Study on dissolution and phase equilibrium in ulexite-water system

Ulexite dissolution in water has been studied in the wide temperature range from 10degreesC to 93degreesC and two higher temperatures at 120degreesC and 240degreesC. The analytical results showed that ulexite dissolved congruently from 10degreesC to 35degreesC and incongruently from 40 to 68degreesC. The solid component of ulexite, NaCaB5O6(OH)(6)(.)5H(2)O was dehydrated to form NaCaB5O6(OH)(6)(H2O)-H-. from 50 to 68degreesC and finally amorphous solid at 68degreesC. This amorphous solid converted into priceite at 71degreesC and then converted completely to priceite at the boiling point(93degreesC) of the solution. At both 120 and 240degreesC, the dissolution of ulexite was an incongruent process. Above 120degreesC, ulexite became amorphous solid and then transformed into priceite. In addition to the solid to solid transformation, crystallization of priceite from the solution has also been observed. Based on our experimental results, mechanisms of dissolution, transformation, and crystallization of borate in ulexite-water system are discussed.