Klaus Freyer

Sampling and measurement of radon-222 in water

Abstract The radon-222 content of water especially is of interest considering aspects of radiation protection or techniques to investigate hydrologie characteristics of aquifers using radon-222 as a natural tracer. Sampling and measurement of radon in groundwater are complicated by the high volatility of the gas. A method including sampling techniques (pumping, flushing time, filling arrangement and sample transportation) and rapid analysis of radon with high reproducibility was investigated and tested. The measurement is based on extraction concentration of radon-222 and liquid scintillation spectrometry. The detection limit of this method is about 0.05 Bql−1. By means of α/β discrimination it can be confirmed that radon-222 is the origin of the measured radioactivity.

Physical and chemical characterization of a complexly contaminated scrubber dust — a by-product of copper smelting in Sachsen-Anhalt, Germany

Abstract A physical and chemical description of a scrubber dust slurry, known as Theisenschlamm, is presented. This material is generated as a by-product during extraction of copper from a mineralized Permian black shale (Kupferschiefer) in Sachsen-Anhalt, Germany. The Theisenschlamm consists of sulphide grains which are a complex solid solution of Pb, Zn, Cu and Fe. The crystal structures are modified forms of galena and sphalerite/wurtzite. Variations in the X-ray diffraction peak positions of these minerals reflect the poorly developed lattice structures of these phases. Anglesite is a secondary phase. The Theisenschlamm contains 18% Zn and 14% Pb as well as significant concentrations of PAH, PCDD and other organic compounds, rare metals and radionuclides (e.g. 210 Po and 210 Pb). The original particles have a median diameter of 1.25 μm, however, these particles are themselves aggregates of still smaller particles, typically of submicron size.

Using the soil gas radon as an indicator for ground contamination by non-aqueous phase-liquids

Abstract1 The ProblemOne of the major problems facing risk assessment at polluted industrial sites and military bases is subsurface contamination by non-aqueous phase-liquids (NAPLs), since tracing the extent of a NAPL plume using conventional methods (drive point profiling) is usually associated with difficulties. In an effort to trace subsurface contamination as precisely as possible, monitoring points are placed in the area that might be affected by contaminants, and groundwater and soil samples are taken to the laboratory for analysis. However, the final number of monitoring points is hardly ever sufficient for distinctive contamination mapping, and this may ultimately result in an unsuitable remediation action being taken.2 ObjectivesTo obtain a more detailed image of a subsurface NAPL plume and, hence, to facilitate remediation measures that are best suited for the site in question, a denser network of monitoring points is desirable. The aim of the investigation described in this paper was therefore to develop a new detection method for subsurface NAPL contamination, which is based on an easily accessibleindicator for NAPLs rather than on the analysis of soil and groundwater samples taken at the site. Based on the good solubility of radon in NAPLs, the idea was put forward that subsurface NAPL contamination should have an influence on the natural radon concentration of the soil gas. Provided this effect is significant, it would be possible to carry out a straightforward radon survey on an appropriate sampling grid covering the suspected site and thus enabling the NAPL contamination to be detected by the localization of anomalous low radon concentrations in the soil. The overall aim of the investigation was to assess the general suitability of the soil-gas radon concentration as an indirect tracer for NAPL contamination in the ground.3 MethodsThe partitioning coefficient KNAPL/air is one of the most influential parameters governing the decrease of the radon concentration in the soil gas in the presence of a subsurface NAPL contamination. Since NAPL mixtures such as gasoline, diesel fuel and paraffin are among the most important NAPLs regarding remediation activities, laboratory experiments were performed to determine the radon-partitioning coefficient for these three NAPL mixtures.Field experiments were carried out as well. The aim of the field experiments was to test the use of the soil-gas radon concentration as a tracer for NAPL contamination on-site. For the field experiments, each site was covered with a suitable grid of soil gas sampling points. Finally, the lateral radon distribution pattern achieved on each of the sites was compared to the respective findings of the earlier research performed by conventional means.4 Results and DiscussionThe results of the laboratory experiments clearly show a very strong affinity of radon to the NAPL mixtures examined. The partitioning coefficients achieved correspond to those published for pure NAPLs (Clever 1979) and are thus in the expected range. The results of the field experiments showed that the minimum radon concentrations detected match the respective NAPL plumes traced previously.5 ConclusionsBoth the results of the lab experiments and the on-site findings demonstrate that the soil-gas radon concentration can be used as an indicator for subsurface NAPL contamination. The investigation showed that NAPL-contaminated soil volumes give rise to anomalous low soil-gas radon concentrations in the close vicinity of the contamination. The reason for this decrease in the soil-gas radon concentration is the good solubility of radon in NAPLs, which enables the NAPLs to accumulate and ‘trap’ part of the radon available in the soil pores.6 Recommendations and OutlookFurther research is required into contamination with rather volatile NAPLs such as BTEX. Further research is also needed to examine whether it is possible to not only localize a NAPL plume, but also to obtain some quantitative information about the subsurface NAPL contamination. The authors also believe that additional investigations should be carried out to study the ability of the method to not just localize a NAPL contamination, but also to monitor on-site, clean-up measures.

