Arsenic Adsorption, The New Al-si Mesoporous Materials

With the rapid development of the social economy and technology, the pollution of arsenic is increasingly serious. Recently, because the arsenic compounds are lethal toxicants and widely used in the agriculture and industry, environmental scientists around the world have paid attention to the problems brought out by arsenic compounds that contaminat the environment, especially the water sources. On the other hand, due to the abundant reserves of arsenic, the background concentration of arsenic in the groundwater in some areas of China is much higher than the maximum standards of drinking water, so that it does some serious harm to the local people. And according to the records, there are about 110,000 tons arsenic compounds by different means to enter the hydrosphere everyyear. Therefore, it makes important sense to remove the arsenic from wastewater or drinking water source at present.Adsorption is a simple wastewater treatment technology, with efficient, convenient and selective advantages, especially for the arsenic wastewater of low concentration, seriously polluted and other methods are difficult to deal effectively with. But adsorbent widely used in industrial for arsenic removal is inefficient, so developing of efficient adsorption for arsenic treatment is an important direction of research.The mesoporous molecular sieve was reported to have many advantages as follows: very high surface area, periodic hexagonal channels, tailoring of pore dimension, high thermal stability and facile modification of surface properties. And so it had very big potential applications in the catalytic chemistry and the adsorption-separation field. The studies of this thesis on the mesoporous molecular sieve SBA-15 included the following two parts:(1)The comparison and selection study on different types of sorbentsFist, MCM-41 was synthesized using CTAB as a structure-directing reagent, SBA-15 was synthesized using P123 as a structure-directing reagent. And then, Al(NO3)3·9H2O was selected as aluminum precursors to incorporate aluminum into MCM-41 and SBA-15 respectively. Last, commercial alumina, clinoptilolite and stilbite were selected as comparisons with SBA-15, MCM-41 and their modified materials in this study. The results showed that As(V) was not adsorbed by mesoporous molecular sieves MCM-41 and SBA-15 under experimental conditions(The initial concentration of arsenic was 44.703mg/l or 11.176mg/l, pH=6.60, room temperature 25±1℃,0.2g adsorbent); It can be found that 400℃-SBA-15-10%Al can achieve higher efficiency of arsenate adsorption compared with other adsorbents(MCM-41, commercial alumina, clinoptilolite and stilbite).(2)The study on adsorbent 400℃-SBA-15-10%AlThe absorbent 400℃-SBA-15-10%Al for arsenic adsorption was studied under static conditions. The effects of pH, adsorption time, initial arsenic concentration, adsorption temperature, coexisting ions and adsorbent dosage were investigated in the adsorption process at the same time.The results showed that the all effects of pH, adsorption time, initial arsenic concentration, adsorption temperature, coexisting ions and adsorbent dosage had different degrees of impact on the adsorption process. Adsorbent 400℃-SBA-15-10% Al had a high As(V) adsorption ability in a wide pH range (2.17～8.16), the maximum adsorption rate(85.23%) was in the vicinity of pH=6.60. The adsorption rate of 400℃-SBA-15-10% Al was decreasing with the increase of initial arsenic concentration. The adsorption rate was very low when initial arsenic concentration was 223.515mg/l. Adsorbent dosage was another important factor for the adsorption rate, the adsorption rate was increasing rapidly with the increase of adsorbent dosage. The absorption rate rapidly growed when the temerature increased in a short time, the impaction diminished after 540mins. The addition of NO3-, Cl-, SO42-, F- and PO43- all affected the As(V) adsorption, whereas the coexisting PO43- greatly interfered with the adsorption. NO3-,Cl- and SO42- had considerable degree of influence on the adsorption.Last, by the means of powder X-ray diffraction(XRD), scanning electron microscopy (SEM), low-temperature nitrogen adsorption-resorption technique, traasimission electron microscop(TEM), the absorbents were characterized.The results showed that aluminum was sucessfully inserted in the channels of SBA-15. The modified SBA-15 mesoporous molecular sieve had good mesoporons structure of chancels.