Polyvalent

In addition to the collector, polyvalent ions may show sufficiently strong adsorption on oxide, sulfide, and other minerals to act as potential-determining ions (see Ref. 98). Judicious addition of various salts, then, as well as pH control, can permit a considerable amount of selectivity. 

It is convenient to describe here certain polyvalent iodine compounds, formed by such substances as iodobenzene and p-iodotoluene. lodobenzeue in chloroform solution reacts readily with chlorine to form iodobenzene dlchlorlde (phenyl iododichloride) (I) ... 

Intramolecular H bond Polyvalent alcohols Chelation 3600-3500 (s) 3200-2500 Sharper than dimeric band above Broad and occasionally weak the lower the frequency, the stronger the intramolecular bond... 

To accomplish any separation of two cations (or two anions) of the same net charge, the stationary phase must show a preference for one more than the other. No variation in the eluant concentration will improve the separation. However, if the exchange involves ions of different net charges, the separation factor does depend on the eluant concentration. The more dilute the counterion concentration in the eluant, the more selective the exchange becomes for polyvalent ions. 

Water-soluble peroxide salts, such as ammonium or sodium persulfate, are the usual initiators. The initiating species is the sulfate radical anion generated from either the thermal or redox cleavage of the persulfate anion. The thermal dissociation of the persulfate anion, which is a first-order process at constant temperature (106), can be greatly accelerated by the addition of certain reducing agents or small amounts of polyvalent metal salts, or both (87). By using redox initiator systems, rapid polymerizations are possible at much lower temperatures (25—60°C) than are practical with a thermally initiated system (75—90°C). 

Other Reactants. Other reactants are used in smaller amounts to provide phenoHc resins that have specific properties, especially coatings appHcations. Aniline had been incorporated into both resoles and novolaks but this practice has been generally discontinued because of the toxicity of aromatic amines. Other materials include rosin (abietic acid), dicyclopentadiene, unsaturated oils such as tung oil and linseed oil, and polyvalent cations for cross-linking. 

Orthophosphate salts are generally prepared by the partial or total neutralization of orthophosphoric acid. Phase equiUbrium diagrams are particularly usehil in identifying conditions for the preparation of particular phosphate salts. The solution properties of orthophosphate salts of monovalent cations are distincdy different from those of the polyvalent cations, the latter exhibiting incongment solubiUty in most cases. The commercial phosphates include alkah metal, alkaline-earth, heavy metal, mixed metal, and ammonium salts of phosphoric acid. Sodium phosphates are the most important, followed by calcium, ammonium, and potassium salts. 

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. 

Many orthophosphate salts, in particular those of polyvalent cations, exhibit incongment solubihty where disporportionation occurs in solution to yield a more basic orthophosphate salt and phosphoric acid. This hydrolytic disproportionation of orthophosphates should not be confused with the... 

Alkali Meta.IPhospha.tes, A significant proportion of the phosphoric acid consumed in the manufacture of industrial, food, and pharmaceutical phosphates in the United States is used for the production of sodium salts. Alkali metal orthophosphates generally exhibit congment solubility and are therefore usually manufactured by either crystallisation from solution or drying of the entire reaction mass. Alkaline-earth and other phosphate salts of polyvalent cations typically exhibit incongment solubility and are prepared either by precipitation from solution having a metal oxide/P20 ratio considerably lower than that of the product, or by drying a solution or slurry with the proper metal oxide/P20 ratio. 

Ion Removal and Metal Oxide Electrodes. The ethylenediamine ( )-functional silane, shown in Table 3 (No. 5), has been studied extensively as a sdylating agent on siUca gel to preconcentrate polyvalent anions and cations from dilute aqueous solutions (26,27). Numerous other chelate-functional silanes have been immobilized on siUca gel, controUed-pore glass, and fiber glass for removal of metal ions from solution (28,29). 

Silicate Grouts. Sodium silicate [1344-09-8] h.3.s been most commonly used in the United States. Its properties include specific gravity, 1.40 viscosity, 206 mPa-s(=cP) at 20°C Si02 Na20 = 3.22. Reaction of sodium silicate solutions with acids, polyvalent cations, such organic compounds as formamide, or their mixtures, can lead to gel formation at rates, which depend on the quantity of acid or other reagent(s) used. 

The hot-water separation process involves extremely compHcated surface chemistry with interfaces among various combinations of soUds (including both silica sand and alurninosilicate clays), water, bitumen, and air. The control of pH is critical. The preferred range is 8.0—8.5, achievable by use of any of the monovalent bases. Polyvalent cations must be excluded because they tend to flocculate clays and thus raise viscosity of the middlings in the separation cell. 

When a potential is appHed across the ceU, the sodum and other cations are transported across the membrane to the catholyte compartment. Sodium hydroxide is formed in the catholyte compartment, because of the rise in pH caused by the reduction of water. Any polyvalent cations are precipitated and removed. The purified NaOH may be combined with the sodium bicarbonate from the sodium dichromate process to produce soda ash for the roasting operation. In the anolyte compartment, the pH falls because of the oxidation of water. The increase in acidity results in the formation of chromic acid. When an appropriate concentration of the acid is obtained, the Hquid from the anolyte is sent to the crystallizer, the crystals are removed, and the mother Hquor is recycled to the anolyte compartment of the ceU. The electrolysis is not allowed to completely convert sodium dichromate to chromic acid (76). Patents have been granted for more electrolytic membrane processes for chromic acid and dichromates manufacture (86). 

Ghelants and Precipitation Inhibitors vs Dispersants. Dispersants can inhibit crystal growth, but chelants, such as ethylenediaminetetraacetic acid [60-00-4] (EDTA), and pure precipitation inhibitors such as nitrilotris(methylene)tris-phosphonic acid [6419-19-8], commonly known as amino trismethylene phosphonic acid (ATMP), can be more effective under certain circumstances. Chelants can prevent scale by forming stoichiometric ring stmctures with polyvalent cations (such as calcium) to prevent interaction with anions (such as carbonate). Chelants interact... 

Whey concentration, both of whole whey and ultrafiltration permeate, is practiced successfully, but the solubility of lactose hmits the practical concentration of whey to about 20 percent total sohds, about a 4x concentration fac tor. (Membranes do not tolerate sohds forming on their surface.) Nanofiltration is used to soften water and clean up streams where complete removal of monovalent ions is either unnecessary or undesirable. Because of the ionic character of most NF membranes, they reject polyvalent ions much more readily than monovalent ions. NF is used to treat salt whey, the whey expressed after NaCl is added to curd. Nanofiltration permits the NaCl to permeate while retaining the other whey components, which may then be blended with ordinaiy whey. NF is also used to deacidify whey produced by the addition of HCl to milk in the production of casein. 

Bond energies of gaseous polyvalent metal halides... 

With strong cation-exchangers (e.g. with SO3H groups), the usual sequence is that polyvalent ions bind more firmly than mono- or di- valent ones, a typical series being as follows ... 

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