Lenz, Markus
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- 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
- PublikationSystematic approach to harness the potential of CRM secondary sources on the example of red mud(05/2017) Ujaczki, Eva; Zimmermann, Yannick; Gasser, Christoph A.; Molnar, Monika; Feigl, Victoria; Lenz, Markus06 - Präsentation
- PublikationRe-usability of critical raw materials recovery residues from Hungarian red mud(05/2017) Feigl, Victoria; Ujaczki, Eva; Farkas, Éva; Molnar, Monika; Lenz, Markus06 - Präsentation
- PublikationRed mud as secondary source for critical raw materials – Extraction study(Wiley, 2017) Ujaczki, Eva; Zimmermann, Yannick; Molnar, Monika; Feigl, Victoria; Lenz, Markus; Gasser, Christoph A. [in: Journal of Chemical Technology & Biotechnology]Red mud is a by-product of alumina extraction from bauxite by the Bayer process produced in the billion tons scale worldwide. Red muds, or more generally bauxite residues, are regarded as waste, but may potentially be valuable sources of critical raw materials (CRM). In the present study both conventional extracting agents (mineral acids) and small molecular weight complexing agents (organic acids) were evaluated regarding their efficiency to extract CRM such as rare earth elements (REEs) from red mud. On a molar base, highest extraction efficiencies for REEs were achieved using HCl compared with the other acids investigated. Consequently, an experimental design approach was used to determine optimal conditions for CRM extraction using HCl. Instead of maximizing the extraction of a number of selected metals, the maximum economic potential as the sum of all metals (total metal extracted × economic value of the respective metal) was chosen as the application relevant response variable. Four explanatory variables (i.e. HCl concentration, contact time, temperature and slurry concentration) were used. RESULTS Optimal conditions maximizing the economic potential were predicted for 5.98 mol L−1 HCl, 21 h contact time, 50°C, and 56.7 g L−1 slurry concentration. Indeed, experimentally determined economic potential corresponded well (71% of predicted) with the predictions, allowing a maximum recovery of 297.6 US $ t−1. CONCLUSION Though the studied red muds were relatively low in CRM concentrations, the systematic approach developed here allows straightforward transfer to other red muds, harnessing the potential of the latter as important secondary source for CRM. © 2017 Society of Chemical Industry01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationRed mud as secondary source for critical raw materials – Purification of rare earth elements by liquid/liquid extraction(Wiley, 2017) Ujaczki, Eva; Zimmermann, Yannick; Gasser, Christoph; Molnar, Monika; Feigl, Victoria; Lenz, Markus [in: Journal of Chemical Technology & Biotechnology]BACKGROUND Critical raw materials (CRM) are crucial to Europe's economy and essential to maintaining and improving our quality of life due to their usage for production of many devices. Red mud is generated from alumina production where bauxite is digested in hot sodium hydroxide solution during the Bayer process. Red mud can contain considerable amounts of CRM such as rare earth elements (REEs). In the present study, purification of CRM from perturbing, co-extracted elements such as Fe and Al from red mud hydrochloric acid leachates was evaluated. RESULTS A first purification was achieved by removing Fe (>87%) from the acidic leachate using precipitation with NaOH. REEs as well as Al were hardly removed by precipitation (21%, and 33%, resp.). A second purification was achieved using liquid/liquid extraction (LLE) with di-(2-ethylhexyl)phosphoric acid (D2EHPA). Here, four explanatory variables (i.e. LLE organic/aqueous ratio, D2EHPA concentration in kerosene, stripping acid organic/aqueous ratio, HCl concentration) were studied. Finally, the optimal extraction conditions maximizing the economic potential (total metal extracted × economic value of the respective metal) of CRM were determined using a design of experiment approach. CONCLUSION The experimentally determined economic potential extracted corresponded well to the prediction (88%; to the predictions, maximum recovery of 17.18 ± 0.59 US $ t−1). Ultimately, more than 40% of the overall REEs (>62% of the leachable REEs) in red mud were purified using LLE, whereas Al was successfully rejected from the concentrate (∼5% of the overall Al present). © 2017 Society of Chemical Industry01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationEvaluation of two Reuse Technologies for a Hungarian Red Mud(2015) Lenz, Markus; Ujaczki, Eva; Zimmermann, Yannick; Molnar, Monika; Gruiz, Katalin; Feigl, Victoria06 - Präsentation