Ondra Sracek - Academia.edu (original) (raw)

Papers by Ondra Sracek

Journal of Geochemical Exploration, Aug 1, 2018

Mining in the former Novátor coal and uranium mine ceased in 1957 and a part of the wastes underw... more Mining in the former Novátor coal and uranium mine ceased in 1957 and a part of the wastes underwent spontaneous ignition in 1959-1970. Since the 1970s, the waste heap has been exposed to continuous weathering. The objective of this study was to assess to what extent the burnt and unburnt parts of the heap contribute to contamination of the local drainage system over a period lasting more than 40 years after the end of the mining. Analyses of water collected by lysimeters located on the slope of the heap have shown that the burnt part of the pile is still a source of aqueous sulfate and volatile elements (F, Se, and Pb) that have accumulated in this part of the heap during the self-ignition processes. The unburned part of the heap is mainly the source of aqueous carbonate, Mo, and U. The pH values of water flowing through the heap are in the narrow interval of 6.9-8.6. Rare layers of unburnt coal-bearing sediments rich in sulfides, where the pH values are between 2.9 and 3.7 are rather exceptional. These layers are the main source of Zn, Cu, and Co as a result of weathering of pyrite, chalcopyrite and sphalerite. The chemical composition of water draining from the heap ranges between the values determined in both its burnt and unburnt parts. The

Minerals

The regional environmental–geochemical surveying of the long-term impacts of mining and ore proce... more The regional environmental–geochemical surveying of the long-term impacts of mining and ore processing on a large part of the Zambian Copperbelt mining district was carried out by the Czech Research Group with cooperation of the Geology Department, University of Zambia, and the Geological Survey of Zambia in the period 2002–2018. This included the characterization of various sources of contamination, the extent of contamination of soils and crops, and the degree of contamination of river water and sediments. Solid speciation studies of potentially harmful chemical elements (PHEs), plant and human bioaccessibility studies, and a range of mineralogical techniques were used to assess the pathways of PHE cycling in terrestrial and aqueous systems and their impacts on human health. Ores of the Zambian Copperbelt mining district are mined for Cu and Co, but a number of other trace elements (Pb, As, Cd, Hg, Pb, Zn) gradually accumulated in soils and stream sediments. It was concluded that ...

GeoHealth

We studied the dust fractions of the smelting slag, mine tailings, and soil from the former Ni‐Cu... more We studied the dust fractions of the smelting slag, mine tailings, and soil from the former Ni‐Cu mining and processing district in Selebi‐Phikwe (eastern Botswana). Multi‐method chemical and mineralogical investigations were combined with oral bioaccessibility testing of the fine dust fractions (<48 and <10 μm) in a simulated gastric fluid to assess the potential risk of the intake of metal(loid)s contaminants. The total concentrations of the major contaminants varied significantly (Cu: 301–9,600 mg/kg, Ni: 850–7,000 mg/kg, Co: 48–791 mg/kg) but were generally higher in the finer dust fractions. The highest bioaccessible concentrations of Co, Cu, and Ni were found in the slag and mine tailing dusts, where these metals were mostly bound in sulfides (pentlandite, pyrrhotite, chalcopyrite). On the contrary, the soil dusts exhibited substantially lower bioaccessible fractions of these metals due to their binding in less soluble spinel‐group oxides. The results indicate that slag...

Journal of Geochemical Exploration, 2022

Journal of Geochemical Exploration, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Journal of African Earth Sciences, 2021

