Effect of ammonium salts on dispersive and adsorptive parameters of silicas precipitated from sodium metasilicate solution

Studies were conducted on precipitation of highly dispersed silicas from sodium metasilicate solution using five types of ammonium salts. Effects of the applied ammonium salts were examined on principal physicochemical parameters of the obtained silica (particle size, bulk density, tendency to form agglomerate structures) and on adsorptive parameters (specific surface area, volume and size of pores). In the course of precipitation the reactive system was supplemented with the hydrophobicity-inducing agent, Rokafenol N-9 (nonylphenyl polyoxyethylene glycol ether) and the system was mixed using a top stirrer or a homogeniser. The most active silicas were precipitated using ammonium hydrogen salts (NH4HCO3 and NH4H2PO4) without supplementation of non-ionic surfactant. Addition to the silica precipitation reactive system of a hydrophobicity-inducing agent and a rapidly revolving mixer clearly improved principal physicochemical, adsorptive and dispersive properties of the silica independently of the employed precipitating agent.