Abstract
Wastewater containing tetrafluoroboric acid-hexavalent chromium was decomposed to fluorine （HF） and boron （H3BO3） in acidic conditions using excess aluminum sulfate at normal temperature. In subsequent processing, boron was separated by coagulation-sedimentation using ettringite and calcium hydroxide in highly alkaline conditions. This processing reduced the boron concentration to 10 mg dm－3 or less in the effluent standard. The ettringite used in this experiment was prepared using aluminum sulfate and calcium hydroxide. Alkaline filtered water containing aluminum ion and calcium ion was pH-adjusted to 6.5－7.0 for fluoride removal. This continuous process produced fluorine concentrations of 8 mg dm－3 or less in the effluent standard. Based on these experiments, we devised a practical advanced wastewater treatment system including processing of tetrafluoroboric acid using ettringite. The contents of this paper will contribute to solving treatment problems for metal surface treatment wastewater containing fluorine and boron, also help in the treatment of other industrial wastewater.
