Abstract
Oxalate is a common contaminant found in industrial wastewater particularly in bauxite refining industries. Crystallization in fluidized-bed processes have been established to be effective toward eliminating the problems associated to sludge disposal. In this study, the effects of oxalate removal in a simulated wastewater were investigated at varying initial oxalate concentration (150 mg/L to 450 mg/L), oxalate to calcium molar ratio (1:2 to 2:1), influent flow rate (0.6 L/h to 1.9 L/h) and pH (4.5 to 8.5) through an unseeded crystallization setup. A homogeneous granulation process in a fluidized-bed reactor was continuously operated for 110 h. The final crystal products were characterized using the scanning electron microscopy and X-ray diffraction analyses. Results showed that the ideal operating conditions for oxalate granulation were at 300 mg/L initial oxalate concentration, 1:1 molar ratio, 0.9 L/h influent flow rate and pH 6.5. These conditions have led to high efficiencies of granulation and total oxalate removal of 94.6% and 96.0%, respectively. For crystal characterization, more than 0.149 mm were formed at a cumulative mass of 67.4% to 67.7%. Furthermore, the results obtained from the characterization of the granule products confirmed the development of spherical pellet shaped calcium oxalate monohydrate crystals.
Acknowledgments
The authors would like to acknowledge the Taiwan Ministry of Science and Technology (MOST 107-2221-E-005-081-MY3) for the financial support of this research.