Iodine adsorption from aqueous solution

In the past, much attention was given to the study of dye and iodine adsorption by active carbons (Bmnauer, 1945 Orr and Dalla Valle, 1959). Many studies have been made with dye molecules of well-known size, shape and chemical properties, but the results have not been easy to interpret (Giles et al., 1970 McKay, 1982, 1984). In a systematic study of iodine adsorption (from aqueous solution) on a carbon black and four activated carbons (Femandez-Colinas etal., 1989b), it was found that the iodine isotherms could be analysed by the as-method. In this way it was possible to assess values of the available volume in pores of effective width of 0.5-1.5 nm. The adsorption of iodine was also featured in a recent study by Ziolkowska and Garbacz (1997), who applied the Langmuir, Freundlich and other isotherm equations. 

Iodine adsorption mg/g ASTMD1510 ISO 1304 amount of iodine adsorbed from aqueous solution as a measure of the specific surface area not applicable for oxidized carbon blacks... 

Molina-Sabio, M., Salinas-Martinez de Lecea, C., et al. (1985). A comparison of different tests to evaluate the apparent surface area of activated carbons. Carbon, 23, 91-6. Femandez-Colinas, J., Denoyel, R., and Rouquerol, J. (1989). Adsorption of iodine from aqueous solutions onto activated carbons correlations with nitrogen adsorption at 77 K. Adsorp. Sci. TechnoL, 6, 18-26. 

Fig. 9 3. Adsorption of iodine from aqueous solution (Carbon J, zinc chloride process Carbon K, calcium chloride process) C, grams iodine/liter...

Fig. 33. Adsorption of iodide and iodine from aqueous solution on Pt(lOO) Solvent contribution to the PMF for I" (diamonds) and 1° (crosses).

The adsorption of iodine from aqueous solutions by a series of non-activated and zinc chloride-activated charcoals was studied by Elnabarawy, El-Shobaky, Youssef, and Mikhail.The adsorption data are not presented, but the authors estimated the monolayer capacity from the isotherm and, using a value of 0.40 nm for the molecular area of E, calculated surface areas of the charcoals which agreed moderately well with values obtained by the BET-N2 method. However, for less active carbons (as<600m g ) the E-area tended to be substantially (15% or more) higher than the BET-N2 areas, whereas for zinc chloride-activated charcoals of surface area >600 g they were consis-... 

Adsorption of Iodine and Acetic Acid from Aqueous Solution... 

Hill A, Marsh H. A study of the adsorption of iodine and acetic acid from aqueous solutions on characterized porous carbons. Carbon 1968 6(l) 31-39. 

Akhrimenko, V. E., Poteryaev, A. V., and Ampllogov, I. E. Kinetics of the Adsorption of Iodine from Aqueous Solutions on Individual Carbon Grains. Russ. J. Phys. Chem. 46, No. 5, 726 (1972). (English translation). 

Adsorption of Iodine from Aqueous I2-KI Solutions by Starch of Various Origins69... 

From Na and Other Inert Gases. Adsorption isotherms for PH3 in mixtures with Na at 293 K were determined on various types of silica gel, activated carbon, and zeolites [3]. The removal from inert gases can be achieved by contact with silica gels [4], zeolites [4, 5], or activated carbon impregnated with CH3CN, picric acid, or maleic acid [4]. The adsorption on activated carbon pretreated with iodine compounds and sulfates or nitrates of ammonium and metals was used in [6]. Cu- or Ag-modified molecular sieves [7] or a soda-lime bed, which may contain nitrite salts, were also used as adsorbents [8]. The removal of PH3 by an aqueous solution of LiCl and HCIO4 was mentioned [9]. Its removal by oxidative methods is described in Section 1.3.1.5.4, p. 222. 

Ziolkowska, D., and Garbacz, J.K., Adaptation of single gas adsorption equations for the description of adsorption from non-aqueous liquid solutions of iodine onto active carbons, Adsorpt. Sci. Technol., 15(3), 155-164 (1997). 

Several papers by Swiatkowski and co-workers, all in Polish, have dealt with various aspects of iodine adsorption by active carbon. Measurements of the adsorption of E from 0.5 M-Nal solutions in aqueous methanol showed that the shift of the inflection point on the isotherm towards lower equivalent iodine concentrations with increase in water concentration in the solvent, was caused partly by the decrease in the solubility of iodine and partly by the effect of water on the polyiodide complex equilibria. For adsorption from solutions of Nal in ethanol, isopropanol, and acetonitrile, the isotherms were of the... 

Akhrimenko has studied the kinetics of adsorption of iodine from aqueous 0.1 m-KI solutions on single carbon grains, and found that the adsorption rate was greatly affected by the pore dimensions of the charcoal. Kinetic adsorption isosteres and isosteric enthalpies of adsorption were determined. 

The need to know the chemical nature of the adsorptive is well illustrated by two simple studies, that of iodine (I2) from an aqueous solution in potassium iodide (KI) and of acetic acid (CH3COOH) from an aqueous solution. The Kl acts as a reservoir for the iodine by forming KI3 (K and IJ). It is necessary to do this because of the limited solubility of iodine, as such, in water. What is needed to be known, for the construction of appropriate isotherms is the chemical nature of the adsorptive, be it (I2) or (If) for the iodine system, or CH3COOH or CH3C00H(H20) for the acetic acid system. Further, there is the need to elucidate if (a) the iodine is adsorbed via pore filling or via capillary condensation mechanisms and (b) to demonstrate uncertainties which exist when adsorbing species can be associated with water molecules in aqueous solution, as for adsorption of acetic acid (Hill and Marsh, 1968). 

Adsorption of iodine from aqueous I2/KI solution resembles adsorption of CO2 at 195 K and N2 at 77 K. That is, adsorption by iodine proceeds in the microporosity by a pore filling mechanism, and by capillary condensation in the mesoporosity, as does nitrogen at 77 K. The adsorption of iodine is apparently not influenced by the solvent, in this case, water which is an inert diluent. 

A procedure for the analysis of natural iodine in aqueous solutions of iodohippuric acid (57) has utilized a freezing technique for the preparation of the sample for irradiation. Irradiation of a frozen sample rather than a solution has a number of advantages, the pressure in irradiation containers caused by the radiolysis of water is reduced substantially losses of iodine due to vaporization and also to adsorption on container walls are greatly minimized and interference from nuclides from container walls is avoided. 

The first in situ X-ray diffraction study of adsorption from an aqueous solution was the investigation by Fleischmann and coworkers of iodine adsorption on graphite. To increase the surface sensitivity in this study, a high-surface-area compressed exfoliated graphite (Papyex) was used as the substrate. This material has a surface area of between 20 and 30m g V ° ... 

Curie quantities of fission-produced iodine have been purified by adsorption on platinum (64). The Irradiated target, enriched uranium alloyed with aluminum, was dissolved In aqueous sodium hydroxide. The solution was acidified with sulfuric acid and sparged with air which was then passed through a sodium hydroxide scrubber. The scrubber solution, which now contained the radioiodine In the form of iodide, was acidified with sulfuric acid and the radioiodide was permitted to be adsorbed on a specially prepared platinum felt (directions for preparation of the felt not given). The iodine was removed from the felt by washing with dilute sodium hydroxide solution. Chemical yields were 65-75% and decontamination factors were greater than 10 for removal of other fission products. The original solution contained about 250 curies of radioiodine. 

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