Zircon data processing

HREE Y, whereas monazite, allanite, synchysite and bastnaesite contain most of the LREE. Based on quantitative data approximately half of the fergusonite mass% is associated mainly with zircon, and <2% of the zircon with fergusonite (i.e., reflecting mass distribution differences in the samples). Therefore, in order to recover the HREE, both minerals must be processed and recovered together. The LREE carriers can be recovered as a group. 

Weber et al. (1999) summarized the temperature-dependent in situ ion irradiation data obtained to date [1500 keV Kr (Weber et al. 1994), 540 keV Pb (one data point at -250K Oliver et al. 1994), 1000 keV Ne (Devanathan et al. 1998), 800 keV Kr (Meldrum et al. 1999), 800 keV Xe (Meldrum et al. 1999a)] and presented an additional curve for zircon irradiated with 600 keV Bi. The amorphization dose increased with increasing energy density (i.e. with increasing ion mass). This observation is consistent with a cascade overlap, defect accumulation process. The ion irradiation data are summarized in Table 2. 

The fa vs. D curves generated from the various models have been compared with the limited amount of experimental data to infer which type of model, e.g. direct impact vs. double overlap, is most applicable. As shown in Figure 7, the measured dependence of fa on D for Cm-doped Ca2Nd8(Si04)602 is consistent with the predicted curve for the direct impact model for ion-irradiated zircon, the measured dependence offa on D is consistent with the double-overlap model SrTiOs, the defect accumulation model (Weber 2000). It has been generally accepted that for heavy ion irradiations, especially at low temperatures, the amorphization process in ceramic materials is the result of amorphization within the cascade. For lighter ions (or electrons and neutrons) or at high temperatures, the dominant mechanism is considered to be cascade-overlap or defect accumulation. 

Industrial by-products that contain zirconium are mainly zircon and zirconia, both of which are insoluble in water, largely inert, and of low toxicity. Water-soluble zirconium compounds are converted at pH 4-9.5 into insoluble zirconia. The only possible atmospheric emission of other zirconium compounds is that of chlorinated and/or hydrolyzed oxychlorides from the processing of sponge zirconium using the Kroll process (reduction of ZrCl4). Analytical data corresponding to the extent of these emissions do not exist (Smith and Carson 1978), but there is no doubt that the exposure of the general population to zirconium compounds is small. 

---