Abstract

The increasing salinity of water sources poses significant operational and environmental challenges, highlighting the importance of developing efficient methods for recovering [SO42−] ions from briny wastewater. In this study, the potential of fluidized bed homogeneous crystallization (FBHC) technology for recovering [SO42−] ions from briny water is explored. FBHC is an innovative technique that enhances scalability and separation efficiency by promoting the growth of crystalline particles in a fluidized state. To achieve maximum [SO42−] recovery and maintain stable fluidized bed conditions, a pH of 8 is recommended. A removal ratio (RR) of 71 % was recorded at a [SO42−] concentration of 0.14 M. Various [SO42−] concentrations exhibited a molar ratio (MR) of [Ca2+]/[SO42−] = 1.5. Smaller particles, which are more soluble and exhibit less nucleation, are typically formed under conditions with lower pH and [Ca2+] levels. Intermediate-sized particles are favored at neutral to slightly alkaline pH levels and near-stoichiometric [Ca2+]/[SO42−] MR. Greater calcium content and higher pH values promote the development and agglomeration of larger particles, with 50 % of the particles exceeding an average size of 0.38 mm. In the XPS study of CaSO4 crystals (gypsum), the Ca 2p1/2 and Ca 2p3/2 peaks are observed at binding energies of 351.5 eV and 347.7 eV, respectively. Gypsum is identifiable due to the presence of clear and distinct peaks in XRD patterns. SEM analysis reveals the coexistence of amorphous patches and tiny crystalline domains on the surface. These gypsum crystals resemble stacked needle-like structures accompanied by small, powdery crystals. In an acidic environment, the primary phase is CaSO4·2H2O, which generates well-formed, elongated, or tabular crystals that are characteristic of gypsum. The FBHC process, characterized by a high crystallization ratio (CR = 68 %) and the recovery of crystal pellets (>0.3 mm), significantly reduces sludge production compared to traditional chemical precipitation methods. Its cost-effectiveness and recoverability make FBHC a promising technology for the recovery of sulfate ions from briny wastewater.

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