Browsing Faculty of Natural and Agricultural Sciences by Author "11087137 - Krieg, Henning Manfred"
Now showing items 1-20 of 53
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Application of novel Anion-Exchange Blend Membranes (AEBMs) to vanadium redox flow batteries
Cho, Hyeongrae; Krieg, Henning M.; Kerres, Jochen A. (MDPI, 2018)Both cation-exchange membranes and anion-exchange membranes are used as ion conducting membranes in vanadium redox flow batteries (VRFBs). Anion-exchange membranes (AEMs) are applied in vanadium redox flow batteries due ... -
Automation of membrane based solvent extraction unit for Zr and Hf separation
Meerholz, Kyle; Van der Westhuizen, Derik Jacobus; Krieg, Henning Manfred (Elsevier, 2017)In recent years, research into metal ion solvent extraction using hollow fibre membranes has grown. Current studies generally use an analogue controlled experimental setup. Although the analogue system is sufficient for ... -
Characterisation of a polyaromatic PBI blend membrane for SO2 electrolysis
Krüger, Andries J.; Kerres, Jochen; Bessarabov, Dmitri; Krieg, Henning M.; Cichon, Patrizia (Elsevier, 2015)The application of a polyaromatic acid–base blend membrane from partially fluorinated and sulfonated aromatic polyether and the polybenzimidazole F6PBI has been investigated for hydrogen production using SO2 electrolysis. ... -
Comparison of extractants for the separation of TaF5 and NbF5 in different acidic media
Ungerer, M.J.; Van der Westhuizen, D.J.; Lachmann, G.; Krieg, H.M. (Elsevier, 2014)To optimise the solvent extraction (SX) of Ta and Nb, eight different extractants were investigated, including the cation exchangers di-iso-octyl-phosphinic acid (PA) and di-(2-ethylhexyl)-phosphoric acid (D2EHPA), the ... -
Comparison of ionically and ionical-covalently cross-linked polyaromatic membranes for SO2 electrolysis
Peach, Retha; Krieg, Henning M.; Krüger, Andries J.; Van der Westhuizen, Derik; Bessarabov, Dmitri (Elsevier, 2014)It has been shown that hydrogen, which can be used for energy storage, can be produced efficiently by the membrane based Hybrid Sulfur (HyS) process. During the HyS electrolysis step, SO2 and H2O are converted to H2 and ... -
Computational chemistry study of zirconium monomers in low acid concentration aqueous solutions
Jansen van Vuuren, D.B.; Krieg, H.M.; Van Sittert, C.G.C.E. (IOP Publishing, 2018)Zirconium and hafnium have to be separated prior to their use in nuclear energy reactors. Therefore, a lot of research has been done on the solvent extraction of zirconium. However, most of this research involved screening ... -
Density functional theory prediction of the aqueous speciation of ZrF4 and HfF4
Jansen van Vuuren, D.B.; Krieg, H.M.; Van der Westhuizen, D.J.; Van Sittert, C.G.C.E. (SAIMM, 2018)Computational chemistry was used to make predictions regarding the stepwise hydrolysis and fluoride dissociation reactions of ZrF4 and HfF4 in aqueous solutions. Specifically, density functional theory was used to predict ... -
Density functional theory study with and without COSMO of H2SO4 reactions in an aqueous environment for metal extraction
Ungerer, Maria Johanna; Van Sittert, Cornelia Gertina Catharina Elizabeth; Van der Westhuizen, Derik Jacobus; Krieg, Henning Manfred (Wiley, 2019)In a recent study investigating the suitability of solvent extraction (SX) for the separation of Ta and Nb, it was shown that speciation data would be required to help explain the data obtained. As traditional speciation ... -
A density-functional theory approach to the separation of K2ZrF6 and K2HfF6 via fractional crystallization
Branken, D.J.; Lachmann, G.; Krieg, H.M.; Bruinsma, O.S.L. (Wiley, 2011)Because of the low absorption cross-section for thermal neutrons of zirconium (Zr) as opposed to hafnium (Hf), Zr-metal must essentially be Hf-free (<100 ppm Hf) to be suitable for use in nuclear reactors. However, Zr and ... -
DFT modelling of tantalum pentafluoride extraction with phosphorus-based extractants – a molecular dynamics study
