Removal and recovery of calcium from aqueous solutions by fluidized-bed homogeneous crystallization

Water hardness removal is an important step in wastewater treatment as it can precipitate out on pipes and interfere with day-to-day chemicals such as soap and detergent. Fluidized-bed homogeneous crystallization (FBHC) process on water hardness removal is of significant interest as it can give removal rates that meet effluent standards while simultaneously produce a pure, reusable source of calcium. The highest % Calcium removal (% Ca-removal) was 99.8% with 98.9% Crystallization Ratio (% CR) at 300 mgL(-1 )influent [Ca2+] concentration, pH of 10.6, and molar ratio (MR) of 1.0 with effluent pH of 10.2 +/- 0.05. The addition of ions resulted to a finer crystal with an average diameter of 0.149, 0.297 and 0.297 mm for [F-], [NO3-], and [SO42-] ions respectively. The presence of ions inhibits the formation of larger crystals. X-ray diffraction (XRD) peaks showed that the recovered crystals were comparable with the reference standard characteristic peak of calcite. Scanning electron microscope (SEM) micrograph showed the agglutination of nuclei forming larger crystals with an average size of 0.5 mm. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.