(238f) Concentration of Titania Waste Acid By Direct Contact Membrane Distillation: Influence of Ferrous Sulfate and Polyacrylamide on Flux and Rejection

Titanium dioxide or titania (TiO₂) is an important compound widely used in many fields. One of the commercial processes to produce TiO₂ is the “sulphate” process, in which for every ton of TiO₂ produced, around 6~8 tons of sulfuric acid (~20wt.%) will be generated. In our previous work, the concentration of the simulated acid by direct contact membrane distillation (DCMD) has been investigated preliminarily, an effort within the overall framework to identify new processes for reducing waste charge in TiO₂ industry. The current research is an extension with the emphases being influence on flux and rejection of DCMD by components brought along from TiO₂ generation: 1) inorganic salts; 2) organic compounds. At present stage, work regarding FeSO₄, a major inorganic salt, has been carried out. The experimental results indicate that crystallization of FeSO₄ evolved during the concentration. FeSO₄ crystals with different polymorphs settled on membrane surface and were also observed inside membrane structure. The rejection coefficient of the membrane in DCMD　did not correlate closely with FeSO₄ precipitation on and in the membrane structure. Additionally, higher feed flow rate changed obviously the surface fouling morphology and membrane flux variation. In the upcoming work, polyacrylamide (PAM) will be investigated in terms of membrane wetting. PAM is organic compound used in the step for flocculation settling of metatitanic acid (H₂TiO₃). The majority of PAM settles down during the process. How the residual PAM influence the MD will be investigated.