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Hydrothermal transformations of kaolinite at 200 and 250°C in the systems Li₂O–Na₂O–MgO–Al₂O₃–SiO₂–H₂O–HCl and Li₂O–K₂O–MgO–Al₂O₃–SiO₂–H₂O–HCl

¹ Departamento de Química Inorgánica, Cristalografía y Mineralogía, Facultad de Ciencias, Universidad de Málaga, and ² Estación Experimental del Zaidín, C.S.I.C. Granada, Spain

^* E-mail: mdruiz{at}uma.es

(Received 15 October 2003; revised 10 February 2004)

ABSTRACT

The hydrothermal reaction of kaolinite in the systems Li₂O–K₂O–MgO–Al₂O₃–SiO₂–H₂O–HCl and Li₂O–Na₂O–MgO–Al₂O₃–SiO₂–H₂O–HCl, at pH between 9 and 11, has been investigated at 200–250°C from 1 to 180 days. The X-ray diffraction study of the K-bearing system indicates that the solid products formed were Li-A(BW) zeolite, crystalline silica, and randomly ordered chlorite-smectite mixed layers, dioctahedral on average, with a chlorite:smectite ratio of ~1:4. Study by electron microscopy reveals, however, the presence of mixtures of very thin particles of smectite, di,trioctahedral chlorite and mixed-layer phases. The X-ray study of the solid products formed in the Na-bearing system reveals that the neo-formed phases were Li-A(BW) zeolite, analcime and partially ordered chlorite-vermiculite mixed-layers with high chlorite:vermiculite ratio. The transmission microscopic study of these phases shows the presence of dioctahedral ‘vermiculitic’ curved particles and di,trioctahedral chlorite-like particles. In both cases, long reaction times cause formation of a 7 Å phase with composition intermediate between kaolinite and serpentine. The composition of the solutions suggests that the stable phases would be chlorite/smectite mixed-layers, with compositions near tosudite in the case of the K-bearing reaction and both a dioctahedral phase (tosudite?) and a trioctahedral one (clinochlore) in the case of the Na-bearing reaction.

KEYWORDS: hydrothermal synthesis, chlorite, kaolinite, mixed-layer minerals, smectite, vermiculite, zeolite