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- FG Geopedologie und Landschaftsentwicklung (23) (remove)
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Phytoremediation of sites contaminated with iron cyanides can be performed using poplar and willow trees. Poplar and willow trees were grown in potting substrate spiked with ferrocyanide concentrations of up to 2,000 mg kg-1 for 4 and 8 weeks respectively. Soil solution and leaf tissue of different age were sampled for total cyanide analysis every week. Chlorophyll content in the leaves was determined to quantify cyanide toxicity. Results showed that cyanide in the soil solution of spiked soils differed between treatments and on weekly basis and ranged from 0.5 to 1,200 mg l-1. The maximum cyanide content in willow and poplar leaves was 518 mg kg-1 fresh weight (FW) and 148 mg kg-1 FW respectively. Cyanide accumulated in the leaves increased linearly with increasing cyanide concentration in the soil solution. On the long term, significantly more cyanide was accumulated in old leaf tissue than in young tissue. Chlorophyll content in poplar decreased linearly with increasing cyanide in the soil solution and in leaf tissue, and over time. The inhibitory concentration (IC50) value for poplars after 4 weeks of exposure was 173 mg l-1 and for willow after 8 weeks of exposure—768 mg l-1. Results show that willows tolerate much more cyanide and over a longer period than poplars, making them very appropriate for remediating sites highly contaminated with iron cyanides.
Analysis of 288 percussion drillings from depths of up to seven meters and a 120 m long excavated section provide new and detailed information on the Late Quaternary to Late Holocene floodplain evolution from the most important Central European iron-mining region of the 15th century. The generalized sequence of the Vils River floodplain is built of five units representing facies of different genesis (rock/saprolite, gravel, sand, loam, peat) that are identified by physical, chemical, and mineralogical parameters (grain size, clast shape, and content, TOC, bulk mineralogy). Along the 87 km length of the valley, different units/facies are found at the Upper Vils River (UVR 1-5) and at the Lower Vils River (LVR 1-4b). In both river sections, fine-grained material (flood loam) forms the major part (up to 4 m) of the alluvial sequence. 29 age determinations (24 14C, 4 IRSL, 1 tree-ring analysis) show increasing accumulation of flood loam in the last millennium. The data correlate with the beginning of mining at the Vils River and hence suggest a causal connection with mining activities in the catchment—both on the slopes and in the floodplain—with intense deposition of flood loams.
Soil contamination with iron-cyanide complexes is a common problem at former manufactured gas plant (MGP) sites. Dissolution of the cyanide, from Prussian Blue (ferric ferrocyanide), creates an environmental hazard, whereas the risk of groundwater contamination depends on the stability of dissolved iron–cyanide complexes. Lack of a standard leaching method to determine the water-soluble (plant-available) cyanide fraction generates potential limitations for implementing remediation strategies like phytoremediation. Applicability of neutral solution extraction to determine the water-soluble cyanide fraction and the stability of Prussian Blue in surface and near-surface soils of an MGP site in Cottbus, undersaturated and unsaturated water conditions, was studied in column leaching and batch extraction experiments. MGP soils used in the long-term tests varied according to the pH (5.0–7.7) and the total cyanide content (40–1718 mg kg−1). Column leaching, after four months of percolation, still yielded effluent concentrations exceeding the German drinking water limit (> 50 μg L−1) and the solubility of Prussian Blue reported in the literature (< 1 mg L−1) from both alkaline and acidic soils. Long-term (1344 h) extraction of MGP soils with distilled water was sufficient to dissolve 97% of the total cyanide from the slightly alkaline soils and up to 78% from the acidic soils. Both experiments revealed that dissolution of ferric ferrocyanide under circum-neutral pH and oxic water conditions is a function of time, where the released amount is dependent on the soil pH and total cyanide content. Unexpectedly high and continuous solubility of Prussian Blue, both in acidic and slightly alkaline MGP soils, implies the need to introduce an additional cyanide fraction (“readily soluble fraction”) to improve and specify cyanide leaching methods. Long-term extraction of cyanide-contaminated soil in neutral solution seems to be a promising approach to evaluate the potential hazard of groundwater pollution at the MGP sites.
Our study deals with agricultural recultivation of open cast brown coal mining areas in Lusatia, Eastern Germany. In this region the largest brown coal (lignite) mining area of Germany is located. Lignite mining activities lead to major disturbances of the landscape. Recultivation efforts attempt to regenerate mining areas for agricultural land use options. The geological “parent” material is of saaleian origin, has a sandy texture and was excavated from several meters depths before mining and is now used for recultivating the excavated area. Consequently, it is free of recent soil organic carbon. The substrate itself is unstructured. The partly wet or dry substrate is subjected to strong mechanical stresses during the excavation, deposition, refilling and levelling processes throughout the year. This practice leads to more or less compacted soils/substrates which may result in small yields of agricultural crops. In this context we investigate the effect of different organic soil additives in combination with different recultivation crop rotations on the development of soil structure for improved agricultural land use. Our experimental site has been heaped up and levelled off in 2006 and 2007. On each of the 24 experimental sub areas undisturbed soil samples have been taken to characterise the substrates according to their mechanical and hydraulic parameters and to determine the scattering of these parameters on a site that is assumed to be recultivated as homogenously as possible. First results of our ongoing experimental study indicate that the soil physical properties such as texture, bulk density, precompression stress, air permeability and saturated hydraulic conductivity are not identical on each of the 24 subplots. The soil physical properties behave differently in relation to each other. E.g. we found a negative correlation between bulk density (∼1.35–∼1.90 g/cm3) and precompression stress (∼30–70 kPa) and no decisive interrelation between bulk density and air permeability or saturated hydraulic conductivity.
