APPLICATION OF MINTEQA2 TO THE EVALUATION OF APATITE AS A PRECIPITANTFOR ACID-MINE DRAINAGE TREATMENT

The apatite drain system is a new method for acid mine drainage (AMD) treatment. Laboratory tests and field experiments showed that this tec hnique can remove high concentrations of iron and aluminum in AMD havi ng a pH below 4.0. In addition, this system removes both ferric and fe rrous iron, whereas a constructed wetlands system removes only ferric iron when converted from the ferrous state in the wetland. A geochemic al model, MINTEQA2, was used to simulate the changes in concentration of aqueous constituents, and in the pH and the potential mineral phase . Results of MINTEQA2 support the conclusions of the laboratory and fi eld experiments. Apatite is effective in removing iron, sulfate, and a luminum from AMD; pH was inversely proportional to the flow rate until the equilibrium point was reached (pH = 4.09 at 25 degrees C). Also, the role of apatite as a precipitant and pH buffer was limited by its solubility.