René Frömmichen

Microbial Fe(III) Reduction in Acidic Mining Lake Sediments after Addition of an Organic Substrate and Lime

To elucidate the role of Fe(III) reduction in mining lake sediments amended with organic substrates, we performed a large (10 m diameter) enclosure experiment in which sediments were amended with Carbokalk, a waste product from sugar industry containing organic carbon and lime. Fe(III) reduction rates were determined monthly by measuring the accumulation of Fe(II) in the sediments in the field. Fe(III) reduction rates were also determined by incubating sediment samples with synthetic Fe(III) oxyhydroxide under in situ temperature in the laboratory. Sulfate reduction was selectively inhibited in the Fe(III) reduction experiments by addition of sodium molybdate. Sulfate reduction was measured by accumulation of reduced inorganic sulfides in the field and by 35S radiotracer using a core injection technique. Sediment incubation and determination of sulfate reduction rates with radiotracer showed that sulfate reduction and direct microbial Fe(III) reduction occured simultaneously in the upper centimeters of the sediments and that both processes contributed to alkalinity generation. However, Fe(III) reduction was the initial process and rates were at least 3.5 fold higher than sulfate reduction rates. The results indicate that the presence of suitable anions for Fe(II) precipitation as carbonate or sulfide is needed in order to prevent loss of potential alkalinity by Fe(II) diffusion and reoxidation in the water column.

Functions of Straw for In Situ Remediation of Acidic Mining Lakes

The addition of straw in combination with ‘Carbokalk’, a by-product from the sugar-industry, was successfully used to stimulate microbial alkalinity generation in an acidic mining lake. To get detailed information about functions of straw, anenclosure experiment was carried out. Straw bundles were placedat the sediment surface of an acidic mining lake (ML 111) and thephysiochemical conditions and the microbiology of the sediment-water contact zone were studied. Straw was degraded by anaerobic microorganisms and dissolved organic carbon (DOC) leached from straw bundles. Pigmented flagellates responded to the DOC supply in the water column anda considerable amount of algal carbon was transported to the sediment. Straw addition led to microbial reduction of iron andsulfate in the sediment. Sulfate reduction was observed at a pHof 5.5. The pH, however, was not high enough to precipitate H2S completely. Thus, some H2S diffused into the watercolumn, where it was reoxidized. Straw did not create orstabilize an anoxic water body above the sediment. Microbial sulfate reduction and pyrite formation only took place in the sediment,whereas iron reduction also took place in the straw. Straw, however, altered the flow conditions above the sediment surfaceand prevented complete mixing of the profundal water. Straw didnot serve as a substratum for a reactive biofilm. We conclude that the most important function of straw for mining lake remediation is to be a long-term nutrient source for microbialalkalinity generation in the sediment.

Chemical Changes in Sediment Pore-Waters of an Acidic Mining Lake After Addition of Organic Substrate and Lime for Stimulating Lake Remediation

In the past five years, enclosures have beeninstalled in an acidic mining lake in Lusatia to investigate insitu remediation processes. They were treated with straw, withstraw and Carbokalk, or with Carbokalk alone, where Carbokalkis a by-product of the sugar industry (solid precipitate ofnon-sugars after lime clarification of extracted sugar beetjuice). Sediment samples were taken as cores to get informationabout the behaviour of organic and inorganic components insediment pore-water with depth. Vertical distributions of pH,soluble reactive phosphate, nitrate, ammonium, silica,aluminium, iron, manganese, calcium, magnesium, sodium,potassium, sulphate, and DOC were measured. The resultingprofiles, each consisting of 15 data points at differentdepths, were compared by cluster analysis. The similarities ofsediment cores from different treated enclosures relating toprofiles of chemical components were discussed. Increasedconcentrations of potassium and sulphate were found in pore-water after substrate treatment. The data imply dissolution ofpotassium iron sulphate hydroxide minerals (jarosite) after anincrease of pH caused by dissolution of lime and by sulphatereducing processes which were stimulated by organic substrateaddition.

Strategies for Remediation of Former Opencast Mining Areas in Eastern Germany

Lignite was for decades the main source of energy and the primary raw material used by the chemical industry in the now German Federal States of Saxony, Saxony-Anhalt, and Brandenburg. Except during the initial phases of extraction, lignite was exclusively recovered by opencast mining. The close ties between industry and mining led to the establishment of major industrial operations such as petrochemical, organochemical, and electrochemical plants located near the mining centers. In terms of its quality and composition, lignite in eastern Germany can be classified into West and East Elbian formations, corresponding to the Central German and the Lusatian mining districts.