Abstract: Precipitated SiO₂ was produced via chemical precipitation method using fluosilicic acid wastewater and aluminum hydroxide as raw materials，meanwhile，the in situ modification was carried out using n-butaol as surface modifier in the pro- ducing process.The influence of the adding amount of n-butyl alcohol on the dispersity and oil absorbed value（DBP）was in- vestigated.Results demonstrated that when the adding amount of n-butyl alcohol was 3%，the average particle size（D 0.5） reduced from 32 μm to 830 nm，the specific surface area（BET） increased from 75 m2/g to 134 m²/g，and the oil absorbed value（DBP） increased from 2.2 mL/g to 3.25 mL/g.The modification enhanced the repulsion between the modified silica particles，weakened the aggregation，and improved the dispersion of modified precipitated SiO₂.

Key words: fluosilicic acid wastewater, precipitated silica, in situ modification, dispersity