Cobalt is one of the most important critical metals which could be potentially extracted from the old metallurgical slags in the Zambian Copperbelt. The slags from Luanshya, the oldest mining and smelting site in the Copperbelt, contain up to 5990 ppm Co (median: 2370 ppm). The detailed mineralogical investigation combined with the sulfuric acid leaching simulating hydrometallurgical recovery indicated that up to 67% of Co can be extracted from slag in a short period of time (24 h). However, despite the dramatic increase of Co prices on the global market, its recovery from the Luanshya slags appears to be non-economical due to the high costs of the mechanical and chemical processing of the slag materials. The paper is freely available via open access:
Ettler V., Mihaljevič M., Drahota P., Kříbek B., Nyambe I., Vaněk A., Penížek V., Sracek O., Natherová V. (2022): Cobalt-bearing copper slags from Luanshya (Zambian Copperbelt): Mineralogy, geochemistry, and potential recovery of critical metals. Journal of Geochemical Exploration 237, 106987. (DOI)
We used an in situ experimental technique with double nylon experimental bags to study the effect of low-cost organic materials (sawdust, wood cubes and hemp shives) on As sulfidation in three naturally As-enriched wetland soils. After 15 months of in situ incubation, all of the organic materials were covered by yellow-black mineral accumulations, dominantly composed of crystalline As4S4 polymorphs (realgar and bonazziite) and reactive Fe(II) sulfides (probably mackinawite). Our findings suggest an authigenic formation of AsS minerals in strongly reducing conditions of experimental bags by a combination of reduced exchange of solutes through the pores of the bag and comparatively fast microbial production of dissolved sulfide. Arsenic sulfide formation, as an effective treatment mechanism for natural and human-constructed wetlands, appears to be favored for As(III)-rich waters with a low Fe(II)/As(III) molar ratio, preventing the consumption of dissolved As and sulfide by their preferential incorporation into natural organic matter, and newly-formed Fe(II) sulfides, respectively.
Peřestá, M., Drahota, P., Culka, A., Matoušek, T., Mihaljevič, M. (2022): Impact of organic matter on As sulfidation in wetlands: An in situ experiment. Science of the Total Environment 819, 152008. (DOI)
We compared analogous healthy topsoils and ones burned by fires of different temperatures for their elemental and isotopic Pb content. The fires only affected the top 5 cm of the soil. We found that soils affected by low-temperature fires had increased Pb compared to healthy soils. The accumulation of Pb was not observed in the soils exposed to higher temperatures. The same results were found in ash. Lead isotopic ratios were affected by the fires. These increased in soils affected by higher temperatures but didn’t change with the low temperatures. We proposed that the temperature dependence is due to anthropogenic Pb (206Pb/207Pb < 1.16) volatilizing at lower temperatures than geogenic Pb (206Pb/207Pb > 1.19). This work suggests that it may be possible to determine the temperature of a forest fire from the Pb isotopic signatures of the burned materials.
Baieta R., Vieira A.M.D, Vaňková M., Mihaljevič M. (2022): Effects of forest fires on soil lead elemental contents and isotopic ratios. Geoderma 414, 115760. (DOI)
On Thursday 30th September 2021, Marek Tuhý successfully defended his PhD thesis entitled “Wildfires in polluted areas: mineralogical transformations and remobilization of metal(loid)s“. The thesis was supervised by prof. Vojtěch Ettler and reviewed by Dr. Isabel Campos (University of Aveiro, Portugal) and Dr. Tomáš Navrátil (Institute of Geology, CAS). Congratulations!
A new book entitled Metallurgical Slags: Environmental Geochemistry and Resource Potential edited by Nadine M. Piatak (USGS) and Vojtěch Ettler has been published by the prestigious publishing house, the Royal Society of Chemistry (link). Vojtech Ettler (co-) authored four of nine chapters in the book: Introduction: Metallurgical Slags – Environmental Liability or Valuable Resource? (DOI), Geochemistry and Mineralogy of Slags (DOI), Slag Leaching Properties and Release of Contaminants (DOI), and Environmental Impact of Slag Particulates (DOI).
