The effect of pre-treatment on crossflow microfiltration of titanium dioxide dispersions

The influence of a coagulant type and operating parameters on crossflow microfiltration of aqueous dispersions of titanium dioxide was examined. Two types of coagulant for series of crossflow microfiltration experiments were used: inorganic * Al2(SO4)3 and organic * PRAESTOL. The experiments were carried out on a tubular ceramic microfiltration membrane with nominal size of pores 0.1 mm at various operating parameters. Preliminary tests were performed before crossflow microfiltration experiments and from results of these tests were chosen optimal doses of coagulants. The value of steady state permeate flux was experimentally evaluated for crossflow microfiltration with and without pre-treatment. The results of the experiments show that aluminium sulphate is a better coagulant for this system and its optimal concentration is 40 mg/L. The results also show that pre-treatment of the feed led to four or five times higher permeate flux than that without any pre-treatment.

TiO2 + 70 mg PRAESTOL TiO2 TiO2 + 50 mg PRAESTOL TiO2 + 30 mg PRAESTOL Fig. 3. Steady state value of the permeate flux as a function of pressure difference and dose of coagulant PRAESTOL. because with higher concentrations were problems with plugging of the pipe for drainage feed from feed tank, but the influence of this coagulant is significant for higher pressures (higher than 100 kPa). The comparison of these two types of coagulants is shown in Fig. 4. From this figure The results of the experiments show that during the ceramic membrane microfiltration of TiO2 dispersion the value of steady state permeate flux was significantly affected by the presence of coagulants. The use of suitable coagulants could significantly decrease the membrane fouling and increase the filtration flux. The more suitable coagulant for TiO2 microfiltration of tested types of coagulants is aluminium sulphate and the optimal dosage is 40 mg/L. The results also show that the value of steady state permeate flux significantly increases with pressure difference and the limit pressure difference was not achieved.