A pilot plant, capable of treating three tons of diatomaceous earth per day, has been operated to obtain optimum design criteria for scale-up to the commercial plant [1]. High quality filter aids, such as DICALITE [2] have been produced. A commercial plant has been completed in Kyongju city by scale up of this pilot plant test. Selective diatom-earth preparation, homogeneous calcination of diatom-cells-mixture, proper delumping and pneumatic concentration of diatom-cells are main process schemes [3]. The most efficient grinding effect has been obtained using a milling blower, as of two-cage disintegrator [4]. Variable-speed rotary kiln has been operated to convert the diatom-cells into more porous and pure products. Diatom-filter-aids, in the size range of 10-40 microns, are completely separated pneumatically by back wash cyclones.