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Publikation Red 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, MarkusBACKGROUND 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 ZeitschriftPublikation Production of superparamagnetic nanobiocatalysts for green chemistry applications(Springer, 23.04.2016) Gasser, Christoph; Ammann, Erik; Schäffer, Andreas; Shahgaldian, Patrick; Corvini, PhilippeImmobilization of enzymes on solid supports is a convenient method for increasing enzymatic stability and enabling enzyme reuse. In the present work, a sorption-assisted surface conjugation method was developed and optimized to immobilize enzymes on the surface of superparamagnetic nanoparticles. An oxidative enzyme, i.e., laccase from Trametes versicolor was used as model enzyme. The immobilization method consists of the production of superparamagnetic nanoparticles by co-precipitation of FeCl2 and FeCl3. Subsequently, the particle surface is modified with an organosilane containing an amino group. Next, the enzymes are adsorbed on the particle surface before a cross-linking agent, i.e., glutaraldehyde is added which links the amino groups on the particle surface with the amino groups of the enzymes and leads to internal cross-linking of the enzymes as well. The method was optimized using response surface methodology regarding optimal enzyme and glutaraldehyde amounts, pH, and reaction times. Results allowed formulation of biocatalysts having high specific enzymatic activity and improved stability. The biocatalysts showed considerably higher stability compared with the dissolved enzymes over a pH range from 3 to 9 and in the presence of several chemical denaturants. To demonstrate the reusability of the immobilized enzymes, they were applied as catalysts for the production of a phenoxazinone dye. Virtually, 100 % of the precursor was transformed to the dye in each of the ten conducted reaction cycles while on average 84.5 % of the enzymatic activity present at the beginning of a reaction cycle was retained after each cycle highlighting the considerable potential of superparamagnetic biocatalysts for application in industrial processes.01A - Beitrag in wissenschaftlicher Zeitschrift