Acid mine drainage (AMD) is a large environmental problem facing mining, mineral processing and coal preparation plants. Due to long term oxidation and weathering, sulfide bearing tailings and overburdens generate sulfuric acid and the acid dissolves heavy metals. The heavy metals contaminate groundwater, rivers and streams. Recently ferrite precipitation process has been applied to treat acid mine drainage. The conventional ferrite precipitation requires air oxidation at high temperature, or long aging time or addition of magnetite powder as promoter. In this investigation, a ferrite modified precipitation process is developed by which highly magnetic ferrite can be produced at an ambient temperature. Acid mine waters from Berkeley Pit (Montana, U.S.A.) and from Noranda Tailings (Quebec, Canada) were used. The coprecipitation of heavy metals from these two acid mine waters is studied as a function of Fe/M molar ratio, oxidation time and settling rate under applied magnetic field. The investigation indicates that the modified ferrite coprecipitation can remove substantially all of the dissolved metal ions from acid mine drainage. The ferrite product obtained after precipitation is characterized by XRD, SEM, TEM and saturation magnetization. The results show that spinel ferrite precipitate can be achieved at room temperature and the saturation magnetization of ferrite product from AMD is comparable to that of some pure ferrites.
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