Iron-mineral accretion from acid mine drainage and its application in passive treatment

This study demonstrates substantial removal of iron (Fe) from acid mine drainage (pH ≈3) in a passive vertical flow reactor (VFR) with an equivalent footprint of 154 m2 per L/s mine water and residence times of >23 h. Average Fe removal rate was 67% with a high of 85% over the 10-month trial. The fraction of Fe passing a 0.22 µm filter (referred to here as Fe-filt) was seen to be removed in the VFR even when Fe(II) was absent, indicating that the contribution of microbial Fe(II) oxidation and precipitation was not the dominant removal mechanism in the VFR. Removal rates of Fe-filt in the VFR were up to 70% in residence times as low as 8 h compared with laboratory experiments where much smaller changes in Fe-filt were observed over 60 h. Centrifugation indicated that 80–90% of the influent Fe had particle sizes <35 nm. Together with analyses and geochemical modelling, this suggests that the Fe-filt fraction exists as either truly aqueous (but oversaturated) Fe(III) or nanoparticulate Fe(III) and that this metastability persists. When the water was contacted with VFR sludge, the Fe-filt fraction was destabilized, leading to an appreciably higher removal of this fraction. Heterogeneous precipitation and/or aggregation of nanoparticulate Fe(III) precipitates are considered predominant removal mechanisms. Microbial analyses of the mine water revealed the abundance of extracellular polymeric substance-generating Fe-oxidizing bacterium ‘Ferrovum myxofaciens’, which may aid the removal of iron and explain the unusual appearance and physical properties of the sludge

Hydrogeochemische Verhaeltnisse im Flutungswasser eines Uranbergwerks - die Lagerstaette Niederschlema/Alberoda

For reasons of economic viability and environmental considerations, the former uranium mine Niederschlema/Alberoda near Aue in the Erzgebirge (Ore Mountains) has been flooded since 1991. In statistical and hydrogeochemical evaluation of analyses, each with up to 60 parameters, it is shown that the water in the mine can be classified into three types: drainage water, intermediary water and mine water. All three types show significant differentiation in their chemical characteristics, whereby drainage water has the least mineral content and mine water the most. During the period of examination from January 1991 to December 1994, drainage and intermediary waters revealed no statistically significant changes in their physiochemical parameters, whereas the value of most of the physicochemical parameters of the mine water have increased more or less constantly up to 1994. At the end of 1994 the rate of increases in many of the parameters had slowed down or come to a halt. This is either a result of saturation of the water or it is a balance reaction of limited duration. To determine the hydrodynamic situation of the mine water a tracer experiment was carried out together with numerous deepness dependent temperature, conductibility, pH and redox measurements. (orig./SR)Aus wirtschaftlichen und umweltrelevanten Gruenden wird seit 1991 das ehemalige Uranbergwerk Niederschlema/Alberoda bei Aue im Erzgebirge geflutet. Wie die statistischen und hydrogeochemischen Auswertungen von Analysen mit jeweils bis zu 60 Parametern zeigen, lassen sich die Waesser im Bergwerk drei Typen zuordnen: Sickerwaesser, intermediaere Waesser und Grubenwasser. Alle drei Typen weisen signifikant unterschiedliche chemische Charakteristika auf, wobei Sickerwasser am wenigsten, Grubenwasser am staerksten mineralisiert ist. Waehrend Sickerwaesser und intermediaere Waesser im Untersuchungszeitraum von Januar 1991 bis Dezember 1994 keine statistisch signifikante Aenderung ihrer physikochemischen Parametern zeigen, sind die Werte der meisten physikalisch-chemischen Parameter des Grubenwassers bis 1994 mehr oder weniger kontinuierlich angestiegen. Ende 1994 hat sich bei vielen Parametern der Anstieg verlangsamt oder ist zum Stillstand gekommen. Dies beruht entweder auf einer Saettigung des Wassers oder einer zeitlich begrenzten Gleichgewichtseinstellung durch Aufloesung oder Ausfaellung anderer Phasen. Zur Bestimmung der hydrodynamischen Situation im Grubenwasser wurden ein Tracerversuch sowie zahlreiche teufenabhaengige Temperatur-, Leitfaehigkeits-, pH- und Redoxmessungen durchgefuehrt. (orig./SR)Available from TIB Hannover: RA 5591(50) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman