Phosphates and Silicates

Approximately 5 g sample is ashed as above and cooled. The content is then mixed with 5-6 times the amount of sodium-potassium carbonate (made by mixing equal weights) and then heated until a clear melt is obtained. On cooling, the solidified melt is then dissolved in distilled water and granular ammonium molybdate is added to it. Then the content is acidified with nitric acid (20%). In the presence of silicate an intense yellow colour or a yellow, crystalline precipitate is produced. 

For testing phosphate contents in the sample, the ash is dissolved in 10 ml nitric acid (20%), filtered and the residue is mixed with 5-6 times the amount of sodium-potassium carbonate and then continue as above. 

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Alkalinity An expression of the total basic anions (hydroxyl groups) present in a solution. It also represents, particularly in water analysis, the bicarbonate, carbonate, and occasionally, the borate, silicate, and phosphate salts which will react with water to produce the hydroxyl groups. 

The corrosion rig has been used to study the effect of inhibitors e.g. silicate and phosphate commonly used to overcome problems with iron. This has revealed that these inhibitors hardly affect the long-term corrosion rate, indeed in certain circumstances they may actually increase it. They produce their effect by stabilising the corrosion product developed, thereby preventing the water quality deterioration which is the real complaint... 

The iron formed in a blast furnace, called pig iron, contains impurities that make the metal brittle. These include phosphorus and silicon from silicate and phosphate minerals that contaminated the original ore, as well as carbon and sulfur from the coke. This iron is refined in a converter furnace. Here, a stream of O2 gas blows through molten impure iron. Oxygen reacts with the nonmetal impurities, converting them to oxides. As in the blast furnace, CaO is added to convert Si02 into liquid calcium silicate, in which the other oxides dissolve. The molten iron is analyzed at intervals until its impurities have been reduced to satisfactory levels. Then the liquid metal, now in the form called steel, is poured from the converter and allowed to solidify. 

The impurities in pig iron, the iron formed in a blast furnace, that make it brittle include four elements phosphorus and silicon, two elements that came from the silicate and phosphate minerals that contaminated the original ore, and carbon and sulfur that came from the coke. 

Chemical effects include stable compound formation and ionization, both of which decrease the population of free atoms in the sample vapour and thereby lower the measured absorbance. Examples of compound formation include reactions between alkaline earth metals and oxyanions such as aluminates, silicates and phosphates, as well as the formation of stable oxides of aluminium, vanadium, boron etc. 

Network polymerization, in silicate and phosphate glasses, 12 574 Neuberg, Carl, 11 8 Neupogen, 3 817 Neural networks, 7 507... 

Golden, D.C. Dixon, J.B. (1985) Silicate and phosphate influence on kaolin - iron oxide interactions. Soil Sci. Soc. Am. J. 49 1568-1575... 

Kandori, K. Tamura, S. Ishikawa.T. (1994) Inner structure and properties of diamondshaped and spherical a-Fe203 particles. Colloid Polym. Sci. 272 812-819 Kandori, K. Uchida, S. Kataoka, S. Ishikawa, T. (1992) Effects of silicate and phosphate on the formation of ferric oxide hydroxide particles. J. Mater Sci. 27 719-728 Kandori, K. Yasukawa, A. Ishikawa,T. (1996) Influence of amines on formation and texture of uniform hematite particles. J. Colloid Interface Sci. 180 446-452 Kaneko, K. Inouye, K. (1974) Electrical properties of ferric oxyhydroxides. Bull. Chem. 

Williams, R.J.P. (1988) The influence of silicate and phosphate on the structural and magnetic properties of synthetic goethite and related oxides. Clays Clay Min. 36 165-175... 

Several types of corrosion inhibitors have been investigated in the last 20 years [53-55] these include calcium and sodium nitrites, sodium benzoate, sodium/potassium chromate, sodium salts of silicates and phosphates, stannous chloride, hydrazine hydrate, sodium fluorophosphate, permanganate, aniline and related compounds, alkalis, azides, ferrocyanide, EDTA and many chelating compounds. However, in terms of field practice and research data, nitrite-based compounds occupy a dominant position. 

In investigations of structures of amorphous solids, MAS NMR spectroscopy has been used effectively (see Chapter 2). Structures of borates, silicates and phosphates have been advantageously studied by this technique. An important advance in this area... 

L. C. Roberts, S. J. Hug, T. Ruettimann, M. Billah, A. W. Khan, and M. T. Rahman, Arsenic Removal with Iron(II) and Iron(III) Waters with High Silicate and Phosphate Concentrations, Environ. Sci. Technol. 2004, 38, 307. 

The ZPC of an unaltered mixed oxide, silicate, or phosphate in a system devoid of specific electrolytes other than the PDI is approximately the average of the IEP(s) s of its component oxides weighted on an atomic (cation) basis. Account must be taken of the correct cation coordination, cleavage and morphological habit, hydration state, and structural modification produced by abrasion. Experimental and calculated ZPC s for a group of silicate and phosphate minerals are compared in Figure 13 to show the accuracy to be expected in prediction. 

Figure 13. Experimental and calculated ZPC s for silicate and phosphate minerals. Arrows connect ZPC s calculated for the fresh fracture surface with limiting values expected to result from unusual morphology...

The effectiveness of zerovalent iron in removing arsenic from water also greatly depends on the properties of the iron. As(III) removal is especially effective with high surface area 1-120 nm spheres of zerovalent iron (Kanel et al., 2005). Provided that interfering anions (such as, carbonate, silicate, and phosphate) are insignificant, colloidal spheres of zerovalent iron could be injected into arsenic-contaminated soils, sediments, and aquifers for possible in situ remediation (Kanel et al., 2005, 1291). 

Zhang et al. (2004) estimated the sorption capacity of an Australian hematite iron ore as 0.4 mg As(V) g-1 ore (Table 7.2). The presence of silicate and phosphates in the ores hindered As(V) sorption, whereas sorption was slightly enhanced by water-soluble sulfate and chloride. Zhang et al. (2004) found... 

Roberts, L.C., Hug, S J., Ruettimann, T. et al. (2004) Arsenic removal with iron(II) and iron(III) in waters with high silicate and phosphate concentrations. Environmental Science and Technology, 38(1), 307-15. 

Inorganic open-framework compounds constitute an important class of materials that has attracted much attention as evidenced by the vast number of research papers published in the last few years. Although work in this area started with aluminium silicates1,2 because of their important uses in sorption and catalysis, much of the recent work pertains to the structure and characterization of open-framework metal phosphates and carboxylates. Both these families of open-framework materials have been reviewed recently.3 7 Since open-framework silicates and phosphates can essentially be... 

Coordination polymers, open-framework materials, and hybrid compounds built up with various anions have been described in the literature. The most common anions employed in open-framework structures are silicates and phosphates.1-3 Metal carboxylates with a variety of structures and dimensionalities have also been described in the recent literature.4 5 In recent years, other oxyanions such as sulfate, selenate, selenite, and tellurite have also been employed to design these structures.6,7 Surprisingly, coordination polymers... 

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