AbstractAmorphous silica (white carbon black) has been prepared via a one‐step hydrochloride acidification of fly ash with the assistance of cetyl‐trimethylammonium bromide (CTAB) and polyethylene glycol (PEG). The effects of surfactant types and their concentration on the properties of amorphous silica have been investigated by X‐ray diffraction (XRD), particle size analysis and dibutyl phthalate (DBP) absorption value measurement. The results show that both the dispersity and hydrophobicity of the prepared silica modified by the mixed surfactants of CTAB and PEG are better than those modified by either CTAB or PEG individually. The particle size and DBP absorption value of the silica products are 3.2 µm and 3.11 cm3 · g−1 at the optimized CTAB concentration of 9 × 10−4 mol · L−1 and PEG dosage of 0.5 wt%, respectively. Consequently, the filtration time for the obtained silica is shortened as little as 3 min. It is worth mentioning that the purity of the products has been improved with the aid of the mixed surfactants. Copyright © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.