Preparation Of SiO₂/CuO Compisite And Light MgO Using Asbestos Tailings As Raw Material

As an asbestos producing country, plenty of asbestos tailings would be produced every year in China, which could occupy cultivated land and pollute the environment and thus become threaten to human health. Therefore many methods have been developed to process asbestos tailings and these methods could make use of the tailings in some extent. On the basis of former studies, some new ways have been developed in this paper. First the tailings should be treated by sulfuric acid solution. The treatment solution would be the Mg2+source of the product, light magnesium oxide (MgO). After treated, the tailings, most of which are amorphous SiO2fibers, would be used as supporting material to prepare SiO2/CuO composite, a kind of photocatalyst. The main results of this paper are as follows:(1) Porous SiO2/CuO composite could be prepared by hydrothermal decomposition method. The product, which is synthetized at120℃and has a high specific surface area146.11m2/g, performes the best catalytic activity and can decompose75%of80mg/L ethyl potassium xanthate in visible range within2h. With the mass proportion of SiO2:CuO increasing, the catalytic activity of the samples increases first, then decreases and is the best when the proportion was2:1.(2) Optimal synthesis conditions for samples prepared by hydro-thermal precipitation method are as follows. The molar ratio of urea/Cu(NO3)2is1.5and the reaction solution is treated at120℃for6h, then the precipitation is calcined at350℃for30min. Nano CuO particles, with particle size of about5nm, could be loaded on the surface of SiO2fibers and disperse over the surface of the fibers without obvious aggregation. The catalyst can decompose75%of150mg/L ethyl potassium xanthate in visible range within2h. Compared to pure CuO, the catalytic activity of the composite is strengthened.(3) Using Na2CO3as precipitating agent, optimal synthesis conditions for MgO precursor are as follows. The concentration of the precipitating agent is2mol/L, and the molar ratio of CO32-/Mg2+is1.8. The reaction solution is aged at80℃for8h. The product, with particle size of1～6μm, is Mg5(CO3)4(OH)2(H2O)4crystal and the yield is97.09%. The MgO powder, produced by calcining the precursor, meets national standards of industrial light magnesium oxide.