Reclaiming Boron as Calcium Perborate Pellets from Synthetic Wastewater by Integrating Chemical Oxo-Precipitation within a Fluidized-Bed Crystallizer

Chemical oxo-precipitation (COP) is a modified precipitation process in which hydrogen peroxide is used to transform boric acid to perborate anions, which are precipitated with calcium salt under ambient conditions. To minimize the production of sludge, chemical oxo-precipitation was performed in a fluidized-bed reactor to reclaim boron as unseeded calcium perborate pellets. Several major experimental parameters, including effluent pH, calcium dosage, and surface loading that affected the degree of supersaturation and the efficiency of boron removal, were tested. A crystallization ratio of around 60% was attained under the following conditions: initial boron concentration = 1000 ppm, molar ratios of [Ca]/[B] = 0.6 and [H₂O₂]/[B] = 2, effluent pH = 10.6, bed height = 80 cm, and hydraulic retention time = 18 min. On the basis of the characterization of XRD, SEM, and Raman spectroscopy, the granules recovered were amorphous calcium perborates Ca(B(OH)₃OOH)₂ and CaB(OH)₃OOB(OH)₃.