The apatite drain system is a new method for acid mine drainage (AMD) treatment. Laboratory tests and field experiments showed that this technique can remove high concentrations of iron and aluminum in AMD having a pH below 4.0. In addition, this system removes both ferric and ferrous iron, whereas a constructed wetlands system removes only ferric iron when converted from the ferrous state in the wetland. A geochemical 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 field experiments. Apatite is effective in removing iron, sulfate, and aluminum from AMD; pH was inversely proportional to the flow rate until the equilibrium point was reached (pH = 4.09 at 25°C). Also, the role of apatite as a precipitant and pH buffer was limited by its solubility.