QuESt – Quantification of the iron sulfide turnover in the Spreewitz glacial channel (Lusatia)

Country / Region: Germany/Brandenburg/Lausatia

Begin of project: January 1, 2020

End of project: June 30, 2025

Status of project: March 18, 2025

a. Location of the Spreewitz glacial channel (green point) in the Spree catchment, and b. distribution of sulfate concentrations in the shallow aquifer of the Spreewitz glacial channel Source: Spree catchment: EU-Hydro – River Network Database, EEA (2020), sulfate concentrations: IWB (2020), groundwater contour lines: LfULG (2016)

Over the past decades, mining-related groundwater subsidence in the Lusatian lignite region has led to iron sulfide oxidation in the unsaturated zone. The subsequent re-rise of the groundwater or the flooding of the remaining holes leads to increased sulphate and iron concentrations in the groundwater and surface water. This can be observed in particular in the southern area of the Lusatian reclamation area in the Spreewitz Basin. Here, the concentrations of iron and sulphate in groundwater are particularly high, with up to 400 mg/l and 1400 mg/l respectively. Due to the largely effluent conditions (inflow of groundwater into the headwater), this area is therefore also a major source of iron and sulphates into the Spree. Although the processes leading to the increased concentrations (iron sulphide oxidation and subsequent mobilisation of the oxidation products) are generally known, the distribution of iron and sulphate in the aquifers as well as the contribution of the individual components (natural sediments, tipping and dump deposits) have not yet been fully clarified. This complicates the development of a targeted recovery concept.

Within the framework of the QuESt project (“Quantification of iron sulfide conversion in the Spreewitz glacial channel”), iron sulfide conversions in the natural sediments of the various aquifers will be evaluated and at the same time new techniques for monitoring such processes will be tested. In a first project phase, laboratory scale column tests are planned on artificial pyrite-enriched sediments under various redox conditions, accompanied by NMR (Nuclear Magnetic Resonance) measurements. This will determine the correlation between iron sulfides and/or dissolved iron and the NMR signal. In the second phase (2023), an in-situ aquifer characterization using surface NMR will be carried out, as well as additional sediment samples from the four aquifers for comparative column tests. The calculation of the material conversion during the column tests will be carried out both by hydrochemical balances and by accompanying laboratory NMR measurements. Continuous isotope tracer measurements are used for the highly precise characterization of the transport properties in the columns.

Goals/Milestones

• Determine the correlation between iron sulfides and/or dissolved iron and the NMR signal (column experiments on artificial sediments)
• Create mass balances for the iron sulfide turnover in the natural sediments of the Spreewitz glacial channel (column experiments on undisturbed samples collected from the Spreewitz channel)
• Conduct a feasibility study for the exploration of iron sulfide hotspots (surface NMR and possibly bore hole NMR)

Partner:

Lausitzer und Mitteldeutsche Bergbau-Verwaltungsgesellschaft (LMBV), Knappenstraße 1, 01968 Senftenberg (Germany)