Analysis of zirconium containing materials using multiple digestion and spectrometric techniques

[摘要] English: The preparation of pure zirconium metal for nuclear applications is difficult due to thenon-reactivity of zirconium minerals, such as zircon. The ability to accurately analysezirconium-containing materials across the whole beneficiation chain is of crucialimportance to the zirconium industry as a whole. The development of such ananalytical technique is problematic, however, as the very properties which make thesematerials desirable also make quantification of their components extremely difficult.Certified reference materials for the fluoride-containing Necsa zirconium processproducts were not available. Therefore in-house reference materials were created bycrystallisation of several (cation)xZrF4+x compounds. Potassium catena di-μ-fluoridotetrafluoridozirconate(IV), cesium hexafluoridozirconate(IV) and tetraethyl ammoniumcatena di-μ-fluorido-bis-(trifluoridozirconate(IV)) monohydrate were prepared andcharacterised by X-ray crystallography and qualitative XRD. Coordination numbers forthe zirconium atoms in each of these crystals were found to be 8, 6 and 7 respectively.Bridging fluorine bond lengths were determined to be approximately 2.06 and 1.97 Åfor the potassium and tetraethyl ammonium complexes while terminal bond lengthswere found to be 2.17 (potassium), 2.007 (cesium) and 2.15 (tetraethyl ammonium) Å.ICP-OES lower limits of detection for zirconium in the 3.25% nitric acid matrix werefound to be 1.6 ppb with lower limits of quantification being ten times this value. ICPOESzirconium recoveries for these crystals were 101(1) and 100(2)% for thepotassium and cesium crystals respectively.Dissolution of various commercial and Necsa process samples was problematic andthus several digestion methods were investigated. Sulphuric acid, ammoniumbifluoride and hydrofluoric acid were all investigated along with microwave assistance.A microwave-assisted acid digestion method was developed capable of completedissolution of all zirconium compounds with ICP-OES analytical recoveries of 102.0(9),100(2) and 101(3)% for 99.98% zirconium metal foil, ZrC and ZrH2 respectively.In order to circumvent the dissolution step a solid state GD-OES method wasdeveloped wherein sample powders were pressed into disks with a binder material,either copper or graphite. Initially instrument response across different samples was inconsistent but after optimisation of several instrument parameters, such as appliedvoltage and pre-burn time, a calibration curve with a R2 value of 0.9805 was achievedusing multiple sample materials. This was achieved using the radio frequency glowdischarge source operating at 900 V applied voltage and 14 W applied power with a5-minute pre-burn period. Results for Necsa process products were largely in line withthose achieved by the ICP-OES method.

[发布机构] University of the Free State