Study On The Preparation Of Porous Iron Hydroxy Phosphate By Phosphating Slag And Its Photo-Fenton Degradation For Simulated Dyeing Wastewater

Phosphating slag is the by-product which generated during the phosphating treatment of metal surfaces.It contains a large amount of metal ions and phosphate ions and belongs to HW17 hazardous solid waste.It will seriously affect the ecological environment if it is discharged to the environment without disposal,therefore,the harmless and resource treatment of phosphating slag is of great significance.In this article,the phosphating slag was used as a raw material,and the hydrothermal purification treatment was performed on it.After purification,the content and crystallinity of the main component iron phosphate in the phosphating slag were improved.The purified iron phosphate was ball-milled.When the ball-to-material ratio was 6,the particle diameters of the iron phosphate and the iron hydroxy phosphate prepared by iron phosphate reached to the minimum values of 1.6μm and 2.9μm.Self-sacrifice template method was used to prepare porous iron hydroxy phosphate,and XRD,SEM,BET and TG-DTG characterization methods were used to investigate the preparation conditions of iron hydroxy phosphate.The results showed that the iron phosphate was completely crystallized to iron hydroxy phosphate when the hydrothermal time was 8 h.When the oxalic acid concentration was 0.4 mol/L,the pore structure of the porous iron hydroxy phosphate was relatively uniform and complete,and its specific surface area reached 10.75 m²/g.XRD,SEM and EDS were used to characterize the porous iron hydroxy phosphate.The results showed that its main components were iron hydroxy phosphate and iron oxide,which mainly contained three main elements of O,P,and Fe,and the mass fractions were 41.64%,16.20%,and 42.15%respectively.Porous iron hydroxy phosphate was used as the catalyst to degrade methylene blue solution in a heterogeneous Photo-Fenton system.The different systems,the amount of catalyst added,the amount of hydrogen peroxide added,the pH value and the initial concentration of the methylene solution,and the number of repeated use of catalysts on the degradation effect of simulated printing and dyeing wastewater were investigated.The results showed that the degradation of methylene blue was best when the catalyst was added at 1.5g/L,the hydrogen peroxide was added at 15 m M,and the printing and dyeing wastewater was weakly acidic in the UV/PIHP/H₂O₂ system and this system was suitable for the treatment of low-concentration printing and dyeing wastewater.The degradation rate of the catalyst after five cycles decreased by 11%,indicating that the catalyst had good reusability.Modified porous iron hydroxy phosphate was applied to degrade dyeing wastewater in the Photo-Fenton system.The modified catalysts were characterized by XRD,FTIR,SEM,TEM,TG-DTA,BET and UV-Vis DRS.The results showed that the photoactive iron ferric oxalate was successfully synthesized on the surface of porous iron hydroxy phosphate.The porous iron hydroxy phosphate precursor and iron oxalate had similar thermal decomposition and oxidation processes.The precursor undergone four stages in the process of heating up,which included loss of free water,loss of crystal water,precursor decomposition and precursor oxidation process.The pore structure of modified porous iron hydroxy phosphate became more complicated and the specific surface area was increased to 15.89 m²/g,the surface was dendritic,and it has excellent ultraviolet and visible light absorption effects.Rhodamine B solution was degradated under ultraviolet light,the effects of different degradation conditions on the degradation effect were investigated.The results showed that Rhodamine B had the best degradation effect in the UV/m-PIHP/H₂O₂ system when the catalyst concentration was 1 g/L,the concentration of hydrogen peroxide was 30 m M and the p H of the system was acidic.The Rhodamine B solution was degraded under visible light,and different degradation conditions were investigated through orthogonal experiments.The optimal degradation conditions were that the concentration of catalyst was 2 g/L,the concentration of hydrogen peroxide was 50 m M,and the pH of the system was acidic,and the primary and secondary order of influence on the degradation effect were the pH of system,the amount of catalyst added and the amount of hydrogen peroxide added.The results of cycling experiments showed that the catalyst gradually deactivated after six cycles,and the degradation efficiency was 15.2%of first degradation.The XPS results showed that the modified catalyst mainly contains four main elements:Fe,C,O,and P.The catalyst adsorbed the dye molecules and partially decomposed during the degradation process.In addition,the valences of Fe and C in the catalyst were both degraded after degradation.