Treatment of mine water to remove manganese

Typical acid mine water contains 1-8 mg/L Mn, but concentrations of 50-100 mg/L are not uncommon. At present, most mine operators with manganese problems use excess alkalinity to raise the pH of water to 10 or higher to facilitate manganese oxidation and precipitation. Excess alkalinity, although it increases treatment costs 20-100 pct, was determined by the Bureau of Mines to be less expensive than NaOCl and KMnO/sub 4/ (chemical oxidants). However, laboratory tests indicate that the manganese precipitated by excess alkalinity is easily resolubilized, while that produced by the oxidizing agents is relatively stable. The Bureau also studied two novel approaches to the manganese problem. One was an inexpensive pipeline treatment system device known as the ILS, which was developed by the Bureau to aerate and neutralize mine water. At three mines with influent Mn concentrations of 10-68 mg/L, use of the ILS reduced Mn concentrations to less than mg/L at pH values of only 6.8-7.3. Another novel approach to mine water treatment is the construction of wetlands on mined sites. Results from ongoing tests indicate that this biological treatment can be engineered to optimize either iron or manganese removal. Moderate Mn concentrations (14-30 mg/L) have been reduced to 2-6more » mg/L in constructed wetlands at four mine sites in western Pennsylvania. 25 references, 3 figures, 3 tables.« less