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.

摘要

草酸盐是工业废水中常见的污染物，特别是在铝土矿精炼工业中。流化床工艺中的结晶已被证实可有效消除与污泥处理相关的问题。在本研究中，在不同的初始草酸盐浓度（150 mg/L 至 450 mg/L）、草酸盐与钙的摩尔比（1:2 至 2:1）、进水流速下，研究了模拟废水中草酸盐去除的效果(0.6 L/h 至 1.9 L/h) 和 pH (4.5 至 8.5) 通过无晶种结晶设置。流化床反应器中的均质造粒过程连续运行 110 小时。使用扫描电子显微镜和 X 射线衍射分析对最终的晶体产物进行了表征。结果表明，草酸盐造粒的理想操作条件是初始草酸盐浓度为 300 mg/L，摩尔比为 1:1，进水流量为 0.9 L/h，pH 为 6.5。这些条件导致了高效率的制粒和总草酸盐去除率分别为 94.6% 和 96.0%。对于晶体表征，在 67.4% 至 67.7% 的累积质量下形成了超过 0.149 毫米。此外，从颗粒产品的表征中获得的结果证实了球形颗粒状一水草酸钙晶体的发展。累积质量为 67.4% 至 67.7% 时形成 149 mm。此外，从颗粒产品的表征中获得的结果证实了球形颗粒状一水草酸钙晶体的发展。累积质量为 67.4% 至 67.7% 时形成 149 mm。此外，从颗粒产品的表征中获得的结果证实了球形颗粒状一水草酸钙晶体的发展。