X-Ray fluorescence analysis of feldspars and silicate glass: effects of melting time on fused bead consistency and volatilisation

Reproducible preparation of lithium tetraborate fused beads for XRF analysis of glass and mineral samples is of paramount importance for analytical repeatability. However, as with all glass melting processes, losses due to volatilization must be taken into account and their effects are not negligible. Here the effects of fused bead melting time have been studied for four Certified Reference Materials (CRM’s-three feldspars, one silicate glass), in terms of their effects on analytical variability and volatilization losses arising from fused bead preparation. At melting temperatures of 1065 °C, and for feldspar samples, fused bead melting times shorter than approximately 25 minutes generally gave rise to greater deviation of XRF-analyzed composition from certified composition. This variation might be due to incomplete fusion and / or fused bead inhomogeneity but further research is needed. In contrast, the shortest fused bead melting time for the silicate glass CRM gave an XRF-analyzed composition closer to the certified values than longer melting times. This may suggest a faster rate of glass-in-glass dissolution and homogenization during fused bead preparation. For all samples, longer melting times gave rise to greater volatilization losses (including sulphates and halides) during fusion. This was demonstrated by a linear relationship between SO3 mass loss and time1/2, as predicted by a simple diffusion-based model. Iodine volatilization displays a more complex relationship, suggestive of diffusion plus additional mechanisms. This conclusion may have implications for vitrification of iodine-bearing radioactive wastes. Our research demonstrates that the nature of the sample material impacts on the most appropriate fusion times. For feldspars no less than ~25 min and no more than ~60 min of fusion at 1065 °C, using Li2B4O7 as the fusion medium and in the context of feldspar samples and the automatic fusion equipment used here, strikes an acceptable (albeit non-ideal) balance between the competing factors of fused bead quality, analytical consistency and mitigating volatilization losses. Conversely, for the silicate glass sample, shorter fusion times of less than ~30 minutes under the same conditions provided more accurate analyses whilst limiting volatile losses

X-ray Fluorescence Analysis of Feldspars and Silicate Glass: Effects of Melting Time on Fused Bead Consistency and Volatilisation

Reproducible preparation of lithium tetraborate fused beads for XRF analysis of glass and mineral samples is of paramount importance for analytical repeatability. However, as with all glass melting processes, losses due to volatilisation must be taken into account and their effects are not negligible. Here the effects of fused bead melting time have been studied for four Certified Reference Materials (CRM’s: three feldspars, one silicate glass), in terms of their effects on analytical variability and volatilisation losses arising from fused bead preparation. At melting temperatures of 1065 °C, and for feldspar samples, fused bead melting times shorter than approximately 25 min generally gave rise to a greater deviation of the XRF-analysed composition from the certified composition. This variation might be due to incomplete fusion and/or fused bead inhomogeneity but further research is needed. In contrast, the shortest fused bead melting time for the silicate glass CRM gave an XRF-analysed composition closer to the certified values than longer melting times. This may suggest a faster rate of glass-in-glass dissolution and homogenization during fused bead preparation. For all samples, longer melting times gave rise to greater volatilisation losses (including sulphates and halides) during fusion. This was demonstrated by a linear relationship between SO3 mass loss and time1/2, as predicted by a simple diffusion-based model. Iodine volatilisation displays a more complex relationship, suggestive of diffusion plus additional mechanisms. This conclusion may have implications for vitrification of iodine-bearing radioactive wastes. Our research demonstrates that the nature of the sample material impacts on the most appropriate fusion times. For feldspars no less than ~25 min and no more than ~60 min of fusion at 1065 °C, using Li2B4O7 as the fusion medium and in the context of feldspar samples and the automatic fusion equipment used here, strikes an acceptable (albeit non-ideal) balance between the competing factors of fused bead quality, analytical consistency and mitigating volatilisation losses. Conversely, for the silicate glass sample, shorter fusion times of less than ~30 min under the same conditions provided more accurate analyses whilst limiting volatile losses

Reducing energy demand and CO2 emissions from industrial ceramic manufacture using novel raw materials and additives

