Precipitated silica

A process for the preparation of precipitated silica with the physical-chemical data:

• ______________________________________ BET surface:
• DIN 66131 100-130 m.sup.2 /g DBP absorption DIN 53601 .gtoreq.275 g/100 g (anhydrous) ASTM D 2414 Loss on drying DIN ISO 787/II (2 h/105.degree. C.) ASTM D 280 3.5-5.5 wt. % JIS K 5101/21 Oversize with ALPINE air-jet sieve:
• >63 .mu.m .ltoreq.10.0 wt. % >150 .mu.m .ltoreq.0.1 wt. % >250 .mu.m .ltoreq.0.01 wt. % ______________________________________
• comprising,
• a) introducing water at a temperature of 90.degree.-91.degree. C. into a precipitation vessel,
• b) adding, while stirring, commercial water glass with an SiO.sub.2 :Na.sub.2 O modulus of 3.34:1 (SiO.sub.2 =26.8 wt. %;
• Na.sub.2 O=8.0 wt. %) until a constant alkali value is reached,
• c) maintaining a constant temperature throughout the precipitation period of 90 minutes and simultaneously adding water glass and sulfuric acid at two separate places in the vessel such that a constant alkali value is maintained in the region of 5-15,
• d) acidifying the silica suspension with concentrated sulfuric acid until a pH-value of 8.5 is obtained,
• e) interrupting the precipitation reaction for 30 minutes with stirring,
• f) continuing with the acidification at 90.degree.-91.degree. C. with concentrated sulfuric acid until a pH-value of 4 is reached,
• g) separating the precipitated silica from the suspension having a solids content of approx. 88 g/l to obtain a filter cake by a chamber filter press,
• h) washing the filter cake obtained,
• i) liquefying the filter cake by means of water and mechanical shear forces, and
• j) drying the silica with the aid of a spray drier with a centrifugal atomizer or a spin flash drier.