Applied Geochemistry, 2019

Abstract The historical mining and processing of Zn–Pb–V ores at Berg Aukas in northern Namibia l... more Abstract The historical mining and processing of Zn–Pb–V ores at Berg Aukas in northern Namibia left large amounts of various wastes. This study focuses on the mineralogical and geochemical investigation of the V-rich slags issued from the processing of the local ores in the Waelz kiln, which was operational between 1968 and 1980 and left ca. 500 kt of slag deposited on the adjacent dump. A combination of mineralogical methods, bulk chemistry, leaching tests and speciation-solubility modeling was used to understand the binding of the major contaminants (Zn, Pb, V) in the solid phase and their potential release under the changing environmental conditions. The average concentrations of the metal(loid) contaminants in the slags are 3.78 wt% Zn, 3370 mg/kg Pb, 5880 mg/kg V, 767 mg/kg Cu, 578 mg/kg As and 92 mg/kg Sb. The mineralogy is dominated by high-temperature silicates (clinopyroxene, melilite, olivine-family phases) and Zn-bearing phases (willemite, zincite). All the primary silicates and oxides are Zn-rich, but vanadium is mainly concentrated in clinopyroxene (up to 5 wt% V2O3). Metallic Fe inclusions, formed under highly reducing conditions in the kiln, are highly weathered. Secondary Fe(III) (hydr)oxides, corresponding to the main weathering products in the slag, efficiently sequester the metal(loid)s (mainly As and Sb). The EU regulatory leaching tests indicated that the release of the metal(loid) contaminants is quite low at the natural pH (deionized water extract: 8.5–10.4) obtained by extraction in the deionized water and only Sb in all the slag samples exceeds the EU limits for the landfilling of inert waste. The pH-static leaching tests revealed up to 5 orders of magnitude higher release of Pb and Zn under acidic conditions (up to 38% and 63% of their total concentration, respectively), compared to the natural pH. In contrast, V exhibits relatively flat pH-dependent leaching patterns with only

Journal of Geochemical Exploration, 2018

Environmental Monitoring and Assessment, 2018

Acid mine drainage from mine tailings at Selebi Phikwe, eastern Botswana, has been investigated u... more Acid mine drainage from mine tailings at Selebi Phikwe, eastern Botswana, has been investigated using a combination of total decomposition, sequential extraction, X-ray diffraction, Mössbauer spectroscopy, and SEM analyses of solid phase samples, water analyses, isotopic analyses, and geochemical modeling. The principal ferric phases in the seepage stream sediments are jarosite and goethite, which incorporate Ni and Cu. The Mössbauer spectroscopy (MS) indicated exclusively 3+ oxidation state of iron with typical features of ferric hydroxides/sulfates. A fraction of dissolved sulfate is also sequestered in gypsum which precipitates further downstream. Significant portions of Fe, Ni, and Cu are transported in suspension. Values of pH decreased downstream due to H + generated by the precipitation of jarosite. Values of δ 2 H and δ 18 O indicate

Chemical Geology, 2019

The dynamics of Cu and Pb were studied in eight soil profiles (Luvisols, Chernozems), located at ... more The dynamics of Cu and Pb were studied in eight soil profiles (Luvisols, Chernozems), located at various distances from the tailing dams near a closed Cu-Pb-(Zn)-Ag mine at Kombat (Namibia) by a combination of isotope and elemental studies, leaching techniques and speciation modelling. Tailings, soils and bedrocks were analysed for the bulk Cu and Pb concentrations, for their chemical forms using the sequential extraction procedure and for the isotope compositions of Cu (δ 65 Cu) and Pb (206 Pb/ 207 Pb, 208 Pb/ 206 Pb). In spite of the differences in the contamination of the studied profiles by tailing dust, both soil types exhibit characteristic trends in the behaviour of metals and distribution of their isotopes. While most Luvisols exhibit an increase in the metal content towards depth in the profile, Chernozems exhibit the opposite trend (decrease in metal content with depth) or similar contents in the whole profile. Luvisols were mostly characterized by changing δ 65 Cu values as a function of depth. The value of δ 65 Cu decreases with depth to the Bt horizon and then the δ 65 Cu value increases with increasing depth. Chernozems mostly yielded uniform Cu concentrations and isotope compositions in all the soil horizons, clearly contrasting with the isotopically lighter compositions of the carbonate bedrocks. Positive δ 65 Cu values in the tailing material affect the surface of the soil, especially soil sampled in its vicinity. In most Luvisols and Chernozems, the isotope composition of Pb exhibits similar patterns with a low 206 Pb/ 207 Pb ratio on the surface of the profile and with a slight increase to depth. The low 206 Pb/ 207 Pb values at the surface of the profiles are caused by dust from the tailings. The elemental and isotopic patterns of both contaminated and uncontaminated soil types reflect not only the distance from the tailing dam but also pedogenetic processes in the profiles and geochemical behaviour of both contaminants. The copper elemental and isotope patterns reflect the formation of more mobile species in the surface environment and movement of solutions and colloids and precipitation onto secondary minerals in Luvisols.

