Synthesis Of Attapulgite Membrane Module And Its Application In Boiler Wastewater Treatment

After decades of development, the membrane separation technology has been widely applied on water treatment, notably the inorganic ceramic membranes. The inorganic ceramic membranes have become the top choice of hot wastewater treatment due to their excellent mechanical property, chemical stability and caustic wash resistance.In this paper, we prepared the tubular ceramic membranes using the commercial 19 channel Al2O3 ceramic tubes (pore size 8μm) as the support and the attapulgite (ATP) with size of 30-40 nm as the coating material. The dispersant selection, the amount of the dispersant, the concentration of the ATP and the sintering temperature were investigated as the factors influencing the ATP film-forming properties. The stable aqueous suspension system of 3wt% ATP nano powders can be obtained with 0.2 wt% sodium hexametaphosphate as a dispersing agent. The film was formed with the suspension system coating on the inner surface of the microporous Al2O3 ceramic tubular support through the dip slurry coating method, followed by being sintered into the asymmetric membrane at 650℃ through the solid-state plasma sintering method. Al2O3 support and the ATP membrane were characterized by mercury porosimetry, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the average pore size of the ATP membrane is 35.56 nm, much smaller than the average pore size of the support (～8μm). Negligible changes of the ATP lattice structure were observed after sintering, in which the original metal/non-metal oxide phase was still retained.We treated the phosphates, sulfates and carbonates contained in the simulated boiler wastewater by the ATP tubular membrane module in cross-flow mode. It suggests that the ATP membrane can efficiently remove the PO43-, SO42-, CO32- whose radius are far less than the membrane pore size. The removal rates for the PO43-, SO42-, and CO32- are 39.40%,58.37% and 49.11%, respectively. The removal mechanism of the ATP membrane may be the adsorption and the donnan exclusion. The effects of oleic, colloidal, and precipitate on the ATP membrane properties were studied and the cleaning procedure was determined. The results show that the ATP membrane has a powerful contamination resistance, the flux of which can recovery to 98.16% after cleaning.In order to improve the removal performance of the ATP membrane, nano-titanium dioxide (TiO2) powder doped ATP membrane was prepared. When the doping ratio of the nano TiO2 and the ATP is 1:4.5, the modified membrane has an improved removal rate for PO43-, SO42- and CO32- contained in the boiler wastewater.