Lewatit® MDS TP 208 is a weakly acidic, macroporous cation exchange resin with chelating iminodiacetic acid groups. It has been designed for selectively binding transition and alkaline earth metal cations. Its monodisperse beads are of high mechanical and osmotic stability. Lewatit MDS TP 208 is a small bead variant of Lewatit MonoPlus TP 208 with excellent kinetic performance. It gives 50-80% higher operating capacities without requiring additional regenerant chemicals. Due to the smaller bead sizing Lewatit MDS TP 208 delivers higher pressure drops across resin beds. Pump designs need to adjusted accordingly. A higher sensitivity towards plugging by suspended particles requires suitable prefiltration of the feed stream e.g. by use of sandfilter candles. Divalent cations are removed from neutralized waters in the following order: Copper>Vanadium (VO2)>Uranium (UO2)>Lead>Nickel>Zinc>Cadmium>Iron (II)>Beryllium>Manganese>Calcium>Magnesium>Strontium>Barium>>>Sodium. Adsorption of trivalent cations also takes place. For instance iron (III) can be adsorbed and can --- in contrast to Lewatit MonoPlus TP 260 and related products – also be desorbed with acid. It is especially suitable for use in:- The secondary purification of brine feed to chloralkali membrane cells (trace of alkaline earth ions are removed after their normal precipitation by carbonates in the pH-range 7-11)
- The secondary purification of brine especially where removal of Sr and Ba is required
- The purification of waste water
- The recovery of valuable metals
In brine purification, the operating capacity of Lewatit MDS TP 208 is pH-sensitive. At pH 10 is approx. three times that achieved at pH8. At pH 10 and a calcium content of 5 ppm, capacities up to 20 g Ca per liter of Lewatit MDS TP 208 (relative to the volume of the di-sodium-form) are obtained. At a service flow rate of 20-30 BV/h, the residual calcium values are well below 10 ppb. Stable plant performance is best achieved by operating two units of equal size in series. Lewatit MDS TP 208 has to be conditioned with caustic soda solution after every regeneration cycle and before every exhaustion cycle. After the conditioning it is in the di-sodium-form and can be used for the next cycle in the final polishing of chloralkali brine feed.Information provided by Lanxess. |