DEVELOPMENT OF AN ACTIVE MINE WATER TREATMENT TECHNOLOGY BY USE OF SCHWERTMANNITE

As a residual of microbial ferrous iron oxidation, large amounts of schwertmannite (Fe₈O₈(OH)₆SO₄) were produced in a pilot plant for lignite mine water treatment in Tzschelln (Lusatia, Germany). The secondary mineral has excellent properties for removal of arsenic and other oxoanions from mine water and rapidly transforms into ferric hydroxides of high specific surface area once exposed to water containing at least some alkalinity. Therefore, the research project SURFTRAP was carried out to investigate the applicability of schwert­mannite for the treatment of ground- and surface water contaminated with arsenic.

Following to fundamental, hydrochemical and structural investigations in the laboratory, a pilot scale test was performed in the bypass of an active water treatment plant for contamina­ted flooding water from uranium ore mining. About 20 mg Fe/L as schwertmannite were necessary to un­der­shoot the governmental described effluent limits (0.3 mg As/L and 0.5 mg U/L). The costs of the higher demand of schwertmannite compared to the conventional FeCl₃ addition (10 mg Fe/L) could be compensated by a reduction of lime milk requirement of about 40%.