Mullitization of Roseki Ore with an Additive of LiF (5.2wt%)

Abstract

Mullite formation at low temperatures from low grade kaolin (Roseki) with the addition of mineralizer (LiF) was described. Samples were sintered for 90 days at 700°-1200°C. Mullite yields of the samples were measured by X-ray internal standard powder method. Relations among mullite yields (α_i) and logarithms of sintering time (t) were represented as follows:
α₁=-4.3+2.3logt (t: 72-1300h) at 700°C. α₄=-0.5+3.0logt (t: 15-1000h) at 900°C. α₆=2.0+3.1logt (t: 1-700h) at 1050°C. α₈=8.9+4.2logt (t: 1-25h) at 1200°C.
It becomes apparent that reaction of mullitization of low grade kaolin containing mineralizer at low temperatures proceeds through the stage of Al-Si spinel phase. Activation energies of the reactions are 10.3kcal/mol at below 950°C and 65.8kcal/mol at above 950°C.