Polyvalent metal ions

Uses. The principal use of monosodium phosphate is as a water-soluble soHd acid and pH buffer, primarily in acid-type cleaners. The double salt, NaH2P04 H PO, referred to as hemisodium orthophosphate or sodium hemiphosphate, is often generated in situ from monosodium phosphate and phosphoric acid in these types of formulations. Mixtures of mono- and disodium phosphates are used in textile processing, food manufacture, and other industries to control pH at 4—9. Monosodium phosphate is also used in boiler-water treatment, as a precipitant for polyvalent metal ions, and as an animal-feed supplement. 

Trisodium phosphate is strongly alkaline many of its appHcations depend on this property. For example, many heavy-duty cleaning compositions contain trisodium phosphate as a primary alkalinity source. The crystalline dodecahydrate itself is marketed as a cleaning compound and paint remover. Traditionally, trisodium phosphate has been used in water softening to remove polyvalent metal ions by precipitation as insoluble phosphates. Because the hypochlorite complex of trisodium phosphate provides solutions that are strongly alkaline and contain active chlorine, it is used in disinfectant cleaners, scouring powders, and automatic dishwashing formulations. 

Chelants, or chelating agents, typically are organic chemicals (although inorganic chelants exist) that react with polyvalent metal ions to form stable ring structures that incorporate the metal ion within the molecule. Chelants tie up metals and deactivate them. 

A study was made of the comparative stabilities at various exposures of an upset stomach remedy suspension. This product consisted of a dispersion of bismuth subsalicylate and phenylsalicylate in an aqueous system. Methyl-cellulose and magnesium aluminum silicate were selected as the suspending agents, because the presence of polyvalent metallic ions precluded the use of hydrocolloids affected by these ions. In addition, it was found that methyl-cellulose contributed a demulcent effect. The viscosity, as well as the suspension characteristics of the combination of protective colloids used, was of a synergistic nature. These colloids formed a thixotropic system. The thixotropy undoubtedly aids in stabilizing this system. In order to make this product palatable and impart elegance, color and flavor were added. Sample 1 (with protective colloids) showed no separation, while sample 2 (without... 

ChemFix Technologies, Inc., has used silicates and silicate setting agents to stable polyvalent metal ions. Usually, there is a need to separate coarse and fine pollutants so as to crush coarse materials and reduce the material size required for the stabilization technology. 

Titrability of polyvalent metal ions employing disodium acetate... 

Chelate is a complex that is formed by the combination of a polyvalent metal ion with a molecule which essentially contains two or more groups that can donate electrons. 

Specifically, disodium ethylenediaminetetraacetate (EDTA) reacts with polyvalent metal ions to result in the formation of a fairly stable water-soluble complex, or a chelate compound. 

Some examples of polyvalent metal ions are given below ... 

TITRABILITY OF POLYVALENT METAL IONS EMPLOYING DISODIUM EDETATE... 

Titrability of Polyvalent Metal Ions Employing Disodium Edetate..164... 

The first important commercial builder was sodium tripol3q)hosphate, NasPsOio, first used with Tide detergent in 1947. Besides sequestering polyvalent metal ions, it prevents redeposition of dirt, buffers the solution to pH = 9 -10, kills bacteria, and controls corrosion and deposits in the lines of automatic washers. 

Considering the efficacy of OH and O - in bridging polyvalent metal ions it might be expected that HS and S - would do likewise, and indeed... 

Geckeis, H., Rabung, Th., Ngo Manh, Th., Kim, J. I. Beck, H. P. 2002. Humic colloid-borne natural polyvalent metal ions Dissociation experiment. Environmental Science and Technology, 36, 2946-2952. 

Geckeis, H. Rabung, T. 2002. Solid-water interface reactions of polyvalent metal ions at iron oxide-hydroxide surfaces. In Hubbard, A. (ed) Encyclopedia of Surface and Colloid Science. Dekker Inc., 4737-4748. 

The observation that the pH of salt solutions, especially of those containing polyvalent metal ions, decreases on heating has lead to a different, yet very elegant, technique to generate well-defined metal (hydrous) oxides. Obviously, the increased acidity of such solutions must be due to the release of protons from the hydrated cations, which in turn change to hydroxide complexes. This process was termed by the senior author as forced hydrolysis (7,9-11). At appropriate temperatures and... 

