On June 17, 2022, Jillian Helser (SIM2 KU Leuven Institute and Early Stage Researcher in the MSCA-ETN SULTAN project) obtained her PhD degree in Science. She successfully defended her PhD thesis entitled “Environmental mobility and oral bioaccessibility of hazardous elements in mine waste and derived products”.
Jillian Helser completed her PhD in the Department of Earth and Environmental Sciences and the Research Center for Economics and Corporate Sustainability under the supervision of Prof. Dr. Valérie Cappuyns. The PhD research was part of the H2020-MSCA-ETN SULTAN project, an EU Training Network targeting the remediation and reprocessing of sulfidic mine waste sites.
The popularized summary of the PhD research along with list of publications are available below; the full text of the thesis will soon be made publicly available.
Sulfidic mine waste can pose environmental and human health risks, especially when it contains high levels of mobile hazardous elements. Under oxidizing conditions, sulfidic mine waste can generate acidity and leach hazardous metal(loid)s into the environment, commonly referred to as acid mine drainage. Proper management and storage of mine waste is one of the main issues that mining industries face. Additionally, there are many historical mining deposits which may, even centuries later, still leach contaminants into the environment.
One solution to minimize the risks associated with the mine waste, with also potential economic benefits, is through the valorization of the waste. This can be done by first recovering valuable metals and removing hazardous contaminants. Then, the remaining residue can be valorized into green construction materials, such as inorganic polymers, ceramics or cement. For some mine waste materials, such as those with only trace levels of metals that are not economically viable to extract, the “waste” can be reused directly without this additional recovery/cleaning step.
This PhD thesis was based on three case studies of sulfidic mines in Europe: an active copper-zinc mine in Neves-Corvo, Portugal, a historical lead-zinc mine in Plombières, Belgium, and a historical copper-lead-zinc mine in Freiberg, Germany. The solid-phase speciation and leaching of hazardous elements under different conditions were investigated in the mine waste itself and in the construction materials in which the mine waste was incorporated. This allowed for the assessment of how leaching changes during the processing and valorization of the mine waste materials. These results were used to evaluate the environmental and health risks posed by the sulfidic mine waste and the derived products.
Results indicated that most of the mine waste materials from Neves-Corvo, Plombières and Freiberg contained highly elevated levels of arsenic, cadmium, copper, lead, and zinc. The leaching tests revealed high mobility of metal(loid)s, especially lead, posing potential environmental risks. The high release of lead is mainly controlled by the dissolution of cerussite (PbCO3) in the Plombières mine waste samples, even under natural pH conditions. Geochemical modeling revealed that, besides dissolution of cerussite, sorption/desorption of lead to other minerals and precipitation could explain some differences of metal(loid) release between the modeling and laboratory experimental results. Additionally, the human health risk assessment indicated carcinogenic and non-carcinogenic risks for most investigated samples in a worst-case exposure scenario.
The Neves-Corvo and Freiberg mine waste samples exhibited a high acid generation potential during a long-term resuspension experiment, where the pH of all samples decreased to <3. The resuspension of the mine waste also resulted in a considerable release of hazardous elements. However, lead exhibited low leaching levels, due to the formation of secondary lead-bearing minerals. Additionally, pyrite was still present in the residues even after 821 days of oxidation.
The studied mine wastes pose environmental and health risks, both short and long term, due to the high mobility and bioaccessibility of metal(loid)s and high acid generation potentials. Nevertheless, the high mobility of some elements also provides opportunities for the valorization of the waste.
The immobilization of metal(loid)s after the incorporation of mine waste in AAMs, ceramics, and cement was evaluated with different leaching tests, showing that some construction materials were more efficient than others in immobilizing metal(loid)s. For example, cements/clinkers effectively immobilized metal(loid)s in most cases, due to physical and/or chemical encapsulation. Overall, AAMs generally showed a decrease in metal(loid) mobility compared to the original mine waste; although, high concentrations of arsenic leaching were observed. Ceramics were found to be more suitable for mine wastes with low concentrations of metal(loid)s and sulfur. Longer curing times of the AAMs, in most cases, improved the immobilization of metal(loid)s. Additionally, for ceramics, the temperature at which the test pieces were fired also played a major role in decreasing the mobility of some metal(loid)s, while increasing others.
Overall, through this detailed characterization, the environmental impacts from the mine waste to the downstream products were evaluated, determining which remediation/valorization methods are the most viable to close the circular economy loop.
List of peer-reviewed publications in scientific journals
1. Z. Mohammadi, H. Claes, V. Cappuyns, M.J. Nematollahi, J. Helser, K. Amjadian, R. Swennen, High geogenic arsenic concentrations in travertines and their spring waters: Assessment of the leachabiilty of estimation of ecological and health risks, Journal of Hazardous Materials (2020) https://doi.org/10.1016/j.jhazmat.2020.124429
2. J. Helser, V. Cappuyns, Trace elements leaching from Pb-Zn mine waste (Plombières, Belgium) and environmental implications. Journal of Geochemical Exploration 220, 106659 (2021) https://doi.org/10.1016/j.gexplo.2020.106659
3. V. Cappuyns, A. Van Campen, J. Helser, Antimony leaching from soils and mine waste from the Mau Due antimony mine, North-Vietnam, Journal of Geochemical Exploration (2021) https://doi.org/10.1016/j.gexplo.2020.106663
4. V. Cappuyns, A. Van Campen, S. Bevandić, J. Helser, P. Muchez, Characterization of mine waste from a former Pb-Zn mining site: reactivity of minerals during sequential extractions, Journal of Sustainable Metallurgy (2021) https://doi.org/10.1007/s40831-021-00455-y
5. J. Helser, E. Vassilieva, V. Cappuyns, Environmental and human health risk assessment of sulfidic mine waste: bioaccessibility, leaching and mineralogy, Journal of Hazardous Materials, 424, 127313 (2022) https://doi.org/10.1016/j.jhazmat.2021.127313
6. J. Helser, V. Cappuyns, Acid generation potential and kinetics of metal(loid) release from resuspended sulfidic mine waste, Journal of Environmental Chemical Engineering, 10, 108158 (2022) https://doi.org/10.1016/j.jece.2022.108158
7. J. Helser, P. Perumal, V. Cappuyns, Valorizing (cleaned) sulfidic mine waste as a resource for construction materials, Journal of Environmental Management, 319, 115742 (2022) https://doi.org/10.1016/j.jenvman.2022.115742
8. H. Niu, J. Helser, I.J. Corfe, J. Kuva, A.R. Butcher, V. Cappuyns, P. Kinnunen, M. Illikainen, Incorporation of bioleached sulfidic mine tailings in one-part alkali-activated blast furnace slag mortar, Construction and Building Materials (2022) https://doi.org/10.1016/j.conbuildmat.2022.127195