High-purity KCl prepared with K(cl, Br) solid solution via controlled-coordination of glycerol

A glycerol-water coordination method was developed to prepare high-pure KCl from K(Cl, Br) solid solutions. • Glycerol inhibits Br − from entering the KCl lattice. 30 wt% mixed solvent shows better separation performance. • KCl with 99.994% purity and 97.30% yield was obtained, while bromide was concentrated in the liquid phase. High-purity KCl is essential for semiconductors and laser crystals, yet even trace bromine severely compromises its performance. During the preparation of KCl via underground brine crystallization, Br − readily enters the KCl lattice to replace Cl − , forming crystals with a single-salt structure rather than a simple mixture. This makes it difficult to use conventional separation methods to produce high-purity KCl. To address this issue, this study proposes a separation strategy that involves intervening in the recrystallization process by regulating coordination interactions within the solvent system, thereby yielding ultra-pure potassium chloride. Systematic studies involving phase equilibrium experiments, solid-liquid phase characterization and molecular simulations indicate that as the number of hydroxyl groups in the alcohol molecule increases, the solvent's separation capacity increases accordingly, with glycerol exhibiting the best performance. As the simplest trihydric alcohol, glycerol's three hydroxyl groups create distinct solvation environments for Cl − and Br − , thereby inhibiting Br − from occupying the KCl lattice during the concentration and crystallization processes. Furthermore, the introduction of 30 wt% mass water inhibits intermolecular hydrogen bonding and self-aggregation of glycerol, releasing free coordination sites and significantly increasing the solubility of KCl in the system (from 1.7 wt% to 9.63 wt%), thereby further optimizing separation efficiency. The separation process, designed based on the phase diagram of the KCl − KBr − Gly(30 wt%) − H₂O system at 298.15 K, enables the efficient recovery of high-purity KCl (purity up to 99.9940%, recovery rate of 97.30%) and the simultaneous enrichment of bromine resources in the liquid phase (bromine content increased from 3.36 wt% to 44.30 wt%).