The possibility of pH value regulation with carbonate rocks as a stage in the passive treatment process was studied by means of dynamic column tests using acid solutions, metal ion solutions and mine wastewater from an abandoned mine containing Pb-Zn-Ba ore. This paper presents the results of experimental study of chemical processes in an anoxic limestone drain (ALD). The dependence of the pH value gradient on the flow rate through ALD and the extent of contamination with different metal ions as parameters influencing buffer capacity were determined. Total acidity and alkalinity were determined using the APHA [Standards Methods for the examination of water and wastewater, A.E. Greenderd, American Public Health Association, 1015th Street, N.W. Washington, DC 2005] titration method and the changes in metal ion content were monitored by means of atomic absorption spectroscopy. The quality of effluents from the laboratory model was below or within the range of MAC for discharge into the recipient.