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Passive water treatment takes advantage of naturally provided physical, chemical and biological purification potentials of locally accumulating mine water. The treatment of mine water is likely to be conducted on a long-term. By means of passive water treatment, solutions can be proposed which are energy and resources conserving and are tailored to the local conditions.

Since passive water treatment is not recognized as state-of-the-art technology yet, the pilot plant RAPS (Reducing and Alkalinity Producing System) is in utilization. The acid seepage is characterized by a pH- value of ~ 3, an acidity > 40 mmol/L, a sulphate concentration between 3.000 and 4.000 mg/L, and an iron concentration of ~ 1.000 mg/L. The acid seepage is treated by means of sulphate reduction, alkalisation, oxidation and iron removal. Within 3-5 days, 10% of the sulphate was reduced, 50% of the acidity compensated and 30% of the iron removed in the RAPS test facility. In an additional container experiment with 4-6 weeks of residence time, 80% of the sulphate has been reduced, the acidity of the seepage has been entirely compensated and more than 90% of the iron has been removed. Based on these experiments, the construction of a passive water treatment facility with a volume flow rate of 0,5 L/s is planned.

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