| China is the largest country in the textile printing and dyeing industry,so printing and dyeing wastewater is China's key polluting industries.Indigo wastewater is a kind of textile printing and dyeing wastewater,which has the characteristics of high color and organic pollutant content,large water quality change,large alkali and large variety of dyes,and poor biodegradability.The traditional pretreatment method is the coagulation sedimentation method,which is one of the physical methods.But the precipitates produced are classified as hazardous waste,pretreatment of wastewater brought new pollution problems at the same time.The photocatalytic reaction equipment is simple and easy to operate,the reaction is fast and efficient,the catalyst has a wide range of sources,more species,cheaper prices,and can meet the needs of different types of dyes.Iron oxyhydroxides are the important catalytic materials used in treatments of environmental pollutants,so they have been attended by many researchers.They can effectively remove heavy metals and nutrient elements in environmental media by coprecipitation,ion exchange,adsorption and so on.The synthesis of hydroxy iron oxide is usually divided into chemical synthesis and bio-mineralization.In this paper,the chemical synthesis of Akaganetite(?-FeOOH)and biosynthesis Schwertmannite(Sch-Bio)were studied.The TiO2 because of its cheap,no secondary pollution,catalytic ability,stable nature,in the photocatalytic performance of excellent performance.However,the catalytic effect of the single catalyst is limited.Therefore,the modification of iron minerals in the channel structure is discussed.The photocatalytic activity of ?-FeOOH,TiO2 and ?-FeOOH/TiO2,compared with the coagulation sedimentation method to explore the feasibility of photocatalysis as a pretreatment method.The nanoparticle material of P-FeOOH with middle pore can be prepared by hydrolysis and neutralization of ferric ion in FeCl3 solutions containing extrinsic surfactants or organic substances,but their amount of products by ferric hydrolysis were very low.Therefore,in this work,we investigated influence of the various temperatures(40,60,80?)on the iron precipitates of FeOOH formed in FeCl3 solutions adding extrinsic Brij30 or glucose(0.01%)after 3-days reaction.Results on XRD and FTIR data testified the formed iron minerals to be?-FeOOH phase with the better crystallinity,TEM and FESEM characterization data showed that all obtained ?-FeOOH particles with "Fusiform" morphology were 200-600nm in size.Brij30 and glucose(0.01%)could promote formation of iron mineral at 40?(little iron precipitate product observed in control treatment),while little difference in size was observed for those obtained from the FeCl3 solutions adding extrinsic glucose(0.01%)or in control treatment at the same temperatures,however,the size of ?-FeOOH from the FeCl3 solutions adding Brij30 at 60? was longer in particle sizes than those of formed products at 80?.The biological Schweitmannite was cultured from A ferrooxidans solution and cultured on shaker for 2 days.Different concentrations of AlPO4 were added to the solution with A ferrooxidans respectively.After 2 days of shaking,the mineral precipitate was collected.It was found that the addition of AIPO4 did not accelerate or slow down the process of oxidizing Fe2+by HX3,but the pH value of the solution reached the equilibrium time,and the mineral precipitation changed from reddish brown to bright yellow.The supernatant was detected.here are phosphorus elements which confirmed that AIPO4 was added to the bacterial growth process.Also,in addition to the formation of Schweitmannite,the discovery of the jarosite phase,indicating that AIPO4 accelerated Schweitmannite to the conversion of jarosite,and the sediment of the ore phase is also significantly different,but did not find out AIPO4 has modified effect on Schweitmannite.?-FeOOH/TiO2 was synthesized by TiO2 modified ?-FeOOH,because the modification of Akaganetite and Schweitmannite was not as good as expected.The degradation of indigo wastewater was observed under the condition of photocatalytic activity of ?-FeOOH/TiO2 composites,?-FeOOH and TiO2.With the prolongation of the irradiation time,the removal rate of COD and chroma of the catalyst increased gradually.After the best time was 2 hours,the removal rate was almost constant.The removal efficiencies of COD by ?-FeOOH,TiO2 and ?-FeOOH/TiO2 were 15%,22%and 31%,respectively.The removal efficiencies of chroma were 35%,42%and 48%,respectively.Under the photocatalytic conditions,the three catalysts are not ideal for the treatment of indigo wastewater.With the increase of catalyst concentration,the removal rate of COD and chromaticity also increased gradually.However,when the catalyst concentration was excessive,the removal rate of COD and chroma decreased.The reason is that the catalyst concentration is too high,the solution is turbid,affecting the light transmittance.Adjust the pH value of the catalyst on the COD and chroma removal rate,indigo in acidic or neutral conditions will precipitate,resulting in "acid discharge" phenomenon,and adjust the pH value in the engineering use is costly,not practical,so the effect of pH on the catalytic photocatalytic indigo wastewater was not discussed in depth.In combination with the Fenton method,the removal rate of COD and chroma was improved by 10%,especially ?-FeOOH/TiO2 on the removal of chroma up to 100%,but the three kinds of catalysts on the COD degradation efficiency is not high,the highest only 45%.The traditional coagulation sedimentation method,under the best conditions,the removal rate of COD is 25%,the removal rate of chroma is 95%.Compared with the conventional coagulation and sedimentation method,it is found that the effect of light-Fenton method on the treatment of indigo wastewater is higher than that of coagulation treatment method.Although the amount of waste produced is higher than that of coagulation treatment,so light-Fenton method can be used as one of the pretreatment of indigo wastewater. |
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