TECHNICAL STRATEGY AND AN ENGINEERING CASE ON ULTRA-LOW DISCHARGE OF HIGH FLUORIDE WASTEWATER RARE EARTH INDUSTRY

Aiming at the problem of ultra-low fluorine discharge from alkaline high-fluorine wastewater produced by a rare earth chemical plant, the technical scheme and condition optimization of fluorine removal was studied. The process scheme was proposed, and an engineering design was carried out. The results showed that the calcium fluoride chemical precipitation method was more suitable for removing fluoride from high-fluorine wastewater. The increase in the calcium-fluorine ratio helped improve the effect of chemical precipitation. However, excessive CaCl₂ dosing (Ca∶F>0.7) would lead to a sharp increase in sludge production, while coagulation sedimentation was more suitable for further deep fluoride removal of low-fluorine wastewater (<20 mg F/L). When the molar ratio of aluminum to fluorine was 13.5, and the initial pH was 6, the fluorine concentration of the effluent could be stabilized at about 0.37 mg/L. The ultra-low discharge process plan for high-fluorine wastewater was proposed, and the engineering design was carried out. The high-calcium acid wastewater produced by the enterprise was used to pretreat the alkaline high-fluoride wastewater, and then the chemical precipitation-coagulation precipitation coupling process was used to stabilize the fluorine concentration of the effluent, to meet the limiting value of the emission standard of 1.5 mg/L below.