Filtration and sedimentation behaviour of fibre/particle binary suspensions

The constant pressure filtration characteristics of cellulose fibres, titanium dioxide (rutile) and mixtures of the two were studied using a well controlled filtration apparatus. To interpret the filtration results, relevant fibre and particle physical properties were determined and the sedimentation behaviour of the binary suspensions quantified. The porosities (εav) of filter cakes formed from pure fibre and rutile suspensions were approximately 0.75 and 0.6 respectively. The general concept of additive porosity for binary mixtures agreed reasonably well with the experimental data. With filtrations at 450 kPa, the average specific cake resistances (αav) for pure fibre and rutile in deionised water were approximately 9.4x1013 and 4.2x1012 m kg-1 respectively, with the variation of αav with fibre fraction showing a minimum. Similar trends were observed at filtration pressures of 150 and 600 kPa. No minimum in αav was observed with 450 kPa filtrations of suspensions made using 0.1 M CaCl2 solution. It is concluded that the influences of solids composition and solution environment on αav are substantial for fibre/particle mixtures whilst the influence of filtration pressure is less evident.