Lewatit® MDS TP 260 is a weakly acidic, macroporous cation exchange resin with chelating amino methyl phosphonic acid groups for the selective removal of transition heavy metals and alkaline earth cations. The monodisperse beads are mechanically and osmotically superior stable. Lewatit MDS TP 260 is produced with significantly smaller beads then eh regular Lewatit MonoPlus TP 260 and therefore performs with strongly increased kinetics. Depending on the operating conditions 50-100% higher operating capacity can be realized under equal chemical consumption in regeneration and conditioning. Divalent cations are removed from neutralized waters in the following order: Uranium > Lead > Copper > Zinc > Nickel > Cadmium > Cobalt > Magnesium > Strontium > Barium >>> Sodium. Adsorption of trivalent cations takes place, but desorption may be difficult. For instance iron(III) can only be desorbed by uneconomically high amounts of specific acid dosage. Due to the smaller beads Lewatit MDS TP 260 beds will deliver higher pressure drops over a resin bed than standard products. This has to be considered in an adequate pump design. Also it has to be considered, that the resin bed is more sensitive against plugging by suspended particles. Therefore a suitable prefilltration of the feed stream (e.g by use of sand filters or filter candles) has to be provided. It is e.g. suitable for use in secondary purification of brine feed to chloralkali membrane cells (traces of alkaline earth ions are removed after their normal precipitation by carbonates in the pH range 7-11) at absence of iron (III) ions and in case of low demand on Sr and Ba removal. In brine purification the operating capacity of Lewatit MDS TP 260 depends on the pH-value of the brine. At pH 10 it is approx. threefold that achieved at pH 8. At pH 10 and calcium content of 5 ppm, a capacity up to 26g Ca per liter of Lewatit MDS TP 260 (related on the resin in the di-sodium-form) is obtained. At a service flow rate of 20-30 BV/h, the residual calcium values are well below 10 ppb. Greater security can be achieved by operating two units of equal size in series. Lewatit MDS TP 260 has to be conditioned with caustic soda solution after every regeneration cycle/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. |