Ondřej Šebek

Primary and secondary phases in copper-cobalt smelting slags from the Copperbelt Province, Zambia

Abstract Pyrometallurgical slags from three Cu-Co smelters (Nkana, Mufulira, Chambishi) in the Copperbelt Province, Zambia, were studied from mineralogical and chemical points of view. The slags were enriched in metals and metalloids, mainly Cu (up to 35 wt.%), Co (up to 2.4 wt.%) and As (up to 3650 ppm). The following primary phases were observed in slags: Ca-Fe silicates (clinopyroxene, olivine) and leucite, oxides (spinel-series phases), ubiquitous silicate glass and sulphide/metallic droplets of various sizes. The presence of glass and skeletal/dendritic crystal shapes indicated rapid cooling of the slag melt. Copper and cobalt were found in low concentrations in the majority of silicates (olivine, clinopyroxene) and oxides, substituting for Fe in their structures (up to 7.15 wt.% CoO in olivine, 4.11 wt.% CuO in spinel). Similarly, up to 0.91 wt.% CoO and 6.90 wt.% CuO were observed in the interstitial glass. Nevertheless, the main carriers of these metals in the slags studied were Cu sulphides (digenite, chalcocite, bornite, chalcopyrite), Co-Fe sulphides (cobaltpentlandite), Co-bearing intermetallic phases ((Fe,Co)2As) and alloys. Weathering features corresponding to the presence of secondary metal-bearing phases, such as malachite (Cu2(CO3)(OH)2), brochantite (Cu4SO4(OH)6) and sphaerocobaltite (CoCO3), were observed on the slag surfaces. They indicate that the slags studied are reactive on contact with water/atmosphere and that their environmental stability and release of potentially harmful metals and metalloids must be evaluated further.

The pH-dependent leaching of inorganic contaminants from secondary lead smelter fly ash

The leaching behaviour of fly ash (FA) from a secondary Pb smelter was assessed using the pH-static leaching experiment according to prEN 14997 (pH range 3-11) coupled with mineralogical investigation of the leached FA by XRD and Rietveld analyses and thermodynamic modelling using PHREEQC-2. The procedure was performed on fresh FA and FA washed at a cumulative L/S ratio of 60l/kg to remove readily soluble salts. For both fresh and washed FA, high amounts of inorganic contaminants were released under acidic conditions, exhibiting L-shaped leaching patterns: up to 300g Pb/kg, 4.5g Cd/kg, 4g Zn/kg, 1.05g As/kg and 70mg Sb/kg. The washing of soluble salts significantly decreased the leachability of Cd, Zn, As and Sb and increased the release of Pb, especially under acidic conditions. The leaching of fresh FA removed part of primary caracolite and all the KPb(2)Cl(5) and NaCl. The Pb release was controlled by the precipitation of anglesite and PbSO(3) under acidic conditions and of laurionite and carbonates (hydrocerussite and phosgenite) under alkaline conditions. In contrast, the washed FA was composed mainly of anglesite and PbSO(3), both phases being the main solubility-controlling phases for Pb over the whole studied pH range.

Cadmium, lead and zinc leaching from smelter fly ash in simple organic acids—Simulators of rhizospheric soil solutions

Emissions from base-metal smelters are responsible for high contamination of the surrounding soils. Fly ash from a secondary Pb smelter was submitted to a batch leaching procedure (0.5-168 h) in 500 microM solutions of acetic, citric, or oxalic acids to simulate the release of toxic metals (Cd, Pb, Zn) in rhizosphere-like environments. Organic acids increased dissolution of fly ash by a factor of 1.3. Cadmium and Pb formed mobile chloro- and sulphate-complexes, whereas Zn partly present in a citrate (Zn-citrate(-)) complex is expected to be less mobile due to sorption onto the positively charged surfaces of hydrous ferric oxides (HFO) and organic matter (OM) in acidic soil.

