Study On The Preparation Of Modified Filter Packing And Its Properties In The Recovery Of Ferrosilicon From Red Mud

The rationally exploit and reuse of the waste resource is the most interesting issue of the environmental protection nowadays.Red mud is the by-product of alumina production through the Bayer chemical process,and it contains to a large number of metallic elements.In order to realize the comprehensive utilization of red mud,a ceramic filter material was prepared by recovered SiO2,which was as major leached component by two-step leaching process from red mud,and then modified by Iron-Titanium biometal oxide,after which was used for the removal of ammonia nitrogen and residual chlorine from drinking water.The main results are as following:(1)A majority of alkaline metal oxide from red mud was leached by low concentration hydrochloric acid in the first-step leaching process.The effects of hydrochloric acid concentration,S/L ratio,leaching temperature and leaching time on the leaching rate of each element were investigated by single factor experiment.The results showed that the concentration of hydrochloric acid was 3mol/L,the ratio of liquid to solid was 1:16g/ml,the leaching temperature was 90?,the leaching time was 1.5h,and most of the metal oxides were leached from red mud.Among them,the iron leaching rate was 95.4%,while that of aluminum leaching rate was 66.7%.SiO2 was enriched in the residue due to its insolubility in hydrochloric acid.(2)Leached residues of first-step as the material was leached by concentrated sulfuric acid(90%)at 90?,with solid to liquid ratio 1:10.The results showed that remaining titanium oxide in the acid residue dissolved in the heated,concentrated sulfuric acid.When acid concentration was 90%,S/L ratio was 1:10(g/ml),contact time was 2h,and temperature was 90 ?,silicon dioxide residue was recovered at a rate of approximately 80%.(3)The spherical ceramic filter material with a diameter of 1-2 mm under study was made of SiO2 as the principal raw material.Pulverized coal,sodium carbonate,limestone,bentonite and polyving akohol(PVA),as additives,which were introduced into a filter material.The effect of pretreatment time,sintering time and temperature,and proportions of raw material was investigated on the removal of ammonia nitrogen.Sintering temperature affects the apparent porosity of the filter material,which affects the adsorption of ammonia nitrogen in the water.The optimum preparing conditions of ceramic filter material was as follows:pretreated at 400? for 30min,sintered at 1000?for 40min and SiO2,bentonite,limestone,pulverized coal,and sodium carbonate were mixed at a mass ratio of 65:25:4:4:2.The BET surface areas of ceramic filter material was 2.3m2g-1,the isoelectric point was 3.0.In the drinking water,the initial concentration of ammonia nitrogen was 0.3mg/L,the removal rate of ammonia nitrogen was 66%.(4)The iron in the red mud was extracted with FeCl3·6H2O,and the ceramic filter material was modified by Fe-Ti biometal oxide.According to the results of characterization,many particle aggregates were on the surface of the material after modification,which can form more mesopore and higher BET surface areas.The results of FTIR showed that Fe-O bonds and Ti-O bonds were formed.And on this basis,Fe2+was utilized to improve the structure and performance of red mud granular filter material and to obtain a modified filter material.Based on the characterization results,the BET surface areas was raised to 18.1m2g-1,which is helpful to the removal of free residual chlorine from drinking water.The residual chlorine removal capacity of Fe2+/Fe-Ti modified ceramic filter material was largest at pH= 7.0,the removal efficiency reached 87.5%.(5)The removal mechanism of ammonia nitrogen and residual chlorine from drinking water was analyzed by characterization.According to the above result,before modification,the removal behavior of ammonia nitrogen were electrostatic adsorption and ion-exchange.After modification,the removal behavior of residual chlorine(ClO-,HCIO)by Fe2+/Fe-Ti modified ceramic filter material could be divided into three kinds of functions:electrostatic adsorption,reduction,and the form of Fe-O-Ti-Cl.The multifunction surafce of ceramic filter material was realized by the loading of Fe2+ and Fe-Ti biometal oxide.