Environment International, 2019

Ore mining and processing in semi-arid areas is responsible for the generation of metal(loid)-con... more Ore mining and processing in semi-arid areas is responsible for the generation of metal(loid)-containing dust, which is easily transported by wind to the surrounding environment. To assess the human exposure to dustderived metal(loid)s (As, Cd, Cu, Pb, Sb, Zn), as well as the potential risks related to incidental dust ingestion, we studied mine tailing dust (n = 8), slag dust (n = 5) and smelter dust (n = 4) from old mining and smelting sites in northern Namibia (Kombat, Berg Aukas, Tsumeb). In vitro bioaccessibility testing using extraction in simulated gastric fluid (SGF) was combined with determination of grain-size distributions, chemical and mineralogical characterizations and leaching tests conducted on original dust samples and separated PM 10 fractions. The bulk and bioaccessible concentrations of the metal(loid)s were ranked as follows: mine tailing dusts < slag dusts ≪ smelter dusts. Extremely high As and Pb bioaccessibilities in the smelter dusts were caused by the presence of highly soluble phases such as arsenolite (As 2 O 3) and various metal-arsenates unstable under the acidic conditions of SGF. The exposure estimates calculated for an adult person of 70 kg at a dust ingestion rate of 50 mg/day indicated that As, Pb (and also Cd to a lesser extent) grossly exceeded tolerable daily intake limits for these contaminants in the case of slag and smelter dusts. The high risk for smelter dusts has been acknowledged, and the safety measures currently adopted by the smelter operator in Tsumeb are necessary to reduce the staff's exposure to contaminated dust. The exposure risk for the local population is only important at the unfenced disposal sites at Berg Aukas, where the PM 10 exhibited high levels of bioaccessible Pb. especially high in arid or semi-arid areas, where the total respirable aerosols (PM 10 ; i.e., particulate matter of grain sizes equal to 10 μm or less) significantly exceed permissible levels as defined by environmental agencies and health organizations (US EPA, WHO) (Ghorbel et al., 2010; Csavina et al., 2012; Thomas et al., 2018). For example, Ojelede et al. (2012) reported that the PM 10 concentration was > 2000 μg/m 3 at higher wind speeds in the vicinity of a mine tailing site in South Africa; this value far exceeds the 24-h limit value of 150 μg/m 3 stipulated by US EPA. Apart from the consumption of contaminated water and food, the incidental ingestion and/or inhalation of dust and soil particles

Chemical Geology, 2018

The Tsumeb mining District (Namibia) is affected by prolonged exposure to multisource contaminati... more The Tsumeb mining District (Namibia) is affected by prolonged exposure to multisource contamination related to the mining and smelting of copper ores. This study was performed to assess the extent of contamination of topsoil and grass shoots on the basis of the copper isotopic composition. Compared to an uncontaminated area (δ 65 Cu soil =-0.01 to +0.14 ‰; δ 65 Cu grass =-0.17 to +0.03 ‰), the soil and grass in the contaminated area are enriched in the heavy isotope (δ 65 Cu soil = +0.13 to +0.76 ‰ and δ 65 Cu grass = +0.15 to +0.64 ‰). The Δ 65 Cu grass-soil value exhibits small variations (+0.06 to-0.17) due to the variable degree of grass surface contamination, depending on the grass washing procedure used. The enrichment of soil and grass in the contaminated area in 65 Cu reflects the Cu isotopic composition of old flotation tailings (δ 65 Cu =+0.95 to +1.1 ‰), slag (+0.11 to +0.55 ‰) and particles which originate from the smelting and flue gas cleaning processes (+0.15 to +0.49 ‰). The long history of mining and processing of copper ores in the Tsumeb area and the different isotopic composition of ore concentrates smelted in the local metallurgical plant do not allow assessment of whether the smelting process leads to isotope fractionation of copper. However, the isotopic composition of Cu in the sulfidic feed, slag and dust particles sampled over several hours showed that the dust collected from the dusthouse of the local smelter is isotopically lighter (δ 65 Cu = + 0.15 ‰) relative to the isotopic composition of the charge (δ 65 Cu = +0.28 and +0.44 ‰). The results of this investigation demonstrate that the isotopic composition of Cu in soils and grasses can be used to assess the intensity of contamination in areas where Cu ores are mined and processed provided that the isotopic compositions of the ore processing products are different from the isotopic compositions of the uncontaminated soils and vegetation.

