Talc has been known as a low reactive mineral under hydrothermal conditions in comparison with the other clays. However, it was expected that grinding treatment increase its reactivity by so-called mechanochemical effect.
In the present study, naturally occurred talc from China was ground in vibrating mill to X-ray amorphous state. The ground talc was then treated hydrothermally with aluminum salts solution for various Al (in reaction systems)/Si (in ground talc) molecular ratios ranging from 0.1 to 2.0. The products were examined by means of X-ray diffractometry, thermal analysis, and infrared absorption spectroscopy.
It was found that the ground talc is successively converted to trioctahedral smectite, dioctahedral smectite, and kaolinite with increasing the Al/Si ratios, by treatment with acidic aluminum bearing solution such as AlCl
3, Al
2(S0
4)
3, and Al (NO
3)
3. Al
24O
11(OH)
44Cl
6 phase and alunite were also formed as the coproducts in the way of AlCl
3 and Al
2(SO
4)
3 solution treatment, respectively.
On the other hand, by the treatment with NaAlO
2, the ground talc changed to a trioctahedral smectite and an analcime at low Al/Si ratios, but a serpentine and a hydroxysodalite were formed at high Al/Si ratios. In these cases, the reaction was proceeded in basic condition, and the pH value was increased with increasing of the Al/Si ratios.
It is concluded that grinding significantly increases the hydrothermal reactivity of talc, and the hydrothermal products of the ground talc are controlled by the Si/Al ratio and pH value in reaction system.
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