Effect of Zeta Potential and Concentration on the Rejection Behavior of Calcium Carbonate by Ceramic Titanium Dioxide Nanofiltration Membrane

Amer Naji Ahmed; Ahmed Faiq Hassan; Mudhaffar Yacoub Hussein

Amer Naji Ahmed Ministry of Science and Technology-Directorate of Environment and Water Treatment
Ahmed Faiq Hassan Department of Chemical Engineering / University of Baghdad
Mudhaffar Yacoub Hussein Department of Oil Engineering / University of Misan

Keywords: Zeta potential, Salt rejection, Nanofiltration, Microelectrophoresis potential

Abstract

The rejection of calcium carbonate salt (CaCO₃) was investigated by using a ceramic titanium dioxide (TiO₂)-Alumina layered (Al₂O₃) nanofiltration membrane possessing a normal pore size of 0.9 nm.

The membrane was operated in the cross flow method. Measurements were conducted using several concentrations of salt (5.0 ppm and 10.0 ppm as under saturation), (13.0 ppm at saturation) and (50.0 ppm as above saturation), over different values of pH (3.0, 6.0 and 9.0), and at applied transmembrane pressure (TMP) changing from 1.0 to 15.0 bar. The feed solution at a flow velocities (1.0 and 2.0 m/s).

At constant pH (6.0) and velocity 1 m/s the rejection increases with increased pressure and reaches the highest value (61.0%) at (TMP), 6.0 bar with concentration (5.0 ppm), and then begins to decline with increasing pressure. Increasing both pH value and flow velocity increases rejection. Increased flow velocity from (1.0 m/s to 2.0 m/s), increases the rejection up to 6% at pH (6.0) and concentration 10.0 ppm. Maximum rejection was found equal to (70%) at (TMP) of 6.0 bar, concentration 5.0 ppm, pH 9.0 and velocity 2.0 m/s.

In the case of saturation, 50.0 ppm the rejection from the beginning decreases with increasing pressure. The monitored rejection characteristics were compared with zeta potentials of fine particles of the membrane were measured from electrophoretic (estimated by using electrophoresis method) material. The isoelectric point (i.e.p.) was at a pH 3.6. The TiO₂ membrane was negatively charged at pH higher than (i.e.p.) and positively charged at pH lower than (i.e.p.).