Abatement of acid rock drainage - results of a six-year-project in the framework of a German-Romanian scientific cooperation.
In: Process Metallurgy, Jg. 11B (2001), S. 297-305
Zeitschriftenaufsatz / Fach: Chemie
In the course of a 6-yr-project in the framework of a German-Romanian scientific cooperation large scale installations were used for controlled expts. on acid rock drainage abatement. These installations imbedded in a waste rock dump were a 4-chamber-percolator (4CP) with a capacity of 65 m3 for each chamber and a 6-column-percolator (6CP) with a capacity of 2.3 m3 for each column. The waste material consisted of about 6-yr old run-off mine waste rock, freshly broken 6-yr old low-grade ore with 4-30 mm grain size, and tailings material from an active pond. The expts. lasted up to now at least 2 yr and were analyzed for depth-dependent cell nos. of leaching bacteria, microbial leaching activity, pH, redox, and total as well as time dependent metal output. Measures to be tested against acid rock drainage were 1 m thick soil/clay covers rich in org. material, layers of alk. materials (mixts. of lime and limestone) for neutralization/hardpan formation, and biocide addn. Two biocides were tested: Na dodecylsulfate (SDS), and isothiazolinone. Each expt. was run with one chamber and/or one column as control. The results demonstrated that org. covers reduce bioleaching transiently, however not completely. About the longevity no information exists. Alk. layers may function as expected, however the thickness has to be sufficient to be able to remain functional after settings. Biocides are an ambiguous measure. They have to be used in a sufficiently high concn. to kill the leaching bacteria, but must not be dangerous to the environment in case of wash-out. Furthermore, they are biodegradable and need to be added constantly. In the case of SDS, the wash-out of metal salts is increased due to the improved wetting, causing a considerable metal output from treated waste. Thus, biocides may possibly be used to stop or rather prevent bioleaching in early stages, but not in case of heaps and dumps with established bioleaching process. Microbial leaching activity measurements performed by microcalorimetry were correlated with the quant. chem. and microbiol. data in order to establish this rapid and simple technique for risk assessment and prediction of the leaching output of a mine waste dump.