Ion-exchanger regeneration

FIG. 16-42 Ion -exchanger regeneration, (a) Conventional. Acid is passed downflow through the cation-exchange resin bed. (b) Counterflow. Regenerant solution is introduced upflow with the resin bed held in place by a dry layer of resin. 

Nickel Sulfamate. Vltramon, a Thomas and Betts subsidiary, installed a 1 gpm ARO system to recover rinses and recycle nickel bath used to plate electronic capacitors. Previously, Vitramon had used an ion exchange system to remove the nickel. Ion exchange regenerant was shipped to a reclaimer. Water was reused. Ion exchange cost of operation was 4,000 per month. The ARO system maintains the rinse at less than 40 ppm nickel. Savings from nickel recovery and avoided treatment cost will provide a payback of approximately 10 months. 

Another factor increasing the cost of distillation in ion exchange regenerant recovery is the need for supplying reflux to the rectifying columns. The boil-up for the reboilers is the distillate product plus the reflux, where in direct distillation the reboiler has to vaporize only the product. 

If ion exchange regenerant recovery as a 13% ammonium bicarbonate solution involves too much distillation for the process to be attractive, might not some other distillation conditions appear more favorable To answer this question the second material balance was made which assumed a still overhead product of a 1 1 1 mole ratio of NH3 C02 H20, the same ratio in which these compounds unite to form anhydrous ammonium bicarbonate. This is the composition of the distillate which gives a minimum amount of distillate product, and still a process which might be feasible. 

Other sources of water for reuse may be from large industrial balance tanks and lakes, process save-all tanks, oxidation ponds, and receiving pits for boiler blowdown, or ion-exchange regeneration effluents. 

This treatment is essential on first use of many ion-exchangers, but is also recommended for regeneration of used ion-exchangers. Regeneration should begin with a high salt wash (1 M - 4 M NaCl) to remove the bulk of any tightly adsorbed sample... 

Another method of avoiding the ion-exchanger regeneration stage uses complex-forming reagents. This method is based on creating the conditions where complexes can be formed only in one of the columns. As a result the stationary front is maintained due to the difference in sorbability of separated and auxiliary ions in one column and the difference in the stability of complexes in the other. 

Separations may also be carried out without a special ion-exchanger regeneration stage in case it is impossible to select the conditions under which the stationary front forms [ 17] in one of the columns. To consider the scheme for processes such as these take as examples the purification of substances from impurities when impurities are sorbed more strongly than the substance purified and when impurities are sorbed more weakly than the substance purified. Assume also in these examples that in the column where the purified product is obtained flow reversal takes place by forming a stationary front. 

To complete the cycle the ion-exchanger regeneration stage for replacement of the A ions remaining in it with C ions is required. 

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. 

Shown in Fig. 20 is a scheme for countercurrent softening of water [9,42]. Divalent cations, Me, are sorbed from strongly acidic cation exchanger in the Na form. Ion exchanger regeneration is then affected with the concentrated solution of NaCl softened earlier by the replacement of all multicharged cations with sodium. 

Countercurrent demineralization of water in a mixed bed is described in [44]. The main difficulty in using a mixed bed is encountered in the separation of cation and anion exchangers before regeneration. Use is made of the difference in ion-exchanger densities to achieve this end. Ion exchangers regenerated in countercurrent columns are put into a mixer. 

After exhausting a part of the bed in the left branch the input and output of solution is stopped, valve 1 is shut and valve 2 is opened. Upon moving the piston to the right the ion exchanger, regenerated, is pumped into the bottom part of the left branch while the exhausted top portion of the bed moves to the top portion of the left branch (Fig. 27b). This operation lasts for 15-60 s. The pressure developed is as high as 8 atm. 

Ion-exchanger regeneration Brine acidification in chlor-alkali industry Wastewater treatment from amino acid processing... 

McGrath, S., The Talosave brine recovery process for treatment of ion exchange regenerant in sugar refineries, Publ. Tech. Pap. Proc. Ann. Meet. Sugar Ind. Technol., 57, 299, 1998. 

If the sample to be analyzed contains organic acids, the metal ion fixed at the ion-exchange group can be removed by complexation, which increases the frequency of ion exchanger regeneration. 

Table 12.2. Comparison of different ion exchange regeneration methods (Ribereau-Gayon et at., 1977)...

Limitation on caustic addition brine acidification maintenance of high cathode CE cell renewal Selection of salt better potash refining use of demineralized water in decomposers and ion-exchange regeneration Selection of salt chemical treatment ion exchange... 

B. Process Parameters. Figure 7.46 shows a typical chemical treatment process. Solutions of caustic and carbonate are stored in feed tanks. While direct use of Na2C03 slurry is possible, this diagram is based on solution feed. There may also be a preparation tank in which carbonate solutions are made off line. The caustic solution is received from the process, preferably before evaporation in a membrane-cell plant. A separate supply of a diluted solution (20% or less) is often used, and ion-exchange regenerant solutions are another possible source of treat liquor (Section 7.5.5.2B). 

As noted, the acid used in dechlorination of depleted brine does not have to be of the highest purity. The dechlorinated brine will circulate back through the treatment system, and any impurity that is removed there can be tolerated at a reasonable concentration in the acid. This may allow the use of byproduct acid or of some of the acidic effluent from ion exchanger regeneration. 

Hydrochloric Acid Specification. The specification in Table 13.2 is generally applicable for electrolyzer feed brine acidification, depleted brine pH control, and ion exchanger regeneration. The contaminant levels relate to normally available commercial concentrations of 32-36% HCl. Hydrochloric acid used for brine acidification should be sufficiently dilute to prevent any risk of salting out. This aspect is covered in Section 7.5.6.1. 

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