Geochemical investigations of slags from the historical smelting in Freiberg, Erzgebirge (Germany)

The Freiberg area in the Saxon Erzgebirge (Ore Mountains) represents one of the oldest mining districts in Germany. Argentiferous ore mineralizations with lead, zinc and copper are dominating in this region. Various waste products of mining can be found around Freiberg. In particular, the slags from ore smelting were and are regarded as unusable waste products. However, they preserve information on the smelting and weathering behaviour of slag, which makes them very useful sources of information for our purposes. To reconstruct the chemical processes during ore smelting, historical slag represents a most valuable archive. Therefore, the historical slag dump in Halsbach (Germany) was examined exemplarily for the Freiberg deposit. The slag was dumped approx. 400 years ago and is rich in lead. An interrelation between the slag and the metallurgical process applied can be made on the basis of chemical composition, appearance and microscopic results. The slags of the heap in Halsbach contain high concentrations of heavy metals (average contents in mg kg⁻¹: Zn 40,000; Pb 10,000; Cu 1500; U 1000). Enrichments of heavy metals in the organic-rich soil horizons within the range of the dump foot (maximum contents in the A-horizon in mg kg⁻¹: Zn 3719; Pb 9198; As 3017; Cu 963) imply a faint discharge of metals from the dump.     

Radionuclides transport at the site of a low- and intermediate-level waste repository,Saligny, Romania

The site of the future Saligny low- and intermediate-level waste repository presents a rather deep unsaturated zone consisting of a pile of loess and clay, underlain by a calcareous aquifer. Van Genuchten parameters were first estimated in laboratory on samples collected from all the horizons, at different depths. In a second kind of test, moisture parameters were estimated from the natural water content profiles, observed in some wells, by inversion of the unsaturated flow equation. Based on the solution of the inverse problem as well as of the sensitivity analyses a simple physical model of the vadose zone was determined, consisting of a layered sequence that was subjected to a constant infiltration flux. Radionuclide migration was simulated in a vertical cross section made along the most probable path from the repository towards the surface water discharge zone. For radionuclide release, a source term was evaluated by ensuring a conservative estimate of cell inventory during the cell-filling operation. According to the simulation results, for the medium half-life nuclides, the unsaturated zone is a perfect barrier, whereas the long half-life isotopes break through in the aquifer at significant concentrations.

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Resumen El sitio del futuro repositorio para desechos de nivel bajo e intermedio, denominado Saligny, presenta una zona no saturada bastante profunda, consistente en un depósito de loess y arcilla, subyacido por un acuífero calcáreo. Los parámetros de Van Genuchten se estimaron por primera vez en laboratorio, a partir de muestras recolectadas de todos los horizontes, a diferentes profundidades. En un segundo tipo de prueba se estimaron los parámetros de humedad a través de la inversión de la ecuación de flujo no saturado, a partir de los perfiles naturales que contienen agua, observados en algunos pozos. Con base en la solución del problema inverso, así como también en análisis de sensibilidad, se determinó un modelo físico simple de la zona vadosa, el cual consiste de una secuencia estratificada sometida a un flujo de infiltración constante. La migración del radioisótopo fue simulada en una sección vertical, hecha a lo largo del camino más probable entre el repositorio y la zona de descarga en el agua superficial. Para la liberación del radioisótopo se evaluó la fuente, asegurando un estimativo conservador del inventario de celdas durante la operación de llenado de celdas. De acuerdo con los resultados de la simulación, para los isótopos con vida media intermedia, la zona no saturada es una barrera perfecta; mientras que los isótopos con vida media larga irrumpen en el acuífero con concentraciones importantes.

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Résumé Le futur stockage de déchets radioactifs de faible et moyenne activité de Saligny est caractérisé par une zone non-saturée assez profonde qui consiste dans des dépôts de loess et dargile qui couvrent un aquifère calcaire. Dans une première étape, les paramètres de van Genuchten ont été déterminés en laboratoires sur des échantillons prélevés de toutes les couches, à des profondeurs différentes. Dans une seconde étape les mêmes paramètres ont été estimés, comme un solution du problème inverse à partir de profils de la saturation en eau, mesurés dans des forages. Les résultats du problème inverse, ainsi que l› analyse de sensibilité ont mené à un modèle multi- couches de la zone non-saturé, rechargé par un flux constant. On a simulé le transport des radionucléides dans une coupe verticale, construite au long du trajet le plus probable entre le stockage et les eaux de surface. Le flux de radionucléides relâchés a été estimé en considérant une valeur consevative pour la masse totale stocké. D› après les résultats de la simulation la zone non saturée forme une barrière presque parfaite pour les radionucléides de période moyenne, denvirons de 30 ans, tendis quelle est traversée avec des concentrations assez importantes par des isotopes à grande période.

