I think that the removal rate (%) of the contaminants is related to the crystallinity of the zeolite. Batch adsorption experiments are always used to get the results. 

Zeolites are efficient adsorbents because of their special crystalline structure, with open cages and interconnected channels, giving them a high surface area. If the crystallinity is partly lost, then for sure the adsorption performances will decrease correspondingly.

Alain

Natural zeolite samples are highly crystalline and if they are loosing their crystallinity, means some of the experimenta lconditions are there which causes the structural damage of the zeolite sample. Structure and property goes hand in hand they are inter-related to each other. If it looses crystallinity then one has to also consider the role (contribution) of amorphised fraction (aluminosilicate) which also shows the adsorption properties.

If you are claiming the decrease in crystallinity based on the powder XRD peak which is most intense in the pattern then you have to keep in mind the following:

The low angle lines are the ones most strongly affected by non-framework species (see Ref. [http://www.iza-online.org/synthesis/VS_2ndEd/XRPD.htm]. In general, these lines are more intense in the calcined material than in the as synthesized form, and similar materials containing different cations or different organic species may have quite different relative intensities at low angles. However, the intensities of the higher angle reflections are generally dominated by the positions of the framework atoms, so these can be compared quite well.

Finally you can calcine your material at high temp 550C then you will regain your crystallinity....