GB727106A - Improvements in the filtration of sludges - Google Patents

Abstract

A process for the continuous filtration of amorphous precipitation sludges comprises plotting a filtering efficiency curve for the sludge, i.e. curve with the rate of filtration of the sludge for a given filter area on the ordinate and the solids concentration of the sludge on the abscissa, determining the point on the curve at which the initial relatively gently-ascending portion gives way to a relatively steeply-ascending portion, and applying sludge to the filter at a concentration corresponding to a point on the steeply-ascending portion of the curve substantially past the point at which the curve begins to ascend steeply. The concentration may be effected in any known manner, e.g. with thickening or settling devices. The concentration of a cobalt hydroxide sludge is increased from 30 g./l. to about 1,200 to 1,300 g./l., the resultant filter cake having a moisture content as low as from 40 to 50 per cent. Mixed iron-compound-containing sludge on being concentrated from 120 to 1,200 g./l. yields, after filtration, filter cakes having a moisture content as low as from 30 to 35 per cent.