Hydrolysis Process And Fromation Mechanism Of Titanium White Pigment Production Via Low Concentration Of Titanyl Sulfate Solution

Hydrolysis is the core of titanium dioxide production via sulfate process, determining structures, the sizes and its distribution of particles, and ultimately determining the quality of titanium pigments. The process of hydrolysis and quality of titanium pigments is affected the uncontrollable factors at present.Rutile titanium dioxide white pigments were prepared via without adding external seed from hot unconcentrated industrial titanyl sulfate solution obtained from titanium dioxide sulfate process. By particle size distribution, XRD, SEM, TEM, XPS, BET, chemical analysis and pigments property measurement, we studied the effects of main factors(pre-adding water volume ratio, feeding rate, aging time, Hydrolysis time, concentration of total titanium and F value) on the structures and pigments properties of rutile titanium dioxide white pigments, and optimized hydrolysis process parameters to produce high quality rutile white pigments, and also discussed the hydrolysis kinetics and hydrolysis mechanism. The results are as follows:(1) Low concentrations industrial titanyl sulfate solution hydrolysis via self-generated seed thermal hydrolysis process was kept at the total TiO2 concentration of about 195g/L, F value of about 1.91, iron-titanium ratio of about 0.25, and controlled 22% of the pre-adding water, 7.5ml/min of feeding rate, 30 min of aging time, 3h of hydrolysis time to obtain better quality of metatitanic particles. After salt treatment and calcination, it turn into rutile pigment Titanium, which have a good structure, a narrow particle size distribution, fine pigment properties.(2) Hydrolysis via low concentrations of industrial titanium solution through three stages: the induction period, the hydrolysis stage and ripening stage. Hydrolysis is first order reaction in the hydrolysis period, and controlled by surface growth. Hydrolysis time of the first derivative curve calculated basically agree with experimental turn grayed point time, and yied of hydrolysis between 15.5% and 17.9% at turn grayed point time, and the hydrolysis reaction line segment fitting linear equation has been calculated, the hydrolysis reaction of the pre-exponential factor lnk0 = 41.78s-1, activation energy Ea = 147.6kJ/mol.(3) Hydrolysis of low concentration industrial titanyl sulfate solution affected SO42-, and obtained metatitanic acid sample predominantly amorphous component, containing a small amount of anatase crystal structure of particles, which Ti O6 octahedral distortion occurs, a-axis reduce, c-axis increases. These samples have a porous structure, having a surface area in the vicinity of 270 m2/g, smaller pore size, larger pore volume, moisture volatiliza and SO42- decompose in metatitanic acid, drastically reduce the specific surface area, grain coalescence than grow, particle gap increases, the pore volume reduce after calcination. With prolonging hydrolysis time, the grain size is increase, and the grain growth can be divided into three stages: rapid growth phase, the transition phase and the grain growth of slow growth. Grain growth and particle aggregation have important relationship, mainly is aggregated between particles in the early, the latter mainly is ion attachment grew up in the particle surface. The obtained metatitanic acid particles via hydrolysis is with the size of 1 ~ 2?m. After 70? drying, metatitanic acid powder with size of 0.2 ~ 1.2?m,and average size of 581 nm. And the particle size of metatitanic acid is affected by the content of colloidal particles, primary particles size and grinding intensity.