The invention pertains to a continuous process for the conversion of inorganic solid starting particles which either are amorphous or possess a degree of order into inorganic solid product particles which (a) when the starting particles are amorphous, possess a degree of order, or (b) when the starting particles possess a degree of order, possess a different order, a different degree of order, or no order, which product particles are suitable for use in or as a catalyst, in or as a carrier, or in or as an adsorbent, in which process the starting particles are dispersed in a liquid thus forming a suspension. The suspension flows through at least two separate conversion vessels (3) which are connected in series and the suspension is agitated in each of these vessels (3). The invention furthermore relates to an apparatus suitable for carrying out the process according to the invention. This invention allows the processing of suspension with a high Solids to Liquid Ratio.