Displacement washing of filter cakes from porous particles

Abstract

• The displacement washing of filter cakes of mesoporous and macroporous silica gel par-ticles is investigated. • The total loading of the filter cakes is reduced to 1% of the initial loading though the inner pores contain 50% of the mother liquor. • Washing curves of porous particles show the same results as for nonporous quartz. • An equation is suggested to calculate the diffusion time of an ion from the inner pores of a material. • In dependence of the pore diameter of a material, it can be estimated whether particle perfusion or diffusion has the higher impact on the washing result. Filter cake washing is an appropriate method to remove mother liquor from filtered solids. The washing behavior of filter cakes consisting of mesoporous and macroporous silica gel particles was investigated. Due to the high porosity of the particles, about 50% of the mother liquor is contained in the inner pores. As the residual loading of the filter cake can be reduced to 1% of the initial loading, the pores are cleaned as well. Comparing the washing results to those of non porous quartz does not show a distinct diffusion area as proposed by literature so far. Therefore, calculations are performed to estimate the time it takes potassium ions to diffuse out of the inner pores and a simplified calculation formula is suggested. Moreover, the perfusion time of the single particle during the filter cake washing is estimated. Depending on the permeabilities of both the particles and the filter cake, the predominant process can be identified. Results show, that porous particles as such are not difficult to wash and that diffusion is not the limiting process. Depending on the pore diameter of a material, perfusion should be considered to be the process supporting the filter cake washing as well.