Halloysite Cation exchange capacity

Garrett, W.G. and Walker, G.F., 1959. The cation exchange capacity of hydrated halloysite and the formation of halloysite salt complexes. Clay Miner., 4 75-80. 

Because of the interlayer water sheet in hydrated halloysite, intercalation (introduction between the imit cells) of chemicals can occur. This also results in a slightly higher cation exchange capacity for hydrated halloysite (5 to 40 meq/100 g) than for kaolinite (3 to 15 meq/100 g). Halloysite also may be more affected by chemicals than kaolinite. 

Dehydrated halloysites have C.E.C. in the range of 6—10 mequiv./lOO g (Van der Marel, 1958 Garrett and Walker, 1959). Garrett and Walker have shown that the exchangable cations are located on the external surfaces of the crystals and not in the interlayer position of halloysite. Until it is possible to obtain accurate chemical analyses of the kaolinite minerals, it will be difficult to determine their exchange capacity and the source of the charge. 

There are inconsistencies in the model for the calculation of activity products for the "clays. Exchangeable cations are disregarded for the low exchange capacity kaolinite, halloysite, chlorite, and moderate capacity illite. For certain expansible layer silicates and two zeolites, the logjo of the activity of selected cations is added into the sum of the activity products. 

Even higher loading capacity can be achieved when porous fillers with hollow cellular stmcture are loaded with organic and/or inorganic inhibitors (Schmidt, 2002). The hollow cellular stmcture material may be represented by zeolite or halloysite nanotubes. Zeolite particles are attractive carriers also because the cations in their stmcture are rather loosely held and can readily be exchanged for the inhibiting cations in the contact solution (Eckler and Ferrara, 1988). 

---