This study of reducing energy demand and CO2 emissions from industrial ceramic manufacture using novel raw materials and additives was undertaken to contribute to the industry's requirement to decrease energy inputs and CO2 emissions and increase material efficiency when manufacturing structural ceramic products whilst maintaining product quality. Weald clay was replaced with additive levels 1-4wt% alkali and alkaline earth carbonates, industrial and inorganic mineral additives and shaped into cylindrical pellets. The admixtures were fired to 850°C, 900°C, 1000°C and 1040°C. Ten characterisation techniques (XRF, XRD, TG/MS, MIP, dilatometry, volumetric shrinkage testing, boiling water absorption testing, compressive strength testing, Mössbauer spectroscopy and Raman spectroscopy) were used to determine the chemistry, microstructure and changes to the resulting ceramics in comparison to a reference standard and existing products. Mineralogically, the additive K2CO3 and Na2CO3 admixtures do not promote new firing phases not already present in the Weald clay ceramics fired to 900°C, 1000°C and 1040°C, as opposed to the effects of the other 12 additives studied. Alkali additives, however, promoted stronger bonds on firing, so the mechanical strength obtained for K2CO3 doped samples was over 85MPa compared to 81.5MPa for the control sample. Of the industrial waste additives, 2wt% container glass and 4wt% mineral wool were promising candidate for other products with resulting ceramic compressive strengths of 58MPa and ⁓54MPa, respectively. Only 4wt% wollastonite and talc additions for inorganic additives increased ceramic strength to 72MPa and 60MPa for ceramics fired to 1040°C, respectively. Nepheline syenite and colemanite additives functioned as pore formers, resulting in ceramics with lower compressive strengths of below 50MPa. Technologically, boiling water absorption, strength, mercury intrusion porosity (MIP), pore size, and shrinkage depended on firing temperature, additive type and proportion of additive. Volatiles in all cases were found to be CO2, re-absorbed water and chemical water. Pore sizes moved towards larger pores (> 1μm) with increased firing temperature (⁓1040°C). The alkaline earth additives controlled excessive expansion caused by carbonate decomposition and promoted reduced sintering temperatures of between 4- 41°C. Meanwhile, adding alkali carbonate additives (Li, K) at levels ⁓ >2wt% caused the clay body to expand again above the quartz transition temperature. The surface scum observed was found to be CaSO4 on 12 samples except for the samples doped with BaCO3 and greater than 2wt% MgCO3, both of which prevented the formation of the scum (whitish stains) on fired ceramic bodies. Fired ceramics with alkali carbonate additives added at 1wt% (Li, Na, and K) were free from surface scum. Surface defects such as patches and darker rims on ceramic surfaces were noticed in the >2wt% Li, Na, and K carbonate ceramic samples. Changes in fired ceramic colour were found due to differences in iron in the paramagnetic and magnetic iron sites. Iron is present in all admixtures as Fe3+ hematite (Fe2O3) except for the unfired Weald clay, which contained iron as Fe2+ and Fe3+. By firing ceramics at 1000°C and 1040°C, 90°C and 50°C temperature reductions have been obtained compared to industrial firing of bricks at 1090°C. This implies that ceramics fired to 1000°C and 1040°C resulted in reduced energy of 64kWh and 23kWh, respectively. Moreover, the additive 1wt% K2CO3 gives better CO2 savings than 1wt% Li2CO3 fired at a lower temperature yet retains the quality of a class B engineering brick. The replaced additives can save about 80,000-320,000 tonnes of clay. It is recommended that direct durability testing is conducted on all samples, but mainly on 2wt% MgCO3, 4wt% Wollastonite, 4wt% Talc, 1wt% K2CO3 samples fired to 1040°C and 1wt% Li2CO3 samples fired to 1000°C, to validate the modified frost resistance for heavy clay ceramic manufacturers. Pilot-scale testing for dopants to prevent efflorescence and scummingformed on fired ceramic products of MgCO3 as an alternative to BaCO3 is also recommended