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Removal of zinc based on a screw manufacturing plant wastewater by fluidized-bed homogeneous granulation process

Udomkitthaweewat, Nutnapong, Anotai, Jin, Choi, Angelo Earvin Sy, Lu, Ming Chun
Journal of cleaner production 2019 v.230 pp. 1276-1286
X-ray diffraction, carbonates, crystallization, elemental composition, energy-dispersive X-ray analysis, factories, fluidized beds, granules, heavy metals, ions, iron, manufacturing, pH, scanning electron microscopes, wastewater, zinc
Wastewater derived from screw producing manufacturing plants contains high zinc concentrations that needs to be treated prior to its discharge. Crystallization through the fluidized-bed reactor has been an effective technology for the removal of heavy metals. In this research, the removal of zinc from a simulated wastewater was investigated by a fluidized-bed reactor. The properties of the granules were characterized by utilizing the X-ray diffraction, energy dispersive spectrometer and scanning electron microscope. A comparison of the fluidized-bed reactor setting was conducted to compare the processes of fluidized-bed homogeneous granulation and fluidized-bed granulation. Results showed that the fluidized-bed homogeneous granulation outperformed fluidized-bed granulation in terms of removal and granulation efficiencies. The essential variables for analysis include chloride concentration (0–7,000 mg/L), pH (6.9–7.5), carbonate to zinc molar ratio (1–2.5) and ferric ion concentration (0–150 mg/L) in the fluidized-bed homogeneous granulation process. The results indicated that the ideal conditions for hydrozincite granulation were at a carbonate to zinc molar ratio of 1.2 and pH 7.2. The elemental composition analysis of the hydrozincite revealed zinc contents of the following: (1) absence of chloride (63.71 wt% zinc), (2) presence of chloride (63.08 wt% zinc) and (3) presence of ferric ions (52.62 wt% zinc). The inclusion of chloride and ferric ions in the system interfered with zinc precipitation and granulation. Furthermore, the hydrozincite granule predominantly reached a diameter of 149 μm (with chloride) and 42 μm (with ferric ions).