FILTRATION STUDIES OF SELECTED ANIONIC DYES USING ASYMMETRIC TITANIUM-DIOXIDE MEMBRANES ON POROUS STAINLESS-STEEL TUBES

Filtration studies using 0.2-mu m titanium dioxide membranes fused on porous stainless-steel tubes is reported for solutions containing sodium nitrate alone and in the presence of commercial anionic, direct and acid dyes. Solution pH was adjusted with dilute sodium hydroxide and nitric acid to maintain maximum solubility of all ions and simplify the system. Electrolyte rejections and color rejections were measured separately from pHvalues of 4-10. Tubes were supplied by Dupont Separation Systems (Seneca, SC, USA). Results show that the charge or ionic nature of the membrane surface was responsible for the ion rejections and decreased to near 0% as the salt concentration was raised to 5000 ppm. Dye rejection did not approach 0% at higher salt concentrations but remained above 20% for the acid dye, Acid Red 1, and 50% for the larger-molecular-weight direct dye, Direct Red 2. The results are interpreted in terms of existing theories for inorganic membranes.