Constraints Of Generation Kinetics On Mineralogy Characteristics And Microbial Reduction Activities Of As(Ⅴ)-ferrihydrite

With the development of human society, As pollution problems are becoming more and more serious, has became an urgent environmental problem in the world today. Ferrihydrite (Fe5HO8·4H2O) is a potential high-efficient environmental material due to its large specific surface area and versatile abilities in holding anion. The most widespread usage of ferrihydrite in both research and application is the treatment of water which containins As. Using titration method, this study synthetised various ferrihydrites considering the titration rate and As concentration, to explore the content of As and the synthesis time effect on the mineralogical characteristics; at the same time, to carry out the aging experiment of the As-ferrihydrite under natural conditions, and the reductive decomposition experiment in presence of DIRB. In order to explore the effect of generated conditions (generation kinetics) on the transdormation and decomposition.Experimental results show that low OH-addition rate will cause the Fe(OH)x(3-x)+ radical polymerization, dehydration and generate the oxygen bridge connected with the Fe, the appearance of oxygen bridge can let 6L-Fh, goethite and hematite with certain crystallinity precipitate from solution directly. H2AsO4- can take over the function of OH-, but because the physical and chemical difference, the crystallinity of ferrihydrite is lower in the presence of As. The aging of ferrihydrite is solid phase transformation under neutral condition, initial product with higher crystallization degree will transform more complete. The crystallization of ferrihydrite which generated slower and less As is higher,performance in 6L-Fh.Natural experiment results show that under the neutral conditions, ferrihydrite transformed to other minerals by soild phase transformation, generated slower, less As added, better crystallinity ferrihydrite will transform faster. The transformed products are gorthite and hematite in mainly, the particle size will vary from 5nm-20nm with the decrease of As and longer synthesis time. A small amount of As will release during the conversion process, the addition of As has less affect on the release of As, the formation rate will affect the release of As more serious, the formation rate is slower, As release less.Microbial experiment results show that DIRB can dissolve ferrihydrite effectively, when adsorption node on ferrihydrite surface is not sufficient to hold As, As will be released into solution; generate time have great influence on crystallinity of ferrihydrite, the longer time the crystallinity of ferrihydrite is higher, the more difficult for DIRB to dissolute ferrihydrite; As content have great influence on ferrihydrite, the more As, the more difficult for the crystallinity of ferrihydrite and DIRB to dissolute ferrihydrite; under the action of DIRB ferrihydrite will transform into a product of higher degree of crystallinity.