In this work, influence of iron on red mud settling was studied. The slurries are prepared from Gia Nghia (GN) and Dac Song (DS) bauxite according to the Bayer process with pre-selected desilication and digestion parameter. The result obtained shows that: - GN bauxite and DS bauxite are goethite rich bauxites, these are gibbsite - goethite bauxites
. Settling process can be divided into three periods
initial period with rapid settling, the settling slowdown in middle period and stop settling in the end
- Most of goethite particles in red mud are in colloid form, its specific density is the smallest compare to other iron oxide compounds. Therefore, goethite also has the worst settling characteristics
- Total iron oxides and goethite in GN bauxite are smaller than those in DS bauxite. Resulted in better settling characteristics of GN bauxite, the turbidity of sodium aluminate solution obtained also smaller than the turbidity of DS solution.