Abstract: A single apparatus including a mixing vessel and mixing means for achieving a slurry of material introduced within the vessel. A filter is mounted within the vessel in the region of the material being mixed so as to be contacted by the slurry created. The filter is mounted within the vessel in such manner as to efficiently filter, efficiently separate particles from liquid, without interfering or hindering the proper mix action. Mixing, reacting, washing, filtering, vacuum or purge drying, and particle sizing of powdered or granular materials stemming from the slurry, for the process industry, is achieved by reason of the incorporation of the filter within the mixing chamber of a positive-action mixer as described.