Oxidations are catalyzed by acids, bases, pH values that are higher than the optimum, polyvalent metal ions, peroxides, hydroperoxides, and exposure to oxygen and ultraviolet (UV) illumination. These reactions may necessitate the use of antioxidant chemicals, inert atmospheres, and opaque packaging. Chelating agents... 

Three (3) classes of interactions can be described. First are the rapid reactions between soluble silicates and the polyvalent metal ions, producing insoluble metal silicates. Second, are reactions between the soluble silicates and the reactive components of the setting agent, producing a gel structure. Third, are hydrolysis, hydration, and neutralization reactions between the setting agent and the waste and/or water. 

Precipitation of Hafnium Hydroxide. In order to interpret the adsorption data it was necessary to determine the conditions which lead to the precipitation of hafnium hydroxide. It is not usually advisable to depend on the solubility product because the information on this quantity is often unreliable for hydroxides of polyvalent metal ions. In addition, "radiocolloids may apparently form much below saturation conditions in radioactive isotope solutions. In the specific case of hafnium hydroxide only two measurements of the solubility seem to have been reported. According to Larson and Gammill (16) K8 = [Hf(OH)22+] [OH ]2 — 4 X 10"26 assuming the existence of only one hydrolyzed species Hf(OH)22+. The second reported value is Kso = [Hf4+] [OH-]4 = 3.7 X 10 55 (15). If one uses the solubility data by Larson and Gammill (Ref. 16, Tables I and III) and takes into consideration all monomeric hafnium species (23) a KBO value of 4 X 10 58 is calculated. 

It is well known that hydrolyzed polyvalent metal ions are more efficient than unhydrolyzed ions in the destabilization of colloidal dispersions. Monomeric hydrolysis species undergo condensation reactions under certain conditions, which lead to the formation of multi- or polynuclear hydroxo complexes. These reactions take place especially in solutions that are oversaturated with respect to the solubility limit of the metal hydroxide. The observed multimeric hydroxo complexes or isopolycations are assumed to be soluble kinetic intermediates in the transition that oversaturated solutions undergo in the course of precipitation of hydrous metal oxides. Previous work by Matijevic, Janauer, and Kerker (7) Fuerstenau, Somasundaran, and Fuerstenau (I) and O Melia and Stumm (12) has shown that isopolycations adsorb at interfaces. Furthermore, it has been observed that species, adsorbed at the surface, destabilize colloidal suspensions at much lower concentrations than ions that are not specifically adsorbed. Ottewill and Watanabe (13) and Somasundaran, Healy, and Fuerstenau (16) have shown that the theory of the diffuse double layer explains the destabilization of dispersions by small concentrations of surfactant ions that have a charge opposite to... 

The above is not to underestimate the role of clay in the hot water process. Tar sands of high clay content generally are difficult to process, owing partly to the tendency of clay to stabilize oil and water emulsions. In addition, polyvalent metal ions act as bridging agents between the oil and clay, particularly at low pH. The association of clay with the oil retards the attachment of air as well as increasing the density of the oil particles. This mechanism is discussed in detail in Ref. 2. 

They prevent polyvalent metal ions from combining with (many) surfacnint(s) to form an adduct which is less effective than the unmodified surfactant in cleansing properties. 

They prevent polyvalent metal ions from combining with various soils, such as lipid residues and clays, to form less dispersible residues, which adhere tenaciously to the surface to be cleaned. 

J.S. D Arrigo, Possible screening of surface charges on crayfish axons by polyvalent metal ions, J. Physiol. 231 (1973) 117-128. 

Water hardness is related to polyvalent metallic ions in water, and it is reported as an equivalent concentration of calcium carbonate (CaC03). A commonly used hardness classification is given in Table 13.9. Hardness is associated with the hard scale (metal-carbonate precipitates) forming in cooking utensils, pipes, hot water tanks, and boilers. This scale reduces the capacity of pipes to carry water and transmit heat well. 

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