Lenz, Markus
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Lenz, Markus
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- PublikationRedox-stat bioreactors for elucidating mobilisation mechanisms of trace elements: An example of As-contaminated mining soils(Springer, 2018) Rajpert, Liwia; Schäffer, Andreas; Lenz, Markus [in: Applied Microbiology and Biotechnology]The environmental fate of major (e.g. C, N, S, Fe and Mn) and trace (e.g. As, Cr, Sb, Se and U) elements is governed by microbially catalysed reduction-oxidation (redox) reactions. Mesocosms are routinely used to elucidate trace metal fate on the basis of correlations between biogeochemical proxies such as dissolved element concentrations, trace element speciation and dissolved organic matter. However, several redox processes may proceed simultaneously in natural soils and sediments (particularly, reductive Mn and Fe dissolution and metal/metalloid reduction), having a contrasting effect on element mobility. Here, a novel redox-stat (Rcont) bioreactor allowed precise control of the redox potential (159 ± 11 mV, ~ 2 months), suppressing redox reactions thermodynamically favoured at lower redox potential (i.e. reductive mobilisation of Fe and As). For a historically contaminated mining soil, As release could be attributed to desorption of arsenite [As(III)] and Mn reductive dissolution. By contrast, the control bioreactor (Rnat, with naturally developing redox potential) showed almost double As release (337 vs. 181 μg g−1) due to reductive dissolution of Fe (1363 μg g−1 Fe2+ released; no Fe2+ detected in Rcont) and microbial arsenate [As(V)] reduction (189 μg g−1 released vs. 46 μg g−1 As(III) in Rcont). A redox-stat bioreactor thus represents a versatile tool to study processes underlying mobilisation and sequestration of other trace elements as well.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationRe-using bauxite residues: benefits beyond (critical raw) material recovery(Wiley, 2018) Ujaczki, Eva; Feigl, Victoria; Molnar, Monika; Cusack, Patricia; Curtin, Teresa; Courtney, Ronan; Ronan, Lisa; Davris, Panagiotis; Hugi, Christoph; Evangelou, Michael; Balomenos, Efthymios; Lenz, Markus [in: Journal of Chemical Technology & Biotechnology]Since the world economy has been confronted with an increasing risk of supply shortages of critical raw materials (CRMs), there has been a major interest in identifying alternative secondary sources of CRMs. Bauxite residues from alumina production are available at a multi-million tonnes scale worldwide. So far, attempts have been made to find alternative re-use applications for bauxite residues, for instance in cement / pig iron production. However, bauxite residues also constitute an untapped secondary source of CRMs. Depending on their geological origin and processing protocol, bauxite residues can contain considerable amounts of valuable elements. The obvious primary consideration for CRM recovery from such residues is the economic value of the materials contained. However, there are further benefits from re-use of bauxite residues in general, and from CRM recovery in particular. These go beyond monetary values (e.g. reduced investment / operational costs resulting from savings in disposal). For instance, benefits for the environment and health can be achieved by abatement of tailing storage as well as by reduction of emissions from conventional primary mining. Whereas certain tools (e.g. life-cycle analysis) can be used to quantify the latter, other benefits (in particular sustained social and technological development) are harder to quantify. This review evaluates strategies of bauxite residue re-use / recycling and identifies associated benefits beyond elemental recovery. Furthermore, methodologies to translate risks and benefits into quantifiable data are discussed. Ultimately, such quantitative data are a prerequisite for facilitating decision-making regarding bauxite residue re-use / recycling and a stepping stone towards developing a zero-waste alumina production process.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationQuantification of methylated selenium, sulfur, and arsenic in the environment(Public Library of Science, 2014) Vriens, Bas; Ammann, Adrian; Hagendorfer, Harald; Lenz, Markus; Berg, Michael; Winkel, Lenny [in: PLOS ONE]Biomethylation and volatilization of trace elements may contribute to their redistribution in the environment. However, quantification of volatile, methylated species in the environment is complicated by a lack of straightforward and field-deployable air sampling methods that preserve element speciation. This paper presents a robust and versatile gas trapping method for the simultaneous preconcentration of volatile selenium (Se), sulfur (S), and arsenic (As) species. Using HPLC-HR-ICP-MS and ESI-MS/MS analyses, we demonstrate that volatile Se and S species efficiently transform into specific non-volatile compounds during trapping, which enables the deduction of the original gaseous speciation. With minor adaptations, the presented HPLC-HR-ICP-MS method also allows for the quantification of 13 non-volatile methylated species and oxyanions of Se, S, and As in natural waters. Application of these methods in a peatland indicated that, at the selected sites, fluxes varied between 190–210 ng Se·m−2·d−1, 90–270 ng As·m−2·d−1, and 4–14 µg S·m−2·d−1, and contained at least 70% methylated Se and S species. In the surface water, methylated species were particularly abundant for As (>50% of total As). Our results indicate that methylation plays a significant role in the biogeochemical cycles of these elements.01A - Beitrag in wissenschaftlicher Zeitschrift