Anion-exchange capacity

TABLE 15. Cation exchange BEAD FORM Capacity (meq/g) ION-EXCHANGE PACK AGINGS Anion exchange Capacity (meq/g)... 

Anion A negatively charged ion in an electrolyte solution, attracted to the anode under the influence of a difference in electrical potential. Chloride is an anion. Anion exchange capacity Sum total of exchangeable anions that a soil can adsorb. Expressed as centimoles of negative charge per kilogram of soil. 

There has been much interest in modifying the ion-exchange properties of conducting polymers with substituents or polymeric counter-ions. Cationic substituents, such as ammonium234 and pyridinium235 groups, increase the polymer s anion-exchange capacity and increase anion trans-... 

Some soils, particularly those in the tropics, have significant anion exchange capacity. For these soils, there is an attraction between soil colloids and the simple halogen and nitrate anions. Bringing these anions into solution for analysis requires an extraction, or replacing anions, just as does the analysis of exchangeable cations. 

Anion exchange capacity can be investigated in a similar manner except that the soil is first leached with an anion [4],... 

The anionic exchange capacity for some LDH compositions is reported in Fig. 13. The values range from 450 to 200meq/100g lower values are difficult to reach since the ratio R = would be too high to maintain... 

Fig. 13 Variation of anion exchange capacity (meq/lOOg) as a function of the amount of trivalent cation x in X xim nH20...

Oxides and hydroxides of Al, Fe, Mn, and Si may exist in the subsurface mainly as a mixture (known also as a solid solution) rather than as pure mineral phases. They are considered amphoteric materials, characterized by no permanent surface charge. Their cation and anion exchange capacities reflect adsorption of potentialdetermining ions such as H+ and OH". Different surfaces have a diverse affinity for H+ and OH" ions and thus exhibit various points of zero charge (PZC). Details of various models for variable charge minerals may be found in the extensive review of McBride (1989). 

The cation-exchange capacity of the copper ferrocyanide gel used was found to be about 2.60 meq/g and its anion-exchange capacity about 0.21 meq/g. In all cases of various doses of gel used and types of anionic surfactants being removed, the tests indicated that a batch contact time of about 12 hours was sufficient for achieving maximum removals. Trials with various fractions of particle size demonstrated that both uptake and desorption (important in material regeneration) were most convenient and maximized on 170-200 BSS mesh size particles. Also, the adsorption of anionic surfactants was found to be maximum at pH 4 and decreased with an increase in pH. 

Figure 11.9 Sorption isotherms for some charged organic compounds interacting with natural solids (a) quinolinium cation on a subsoil of /oc = 0.024 and cation exchange capacity of 84 mmol/kg (Zachara et al., 1986), ( >) anilinium cation on a surface soil with /oc = 0.013 and cation exchange capacity of 112 mmol/kg (Lee et al., 1997), and (c) sorption of 4-(2,4-dichloro-phe-noxy)-butyrate anion on a sediment with/oc = 0.015 and unknown anion exchange capacity (Jafvert, 1990).

Molybdate or tungstate were introduced by ion exchange with solutions of the Na+ salts under N2 atmosphere at a pH of 10 (for Mg,Al-LDH) or 7 (for Zn,Al-LDH). Organophilic LDHs were prepared by ion exchange with a double excess (with respect to the anion exchange capacity) of the Na+ salts of toluene-4-sulfonate and dodecyl sulfate. 

All adsorbents have upper limits to the amount of arsenic that they can adsorb from air, water, or other fluids. That is, there is a finite number of adsorption sites on each gram of adsorbent. The maximum adsorption capacity, which is often measured in molal, represents the highest concentration of a solute (such as arsenic) that can be adsorbed by a given mass of a particular adsorbent. The maximum adsorption capacity is routinely obtained from laboratory experiments and measurements, and is closely related to the cation exchange capacity (cec) or anion exchange capacity (aec) of the materials. The cec or aec provide... 

Anion exchange capacity The ability of a solid substance to adsorb anions. The anion exchange capacity of a material represents the total positive charge on the surface of the material and is generally expressed in miWiequivalents per 100 grams of material (compare with cation exchange capacity). 

Equivalent The amount of a substance that will react with one mole of H+ or OH-. The related term equivalent mass ( weight ) refers to a molar mass of a substance divided by the absolute value of its valence state. For anion exchange capacity and cation exchange capacity measurements, the results are usually reported in milliequivalents (1/1000 of an equivalent) per 100 g of material. 

Poly(ethyleneimine) cross-linked (CPEI) with ethylenedichloride forms stable complexes with copper (II) as well as with cobalt (II). The RC1 type of cross-linked poly(ethyleneimine) having an anion-exchange capacity of 6.8 meq g 1 retains copper from CuS04 and cobalt from 1 M aq. CoCl2 solutions [55], PEI is by itself a weak basic anion-exchange resin and forms stable complexes with anions and cations. The process is probably accompanied with chelate ring formation ... 

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