Ungerer, M.J.; Van Sittert, C.G.C.E.; Van der Westhuizen, D.J.; Krieg, H.M. (Elsevier, 2019)Solvent extraction (SX) is a powerful method for both the separation and extraction of metals, resulting in high purity metals. The transition metals tantalum (Ta) and niobium (Nb) are of considerable significance, for ... -
Direct synthesis of a titania membrane on a centrifugally casted tubular ceramic support
Patterson, V.A.; Krieg, H.M.; Kriek, R.J.; Bisset, H. (Elsevier, 2006)In-house manufactured tubular ceramic supports prepared by centrifugal casting have a smooth inside surface and are ideal for thin defect-free coatings. The aim of this study was to directly coat a thin defect-free titania ... -
A dual-channel gas chromatography method for the quantitation of low and high concentrations of NF3 and CF4 to study membrane separation of the two compounds
Branken, D.J.; Le Roux, J.P.; Krieg, H.M.; Lachmann, G. (Elsevier, 2013)A dual-channel gas chromatographic method is described in this paper that can be conveniently used for quantitation of NF3/CF4 mixtures with a thermal conductivity detector (TCD) on one channel for the quantitation of ... -
Effect of H2S on SO2-depolarised water electrolysis
Krüger, Andries J.; Krieg, Henning M.; Bessarabov, Dmitri (Elsevier, 2015)The performance of a PEM SO2 electrolyser, used for the production of H2 gas and liquid H2SO4, was evaluated when the feed was contaminated with hydrogen sulfide. Transient voltage response at constant current density and ... -
The effect of molar ratio and flow velocity on the surface area required for pertraction of a Zr/Hf mixture
Malan, D.; Van der Westhuizen, D.J.; Neomagus, H.W.J.P.; Krieg, H.M. (IOP, 2019)Zirconium (Zr) and hafnium (Hf) need to be separated before being used in nuclear applications. Equilibria data have shown that Hf can be selectively extracted over Zr from a sulphate medium using organophosphorus ... -
The effect of α-irradiation from enriched uranium on the leaching properties of PTFE
Badenhorst, J.J.; Krieg, H.M.; Meyer, W.C.M.H.; Van Rooyen, T.J. (Elsevier, 2017)In the uranium enrichment plants of the South African Nuclear Energy Corporation SOC Ltd (Necsa), sintered polytetrafluoroethylene (PTFE) filters were used to remove gas entrained solid particles, in order to prevent ... -
Electrowinning of iron from spent leaching solutions using novel anion exchange membranes
Badenhorst, Wouter Dirk; Rossouw, Cloete; Kerres, Jochen; Bruinsma, Dolf; Krieg, Henning (MDPI, 2019)In the Pyror process, electrowinning (EW) is used to recover acid and iron from spent leaching solutions (SLS), where a porous Terylene membrane acts as a separator between the cathode and anode. In this study, a novel ... -
Evaluation of covalently and ionically cross-linked PBI-excess blends for application in SO2 electrolysis
Krüger, Andries J.; Kerres, Jochen; Bessarabov, Dmitri; Krieg, Henning M. (Elsevier, 2015)Proton exchange membranes (PEM) containing various combinations of PPOBr (pol(2,6-dimethylbromide-1,4-phenylene oxide, covalently cross-linked) or PWN (poly(tetrafluorostyrene-4-phosphonic acid), ionically cross-linked) ... -
Evaluation of MEA manufacturing parameters using EIS for SO2 electrolysis
Krüger, Andries J.; Krieg, Henning M.; Van der Merwe, Jan; Bessarabov, Dmitri (Elsevier, 2014)Membrane electrode assembly (MEA) manufacturing parameters such as hot pressing pressure and pressing time were investigated for the use in a SO2 electrolyser. The SO2 electrolysis was optimised in terms of cell temperature, ... -
Extraction of uranium from synthetic nuclear conversion plant waste
Potgieter, M.; Van der Westhuizen, D.J.; Krieg, H.M.; Barry, J.C. (Taylor & Francis, 2019)The nuclear conversion plant operated at Necsa in the past resulted in the formation of a large amount of waste material containing ~ 50% U, which has reuse potential if the recovery thereof can be achieved. The waste ... -
Feasibility of electro-reduction of U(VI) in oxalic acid using an electrolytic CEM-separated cell
Potgieter, M.; Van der Spoel Badenhorst, W.D.; Van der Westhuizen, D.J.; Krieg, H.M. (Springer, 2020)The feasibility of electrolytic stripping of U(VI) using an electrolytic separation cell with anode and cathode compartments, separated by a cation exchange membrane (CEM), was investigated as a possible final step in a ...