Well, that depends on the ions in question, but I agree that ammonia binding is extremely limited as to be negligible. On the other hand, phosphate has been shown to be bound regardless of any cation concentrations here:
Phosphate removal in marine electrolytes by zeolite synthesized from coal fly ash
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Qingyu Guana, Xiaozhen Hub, Deyi Wua, Xiao Shanga, Chun Yeb and Hainan Konga
aSchool of Environmental Science and Engineering, Shanghai Jiao Tong University, No. 800, Dongchuan Rd., Minhang District, Shanghai 200240, China
bChinese Research Academy of Environmental Sciences, No. 8, Dayangfang, Beiyuan, Chaoyang District, Beijing 100012, China
Received 11 September 2008;
revised 23 December 2008;
accepted 21 February 2009.
Available online 13 March 2009.
Abstract
The aim of this study was to examine the influence of seawater electrolytes on removal of phosphate by zeolite synthesized from fly ash (ZFA). A low-calcium ZFA was initially saturated with Na+, Mg2+, Ca2+, Al3+, and Fe3+. Al- and Fe-ZFA showed nearly complete removal of phosphate regardless of the major seawater electrolytes, pH, and salinity. This result was explained primarily on the basis of the adsorption mechanism through the formation of inner-sphere complexes. The remaining ZFAs showed lower phosphate removal performance, in general with the order of Ca-ZFA > Mg-ZFA > Na-ZFA. Compared with pure water, increase of electrolyte concentration or salinity initially enhanced phosphate uptake but then reduced phosphate removal. The individual presence of major seawater electrolytes all facilitated the retention of phosphate, with CaCl2 being the most effective. The mechanism for phosphate removal by Na-, Mg-, and Ca-ZFA was due mostly to precipitation. Repeated batch equilibration experiments indicated that, compared with pure water, ZFA had greater sorptive capacity for phosphate (except for Ca-ZFA, whose capacity decreased slightly) and had lower reversibility for sorbed phosphate in marine electrolytes. In conclusion, our results suggest that presence of seawater electrolytes had roughly no effect, or even positive effects, on the removal of phosphate by ZFA.
As far as unique in the way you say, it really isn't. Many organic particles probably have a higher exchange capacity. Maybe in the amount, spectrum, and convenient forum in which it is able to do so, but not unique altogether. That being said, is it really providing that much benefit for organic carbon dosing systems? Given the results of people who don't use it, I just don't see that much merit in using it, let alone spending the kind of money on it that KZ asks. But, if it is working for you and you don't mind paying the price for something that is somewhat more unproven (especially given in these circumstances), that is fine. Many people have splendid results with zeovit in terms of color. Whether or not that is purely or even partly attributable to the use of zeolite, I'm not so sure. Then again, I don't really like organic carbon dosing and all the variables/unknowns that ensue. That's a different argument altogether, though.
