Ion-exchange column, fixed-bed

The fixed bed ion exchange column provided a much higher level of decontamination and since the goal was to produce an effluent with mini mi im contamination, it was eventually considered to be the baseline process. In this approach, the waste solution which were approximately IM in HNOo, were adjusted to a pH of 0.5-1 by addition of sodium hydroxide and flowed through a titanate bed at one column volume per hour. The columns were subsequently washed with water to remove excess sodium. 

Figure 5.14 Variation of uranium concentration with time and position in fixed-bed ion-exchange columns. Feed concentration, 0.5 g UgOg/liter feed rate, 9.61 bed volumes/h.

Figure 5.16 Steps in elution of uranium from fixed-bed ion-exchange column, (From Hargrove IHl].)...

Using fixed bed ion-exchange column techniques, the quantitative exchange of ions can also be attained in those cases where the selectivity conditions are not very favorable. In these cases the length of the column and flow rate must be chosen properly. 

Zou, W., Zhao, L. Han, R. (2009) Removal of uranium (VI) by fixed bed ion-exchange column using natural zeolite coated with manganese oxide. Chinese Journal of Chemical Engineering, 17 (4), 585-593. 

In columns with a fixed bed, ion-exchanger capacity is not completely used since the process is performed up to breakthrough, that is until the appearance of the substance injected into the column in the outlet of the column. So a considerable part of ion-exchange capacity which is within the zone of the sorption front is not used. The counter-current process is carried out so that completely exhausted ion exchanger is in equilibrium with the injected solution when it leaves the column. In this case the capacity is fully used. 

Among U.S. mills, the moving bed system is used in the mill of the Lucky Me Uranium Company at Gas Hills, Wyoming [D2a]. The moving-bed process is a modified batch-operated, fixed-bed ion-exchange system. Adsorption of uranium from leach liquor is carried out in two parallel sets of three columns in series. Each set is operated cyclically as in the fixed-bed system described earlier, with the feed point moved progressively around the cycle as the last bed in flow sequence becomes saturated. The novelty of the moving-bed system is in the diysical transfer of loaded resin from an adsorption cdumn to one of three elution columns, also operated cyclically in series. After elution is complete, the stripped resin is transfened back to one of the two adsorption sets, vdiere it is placed last in flow sequence. 

In fixed bed ion exchange the resin is held stationary in a column and the dilute silicate is passed up or down through the acid form resin. This process is illustrated in Figure 12.3. As it passes through the column, sodium is removed, and transferred to the ion exchange resin. The hydrogen ions from the resin are transferred to the silica... 

In a theory of fixed bed performance for application to ion exchange columns, Thomas(14) assumed that the rate was controlled by the ion-exchange step itself. A rate equation may be written as ... 

Column performance studies for fixed-bed columns are concerned with the concentration history of the column effluent—that is, with the variation in concentration as a function of time or of volume of effluent. Concentration-history calculations for fixed-bed adsorption and ion-exchange columns must make use of one or another of a group of specialized results which take the place of a general solution to the problem. The specialized results can be identified on the basis of controlling mecha-... 

Different batch adsorption processes were modeled using a multilayer fccdforwaKl neural network to predict water sorption [28] or adsorption of binary vapor mixtures [29]. Breakthrough parameters of an ion-exchange column [30] or a granular activated carbon fixed bed [31] were also predicted using the same kind of perceptions. 

If the solution were removed from Tank 1 and added to Tank 2, which also contained 1 eq of resin in the X ion form, the solution and resin phase would both contain 0.25 eq of Y ion and 0,75 eq of X ion. Repeating the procedure in a third and fourth tank would reduce the solution content of Y ions to 0.125 and 0.0625 eq. respectively. Despite an unfavorable resin preference. using a sufficient number of stages could reduce the concentration of Y ions in solution to any level desired. This analysis simplifies the column technique, but it does provide insights into the process dynamics. Separations are possible despite poor selectivity for the ion being removed. Most industrial applications of ion exchange use fixed-bed column... 

The column is filled with ion-exchange resin containing zirconium hydroxide. Acidic brine containing iodate ion is supplied to the column from the top. Iodate ion is adsorbed in the following reaction by way of the fixed bed ... 

Lapidus, L. and Amundson, N. R. J. Phys. Chem. 56 (1952) 373. Mathematics of adsorption in fixed beds — The rate determining steps in radial adsorption analysis ibid 56 (1952) 984. The effect of longitudinal diffusion in ion exchange and chromatographic columns. 

In connection with the engineering content of the book, a large number of reactors is analyzed two- and three-phase (slurry) agitated reactors (batch and continuous flow), two-and three-phase fixed beds (fixed beds, trickle beds, and packed bubble beds), three-phase (slurry) bubble columns, and two-phase fluidized beds. All these reactors are applicable to catalysis two-phase fixed and fluidized beds and agitated tank reactors concern adsorption and ion exchange as well. 

In the downstream processing of bioprocesses, fixed-bed adsorbers are used extensively both for the recovery of a target and for the removal of contaminants. Moreover, their performance can be estimated from the breakthrough curve, as stated in Chapter 11. The break time tg is given by Equation 11.13, and the extent of the adsorption capacity of the fixed bed utilized at the break point and loss of adsorbate can be calculated from the break time and the adsorption equilibrium. Affinity chromatography, as weii as some ion-exchange chromatography, are operated as specific adsorption and desorption steps, and the overall performance is affected by the column capacity available at the break point and the total operation time. 

Countercurrent process schemes for replacing ions of one kind by ions of another are analogous to those carried out in fixed ion-exchange resin beds. The use of countercurrent columns enables one, in these cases, to employ ion-exchanger capacity more effectively, to reduce expenditures for resin regeneration, and to decrease the amount of waste. It also permits automated control of the process. 

In the general case [6] different auxiliary ions are used in columns I and II. In order to affect a closed process the regeneration of ion exchanger, that is, its conversion from the DR-form into the CR-form is required. Regeneration can be effected either in the column with a fixed bed of resin or in the countercurrent column. The quantity of C ion needed... 

One important feature characteristic of the processes under consideration should be noted. Movement by the sorption front between alkaline and neutral zones or acidic and alkaline ones relative to the column walls is matched by the movement of the section 1 and 2 border. In particular it becomes possible to carry out separation in a fixed bed of ion exchanger. In both cases, namely using a fixed bed or employing a countercurrent column ion exchanger, regeneration is not required. 

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