Ceramics-Silikáty 59, (4) 275 - 282 (2015)

While the published research papers describe preparation of amorphous silica from water glass or using special methods (e.g. hydrolysis of alkoxides), the present study demonstrates a feasible solution for the cheaper synthesis of highly reactive silica using two-stage (acid and alkaline) leaching of serpentinite (Mg₃Si₂O₅(OH)₄). The alkaline leaching, the purification of sodium metasilicate solution and the effect of impurities on the precipitation of amorphous silica under the conditions of maximum sol stability using HCl, CO₂ and (NH₄)₂CO₃ as the precipitating agents were examined in more details. The prepared samples of silica were of high purity (99.4 % SiO₂), did not contain residues of the original raw serpentinite, and the size and shape of the particles were given by the conditions of precipitation. The presence of impurities in the sodium silicate solution had a beneficial effect on the specific surface area - in all cases the values for SiO₂ powders prepared from serpentine were higher than those of SiO₂ prepared from a synthetic solution of Na₂SiO₃. The specific surface area of SiO₂ samples synthesized under alkaline conditions has been much more affected by the presence of impurities if compared to that achieved by acidic precipitation.