Multi-metal contaminated stream sediment in the Mansfeld mining district: metal provenance and source detection

In metal mining districts, element and radionuclide patterns in contaminated stream sediment can be used as tracers to detect and track the sources of pollution, and to distinguish geogenic from anthropogenic input, a prerequisite for rehabilitation planning. An example is given from the Mansfeld mining district in central Germany, where mining of ‘Kupferschiefer’ was conducted for over 800 years and led to extensive environmental pollution, considered to be mainly of geogenic origin. In consequence, only emergency measures have been implemented. The aim of the present study was to identify the metal sources in the mining district and to assess the range of pollutant migration. In combining conventional geochemistry, mineralogy and radiometry, it was shown that most of the multi-metal pollution in the Mansfeld mining district is of anthropogenic origin. The major sources of metals are low-grade ore, metalliferous flue dust and slag. Conventional geochemistry provided information on the spread of contamination in the rivers of the mining district. Mineralogy and microchemistry added data on the composition of the source material and pointed to the potential sources of contamination. Finally, the fraction of these sources in environmental pollution was estimated by gamma-spectroscopy.

Optimization of time resolution and detection limit for online measurements of 222Rn in water

The online measurements of radon in flowing water with high temporal resolution and a lower limit of detection of some Bq/l is of growing interest in environmental research and earth sciences. Promising new fields of application in hydrogeology are the study of exchange and mixing processes and the monitoring of pumping procedures before and during groundwater sampling. A suitable, simple method has been proposed by Surbeck based on the separation of air and water by a diffusion membrane. Process parameters influencing the temporal resolution as well as the radon detection efficiency have been studied. Considering these results a new instrument has been developed enabling online radon-in-water measurement with time resolution of about one minute.

Boron determination using PC nuclear track detector and252Cf neutron source

The possibility of quantitative boron determination via (n,α) reaction in silicon and B2O3+PVA samples has been studied. As alpha-sensitive track detector Makrofol-E polycarbonate foil and as neutron source lmg252Cf with a cadmium ratio of 8 were applied. It was shown that, if the lowest acceptable track density was 103 tracks cm−2 the method could be used to measure B concentrations down to 1 ppm.