The temperature-dependent releases of metal(loid)s (As, Cd, Cu, Pb, Zn) from biomass-rich savanna soils collected near a Cu smelter in Namibia have been studied under simulated wildfire conditions. For this purpose, new wildfire-simulating setups were introduced. Laboratory single-step combustion experiments (250–850 °C) and experiments with a continuous temperature increase and online ICP-OES detection (25–750 °C) were coupled with mineralogical investigations of the soils, ashes, and aerosols. The results indicate that metals are dominantly concentrating in the ash residue, and part of As is remobilized depending on temperature. Therefore, the active and abandoned mining and smelting sites, especially those highly enriched in As, should be protected against wildfires, which can be responsible for substantial As re-emissions.
Tuhý M., Ettler V., Rohovec J., Matoušková Š., Mihaljevič M., Kříbek B., Mapani B. (2021): Metal(loid)s remobilization and mineralogical transformations in smelter-polluted savanna soils under simulated wildfire conditions. Journal of Environmental Management 293, 112899. (DOI)
The paper presents a geochemical analysis of a remarkable assemblage from the early La Tène period (4th century BCE): the Duchcov hoard found in the late 19th century in north-western Bohemia. More than a thousand pieces of bronze jewellery in a bronze cauldron were deposited in a natural spring. This possibly ritual offering of unknown purpose might have involved a large community whose origin and structure could be discussed using archaeometric data from the hoard. This assemblage offers a unique opportunity to study Iron Age bronze metalworking. The results show that this seemingly homogeneous assemblage contains several chemically distinctive groups that are compatible with the spread of the so-called Duchcov-Münsingen horizon in the 4th century BCE.
Danielisová A., Pajdla P., Bursák D., Strnad L., Trubač J., Kmošek J. (2021): Claiming the land or protecting the goods? The Duchcov hoard in Bohemia as a proxy for ‘Celtic migrations’ in Europe in the 4th century BCE. Journal of Archaeological Science 127, 105314. (DOI)
We used pine tree rings and soil geochemistry to expose the activity of a Pb-Zn smelter in Kabwe, Zambia. We found that local soils are extremely contaminated (up to 16000 mg/kg Pb; 14000 mg/kg Zn; 600 mg/kg Cu in the topsoil). Also, metal bearing particles share their Pb isotopic signature with smelting by-products, and more concerning, metals in tree biomass. We concluded that these metals enter the tree though the bark and leaves, not the roots, implying airborne contamination. Using Pb and C isotopes we mapped the dendrochronology of the tree and verified its susceptibility to changes in smelter production throughout the late 20th century.
Baieta R., Mihaljevič M., Ettler V., Vaněk A., Penížek V., Trubač J., Kříbek B., Ježek J., Svoboda M., Sracek O., Nyambe I. (2021): Depicting the historical pollution in a Pb–Zn mining/smelting site in Kabwe (Zambia) using tree rings. Journal of African Earth Sciences 181, 104246. (DOI)
Arsenic-rich stalactites (0.13-294 g/kg As) collected from abandoned adits of the Plavno and Mikulov mines (NW Czech Republic) consist of HFA, HFO, kaňkite, schwertmannite, and hydrous manganese oxide mineral phases. These phases were often combined in one stalactite, forming domains, layers and coprecipitates. The microbial communities indicated autotrophic oxidation of Fe(II), As(III), and reduced sulphur compounds as the most notable biological processes influencing the mineralogy in studied stalactites.
Jelenová H., Drahota P., Falteisek P., Culka A. (2021): Arsenic-rich stalactites from abandoned mines: Mineralogy and biogeochemistry. Applied Geochemistry 129, 104960. (DOI)
Vojtěch Ettler will give a plenary lecture entitled “The leaching behavior of smelting slags: from contaminants to critical metals” on the 7th International Slag Valorization Symposium (SVS7). The conference, originally planned to take place in Leuven, Belgium, will finally run in a virtual mode. SVS7 is a major event on characterization and applications of metallurgical slags and will bring together people from R&D sector and industry.