Fluidized-bed crystallization of barium perborate for continuous boron removal from concentrated solution: Supersaturation as a master variable

The development of treatment process for boron removal is urgent to control the anthropogenic emission of boron to freshwater. Barium-based chemical oxo-precipitation (Ba-COP) is an effective method to treat boron-rich streams in ambient condition by the precipitation of barium perborate (BaPB), but it is limited to batch operation and mass production of sludge. This study aims to circumvent these drawbacks by performing Ba-COP in fluidized-bed crystallization system (Ba-COP@FBC) to immobilize BaPB on the surface of the fluidized granules continuously. When Ba-COP@FBC was operated at pH 10, 85% of total removal (TR) and 83% of crystallization ratio (CR) were attained from an input boron level of 600 mg-B/L, indicating that the homogeneous nucleation could be suppressed. Despite that both TR and CR varied greatly upon the dosage of H2O2 and Ba, initial concentration and reflux ratio, the influence of these parameters can be summarized by supersaturation. TR was related to the supersaturation at the effluent (SE), which was fixed at 1.15 ± 0.04; the sludge production rate increased drastically with the supersaturation at the mixing zone (SM), which in turn reflects on CR. Accordingly, an algorithm based on the supersaturation ratio was developed to predict the performance of Ba-COP@FBC based on the initial concentration, hydraulic condition, dosages and ionic strength. The economic analysis reveals that Ba-COP@FBC is more competitive than the Ba-COP conducted in batch stirred-tank reactor in terms of solid disposal cost due to the difference of water content between granule and sludge.