Vacuum Filtration of Metal Hydroxide Sludges

The characterization of metal hydroxide sludges was approached from the viewpoint of developing a fundamental understanding of the mechanisms that define the response of these sludges to vacuum dewatering. Both individual metal and mixed-metal sludges were characterized by standard dewatering test procedures. Of the sludge parameters investigated, the characteristic floc size distribution had the greatest effect on the observed sludge dewatering rate. An empirical equation was developed that allowed for the rapid prediction of sludge specific resistance based upon a measurement of particle size. Metal hydroxide sludges were found to be amenable to polymer conditioning for improved vacuum dewatering rates. The mechanism of polymer action was determined to be interparticle bridging. Optimum polymer conditioning doses were correlated to the available floc surface area present in a sludge sample.