Abstract: The underground brine resources in northeastern Sichuan are abundant, especially in the Puguang region where underground brines are rich in high-quality potassium resource. In this work, computational simulation and experimental verification were carried out to investigate the crystallization stages and features of NaCl, KCl, KCl·MgCl₂·6H₂O, and H₃BO₃ under high temperature evaporation. The results showed that ~85% of NaCl crystallized when the rate of water loss was about 80% and KCl saturation was reached; under continuing evaporation, sylvite was produced. As the rate of water loss reached 94%-95%, almost 80% of potassium (KCl) precipitated and the KCl concentration in the precipitant could be as high as ~45% (mass fraction). Subsequently, as the resulting brine cooled down to room temperature, NaCl, KCl, KCl·MgCl₂·6H₂O, and H₃BO₃ co-crystallized, including ~80% of boron. Notably, after 80% of water evaporated and most of NaCl precipitated, directly cooling of brine could yield sylvite of grade up to 70%, with 50% of KCl crystallized. Finally, two potassium extraction processes were suggested, one focuses on the production of KCl and H₃BO₃, the other on high-quality KCl.

Key words: northeastern Sichuan, Puguang region, potassium-rich brine, high temperature evaporation