Mixed Beds for Selective Removal of Ammonium Carbonate in Dialysate

We have studied experimentally and theoretically the exchange of NH₄ ⁺, Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, and H⁺ ions in zeolite beds, weakly-acidic resin beds, and mixed beds of the zeolite and the resin. The zeolite is highly selective for NH₄ ⁺ and K⁺, whereas the resin with carboxyl functional groups is highly selective for Ca⁺⁺ and Mg⁺⁺. The effluent histories of single exchanger beds can be well predicted by the Multicomponent Chromatography Theory developed by Helfferich and Klein (1970). These histories are mainly the result of ion competition for ion exchanger sites; they can not be adjusted to meet the goal that NH₄ ⁺ ions are removed and simultaneously the pH and concentrations of all the major physiological cations are maintained at normal values. The effluent histories of mixed beds, on the other hand, can be adjusted. We have designed a mixed bed which can meet the goal except that for each equivalent of NH₄ ⁺ removed, 0.3 equivalents of Na⁺ are returned. The effluent histories of K⁺ and NH₄ ⁺ for the mixed beds are similar to those of the zeolite beds, whereas the Ca⁺⁺ and Mg⁺⁺ histories are similar to those of the resin beds.