Лако-красочные материалы — производство

After hydrolysis, the liquid phase of the titanium oxide hydrate suspension contains 20-28% H2SO4 and various amounts of dissolved sulfates, depending on the raw material. The hydrate is filtered off from the solution (p4) (weak acid), and washed

with water or dilute acid. Even with acid washing, too many heavy metal ions are adsorbed on the hydrate for it to be directly usable in the production of white pigment. Most of the impurities can be removed by reduction (bleaching), whereby the filter cake is slurried with dilute acid (3-10%) at 50-90 °C and mixed with zinc or aluminum powder (q). Bleaching can also be carried out with powerful nonmetallic reducing agents (e. g., HOCH2-SO2Na). After a second filtration and washing process (p2), the hydrate only has low concentrations (ppm) of colored impurities but still contains chemisorbed 5-10% H2SO4. This cannot be removed by washing and is driven off by heating to a high temperature.