First International Conference on MOLDAVIAN RISKS – FROM ...

<strong>First</strong> <strong>International</strong> <strong>Conference</strong> on MOLDAVIAN RISKS - FROM GLOBAL TO LOCAL SCALE
16-19 May 2012, Bacau, Romania
ASPECTS OF WATER DEMINERALIZATION WITH MIXED-
LAYER ION-EXCHANGERS
Iuliana Rogoveanu Radosavlevici, Dan Niculae Robescu
Politehnica University of Bucharest, Power Engineering Faculty
Iuliana Rogoveanu Radosavlevici, rad_iu@yahoo.com
Abstract: Ion exchange is used for water treatment on a large number of separations from
water-based and non-water-based media, it has a special use in chemical synthesis, medical
research, agriculture and food processing. The utility of ion exchange is primarily that the
ion-exchanger can be regenerated and reused. Ion exchange is being used more often in the
nuclear industry for recuperation and separation of radioactive elements such as Uranium,
Plutonium, fission products and other impurities. This experimental application sets to
investigate total water demineralization for the public water distribution network in
Bucharest, Romania, which is achieved through a method of passing the water flow
through an acid cation mixed layer (Purolite C100) and an alkaline anion (Purolite A400).
For this purpose, the qualitative and quantitative influence of the flow speed through the
layer, the total volume of ion exchangers and working temperature over the process
dynamics and the quantitative characterization of the investigated process using a 3-factor
experimental research plan were tracked. A mathematical model was elaborated in order to
describe the process dynamics for ion exchange in fixed and mixed layer with ion
exchanging resin. In order to achieve this objective some simplifying assumptions were
made:
- The cation and anion particles are identical, sphere shaped objects with a diameter of dp;
- Ion exchange takes place between H+ ions that are initially found in the cationite and the
j cationites in water and the anions exchange takes place between the OH- anions initially
found in the anionite and the k anions in water; for simplicity consider j=Ca2+, k=HCO3-;
- The ion exchange process takes place on the ion changer’s particles’ surface;
- The global ion exchange speed depends on the speeds of elemental surface retention and
release processes;
- The ion retention process speed is directly proportional to the number of active loci in the
exchanger and the ion concentration in liquid state;
- The ion release process speed is directly proportional to the concentration of ion in solid
state;
- Piston flow with axial dispersion of the liquid state;
- The axial dispersion coefficient is determined with the Levenspiel formula;
- The ion exchange process is isothermal.
Keywords: Ion exchange, demineralization, cationite, anionite, axial dispersion.
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