We analyzed the mineralogy and chemistry of clay materials from collected claystone samples by using XRD and the exchangeable cations (NH4OAc and water extractable cations), i.e. Ca, Mg, K and Na. Most of them are dominated with smectite minerals. There are two kinds of the dominated cations, Ca and Na, respectively.
Dear Mohammad,
most natural smectites have Ca in their interlayer space, only vew of them are naturally Na smectites (e.g. Wayoming bentonites).
For technical reasons Ca smectites are very often transformed to an Na form to get better rheological properties.
The best way to see what interlayer cations are present is to measure the exchangable cations as you already did.
When the Ca-Na exchange procedure wasn´t done properly you can find small amounts of Na CO3 by XRD and you will measure a very high alcaline pH-value beyond 10.
Greetings from Vienna
Franz
As Franz wrote, the question is the presence (domination) of Ca or Na as cation between the layers.
If you boil the bentonite in strong minerla acids (e.g. in 15 % HCl) for 4 h, and measure the Ca and Na content of the solution (ICP, AAS) this question can be decided easily. Swelling properties are very different, this is the reasonf or exchange of Ca (into Na) in the practice.
Thank you very much Franz and Kotai. Your informations are very usefull for me.
Regards
M nurcholis
Depending on the dominant exchangeable cations present the clay may be refereed to as either calcium bentonite or sodium bentonite the two varieties exhibiting markedly different properties and thus uses.
The Na-bentonite dispersion contains a lot of small units whereas the Ca-bentonite dispersion contains a few large units. Sodium-saturated bentonite dispersions have a more pronounced yield stress than calcium-bentonite dispersions.
The 001 ,the basal spacing of bentonite clay as Ca-saturated and Na-saturated is different. Na-clay may have lesser d-spacing than Ca-clay.
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