Reaction Behavior of Dolomite Accompanied with Formation of Magnetite Solid Solution in Iron Ore Sintering Process

Abstract

To discuss assimilation of dolomite with sinter mixture and the influences of dolomite use on the performance and on sinter quality, pot tests and small scale assimilation tests have been conducted. In particular, a microstructural evolution during sintering with using dolomite was focused on. Dolomite with mean size of 1 mm showed fairly good performance in pot tests. Using excessive fine or coarse dolomite resulted in loss of strength due to different mechanisms. Assimilation rate of dolomite was in the range between limestone and serpentine. Fluxes with large particle size above 1 mm tended to influence on microstructural evolution during sintering. Reaction behavior of dolomite during sintering consisted of 4 steps, calcination, formation of magnetite s.s by solid-state diffusion, formation of calciumferrite melt and formation of magnetite by reaction between MgO and calciumferrite melt. The last step was associated with the decrease in strength or yield of sinter. Difference in the nature of the magnetite s.s formed by two different mechanisms seemed to be related to the difference of sinter quality. In comparing reactions of dolomite and serpentine, microstructural evolution process differed by properties of formed melt during assimilating, reducible conditions in equilibrium state, fluidity and diffusion rate of Mg²⁺. Results of plant trials to examine proper amount of use and size distribution of dolomite showed that dolomite with 1.0 mm mean size could replace dunite or Ni-slag as MgO-bearing fluxes without significant worse effect in the limited amount of use.