Biological Water Covers - A Preliminary Assessment

Abstract

Natural oxidation of sulphide minerals in mine wastes leads to the production of acid mine drainage which is environmentally undesirable. One preferred method to minimize the oxidation of mine residues is to store them under a water cover. Although efficient, water covers might not always stop the oxidation. Inclusion of a biologically active organic layer on top of tailings was considered to further improve the effectiveness of the water cover. The capacity of the organic layer to act as an oxygen barrier and metals confiner was verified with laboratory tests.

Diffusion cells were used to assess the capacity of organic materials to consume oxygen and prevent upward diffusion of zinc into the water column. A mixture of algae and duckweed was tested as an organic layer with sand used as a control. The results showed that the organic layer could completely consume oxygen and retain metals. Zinc concentrations in the surface water of the diffusion cells did not exceed lmg/L whereas in the control cells, concentrations were up to 10 mg/L. In Organic cells inoculated with sulphate-reducing bacteria, the Zn concentration in the surface water has been maintained to less than 0.5 mg/L.

Keywords:

• Water cover
• oxygen consumption
• metal diffusion
• organic layer