     

A low-cost,large-volume general purpose water sampler

Here we describe the design, construction and subsequent routine use of a large-volume general purpose water sampler. The sampler is designed to be used in both remote sites and deep lakes with a minimum of logistical support, and can be made from commercially available parts at low cost.     

Ways of investigating radionuclide migration processes in the lithosphere and hydrosphere

In Russia, until recently, it was considered that groundwater was protected from surface radioactive contamination by soil and rocks in the zone aeration. Groundwater was not a subject of radiation control. The accident at the Chernobyl Nuclear Power Plant showed, however, that groundwater is vulnerable to radioactive contamination. In this connection, the vulnerability of groundwater to and the problems of protecting groundwater from radioactive contamination became urgent. The assessment of natural protection of groundwater from radioactive contamination is now considered a top priority. The zone of aeration is generally considered to be the zone separating groundwater from surface contamination. In respect to radioactive contamination, soils that may fix a large quantity of radionuclides serve as a protection zone of a higher order. The mapping of protectibility was done for each radionuclide taking into consideration the specific structure of the flow medium and migration properties of a radionuclide.⁹⁰Sr and¹³⁷Cs have different mechanisms of transport; convective transport is characteristic of the former and diffusive transfer of the latter. This is conditioned by different physico-chemical properties of the radionuclides and principally by their sorption capacities. The coefficient of distribution of⁹⁰Sr is in many times less than the coefficient of distribution of¹³⁷Cs. The environmental protection problem in regions with nuclear power plants and in areas subjected to radioactive contamination may be solved using a monitoring, system including interrelated systems of observation and prediction of the lithosphere and the hydrosphere. The problem of mathematical modeling of migration processes is related to the complexities of modeling the processes of flow, mass transfer, and the accompanying physicochemical processes in zones of full and partial saturation, as well as difficulties in mathematical calculations.     

Comparison of the sediment composition in relation to basic chemical,physical,and geological factors

Sediment constitutes an interesting and valuable material for observation of human impact on the environment.Based on the sediment core samples in two Tatra Mountains lakes,determination of the selected elements(including cesium 137 radionuclide activity and heavy metals' concentrations) and dating of the obtained layers by the lead 210 method,chemometric analysis of the resulting data set was done.It was established,as a result of Cluster Analysis,that the variability of the determined parameters was distinct in the lakes with much higher concentrations of heavy metals in Smreczynski staw lake.Also,the influence of human activity(long distance transport of contaminants) is notable on the north slopes of the Tatras(Smreczynski staw lake) comparing to Popradske pleso lake.The examined elements can be divided into two groups-natural to the site origin(iron,manganese,and magnesium),and elements whose accumulation in the sediments can be related(at least in part) to human activity(~(137)Cs,zinc,copper,cadmium,lead,and chromium).The results confirm the existence of the so called "screen effect",meaning that the Tatra Mountains' crest delimits to a considerable extent further transport of pollutants to the south side of the Tatra Mountains slopes.     

US Geological Survey research on the environmental fate of uranium mining and milling wastes

Studies by the US Geological Survey (USGS) of uranium mill tailings (UMT) have focused on characterizing the forms in which radionuclides are retained and identifying factors influencing the release of radionuclides to air and water. Selective extraction studies and studies of radionuclide sorption by and leaching from components of UMT showed alkaline earth sulfate and hydrous ferric oxides to be important hosts of radium-226 (²²⁶Ra) in UMT. Extrapolating from studies of barite dissolution in anerobic lake sediments, the leaching of²²⁶Ra from UMT by sulfate-reducing bacteria was investigated; a marked increase in²²⁶Ra release to aqueous solution as compared to sterile controls was demonstrated. A similar action of iron(III)-reducing bacteria was later shown. Ion exchangers such as clay minerals can also promote the dissolution of host-phase minerals and thereby influence the fate of radionuclides such as²²⁶Ra. Radon release studies examined particle size and ore composition as variables. Aggregation of UMT particles was shown to mask the higher emanating fraction of finer particles. Studies of various ores and ore components showed that UMT cannot be assumed to have the same radon-release characteristics as their precursor ores, nor can²²⁶Ra retained by various substrates be assumed to emanate the same fraction of radon. Over the last decade, USGS research directed at offsite mobility of radionuclides from uranium mining and milling processes has focused on six areas: the Midnite Mine in Washington; Ralston Creek and Reservoir, Colorado; sites near Canon City, Colorado; the Monument Valley District of Arizona and Utah; the Cameron District of Arizona; and the Puerco River basin of Arizona and New Mexico.     

