Lewatit® TP 208 is a weakly acidic, macroporous cation exchange resin with chelating imino-diacetat groups for the selective removal of alkaline earth cations. Lewatit TP 208 has a heterodispersed bead size. In comparison to Lewatit TP 207 and Lewatit MonoPlus TP 207 this resin has a modified polymer structure and also a modified substitution grade of the imino-diacetate groups to make it especially suitable for the adsorption of earth alkali ions in the presence of alkali ions. It is especially suitable for use in: final polishing of brine feed to chloraklai membrane cells (traces of alkaline earth ions are removed after their normal precipitation by carbonates in the pH-range 8-11) in the presence of iron (III) ions and in case Sr and Ba have also to be removed besides Ca and Mg. The operating capacity of Lewatit TP 208 depends on the pH-value of the brine. At pH 10 it is approx. three fold of that achieved at pH 7. At pH 10 and calcium content of 5 ppm, an operating capacity of approx. 12 g Ca/l Lewatit TP 208 (volume of resin in di-sodium-form) is obtained. At a service flow rate of 20-30 BV/h, the residual calcium concentration is well below 20 ppb. Greater security can be achieved by operating two units of equal size in series. Lewatit TP 208 has to be conditioned with caustic soda solution after every regeneration cycle/before every exhaustion cycle. After the conditioning it is in di-sodium-form and ready to use for the final polishing of chlorakali brine feed. Aside from its major application in brine purification Lewatit TP 208 can be used for the removal or recovery of heavy metals out of process-, waste water- and potable water streams. Thereby, it removes heavy metal cations from neutralized aqueous solutions in the following order: Copper>Vanadium (VO2)>Uranium (UO2)>Lead>Nickel>Zinc>Cadmium>Iron (II)>Beryllium>Manganese> Calcium>Magnesium>Strontium>Barium>Sodium. Lewatit TP 208 does not remove heavy metals from solutions containing EDTA or NTA respectively. Only cadmium is removed from solutions containing cyanides.Information provided by Lanxess. |