Expanded concrete or mica used as filter bed - efficient as and more durable than carbon and pumice media

摘要

Filter bed granular material comprises artificially expanded solid particles, partic. cellular concrete and expanded mica. Expanding concrete and mica at different temps. can give prods. of controlled specific wts. 1.0-2.4 kg per dm3 and the particles are pref. employed in ranges of grain sizes of which the smallest is 0.7-1.4 mm and the biggest is 3-5 mm; this facilities the use of multi-layer filter beds with a different grain size range in each layer. The matl. is useful as a filter medium partic. for purifying drinking water. The new material is pref. to sand since it requires much less water for backwashing. About the same as carbon and pumice media. It has a surface coating which makes it more durable than carbon and pumice media.