Abstract: The phase equilibrium of 2MgO•2B2O3•MgCl2•14H2O-MgCl2-H2O system at 30 ℃ has been studied. The experimental results showed that the phase transformation product was inderite(2MgO•3B2O3•15H2O) when the mass fraction of MgCl2 is in the range 0 to 2％, pinnate(MgO•B2O3•3H2O) in the range 2％ to 13.8％, demonstrating a great reduction in the temperature of formation of MgO•B2O3•3H2O and providing some physico-chemical basis in explaining the formation of pinnoite mineral in the salt lakes. When the mass fraction of MgCl2 was higher than 13.8％, the chloropinnoite dissolved congruently and did not transform. The mechanisms of the dissolution and phase transformation have been proposed.

Key words: Chloropinnoite, Magnesium chloride, Phase equilibrium