The Study On Filtration Properties And Backwashing Efficiencies Of Iron Oxide Coated Sand

Modified filter is a kind of new and ffective filter in recent years, the method for high temperature firing is adopted to get iron oxide coated sands filter inthis paper (hereinafter referred to as "IOCS"), put the IOCS filter as the main re-search object, with the small experimental device (mainly including coagulation, precipitation, filtering, backwash four systemic equipment), study the filtering properties and backwash experimental result of IOCS about the suspended in the water, organic matter, heavy metal three pollutants.Firstly, slap IOCS filter to the effect of remove kaolin quartz comparied with the original sand filter material, actived carbon-iron-coated sands combined filter performance, to explore IOCS’filtering effect of the turbidity and best backwash experimental plan. The experiment results show that IOCS filter has adventages on the small filter head loss, long operation cycle, strongly cut corrupt capability, its filtering properties is better than that quartz sands filter. The best experimental parameters of gas-water backwash are air rushed.qgas=12L/m2·s, t=2min;Gas-water mixing flush, qgas=13L/s·m2, qwater (the second stage)=8L/s·m2, t=5min;Rinse,qwater (the third stage)=6L/s·m2, t=4min.Put iron content ended drainage of backwash as the index, discuss the deciduous law of iron oxides by continuous experiments on the surface of IOCS, Iron oxides on the surface layer of besmeariris not openended fall off, along with the increase of number of backwash,quantity falled gradually tends0,after11filter cycle,the difference between IOCS with iron content and the original IOCS with iron content is very small, about0.0016g.SEM photos and energy dispersive X-ray spectrometer (EDS) analysis and detection show that the form of particles of kaolin adhesion in the surface of IOCS. After filtering, besmear of IOCS particles mainly include three kinds of elements Fe,O, Si. Gas-water backwash, kaolin particles adhesion on the coating are flushed away, the surface block (magnetite Fe3O4), needle (goethite alpha FeOOH) oxide to bare out, and its removal rate recovery.Secondly, doing the comparative experiments among IOCS filter and original quartz sand, active carbon-iron-coated sands combined filter about the removal efficiency of organic matter, the results show that the removal efficiency of organic matter of the IOCS, combined filter is significantly better than quartz sands filter. Using NaOH, FeCl3, FeCl3+NaOH, C6H8O7·H2O, KMnO4five kinds of agents on the IOCS filter material to regenerate, the experimental results show that:FeCb solution and NaOH+FeCl3solution, the regeneration effect on the two groups is good, can restore the removal rate of IOCS. The backwash best experimental parameters of the coated sands filter:ferric chloride solution soaking, q (=12L/s·m2, t=2min; q c=13L/s·m2, FeCl3solution and NaOH solution flush strength is8L/s·m2;Creci3=0.015mol/L, FeCl3solution flush time before, t=3min, NaOH solution flush time behind, t=3min, the flush time of gas and liquid mixing is6min; Rinse strength is8L/s·m2; t=4min. Backwash which took12min.SEM photos and energy dispersive X-ray spectrometer (EDS) analysis and detection shown: the surface of IOCS filter particle was closegrained covered by layers of humic acid, located in the surface layer of humic acid is easy to be washed out, adhesion of humic acid close to the coating layer is relatively difficult to be washed out. And humic acid layer cover on the coated iron sand particles combined filter is loose, can be cleaned by gas-water backwash. After filtering, IOCS filter particle coating’components elements mainly are Fe, O, C.Fe, O elements at the first, second, Celements in the third,its weight percentage is5.48%.Multilayer humic acid adhesion on the surface of IOCS closely, lead to backwash’s difficulty increase greatly.Finally, the filter removal experiments on heavy metal Fe3+show that IOCS filter to Fe3+significantly higher than the removal rate of quartz sand filter, removal rate is55%-90%, and filter cycle is long, about40h. The Fe3+removal rate of Quartz sand is low, removal rate is20%-40%, filter cycle to22h, removal rate has dropped significantly, filter cycle is short, about3Oh. Using common gas-water backwash, hydrochloric acid elixir backwash, sodium hydroxide elixir backwash, renewable experiment results show that:the common gas-water backwash, hydrochloric acid being added to backwash for IOCS was no regeneration effect, after the backwash the removal rate is20%-40%. Sodium hydroxide elixir backwash can fully recover the Fe3+removal rate on IOCS filter, after backwash,the average of Fe3+removal rate is more than90%.The best backwash conditions:q,t=12L／s·m2,NaOH solution soaking filter column t=2min； q(?)=13L／s·m2, qNaoH=6L／s·m2,t=5min；Rinse intensity9L／s·m2,t=4min.