SOME ASPECTS OF TRICALCIUM ALUMINATE HEXAHYDRATE FORMATION ON THE BAYERrnPROCESS

摘要

Tricalcium aluminate hexahydrate (TCA) - Ca_3Al_3(OH)_(12) - is usedrnin the Bayer process as a filter aid during the pregnant liquorrnpolishing. The filtration efficiency depends on some TCArncharacteristics, such as particle size distribution and morphologyrnand how these particles are formed by physical-chemical reactionsrnthat take place during the alumina production. To reach a highrnperformance in the filtration step, it is important to understand therninfluence of variables like source of calcium - CaO or Ca(OH)_2 -rnresidence time, stirring speed and temperature in the TCArnformation. This study is being developed as partnership CETEM/rnAlunorte – Alumina do Norte do Brasil S.A., using liquor fromrnthe plant streams, to evaluate the efficiency of their process.rnPreliminary results shown that the formation of TCA particlesrnbegins partially, in the first minutes of reaction, and that itsrnmorphology and particle size distribution can change, during thernexperiment, depending on the particle size distribution of lime andrnimpurities, which play an important role in the lime reactivity andrnin the kinetic of the TCA formation.