Selective leaching definition

Thus, the secant relationship (4.20) with the angular definition modified for aluminosilicates (MacKenzie et al. 1985) has been used to shed light on the possible existence of a Si-Al spinel suggested to form when the clay mineral kaolinite is heated to 980°C. On the basis of the known structure of the closely-related 7-alumina spinel, the T-O-T angle of the postulated tetrahedral Si site in such a structure predicts a chemical shift of - 79 ppm for this site. Such a resonance would normally be masked by the broad resonance of the amorphous Si02 also present, but when this material was selectively removed by leaching with KOH solution, the predicted Si peak was detected (MacKenzie et al. 1996) (Figure 4.13). Measurements of the relative intensity of this... 

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