Environmental pollution (Barking, Essex : 1987), 2018

We studied arid desert soils from Namibia (Rosh Pinah) that were contaminated with up to 7 mg kg ... more We studied arid desert soils from Namibia (Rosh Pinah) that were contaminated with up to 7 mg kg of thallium (Tl) via dust emitted from a local flotation tailing dam. Chemical extractions of waste and soil materials indicated that most of the Tl is strongly bound, in accordance with X-ray diffraction and X-ray absorption spectroscopy data that point to the predominant association of Tl with metal sulfides and phyllosilicates. The isotope fractionation factor εTl of the soil samples (from -0.4 to +3.8) shows a positive linear relationship (R = 0.62) with 1/Tl, indicative for the mixing of two major Tl pools, presumably anthropogenic Tl and geogenic Tl. The εTl value for the topmost soil samples (∼+3) closely matches the εTl value for post-flotation waste particles with a diameter of <0.05 mm, whereas the bulk flotation waste exhibits a significantly larger εTl value (∼+6). These variations are in accordance with predominant atmospheric transfer of Tl from the tailings to the adjac...

The Science of the total environment, Jan 15, 2018

The copper (Cu) content and isotopic composition were studied in soils and in pine tree rings at ... more The copper (Cu) content and isotopic composition were studied in soils and in pine tree rings at locations close to and far from the Cu smelter, located at Kitwe, Zambia. The soil in the remote area contained 25-75mgkg Cu, whereas the soil close to the smelter contained 207-44,000mgkg Cu. The δCu at the remote area and close to the smelter varied in the range -0.40 to -0.11‰, and -0.44 to 0.01‰ respectively. The δCu of the surface soil at both profiles (-0.44 to -0.40‰) is similar to the isotopic composition of the concentrates processed in the smelter (-0.75 to -0.45‰), i.e. both locations are affected by Cu ore dust. The increase in the δCu in the direction towards the centre of the profile is caused by the oxidative dissolution of Cu(I) from ore minerals, during which heavier Cu is released. In deeper parts of the profile, there is a slight decrease in δCu because of easier mobilisation of the lighter isotope. The tree rings at the two locations differ in the total contents and i...

Journal of Geochemical Exploration, 2015

A survey of groundwater from six geothermal springs in Namibia showed high concentrations of diss... more A survey of groundwater from six geothermal springs in Namibia showed high concentrations of dissolved fluoride, with values up to 18.9 mg/l. All values are higher than both the WHO limit and the Namibian guideline. High concentrations of fluoride are linked to Na-HCO 3 or Na-SO 4-HCO 3 groundwater types, with increasing sulfate and chloride concentrations towards the south of Namibia. Values of δ 2 H and δ 18 O are more negative for the north of the country, and with increasing altitude of springs and distance from precipitation sources towards the southeast from the Indian Ocean. A shift of about 1‰ from the LMWL for Windhoek was observed for δ 18 O samples, which was probably caused by the exchange with reservoir rocks. Values of δ 34 S(SO 4) reflect mixing of two principal sulfate sources, i.e., dissolution of gypsum originating from playas and interaction with sulfidic mineralization in tectonic bedrock zones. Values of δ 13 C(DIC) seem to be affected by a variable vegetation cover and mainly by the input of endogenous CO 2. Estimated reservoir temperatures vary from 60°C to 126°C, with a maximum value at the Ganigobes site. The geothermal springs of Namibia in this study do not meet drinking water standards and thus their water can be used only for other purposes e.g. for thermal spas. Treatment would be necessary to decrease dissolved fluorine concentrations for drinking water purposes.