The soil in the vicinities of former Manufactured Gas Plant (MGP) sites is commonly contaminated with iron-cyanide complexes (ferric ferrocyanide). The phenomenon of cyanide mobility in soil, according to the literature, is mainly governed by the dissolution and precipitation of ferric ferrocyanide, which is only slightly soluble (<1 mg L¡1) under acidic conditions. In this paper, retention properties of the sandy loam soil and the potential vertical movement of the solid iron-cyanide complexes, co-existing with the dissolution, sorption and precipitation reactions were investigated. Preliminary research conducted on a former MGP site implied colloidal transport of ferric ferricyanide from the initial deposition in the wastes layer towards the sandy loam material (secondary accumulation), which possibly retarded the mobility of cyanide (CN). A series of batch and column experiments were applied in order to investigate the retardation of iron-cyanide complexes by the sandy loam soil. Batch experiments revealed that in circumneutral pH conditions sandy loam material decreases the potassium ferro- and ferricyanide concentration. In column experiments a minor reduction in CN concentration was observed prior to addition of iron sulfide (FeS) layer, which induced the formation of the Prussian blue colloids in circumneutral pH conditions. Precipitated solid iron-cyanide complexes were mechanically filtered by the coherent structure of the investigated soil. Additionally, the reduction of the CN concentration of the percolation solutions by the sandy loam soil was presumably induced due to the formation of potassium manganese iron-cyanide (K2Mn[Fe(CN)6]).
Soils of former Manufactured Gas Plants (MGPs) are often contaminated with iron-cyanide (Fe-CN) complexes that originate from gas purification process. Cyanide is a potentially toxic substance and its presence in soil and groundwater may cause risk for human health as well as for the environment. MGPs were commonly built on the city suburban areas, which have spread ever since. Nowadays, these sites are typically located in inner cities, causing environmental thread, due to the leaching of pollutants. More recently, columns and batch experiments have been used to study fate and mobility of contaminants is soil. The release of iron-cyanide complexes under unsaturated flow conditions was evaluated with eight columns of 30 cm length and a diameter of 5,4 cm. Cyanide concentrations in the collected leachates were measured with Flow Injection Analysis (FIA). Additionally pH, electrical conductivity (EC) and various ion concentrations were determined. In order to compare the release of Fe-CN complexes in saturated conditions a batch experiment was conducted, where in defined time intervals, 1 ml of the extract water phase was analyzed for CN concentration. Study revealed an analogous trend of cyanide release in both experiments indicating primarily the release of formerly dissolved phase (hexacyanoferrates) followed by continual dissolution of ferric ferrocyanide. We conclude that batch experiments, conducted prior to column analysis, can serve as preliminary prediction of the water soluble cyanide fraction under unsaturated conditions.
Iron-cyanide (Fe-CN) complexes have been detected at Manufactured Gas Plant sites (MGP) worldwide. The risk of groundwater contamination depends mainly on the dissolution of ferric ferrocyanide. In order to design effective reme- diation strategies, it is relevant to understand the contaminant’s fate and transport in soil, and to quantify and mathe- matically model a release rate. The release of iron-cyanide complexes from four contaminated soils, originating from the former MGP in Cottbus, has been studied by using a column experiment. Results indicated that long-term cyanide (CN) release is governed by two phases: one readily dissolved and one strongly fixed. Different isotherm and kinetic equations were used to investigate the driving mechanisms for the ferric ferrocyanide release. Applying the isotherm equations assumed an approach by which two phases were separate in time, whereas the multiple first order equation considered simultaneous occurrence of both cyanide pools. Results indicated varying CN release rates according to the phase and soil. According to isotherm and kinetic models, the long-term iron cyanide release from the MGP soils is a complex phenomenon driven by various mechanisms parallely involving desorption, diffusion and transport processes. Phase I (rapid release) is presumably mainly constrained by the transport process of readily dissolved iron-cyanide complexes combined with desorption of CN bound to reactive heterogeneous surfaces that are in direct contact with the aqueous phase (outer-sphere complexation). Phase II (limited rate) is presumably driven by the diffusion controlled processes involving dissolution of precipitated ferric ferrocyanide from the mineral or inner-sphere complexation of fer- ricyanides. CN release rates in phase I and II were mainly influenced by the pH, organic matter (OM) and the total CN content. The cyanide release rates increased with increasing pH, decreased with low initial CN concentration and were retarded by the increase in OM content.