Thallium uptake by white mustard (Sinapis alba L.) grown on moderately contaminated soils—Agro-environmental implications

The work focused on Tl uptake by white mustard (Sinapis alba L.) grown on moderately contaminated soils with different characteristics. The data presented here clearly demonstrate the ability of white mustard to (hyper)accumulate Tl. Substantially higher Tl levels were was found in mustard grown on the Arenosol as compared to the carbonate-rich Leptosol; a relationship between the content of labile Tl (adsorbed, bound to carbonates etc.) in soil and its uptake by the plant is suggested. Approximately 3-fold lower concentrations of Tl in roots and stems of the mature mustard (compared to the young plant) indicate a decreasing trend of Tl uptake with the age of the plant. The exchangeable/acid-extractable and reducible Tl fractions were evaluated as the dominant fractions controlling Tl transfer from both contrasting soils. Thallium associated with the residual fraction (e.g., incorporated into silicates) was rather stable in the rhizosphere, proving a negligible influence of root exudates on Tl release from such an operationally defined fraction, despite the anthropogenic origin of Tl. Regarding our results, when mustard is cultivated for nutrition purposes and/or as green manure, it may pose an important source of Tl introduction into the food chain.

Effect of illite and birnessite on thallium retention and bioavailability in contaminated soils.

The influence of illite and birnessite (δ-MnO(2)) amendments on the retention and bioavailability of Tl in contaminated soils was investigated. The efficiency of both phases was evaluated using Tl uptake by white mustard (Sinapis alba L.), sequential extraction and sorption experiments. The obtained data demonstrate that the application of birnessite can effectively transform Tl from the labile (easily mobilizable) fraction to its reducible form, thus lowering Tl bioavailability in soil and subsequent accumulation by plants. The Mn oxide added to the soils reduced substantially Tl uptake; Tl levels in the plants decreased by up to 50%, compared to the non-amended soil. The effect of illite on the immobilization and uptake of Tl was less pronounced, and in the carbonate-rich Leptosol has not been proved at all, suggesting the importance of bulk soil mineralogy and nature of the soil sorption complex on the behavior of this amendment. Therefore, the general applicability of illite for Tl stabilization in soils seems to be limited and strongly dependent on soil composition. In contrast, the use of birnessite like soil additive might be an efficient and environment-friendly solution for soil systems contaminated with Tl.

Combined Chemical and Mineralogical Evidence for Heavy Metal Binding in Mining-and Smelting-Affected Alluvial Soils

The binding of metallic contaminants (Pb, Cd, and Zn) and As on soil constituents was studied on four highly contaminated alluvial soil profiles from the mining/smelting district of Přibram (Czech Republic) using a combination of mineralogical and chemical methods. Sequential extraction analysis (SEA) was supplemented by mineralogical investigation of both bulk samples and heavy mineral fractions using X-ray diffraction analysis (XRD) and scanning electron microscopy with an energy dispersive X-ray spectrometer (SEM/EDS). The mineralogy of Fe and Mn oxides was studied by voltammetry of microparticles (VMP) and diffuse reflectance spectrometry (DRS). Zinc and Pb were predominantly bound in the reducible fraction attributed to Fe oxides and Mn oxides (mainly birnessite, Na4Mn14O27•9H2O), which were detected in soils by XRD and SEM/EDS. In contrast, Cd was the most mobile contaminant and was predominantly present in the exchangeable fraction. Arsenic was bound to the residual and reducible fractions (corresponding to Fe oxides or to unidentified Fe-Pb arsenates). SEM/EDS observations indicate the predominant affinity of Pb for Mn oxides, and to a lesser extent, for Fe oxides. Thus, a more suitable SEA procedure should be used for these mining-affected soils to distinguish between the contaminant fraction bound to Mn oxides and Fe oxides.

Surprisingly contrasting metal distribution and fractionation patterns in copper smelter-affected tropical soils in forested and grassland areas (Mufulira, Zambian Copperbelt)

