The invention relates to a process for producing aqueous silica-based sols which comprises providing a cationic ion exchange resin having at least part of its ion exchange capacity in hydrogen form; bringing said ion exchange resin in contact with an aqueous alkali metal silicate to form an aqueous slurry; adjusting the pH of the aqueous slurry and separating the ion exchange resin from the aqueous slurry, as well as the silica-based sols obtained by the process.The invention also relates to silica-based sols obtained by the process, as well as a process for producing paper which comprises providing an aqueous suspension comprising cellulosic fibres; adding to the suspension one or more drainage and retention aids comprising a silica-based sol according to the invention; and dewatering the obtained suspension to provide a sheet or web of paper.