IMPACT OF THERMAL PRETREATMENT ON ALUMINA DISSOLUTION RATE AND HF EVOLUTION

Alumina dissolution rates in cryolitic electrolytes have been a subject of intensive study over the last several decades. Alumina dissolution rate can be affected by the physical, chemical, morphological and microstructural properties of the ore, the dynamics of the feeding process, the chemistry of the bath and the superheat of the pots. in this study, smelting grade alumina (SGA) samples were subjected to various temperature pretreatment conditions prior to feeding to molten bath. The HE evolution profiles were measured and correlated with ore pretreatment and stage of alumina ore dissolution. Oven based studies of SGA/bath mixtures were employed to slow overall reaction kinetics to better resolve the inter-particle adhesion of alumina leading to clumping or raft formation on the ore upon feeding to the pot. Dissolution mechanisms are proposed based on the dissolution rate and observation of morphological and microstructural changes of flats/crust formed prior to being dissolved.