Removal of MoF6 and HF from a helium-MoF6 gas mixture

Abstract

Klydon developed an aerodynamic separation process (ASP) with the aim of establishing an industrial method for isotope enrichment with respect to molydenum-100 for medical usage. Helium is used as carrier gas for molybdenum, present in the form of molybdenum hexafl uoride (MoF6). MoF6 is separated as product from the helium by freezing. The helium has to be purifi ed subsequently and traces of hydrogen fl uoride (HF) and MoF6 have to be removed. Several gas separation technologies were considered with the fi nal choice being the use of adsorbents, with emphasis on ion exchange resins. The reason for the choice was the fact that resins are easily obtainable synthetic polymeric materials, capable of exchanging or trapping specifi c ions. Because of the reactivity of both HF and MoF6, it is more likely that both compounds will react irreversibly with the the solid resins. The experimental results indicated that MN102 and A100Mo showed potential for removal of MoF6 from the helium stream in the fi nal polishing step. The results were not suprising; A100Mo is a macroporous, mixed base-ion resin, used for removal of molybdenum form acid solutions, and MN102 is a macroporous, hydrophobic weak base-ion material. Alumina and activated carbon showed showed potential for removing HF. Further work is required for with mixtures of HF and MoF6 to confi rm the selective nature of the reactions.

Klydon het die aërodinamiese skeidingsproses (ASP) met die doel van isotoopverryking in molibdeen-100 vir die doeleindes van mediese-isotoopproduksie ontwikkel. Helium word as draergas saam met molibdeen in die vorm van molibdeenheksafl uoried (MoF6) tydens die proses gebruik. Die MoF6 word as produk uit die heliumstroom verwyder deur dit uit te vries. Die helium moet gesuiwer word en indien waterstoffl uoried (HF) of MoF6 nog teenwoordig is, moet dit effektief verwyder word. Nadat verskillende moontlikhede van gasskeiding en verwydering van HF en MoF6 ondersoek is, het die keuse op adsorbente geval met die oorwig van keuse op ioonuitruilharse. Die rede vir die keuse was dat harse maklik bekombare sintetiese polimeermateriale is, wat in staat is om spesifi eke ione uit te ruil of vas te lê. As gevolg van die reaktiwiteit van beide MoF6 en HF, is dit meer waarskynlik dat die twee reagense onomkeerbaar met die vaste stowwe reageer. Die eksperimente het getoon dat MN102 en A100Mo potensiaal het om MoF6 in die fi nale poleringsstap uit helium te verwyder. Verder het die eksperimente getoon dat alumina en koolstof moontlik die potensiaal het om HF selektief uit ’n heliumstroom te verwyder. Die resultate was nie verrassend nie want A100Mo is ’n makroporeuse, gemengde basisanioon hars, wat juis gebruik word om molibdeen uit suuroplossings te verwyder. MN102 is ’n makroporeuse hidrofobiese, swak basisanioon hars. Verdere studie en eksperimentering met ’n mengsel van HF en MoF6 om die selektiewe reaksie van HF te ondersoek word dus sterk aanbeveel.