Deep removal of fluoride from tungsten smelting wastewater by combined chemical coagulation-electrocoagulation treatment: From laboratory test to pilot test

Previous studies have shown that coexisting ions in tungsten smelting wastewater (TSW) will have a significant impact on fluoride removal by calcium ions. Therefore, in this work, the removal of fluoride from TSW by aluminum ions was studied. Electrocoagulation (EC) is essentially the use of aluminum ions to remove fluoride. The EC technology is widely favored by researchers due to its advantages of high treatment efficiency, simple operation, and easy automatic control. However, in the current research, EC technology as a deep defluorination method is mostly in the laboratory research stage, and there are few pilot test studies on large processing capacity, which slows down the industrial application of this technology to a certain extent. In this work, laboratory tests were carried out to study the removal of fluoride in wastewater by chemical coagulation and EC in detail. On this basis, the combined process of chemical coagulation pretreatment and EC advanced treatment was used to treat TSW with a capacity of 250–500 L/h. The results show that the coexisting ions in TSW have no effect on the defluorination of aluminum ions, and the optimal defluorination final pH of chemical coagulation and EC is 6–7. The pilot test could stably reduce the concentration of fluoride in TSW from 66 to 128 mg/L to less than 10 mg/L, and the total operating cost was 0.99–1.51 USD/m3 of wastewater. Cost analysis showed that the three items with the highest proportions in the chemical coagulation pretreatment costs were liquid caustic soda fee, aluminum sulfate fee, and solid waste treatment fee; while the three items with the highest proportions in the EC advanced treatment costs were aluminum plate loss fee, electricity fee, and solid waste treatment fee. This study is helpful to promote the application of EC advanced treatment technology in the defluorination of industrial wastewater.