Two Perspectives on the Evolution and Future of Alumina

摘要

Over the 125 year history there have been a number of stepchangesrnin the Hall-Heroult process, despite a remarkablernadherence to the original concepts of the invertors. In addition tornthe steady increment in scale, most noteworthy perhaps have beenrnthe introduction and impending disappearance of Soderbergrntechnology, the introduction of magnetically compensated cellrndesign, changes in dynamics of alumina feeding and thernintroduction of dry-scrubbers for HF control and fluoridernrecovery.rnThe Bayer process has also seen some significant advances,rndriven by the demands of energy and environmental imperativesrnand the steadily narrowing window of product specifications,rndriven in turn by refinements in the Hall-Heroult process.rnDemands for coarser particle size distribution, higher specificrnsurface areas and lower attrition index have been accompanied byrnchanges in precipitation strategy and conversion to more energyrnefficient stationary calcination processes.rnThe properties of a “typical” metallurgical alumina have thusrnchanged. Indeed the term "alumina" is now more indicative ofrnstoichiometry than it is of structure, and even in this, it is less thanrnprecise. In this paper we discuss how new scientific tools andrninsights are changing the way we define (and perhaps shouldrnspecify) this material.