Towards Redefining the Alumina Specifications Sheet — The Case of HF Emissions

Solar-driven alumina calcination for CO2 mitigation and improved product quality

“…It can also be seen from a comparison with reported mean pore sizes of typical SGAs produced with industrial flash calciners ( presented as the open symbols in Fig. 10), 28,32,34 the solar process generates larger values of d pore for a given value of X than does the conventional process. Extrapolation suggests that d pore will continue to increase with X, so that solar-processed alumina has potential to achieve a larger mean pore size than the majority of conventionally-processed aluminas, noting the exception for two SGAs with pore size larger than 8 nm.…”

“…Table 3b presents the parameters used to characterise the product quality for the present alumina product with greatest X (run #14), together with typical properties of SGA produced in industrial flash calciners as reported in the literature. 24,28,29,[31][32][33][34] This shows that the minimum LoI 1273 of 1.20% achieved in the present investigation is somewhat higher than the typical value of alumina produced in industrial flash calciners. However, given that extent of conversion increases with τ, it can be deduced that the LoI 1273 would decrease to <1% with scale up of the solar reactor, which would comply with industrial requirements.…”

“…where, n Al 2 O 3 and n Al(OH) 3 are the molar quantities of alumina product and unreacted Al(OH) 3 in the solar-processed alumina (as determined from LoI X ). The ISO standard for reporting alumina moisture content is by the LoI 1273 , evaluated over the temperature range 573-1273 K. 30,34,38 However, it has been shown that the reactant Al(OH) 3 begins to decompose at temperatures below 573 K, which means that the LoI 1273 underestimates the amount of unreacted Al(OH) 3 . This provides justification for the use of LoI ads and LoI X in the present investigation.…”

“…Also shown with open symbols are the typical mean pore diameter of nine SGAs produced with industrial calciners as reported in the literature. 28,32,34 Fig. 11 Specific surface area, SSA, of the present solar-produced aluminas as a function of the extent of chemical conversion, X, for experimental runs 1 to 17.…”

“…Hence the final α-alumina has the lowest SSA of the various alumina phases, 6,7,23,33 and there is a trade-off between the desire to obtain both a low residual water content and a high SSA. 29,34 It has been proposed, however, that under rapid heating, such as tends to occur with flash calcination, the structural rearrangement of the gibbsite calcination sequence can be decoupled from the water removal. 33 The high heating rates possible with directly irradiated CST therefore offer the potential to produce alumina with both favourable residual moisture content and favourable microstructural properties.…”