 

Manning, B.A. Goldberg, S. (1996) Modeling competitive adsorption of arsenate with phosphate and molybdate on oxide minerals. Soil Sci. Soc. Am. J. 60 121-131 Manning, B.A. Fendorf S.E. Goldberg, S. (1998) Surface structures and stability of ar-senic(lll) on goethite spectroscopic evidence for inner-sphere complexes. Environ. Sci. Techn. 34 2383-2388... 

An analysis of the thermodynamic stability models of various nickel minerals and solution species indicates that nickel ferrite is the solid species that will most likely precipitate in soils (Sadiq and Enfield 1984a). Experiments on 21 mineral soils supported its formation in soil suspensions following nickel adsorption (Sadiq and Enfield 1984b). The formation of nickel aluminate, phosphate, or silicate was not significant. Ni and Ni(OHX are major components of the soil solution in alkaline soils. In acid soils, the predominant solution species will probably be NE, NiS04°, and NiHP04° (Sadiq and Enfield 1984a). 

T0830 U.S. Naval Academy, Air Classifier with Removal of Metals from Soil T0832 UFA Ventures, Inc., Phosphate-Induced Metal Stabilization (PIMS)... 

The Metals Treatment Technology (MTT ) is a chemical fixation process that stabilizes heavy metals in soils, slndges, and sediments. The process nses bnffered phosphate componnds to convert heavy metals into insolnble metallic salts. The process chemicals may be applied to contaminated media in situ or ex situ. 

Apatite, a natural calcium fluoride phosphate, can adsorb low to moderate levels of dissolved metals from soils, groundwater, and waste streams. Metals naturally chemically bind to the apatite, forming extremely stable phosphate phases of metal-substituted apatite minerals. This natural process is used by UFA Ventures, Inc., and is called phosphate-induced metals stabilization (PIMS). The PIMS material can by used in a packed bed, mixed with the contaminated media, or used as a permeable barrier. The material may be left in place, disposed of, or reused. It requires no further treatment or stabilization. Research is currently being conducted on using apatite to remediate soil and groundwater contaminated with heavy metals, and the technology may also be applicable to radionuclides. The technology is not yet commercially available. 

Phosphate-induced metals stabilization can be used for the remediation of metals in mixed waste streams concurrently with other remediation technologies such as vapor stripping or bioremediation of organics. Using apatite to treat soils contaminated with lead, cadmium, and/or zinc can significantly reduce the amount of metals leached from the soil. The amount of apatite needed for treatment is less than 1% by weight. The reaction between metals and apatite is immediate, and the apatite can be heavily loaded with metals. 

The use of phosphate has been widely evaluated and subjected to field trials for Pb-contaminated soils. Most treatment systems involve excavation, pug milling of the soil with the stabilization agent, and either replacement or landfill disposal. Occasionally, for larger sites and deeper contamination, in situ mixing with large augers is used. 

Phosphate is widely used as a chemical stabilization agent for MSW combustion residues in Japan and North America and is under consideration for use in parts of Europe. The application of this technology to MSW ashes generally parallels its application to contaminated soils. Metal phosphates (notably Cd, Cu, Pb and Zn) frequently have wide pH distribution, pH-pE predominance, and redox stability within complex ash pore water systems. Stabilization mechanisms identified in other contaminated systems (e.g., soils), involving a combination of sorption, heterogeneous nucleation, and surface precipitation, or solution-phase precipitation are generally observed in ash systems. 

Nriagu, J. O. 1984. Formation and stability of base metal phosphates in soils and sediments. In Nriagu, J. O. Moore, P. B. (eds) Phosphate Minerals. Springer-Verlag, Berlin, 318-329. 

Raicevic, S. 2001. Remediation of uranium contaminated water and soil using phosphate-induced metal stabilization (PIMS). Hemijska Industrija, 55, 277-280. 

Xenidis, A., Stouraiti, C. Paspaliaris, I. 1999. Stabilization of oxidic tailings and contaminated soils by monocalcium phosphate monohydrate addition the case of Montevecchio (Sardinia, Italy). Journal of Soil Contamination, 8, 681-697. 

These examples illustrate that biomolecules may act as catalysts in soils to alter the structure of organic contaminants. The exact nature of the reaction may be modified by interaction of the biocatalyst with soil colloids. It is also possible that the catalytic reaction requires a specific mineral-biomolecule combination. Mortland (1984) demonstrated that py ridoxal-5 -phosphate (PLP) catalyzes glutamic acid deamination at 20 °C in the presence of copper-substituted smectite. The proposed pathway for deamination involved formation ofa Schiff base between PLP and glutamic acid, followed by complexation with Cu2+ on the clay surface. Substituted Cu2+ stabilized the Schiff base by chelation of the carboxylate, imine nitrogen, and the phenolic oxygen. In this case, catalysis required combination of the biomolecule with a specific metal-substituted clay. 

In most applications, a small amount of binder powders is mixed with a large volume of inexpensive hllers and then the entire mixture is stirred in water to form the reaction slurry. For example, if the phosphate binders are used for manufacturing construction products, invariably the hllers are sand, gravel, ash, soil, or some mineral waste. The phosphate binders provide adhesion between the particles of these hllers and bind them into a solid object. Thus, these mixtures mimic conventional concrete mixmres in which Portland cement binder is mixed with large volume of sand and gravel to produce cement concrete. When phosphate binders are used, the products may be termed as phosphate concrete . In waste stabilization, the waste itself becomes the hller and the hnal product is termed as a waste form . 

The examples given above and the work done in the last 10 years on phosphate washing demonstrate that phosphates are very powerful stabilizers of inorganic hazardous contaminants. Phosphate washing is very economical, and once the treated waste is disposed, because phosphates are common fertilizer components, the soil becomes enriched with phosphates. Hence, the entire disposal process is ecologically sound. 

A. Wagh, S. Jeong, D. Singh, R. Strain, H. No, and J. Wescott, Stabilization of contaminated soil and wastewater with chemically bonded phosphate ceramics, Proceedings of the Waste Management Annual Meeting, WM 97, eds. R. Post and M. Wacks, Tucson, AZ, 1997. 

Moreno, E.C, Brown, W.E, and Osborn, G. Stability of dicalcium phosphate dihydrate in aqueous solutions and solubility of octacalcium phosphate. Soil Sci. 24, 99-102 (1960). ... 

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