Filtration Characteristics of Shirasu

Abstract

Shirasu is a kind of volcanic ash covering widely the area of South Kyushu. The mineral components of Shirasu consist of 60-80wt% volcanic glass and 40-20wt% crystalline minerals. The volcanic glass is porous and irregular and has small apparent density.For the purpose of using the volcanic glass contained in Shirasu as filter aid and filter medium, the authors carried out the compression permeability tests and measurement of porosity in case of loose and tight packings and surface factor on three samples: Shirasu A, B and C. The range of particle size of Shirasu B and C was 1190-37μ. Shirasu A was obtained by crushing Shirasu B and the particle size was in less than 44μ.The experimental results obtained are as follows.1) Shirasu B which is raw volcanic glass powder, has much porosity and irregularity in the region of more than about 300μ, and Shirasu C which is crushed volcanic glass powder, has the same properties in the region of more than about 200μ. Furthermore, Shirasu C is more porous and irregular than Shirasu B.2) Shirasu B and Shirasu C are more porous and irregular than sand. Therefore, it is considered that Shirasu is superior to sand as a filter medium.3) The compression permeability characteristics of Shirasu A are between those of Kaolin and Cement material and those of filter aids.The experimental equations of equilibrium porosity, ex, and permeation resistance, αx, are as follows.ex=0.613-0.578ps0.0536 αx=0.280×1011+0.337ps1.28Where ps is compressive pressure.