Ion removal

One can write acid-base equilibrium constants for the species in the inner compact layer and ion pair association constants for the outer compact layer. In these constants, the concentration or activity of an ion is related to that in the bulk by a term e p(-erp/kT), where yp is the potential appropriate to the layer [25]. The charge density in both layers is given by the algebraic sum of the ions present per unit area, which is related to the number of ions removed from solution by, for example, a pH titration. If the capacity of the layers can be estimated, one has a relationship between the charge density and potential and thence to the experimentally measurable zeta potential [26]. 

Ammonium Ion Removal. A fixed-bed molecular-sieve ion-exchange process has been commercialized for the removal of ammonium ions from secondary wastewater treatment effluents. This application takes advantage of the superior selectivity of molecular-sieve ion exchangers for ammonium ions. The first plants employed clinoptilolite as a potentially low cost material because of its availability in natural deposits. The bed is regenerated with a lime-salt solution that can be reused after the ammonia is removed by pH adjustment and air stripping. The ammonia is subsequentiy removed from the air stream by acid scmbbing. 

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). 

The corrosion rate is controlled mainly hy cathodic reaction rates. Cathodic Reactions 5.2 and 5.3 are usually much slower than anodic Reaction 5.1. The slower reaction controls the corrosion rate. If water pH is depressed. Reaction 5.3 is favored, speeding attack. If oxygen concentration is high. Reaction 5.2 is aided, also increasing wastage hy a process called depolarization. Depolarization is simply hydrogen-ion removal from solution near the cathode. 

The behavior of a polar dielectric in an electric field is of the same kind. If the dielectric, is exposed to an external electric field of intensity X, and this field is reduced in intensify by an amount SX, the temperature of the dielectric will not remain constant, unless a certain amount of heat enters the substance from outside, to compensate for the cooling which would otherwise occur. Alternatively, when the field is increased in intensity by an amount SX, we have the converse effect. In ionic solutions these effects are vciy important in any process which involves a change in the intensity of the ionic fields to which the solvent is exposed—that is to say, in almost all ionic processes. When, for example, ions are removed from a dilute solution, the portion of the solvent which was adjacent to each ion becomes free and no longer subject to the intense electric field of the ion. In the solution there is, therefore, for each ion removed, a cooling effect of the kind mentioned above. If the tempera-... 

Similarly, if a small concentration of hydroxide ions be added, the latter will combine with the hydrogen ions arising from the dissociation of the acetic acid and form water the equilibrium will be disturbed, and more acetic acid will dissociate to replace the hydrogen ions removed in this way. In either case, the concentration of the acetic acid and acetate ion (or salt) will not be appreciably changed. It follows from equation (21) that the pH of the solution will not be materially affected. 

A further problem that may cause contamination of the treated MU water is anion leakage as a result of organic fouling. This significantly affects anion resins, preventing ion removal by ion exchange and thus reducing bed capacity. 

Figure 8.21. (a) Effect of the rate, I/2F, of electrochemical oxygen ion removal (I<0) on the induced increase in the rate of propylene oxidation on Pt/YSZ.28 (b) Effect of catalyst potential and work function change on the rate enhancement ratio p (=r/r0) at a fixed gaseous composition. Reprinted with permission from Academic Press. 

This solution has pH > 7. When a few drops of a solution of strong base are added, the incoming OH ions remove protons from NH4+ ions to make NH3 and H20 molecules. When instead a few drops of a strong acid are added, the incoming protons attach to NH3 molecules to make NH4+ ions and hence are removed from the solution. In each case, the pH is left almost unchanged. 

To draw molecular pictures illustrating a proton transfer process, we must visualize the chemical reactions that occur, see what products result, then draw the resulting solution. When a strong base is added to a weak acid, hydroxide ions remove protons from the molecules of weak acid. When more than one acidic species is present, the stronger acid loses protons preferentially. 

The oxalic acid solution contains water molecules and H2 C2 O4 molecules as major species. Added hydroxide ions remove protons from the strongest acid, H2 C2 O4 ... 

Vourch et al49 studied the applicability of the RO process for the dairy industry wastewater. The treated wastewater total organic carbon (TOC) was <7 mg/L. It was found that in order to treat a flow of 100 m3/d, 540 m2 of the RO unit is required with 95% water recovery. Dead-end NF and RO were studied for the treatment of dairy wastewater.50 Permeate COD, monovalent ion rejection, and multivalent ion rejection for the dead-end NF were reported as 173-1095 mg/L, 50-84%, and 92.4-99.9%, respectively. When it comes to the dead-end RO membranes, the values for permeate COD, monovalent ion removal, and multivalent ion removal were 45-120 mg/L, >93.8%, and 99.6%, respectively. Membrane filtration technology can be better utilized as a tertiary treatment technology and the resultant effluent quality will be high. There can be situations where the treated effluents can be reused (especially if RO is used for the treatment). 