Geoderma, 2017

We studied Fe-Mn concentric nodules from Cutanic Luvisol in the northern part of Namibia, where a... more We studied Fe-Mn concentric nodules from Cutanic Luvisol in the northern part of Namibia, where agricultural fields are irrigated with the drainage water from the Kombat Cu-Pb-(Zn) mine (pH 7, metal concentrations in μg l −1 : Fe 7, Mn 10, Zn 7, Cu 18). Concentric nodules (0.5-2 cm in size) were mostly found towards the bottom of the sampled soil profile (Btcg2 horizon, depth 100-120 cm). Comparisons with the bulk chemical composition of the soil matrix showed that Fe-Mn nodules were enriched in metals, metalloids and other trace elements (with a few exceptions, enrichment factors varied in the range 1.3-6.4). The concentrations of the elements of interest in the Fe-Mn nodules were as follows (mg kg −1): As 23.1, Ba 3840, Cd 6.83, Cu 450, Pb 597, Zn 137. The X-ray diffraction analysis indicated that the nodules were composed of quartz, goethite, hematite, illite/mica, pyrochroite, lithiophorite and birnessite. The scanning electron microscopy (SEM) observations confirmed that the internal structure of the nodules with concentric rings reflected seasonal changes in the redox conditions. Spot analyses and X-ray elemental maps performed using energy/wavelength dispersion spectrometry (EDS/ WDS) showed that the concentrations of metalloids were rather low except for the slightly elevated Ba concentrations, which were observed only within the Mn oxide-rich zones. Selective extractions were used to understand the partitioning of trace elements within the individual phases. Whereas Mn oxides sequestered the majority of the Cd (up to 98%), Ba, Pb and rare earth elements (REEs) (up to 78%), other metals such as Cu and Zn exhibited much lower values (47-65%) and, together with oxyanionic species (As, Cr, V), were also significantly bound to Fe oxides. The pH-static leaching test conducted in the pH range 2-12 indicated that the majority of the trace elements were mostly leached under acidic conditions with the exception of As, which was highly solubilized at pH 12 (up to 17%). Whereas Ba, Cd, Cu and Zn were significantly released under acidic conditions (up to 12%), the leaching of Pb was almost negligible over the entire pH range. Our results show that Fe-Mn nodules act as significant traps for trace metals in Luvisols irrigated by mine water. However, an abrupt decrease in the pH and changes in the redox conditions may cause the dissolution of Fe-Mn nodules and subsequent release of contaminants into the soil system.

Science of The Total Environment, 2016

Mining-and smelter-derived particles identified in subtropical and semi-arid soils • Sulphides, o... more Mining-and smelter-derived particles identified in subtropical and semi-arid soils • Sulphides, oxides, and metal-bearing arsenates most frequently encountered • Soluble sulphates and arsenolite from primary smelter dusts not detected in soils • Higher metal availability and greater weathering of particles in subtropical soils • Complex Ca-Cu-Pb arsenates efficiently control mobility of metal(loids).

Applied Geochemistry, 2016

The area of the city of Tsumeb in northern Namibia is strongly affected by gaseous emissions and ... more The area of the city of Tsumeb in northern Namibia is strongly affected by gaseous emissions and by dust fallout from the local smelter. This is also reflected in increased concentrations of lead and arsenic in blood and urine of the residents. Consequently, modeling of the dispersion of dust and SO 2 emissions from the smelter was used in this study to delineate the contaminated area and to assess the health risks. The modeling results were verified by ground-based geochemical survey of soil and grass in the area. The results of modeling revealed that the concentrations of SO 2 in the Tsumeb town were relatively low, whereas the highest dust fallout concentrations were found around the Tsumeb smelter. The Tsumeb town residential area was less affected due to favorable landscape morphology between the smelter and the city (the Tsumeb Hills). The results of modeling of dust fallout and geochemical survey coincided very well. Since the anthropogenic contamination was bound only to the surface layer of soil, the local soils were sampled at two depth horizons: topsoil and the deeper soil horizon. This enabled us to distinguish between the anthropogenic contamination of soil surface from natural (geogenic) concentrations of studied metals in the deeper part of the soil profile. Concentrations of metals in grass correlated with the concentration of metals in topsoil. In contrast to a good conformity with the modeling of dust fallout from the smelter and geochemical survey, the results of modeling of SO 2 contents in the air, and total sulfur content in soils were different. Differences can be explained by additional sources of contamination, as for example a sulfate-rich dust fallout from local tailings ponds and slag dumps that were not considered in the SO 2 dispersion model. The results of the present investigation can be used by the mining companies in the management of air quality, assessment of the efficacy of applied remediation measures, and in reducing the impact of dust fallout on the local ecosystem. The Municipal Administration may use these results to plan further development of the city of Tsumeb, especially in terms of further expansion of housing construction.