Six soil profiles located near Mufulira (Zambian Copperbelt) were studied to evaluate and compare the extent of environmental pollution of Cu-ore mining and smelting in both forested and grassland areas. The highest metal concentrations were detected in the uppermost soil layers with the following maxima: Co 45.8 mg kg(-1), Cu 8,980 mg kg(-1), Pb 41.6 mg kg(-1), and Zn 97.0 mg kg(-1). Numerous anthropogenic metal-bearing particles were detected in the most polluted soil layers. The spherical smelter-derived particles were mainly composed of covellite (CuS) and chalcocite (Cu2S), while the angular mining-derived particles were mostly composed of chalcopyrite (CuFeS2). Additionally, Fe-Cu oxide particles predominantly corresponding to tenorite (CuO) and delafossite (Cu(1+)Fe(3+)O2), along with hydrated Fe-oxides corresponding to secondary weathering products, were detected. In contrast to smelter-affected soils in temperate climates, where forest soils are significantly more enriched in metals than tilled soils due to high canopy interception, our data indicate a higher proportion of metal-bearing anthropogenic particles and higher metal concentrations in soils from unforested sites. This phenomenon is probably related to the more frequent and intense bushfires in forested areas, leading to the mobilization of pollutants contained in the biomass-rich surface soils back into the atmosphere.

Experimental in situ transformation of Pb smelter fly ash in acidic soils.

Soils in the vicinity of nonferrous metal smelters are often highly polluted by inorganic contaminants released from particulate emissions. We used a technique with double polyamide experimental bags (1-μm mesh) to study the in situ transformation of fly ash (FA) from a secondary Pb smelter in acidic soil profiles. Between 62 and 66% of the FA dissolved after one years exposure in the soils, leading to complete dissolution of primary caracolite (Na(3)Pb(2)(SO(4))(3)Cl) and KPb(2)Cl(5), with formation of secondary anglesite (PbSO(4)), minor PbSO(3), and trace carbonates. Release of Pb was pH-dependent, whereas not for Cd and Zn. Significant amounts of metals (mainly Cd and Zn) partitioned into labile soil fractions. The field data agreed with laboratory pH-static leaching tests performed on FA, which was washed before the experiment to remove soluble salts. This indicates that appropriate laboratory leaching can accurately predict FA behavior in real-life scenarios (e.g., exposure in soil).

Alteration of arsenopyrite in soils under different vegetation covers.

The weathering of arsenopyrite (FeAsS) has been monitored in soils using an in situ experimental approach. Arsenopyrite in nylon experimental bags was placed in individual horizons in soils in spruce (litter, horizons A, B, and C), beech (litter, horizons A, B, and C) and unforested (horizons A, B, and C) areas and left in contact with the soil for a period of 1 year. The individual areas on the ridge of the Krusné hory Mts., Czech Republic, had the same lithology, climatic and environmental conditions. Scorodite (FeAsO(4).2H(2)O) was identified as a principal secondary mineral of arsenic (As) formed directly on the surface of the arsenopyrite. Scorodite was formed in all the areas in all soil horizons. The amount of scorodite formed decreased in the series beech, spruce and unforested areas. In forested areas, there was a larger amount of scorodite on arsenopyrites exposed in organic horizons (litter, A horizon). The greater rate of arsenopyrite alteration in organic horizons in the beech stand compared to spruce stand is probably a result of faster mineralization of organic material with resulting production of nitrate and better seepage conditions of soil in this area. Speciation of As determined using the sequential extraction technique demonstrated that As was bonded in the soils primarily in the residual fractions prior to the experiment. The As content in the mobile fractions increased in the organic horizon in the forested areas after the experiments.

Natural attenuation of arsenic in soils near a highly contaminated historical mine waste dump

Arsenic-contaminated soils near historical As-rich mine waste in Jáchymov (Czech Rep.), resulting from the smelting and seepage of the mine waste pore water, were studied to examine As partitioning between solid phases and pore waters. Mineralogical and geochemical analyses showed that As is exclusively associated with unidentified amorphous Fe oxyhydroxides, poorly crystalline goethite and hematite as adsorbed and coprecipitated species (with up to 3.2 wt.% As). Adsorption of As by Fe oxyhydroxides is likely to be a major control on the migration of As in the soil pore water containing only up to 15 μg L(-1) As(V). The slight variations in the dissolved As(V) concentrations do not follow the total contents of As in the soil or adsorbed As, but appeared to be a function of pH-dependent sorption onto Fe oxyhydroxides. The geochemical modelling using PHREEQC-2 supported the efficiency of As(V) adsorption by Fe oxyhydroxides in the soil affected by As-rich waste solution seepage. It also suggested that active Fe oxyhydroxides has a strong attenuation capacity in soil that could effectively trap the aqueous As(V) from the unremitting waste seepage for the next approx. 11600 years.