Ion exchange. Ion exchange is used for selective ion removal and finds some application in the recovery of specific materials from wastewater, such as heavy metals. As with adsorption processes, regeneration of the medium is necessary. Resins are regenerated chemically, which produces a concentrated waste stream requiring further treatment or disposal. 

Continuous ion-exchange units are also available in which ion exchange and resin regeneration both occur constantly. In this case both the resin bed and the fluid being purified are in motion. Continuous units are usually more economical than batch units when the rate of ion removal exceeds 1 lb/min (0.5 kg/min).39... 

The maximum in optical absorption for anodic oxides on Au as determined by McIntyre and Kolb [66] at a photon energy of 4.0 eV may be attributed on the basis of the UPS data to a transition from the maximum of the valence band to the conduction band. The differences between the spectra of the anodized and rinsed sample in Fig. 17 is due to counter ion removal after rinsing the sample with H20 [67]. 

Cao, C., Cui, Z., Chen, C., Song, W. and Cai, W. (2010) Ceria hollow nanospheres produced by a template-free microwave-assisted hydrothermal method for heavymetal ion removal and catalysis. Journal of Physical Chemistry C, 114, 9865-9870. 

Bromomethyl-5-nitrofuran offers an incoming nucleophile a choice of reaction sites product formation seems to be determined mainly by the nature of the nucleophile but is also strongly dependent upon the solvent and other conditions. The hard base hydroxide ion removes a methylenic proton from the active methylene group and the new nucleophile displaces bromide from another molecule to produce, eventually, the bis(5-nitro-2-furyl)ethene (Scheme 35, A).191... 

Robinson and Walsh have reviewed earlier cell designs. The performance of a 500 A pilot plant reactor for copper ion removal is described. Simplified expressions were derived for mass transport both in single pass [243] and batch recirculation [244]. For a detailed discussion of the principle and the role of the rotating cylinder electrode reactor in metal ion removal the reader is referred to Refs. [13] and [241] (46 references). 

Walsh FC, The role of the rotating cylinder electrode reactor in metal ion removal in ref (23), p 101, and references therein... 

Ammonium ion removal, molecular sieves in, 16 846-847 Ammonium lactate, 14 117 Ammonium laureth sulfate, cosmetic surfactant, 7 834t... 

Radioactive ions, removal of, 14 423 Radioactive isotopes of iodine, 14 373... 

It is common to concentrate organic components extracted from soil before analysis is conducted. Concentration of ionic species is not as common. However, the use of ion exchange resins to remove ionic species from soil is a well-established ion removal method. Although this method is not commonly discussed in terms of concentration of ions found in soil, it can lead to increased ion concentration and increased ability of analytical methods to measure trace amounts of ions in soil [26],... 

Buffers contain mixtures of weak acids and their salts (i.e., the conjugate bases of acids), or mixtures of weak bases and their conjugate acids. Typical buffer systems used in pharmaceutical dosage forms include mixtures of boric acid and sodium borate, acetic acid and sodium acetate, and sodium acid phosphate and disodium phosphate. The reason for the buffering action of a weak acid, HA (e.g., acetic acid) and its ionized salt, A" (e.g., sodium acetate) is that A" ions from the salt combine with the added hydrogen ions, removing them from solution as undissociated weak acid. 

Schematically the apparatus used for sputtering consists of a bell jar maintained at a reduced pressure of an inert gas such as argon. The gas is subjected to a potential difference of several kilovolts, producing a glow discharge from which positive ions are accelerated towards the target (the cathode). These high-energy ions remove...

Adding copper(l) chloride to the molten glass makes the process reversible. When light intensity diminishes, copper ions remove electrons from silver atoms, converting the silver atoms into silver ions. The silver ions then migrate back to the silver chloride crystals. The glass becomes transparent again. 

To the other test tube, add a few drops of HCl(aq) until you see a change. Again note the colour change. (The H " ions combine with the OH ions, removing them from the equilibrium mixture.)... 

Metal ions can assist in the dissociation (hydrolysis) of complexes containing multidentate ligands. The metal ion may not necessarily complex with the detached ligand, for example, in the metal-assisted acid-catalyzed aquation of Cr(C204)3. Ref. 112. Usually however the metal ion removes and complexes the ligand as in... 

A basic buffer consists of a solution of a weak base and one of its salts, such as a solution of ammonia and ammonium chloride. The weak base, ammonia, removes any added hydrogen ions. The conjugate acid, the ammonium ions from the ammonium chloride salt, replaces any hydrogen ions removed when the alkali was added. 

Membrane treatment is a very effective technology used in a broad range of applications. It has been used for desalinization, specific ion removal, nutrients and suspended solids removal, and nowadays plays an important role in removal of trace-level organic contaminants dissolved in water. It is a very advantageous... 

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