Preparation Optimization And Properties Of Hydrated Ferric Oxide Composites

Water eutrophication is caused by the phosphorus concentration in water exceeds0.02mg/L.Thus,it is an important measure of controlling water eutrophication to reduce phosphorus concentration in water.It is necessary to carry out deep phosphorus removal before discharging the secondary effluent,because the secondary effluent is an important source of phosphorus in water.At present,hydrated ferric oxide(HFO)composite adsorbents had become the focus of in-depth phosphorus removal research,because of large adsorption capacity,strong phosphorus selective adsorption and high elution performance.In this study,the three-step method of“Fe Cl₄^-ion exchange-Na OH precipitation-Cl^-transformation”was used to made composite adsorbent HFO-D213,the nanoscale HFO had been effectively loaded on the D213.First of all,eight kinds of composite adsorbents were made by adjusting the mixing mode of solution and resin in the three steps(B is Batch,C is Column),for screening out the best mixing mode,the material properties and adsorption properties of HFO-D213 were tested.Then,six kinds of composite adsorbents were made by controlling the concentration of HCl in the"Fe Cl₄^-ion exchange"step,and the greatest concentration of HCl was determined according to the material properties and adsorption properties.Finally,on the basis of optimized preparation conditions(mixing method and HCl concentration),single factor adsorption experiment was carried out with the response surface method to determine the optimal phosphorus removal conditions.(1)Changing the mixing method of the three steps of preparation,eight kinds of composite adsorbents were made by BBB,BBC,BCB,BCC,CBB,CBC,CCB and CCC,respectively.The results showed that the HFO loading(Fe%)of composite adsorbents(BBB,BBC,CBB,CBC)were made by batch mixing method was about 13%,which was significantly higher than 9%of column mixing method(BCB,BCC,CCB,CCC).There was no significant difference in the loading capacity of HFO made by different mixing methods in Fe Cl₄^-ion exchange and Cl^-transition steps.In addition,the distribution of HFO in the compound adsorbent showed U-shape,and the closer it was to the surface,the more it increased.Meanwhile,HFO was amorphous nanoparticles with an average particle size of about 3nm.The maximum adsorption capacity of BBB,BBC,CBB and CBC loaded HFO was about 12mg/g,which was significantly higher than that of column mixing mode 8mg/g.There was no significant difference in the maximum adsorption capacity of the eight kinds of composite adsorbents,which was about 40mg/g.The composite adsorbents reached adsorption equilibrium at 240min,and the R~2numerical values of quasi-first-order kinetic model were all greater than 0.997.When p H was 6?8,the equilibrium adsorption capacity of the HFO-D213was about 19.50mg/g,which is the best.When the concentrations of SO₄^2-,Cl^-and NO₃^-were all 600mg/L,the phosphorus adsorption capacity of the composite adsorbent decreased by55?73%,44?57%and 39?52%,respectively,and the inhibition effect was as follows:SO₄^2->Cl^-?NO₃^-.The optimum mixing mode was determined as BBB mode by considering the preparation operation,HFO loading capacity,phosphorus adsorption capacity,adsorption equilibrium time and influence of competing ions.(2)Adjusting the HCl concentration of"Fe Cl₄^-ion exchange"step(0?7mol/L),making six kinds of composite adsorbents(HFO-D213-0M,HFO-D213-0.5M,HFO-D213-1.0M,HFO-D213-3.0M,HFO-D213-5.0M,HFO-D213-7.0M).The results showed that with the increase of HCl concentration,HFO loading increased from 8.3%to 14.4%.The distribution of HFO in the HFO-D213 obeyed U-shape,and HFO was amorphous nanoparticles.As the HCl concentration increased from 0 to 7 mol/L,the maximum adsorption capacity of HFO increased first and then stabilized,and the adsorption capacity of HFO-D213-5.0M and HFO-D213-7.0M loaded HFO were about 17.0 mg/g.The maximum adsorption capacity of the six composite adsorbents was about 40mg/g.The composite adsorbent reached adsorption equilibrium in 240min,and the optimal p H was 6?8.When the concentration of competing ions was 600mg/L,the adsorption capacity of SO₄^2-,Cl^-and NO₃^-decreased by 56?69%,42?54%and 39?50%,respectively,and the inhibition order was SO₄^2->Cl^-?NO₃^-.Based on the results of preparation cost,environmental protection,material characterization and adsorption performance,5mol/L was determined as the optimal concentration of HCl.(3)Fixing HCl at 5mol/L,the composite adsorbent HFO-D213 was made by BBB mixing method,and the optimal phosphorus removal conditions were studied.Firstly,the upper and lower levels and ranges of temperature,p H,compound adsorbent dosage and initial phosphorus concentration were determined by single factor experiment as 15?35?,4.5?10.5,0.25?0.75g/L and 5?15mg/L,respectively.On this basis,according to Box-Behnken Design principle,the equilibrium adsorption capacity and phosphorus removal rate were used as evaluation indexes for response surface optimization.The optimal phosphorus removal conditions were as follows:temperature 23.5?,p H 6.45,compound adsorbent dosage 0.45g/L,initial phosphorus concentration 5.55mg/g.