Manzala lagoon, Nile delta, Egypt: modern sediment accumulation based on radioactive tracers

 This study was undertaken to determine whether recent anthropogenic changes in the Nile basin have affected the modern rate of sediment accumulation in the Nile delta. Excess ²¹⁰Pb, ¹³⁷Cs, and ^239,240Pu were used to develop a sediment chronology for a core from central Manzala lagoon, the delta sector which has had the highest average rate of sediment accumulation during the Holocene (to about 0.7 cm year^–1). Excess ²¹⁰Pb was detected in the top 32 cm of the core, yielding an accumulation rate of 1.2 cm year^–1, higher than the mean rate for the Holocene. A high ¹³⁷Cs/^239,240Pu ratio requires a reactor source (possibly Chernobyl) for these nuclides. Low concentrations of excess ²¹⁰Pb and weapons-fallout nuclides precluded recognition of changes in sediment accumulation rate in Manzala lagoon during this century and may limit the use of tracer radionuclides for modern sediment chronology in the Nile delta. Received: 18 March 1997 · Accepted: 22 July 1997     

The estuarine chemistry and isotope systematics of U in the Amazon and Fly Rivers

Natural concentrations of ²³⁸U and δ²³⁴U values were determined in estuarine surface waters and pore waters of the Amazon and Fly (Papua New Guinea) Rivers to investigate U transport phenomena across river-dominated land–sea margins. Discharge from large, tropical rivers is a major source of dissolved and solid materials transported to the oceans, and are important in defining not only oceanic mass budgets, but also terrestrial weathering rates.On the Amazon shelf, salinity-property plots of dissolved organic carbon, pH and total suspended matter revealed two vastly contrasting water masses that were energetically mixed. In this mixing zone, the distribution of uranium was highly non-conservative and exhibited extensive removal from the water column. Uranium removal was most pronounced within a salinity range of 0–16.6, and likely the result of scavenging and flocculation reactions with inorganic (i.e., Fe/Mn oxides) and organic colloids/particles. Removal of uranium may also be closely coupled to exchange and resuspension processes at the sediment/water interface. An inner-shelf pore water profile indicated the following diagenetic processes: extensive (1 m) zones of Fe(III)—and, to a lesser degree, Mn(IV)—reduction in the absence of significant S(II) concentrations appeared to facilitate the formation of various authigenic minerals (e.g., siderite, rhodocrosite and uraninite). The pore water dissolved ²³⁸U profile co-varied closely with Mn(II). Isotopic variations as evidenced in δ²³⁴U pore waters values from this site revealed information on the origin and history of particulate uranium. Only after a depth of about 1 m did the δ²³⁴U value approach unity (secular equilibrium), denoting a residual lattice bound uranium complex that is likely an upper-drainage basin weathering product. This suggests that the enriched δ²³⁴U values represent a riverine surface complexation product that is actively involved in Mn–Fe diagenetic cycles and surface complexation reactions.In the Fly River estuary, ²³⁸U appears to exhibit a reasonably conservative distribution as a function of salinity. The absence of observed U removal does not necessarily imply non-reactivity, but instead may record an integration of concurrent U removal and release processes. There is not a linear correlation between δ²³⁴U vs. 1/²³⁸U that would imply simple two component mixing. It is likely that resuspension of bottom sediments, prolonged residence times in the lower reaches of the Fly River, and energetic particle–colloid interactions contribute to the observed estuarine U distribution. The supply of uranium discharged from humid, tropical river systems to the sea appears to be foremost influenced by particle/water interactions that are ultimately governed by the particular physiographic and hydrologic characteristics of an estuary.     

Fallout radionuclide tracers identify a switch in sediment sources and transport-limited sediment yield following wildfire in a eucalypt forest

Fire can alter sediment sources and transport rates in river basins, changing landforms and aquatic habitats and degrading downstream water quality. Variability in the response between environments, between fires, and with time since fire makes predicting the catchment-scale effect of individual fires difficult. This study applies the fallout radionuclides ¹³⁷Cs and ²¹⁰Pb_xs to trace the sources and transport of fine sediment through a river network following a wildfire of moderate to extreme severity in the 629-km² eucalypt-forested Nattai River water-supply catchment near Sydney, Australia. The tracer analysis showed that post-fire erosion caused a switch in fine (< 10 µm) sediment sources from 80% subsoil derived from gully and river bank erosion to 86% topsoil derived from hillslope surface erosion. The fine sediment phosphorus content increased 4–10 fold over pre-fire levels. Annual post-fire sediment yields estimated from suspended solids rating curves were 109–250 times higher than they would have been without fire. A large additional amount of sediment remained stored within the river network for at least four years, particularly in lower-gradient reaches. Analysis of a sediment core showed that surface erosion following a previous fire had supplied at least 29% of total catchment sediment yield over the past 36 years. It is concluded that wildfire can alter catchment sediment budgets in two ways. Firstly, a spatially-diffuse pulse of elevated erosion is associated with moderate or intense rainfall events in post-fire years. Secondly, pulses of elevated catchment sediment yield are driven by the timing and river sediment transport capacity of runoff events. Severe post-fire erosion and high interannual hydrologic variability can result in large sediment stores persisting within the river network for many years. Fallout radionuclide tracers are shown to be useful in quantifying fine sediment sources and transport dynamics following wildfire, and the contribution of wildfire to catchment sediment yield.