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

Abstract

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).