| Rutile titanium dioxide is an important white pigment, the main route to its production is via sulfate process. Hydrolysis, washing and calcining sections have significant influence on titanium dioxide pigment properties. In this paper, condensed industrial titanyl sulfate solution was used as titanium source. Systematic study on titanium dioxide production process was taken according to self-generating seeded precipitation method.Washing process was investigated by adding washing times and using new reductant. Experimental data indicated that about 20ppm iron can not be removed from metatitanie acid, including 5-7ppm ilmenite which have not been solved in leaching section and 14ppm FeSO4 which have been occluded in metatitanic acid through hydrolysis section. The conclusions were convinced by EDS data.The influences of operation conditions such as titanyl sulfate concentration, Fe/TiO2 mass ratio, F value and base water volume on hydrolysate filtration efficiency and calcined product pigment properties were also investigated. The study found that with titanyl sulfate concentration increasing, rate of hydrolysis was increased, mean particle size and filtration efficiency of metatitanic acid were decreased; with Fe/TiO2 mass ratio increasing, rate of hydrolysis, mean particle size and filtration efficiency of metatitanic acid were decreased; with F value increasing, rate of hydrolysis was decreased, mean particle size and filtration efficiency of metatitanic acid were increased; with base water volume increasing, rate of hydrolysis was increased, mean particle size and filtration efficiency of metatitanic acid were firstly increased and then decreased when base water volume was more than 298 ml. The optimized titanyl sulfate concentration was of 240 g/L, the Fe/TiO2 mass ratio was of 0.28, the F value was of 1.8 and the base water volume was of 298 ml. The prepared TiO2 pigment was with low particle size, narrow particle size distribution and excellent pigment properties.Hydrolysate and calcined product were characterised by XRD and SEM. Mechanism of aggregate fonnation was put forword to explain partical agglomeration during metatitanic acid precipitation. In this theory, aggregation was divided into two period:metatitanic acid nuclei firstly aggregated to make up a primary agglomerate, then primary agglomerates aggregated to make up a secondary agglomerate. Primary agglomerates sintered into rutile titanium dioxide crystal, so that the mean particle size of primary agglomerates is a direct result of how calcined product performs. While secondary agglomerate re-dispersed in high temperature atmosphere, the mean particle size of secondary agglomerates just affect the filtration efficiency of hydrolysate. Hydrolysis operation conditions affect the formation of primary agglomerates and secondary agglomerates, therefore the titanium dioxide pigment properties can be improved by process optimization. |
