1 METHODS FOR PASSIVE REMOVAL OF MANGANESE FROM ACID MINE DRAINAGE

Manganese can be passively removed from acid mine drainage if the chemical and microbial conditions are right. Consideration of Mn and Fe geochemistry indicates that Mn removal can occur at near-neutral pH in well aerated solutions from which essentially all Fe has been precipitated. Limestone forms a good substrate because of its effect on pH. Mn-oxidizing bacteria are essential for a significant rate, but a number of field tests suggest that special inoculation is not necessary, though it may improve startup and rates. Observations of field sites show that many Pyrolusite Systems and other limestone beds show problems from plugging by silt, leaves, Fe-hydroxide, Al-hydroxide and other materials. Observations at one limestone bed indicate that Mn precipitation is more rapid near the water surface, probably because of dissolved O2 depletion below the surface. Several examples of open limestone channels show good Mn removal, and such channels may be a satisfactory alternative to beds. A Mn removal rate of 2 to 10 g/m2/d may be obtainable, but further study is needed to clarify the kinetic relations