Evaluation of a dry-cover treatment consisting of vegetation, sewagesludge and fly ash

摘要

The influence of plants on a dry cover-treatment of sewage sludge (SS) and fly ash (FA)constructed to prevent formation of acid mine drainage from sulfidic mine tailings wasinvestigated in field and greenhouse. The main questions were what plant species thatshould be established, and how to construct the cover, to minimize the metal and nutrientleakage and to avoid root penetration of the sealing layer. This paper summarizes datafrom investigations performed during five years. The results demonstrate that covers ofSS and FA can decrease the metal release from tailings compared with if the tailings areleft uncovered. Though, high levels of nitrogen may leach from the SS. Leakage ofmetals and nutrients can, however, be decreased by plants, in particular by fast growingcrops such as Phalaris arundinacea. Metals taken up from the materials were mainlyaccumulated in plant roots, and the risk to grazing animals was considered to be low.Root penetration was prevented if the sealing layer consisted of FA, without addition ofSS, and had a high penetration resistance. In field, even FA with low curing ability couldprevent root growth, after formation of shale-like layers.