Oxidation treatment of a sulphide-bearing scrubber dust from the Mansfeld Region, Germany: Organic and inorganic phase changes and multi-element partition coefficients between liquid and solid phases

Abstract A low temperature oxidation process has been developed to separate Pb from Zn in a complexly contaminated scrubber dust. The material consists of approx. 50% galena (PbS) and sphalerite/wurtzite (ZnS), and also an amorphous component, a variety of different silicate and carbonate phases as well as naturally-occurring radionuclides and oil and grease. The two-stage process consists of a grinding stage followed by placing this material into a hydrogen peroxide solution. The resultant oxidation reaction is violently exothermic — the temperature rises spontaneously to approx. 96°C. The amount of solid phases remaining after completion of the reaction was reduced by approx. 40% and consisted largely of insoluble lead sulphate which retained the bulk of the radionuclides. Almost all of the zinc was placed into solution by this process as was the Cd, Re and Cu. The total PAH content of the original Theisenschlamm (468 ppm) was reduced to 11.25 ppm in the residual sediment and the PCDD/PCDF concentrations were reduced by approx. 40%. The radionuclides are almost totally concentrated in the solid phase. The method shows considerable promise as a separation technique for very fine-grained sulphide-bearing residues.

Studies on nitrogen mapping by various CR-39 track detectors

The possibility of using CR-39 track detectors for nitrogen distribution measurements via 14N(n,p) 14C reaction is studied. In this respect the proton detection properties of different CR-39 products have been analyzed. By PIXE and neutron activation methods the possible disturbing impurity content of the detector sheets is determined. It is found that the main contaminant is chlorine which remains in the CR-39 monomer during its manufacture. The variation of background track density induced in the bulk of detectors is examined under different conditions of neutron irradiation. The analysis of our experimental data has led to the conclusion that the sources of proton background tracks are the fast neutron component of neutron source, chlorine in detector and nitrogen diffused from air into the upper layer of detector. Efforts have been made to decrease the nitrogen content of diffusion origin by removing the upper detector layer and by outgassing the CR-39 sheet in vacuum before irradiation. Finally the “signal/noise” ratio for steel specimen and the sensitivity of nitrogen determination are given.

Vergleich verschiedener quantitativer Auswerteverfahren für Autoradiograimme

Es wurden ein Joyce-Loebl-Mikrodensitometer mit angebauter Auswerteanlage, ein Zeiss-Schnellphotometer, das Geratesystem „, Densitron” und das Agfacontour-Professional-Verfahren zur Auswertung desselben Autoradiogrammes angewandt. Dabei wurden mittlere Schwarzungen und die Homogenitat bestimmt, sowie auch eine Teilung der Autoradiogrammflache in Schwarzungsbereiche (Bestimmung von Schwarzungssummen) vorgenommen. Bei der Answertung der Autoradiogramme von Struklur- und Mikrosegregationsuntersuchungsproben ist die auf der Basis des Joyce-Loebl-Densitometers gebaute Anlage die praziseste und das Geratesystem „Densitron” eine prazise und wenig arbeitsaufwendige Anlage. Bei den Autoradiogrammen mit Zonen. oder Bandschwarzungsverteilungen bieten das „Densitron” und das Agfacontour-Professional-Verfahren fast die gleichen Darstellungsmoglichkeiten, das „Densitron”-System ermoglicht aber eine quantitative und die Agfacontour-Technik nur eine halbquantilative Auswertung des Autoradiogrammes. Schwarzungsverlaufe (z...

Surfactant separation as a technique for physical and chemical characterization of ore processing residues

When characterizing multi-phase materials, several authors have recommended separating the material into various fractions consisting of a reduced number of minerals. However, the common separation techniques are of limited value when treating ultra-fine-grained materials. We present in this paper a separation technique using tensio-active solutions which break up any particle agglomerates which may be present and facilitates sedimentation of component particles according to grain size. These fractions have a distinctive mineralogy and chemistry. The technique has been applied to two selected samples from two mining residue sites in Germany. Results from Bielatal, a tin residue, show that a large proportion of the arsenic and heavy metals are concentrated in a suspension fraction, which consists of clay minerals and amorphous iron oxyhydroxides. Silicates such as a micas and feldspar settle out quite rapidly, whereas, other minerals, such as hematite take longer. In the case of Dankritz, a uranium mine waste, the same technique was applied and similar results were obtained for the heavy metals distribution. Additional study indicated that radium is with barite and other radio-isotopes were associated with the fine suspension fraction.