EFFECT OF GAS NUCLEI ON THE FILTRATION OF FINE PARTICLES WITH DIFFERENT SURFACE-PROPERTIES

The filtration response to degassing the slurry and refiltering the fi ltrate was studied on the following systems: naturally hydrophobic par ticles (d(50) approximate to 5 mu m coal), chemically induced hydropho bic particles (d(50) approximate to 3.5 mu m silica in 10(-4) M dodecy lamine hydrochloride, (DAH)), and hydrophilic particles (d(50) approxi mate to 3.5 mu m silica in the presence/absence of 10(-2) M Ca2+). For coal, degassing the slurry increased filtration rate, while the oppos ite occurred for silica in DAH solution. Upon re-filtering the filtrat e, a constant filtration rate was obtained for all the degassed sample s, while un-degassed samples gave a response similar to the filtration of the original slurry. It is proposed that the above differences res ult from gas nuclei in water and their effect on the interaction betwe en particles, which controls the apparent particle size and the effect ive surface area for filtration.