Solubility products of sparingly soluble barium perborates in aqueous solution that contains B(OH) 3 and H 2 O 2 at 25°C.

Chemical oxo-precipitation (COP) has become a promising method for treating boron wastewater at room temperature; it uses hydrogen peroxide to convert boric acid to perborate species, which are precipitated using alkaline earth metals. In this work, solubility models of barium perborates were established to predict residual boron levels from COP. The solubility product constants (pKsp ) of two major barium perborates - amorphous Ba(B(OH)3 OOH)2 (A-BaPB) and crystalline BaB(OH)2 (OO)2 B(OH)2 (C-BaPB) - were experimentally estimated (8.335±0.109 and 9.190±0.057, respectively) to define the solubility curves of BaPBs at given pH, ionic strength and concentrations of barium and peroxide species. The characterization of precipitates that were formed by COP confirmed that the boron levels in aqueous solution were governed by the phase transformation of A-BaPB to C-BaPB. The predictive solubility models of barium perborates can perfectly predict the residual concentration of boron after COP treatment and can be used to optimize the process for reducing boron concentrations in wastewater.