| Abstract: | The impact of organic waste material and fly ash on microbial and chemical pyrite oxidation was investigated in a field experiment,
as well as in column tests under laboratory conditions. For the field experiment, pyritic mine spoil was ameliorated with
fly ash and treated either with mineral fertiliser, with sewage sludge or with compost. Independent of treatment, during the
18 months following application, the pyrite-S contents decreased steadily in the top spoil (0–30 cm depth). However, high
variations of the pyrite-S content were observed. Compared to other pyrite oxidation studies, the pyrite content of the mine
spoil at the experimental site was low. Therefore, a model spoil with a higher pyrite content, derived from Tertiary strata
of the overburden sequence in the same open-cast mine, was used for the column experiments. For the first column experiment,
the model spoil was mixed with fly ash and mineral fertiliser, reflecting the common reclamation practice in the Lusatian
open-cast lignite mining district. Columns with this spoil were either inoculated with different cell numbers of autochthonous
acidophilic bacteria, isolated from the model spoil, or with a commercial strain of Thiobacillus ferrooxidans. The ratio of
sulphate-S to total S was used as a measure for the degree of pyrite oxidation. The ratio of sulphate-S to total S increased
within 28 days of incubation. The increase was related to the inoculated cell numbers of bacteria, but independent of the
origin of the bacteria. It can be stated, that autochthonous bacteria from the model spoil oxidised pyrite at a similar rate
as did the commercial T. ferrooxidans strain. For the second column test, mineral fertiliser, sewage sludge or compost were
applied to the model spoil. The columns were inoculated with autochthonous bacteria, isolated from the model spoil. Application
of sewage sludge and compost seemed to promote the weathering of pyrite, as the ratio of sulphate-S to total S increased more
rapidly in these treatments compared to control or mineral fertiliser application. Both experiments showed an increase of
cell numbers of inoculated bacteria, independent of the ratio of sulphate-S to total S.
This revised version was published online in June 2006 with corrections to the Cover Date.
This revised version was published online in June 2006 with corrections to the Cover Date.
This revised version was published online in June 2006 with corrections to the Cover Date. |
