The Preparation Of Natural Mineral Ceramic Microfiltration Membrane And The Study Of Removing Ions Mechanism

Porous ceramic membranes, as one kind separation material, have been playing an important role in industrial process because of their excellent chemical stability and mechanical strength, high temperature resistant, good acid and alkali resistant. Currently, the domestic microfiltration and ultrafiltration ceramic membrane fatories use α-Al2O3(purity99%or higher) as support raw materials and pure Al2O3, TiO2, ZrO2and their mixture as membrane materials. Prices of pure oxides are expensive. High costs limit application and popularization of ceramic membranes. In order to solve this problem, the inexpensive natural mineral materials, such as attapulgite and kaolin, were chosen as raw materials of membranes. Preparation methods of natural mineral ceramic membrane were studied. Characterizations of the structure and morphology of natural mineral ceramic membranes and separation effects of inorganic ions through natural mineral ceramic membranes were examined.Attapulgite membranes were prepared on the plane supports, clay-acid-modified-fly-ash, and tubular Al2O3supports by solid state sintering method. The influences of different factors during membrane preparation process were discussed and the optimum technological parameter was drawn. After the comparison of the plane and the tubular attapulgite membranes on surface morphology, pore size distribution and removal effects of inorganic ion (Fe2+and PO43-), the conclusion that performances of tubular membranes could compete those of plane membranes in all those aspects or even better could be drawed. The thickness of attapulgite membrane was about30μm. The pore size distribution was range from5to1000nm, mainly between7and70nm. Those parameters showed that the process from plane membranes to tubular membranes was successful. After treating simulated wastewater including inorganic ions with attapulgite membranes, the elimination mechanisms of inorganic ions were explored. The attapulgite membranes showed the minimum removal ratio of Ca2+, PO43-, Cl-at some specific pH. The highest removal ratio occurred at the specific concentration when dealing with different concentrations ions solution. Those two phenomena proved that adsorption, dielectric exclusion and donnan effect were the main elimination mechanism of the attapulgite membranes.The kaolinite membranes were successfully prepared on SiO2supports that had larger pure water flux. The morphology, structure and pore size distribution of the kaolinite membranes were studied. The thickness of kaolinite membrane was about30μm and most pores were around10nm. The removal ratios of Fe2+and PO43-through kaolinite membranes were extremely high. Moreover, the removal ratio decreased very little with the time increasing. The removal ratio of28mg/L Fe2+remained above99%in350minutes and the removal ratio of54mg/L PO43-was over90%in150minutes. SiO2supports could eliminate a part of inorganic ions because of adsorption. A large number of hydroxyl groups exist on the surface of SiO2and internal, which could increase the pure water flux of supports and reduce the removal ratio of inorganic ions. After preparation of membranes, membranes reinforced the removal efficiencies of inorganic ions (Fe2+and PO43-), particle sizes of which were smaller than the pore diameter, by dielectric exclusion and adsorption.