Brine treatment using fluidized bed homogeneous crystallization technology for the simultaneous recovery of calcium and magnesium as dolomite-like granules

Fluidized bed homogeneous crystallization (FBHC) technology is an effective method to treat metal-contained wastewater at ambient temperature and pressure. Seawater desalination is common to produce fresh water and concentrated brine. This highly hardness-contained brine decreases the lifetime of membranes by fouling during desalination process. This study recovers calcium and magnesium by carbonate reagent from synthetic brine wastewater to be dolomite-like particles. The greatest total removal is 90.7 % for calcium and 76.0 % for magnesium, with a crystallization ratio of 89.5 % for Ca and 75.7 % for Mg, using a 40 min of hydraulic retention time, 9.5 of effluent pH, 2.0 of molar ratio, and 24 of reflux ratio. The effluent from the fluidized bed reactor (FBR) is aged in a sedimentation tank for 24 h to increase removal efficiency to 99.98 % for Ca and 84.7 % for Mg. XRD, SEM, FTIR, and Raman analysis reveal that particles are composed of CaCO3·H2O and MgCO3·3H2O with a dolomite-like structure and a core-shell morphology. In a real brine wastewater treatment by FBHC system, 86 % of Ca and 74 % of Mg are crystallized, so disposal costs are 75 % less than those for chemical precipitation, a conventional treating method. Therefore, FBHC technology has high potential to treat hardness-contained brine by reclaiming as dolomite-like granules.