Research On Iron (Hydr) Oxide Preparation And Loading And Adsorption Of HIOCs Pollutants

Iron belongs to a common variable-valence element with a small number in thenature which widely exists in soil particles and rock, aquatic sediment. They have a larger surface area and high reactivity, environmental compatibility, low price that have a good adsorption property on heavy metals and organic contaminants.Pentachlorophenol (PCP) is a typical representative of hydrophobic ionizable organic compound (HIOCs) which widely exists in soil, surface water and groundwater, in liquid, its existing form is PCP molecule and PCP ion, and different forms by pH values. Physical and chemical properties are extremely determined by environment pH value, complex environmental behavior. At present, its environmental effects and treatment process are not in-depth yet.To better understand the interaction mechanism on PCP of iron oxide (or hydroxide) minerals which widely exist in soil and liquid, the method that use interface interaction of iron oxide (or hydroxide) mineral to treat the hydrophobic ionizable organic compound contaminants in the soil and liquid is performed, so as to realize economical and safety soil remediation and liquid purification, and develop iron oxide (or hydroxide) mineral unit reactor to treat organic contaminants. Based on the previous researches, this essay presented researches on preparations, loads and characterizations of three kinds of iron oxide,α-FeOOH,α-Fe₂O₃, Fe₃O₄, as well as the property of adsorption on PCP which is a typical representative in HIOCs contaminants.Preparedα-FeOOH by aging chemical precipitation from the solution of FeCl₃-6H₂O and NaOH for 4 days under the constant temperature 40℃, and then carried out analysis and characterization in the preparation sample through X-ray diffraction, RTIR, TEM, laser particle sizer, BET surface area, acid-base titration and so on, as well as the related compared performances between natural and syntheticα-FeOOH. The result indicated that the FTIR characteristic absorption peak for syntheticα-FeOOH were 893cm^-1 and 796cm^-1, average particle radius was 364.9nm, BET surface area was 52m²/g, point of zero charge pH_ppzc =7.82; natural goethite be mainly divided into Fe₂O₃, followed by A1₂O₃ and SiO₂, with a high loss on ignition, and besides the crystal water, it also contained polysaccharide organic volatile. The FTIR characteristic absorption peak for syntheticα-FeOOH were 976cm^-1 and 464cm^-1, the micro-morphology was presented as helical and solid tube form, the tube radius is less than 2μm, BET surface area was 179.8m²/g which was 3.458 times of syntheticα-FeOOH's;point of zero charge of natural a-FeOOH pH_ppzc=7.18.The research on the adsorption property of synthetic and naturalα-FeOOH static on PCP indicated that, the adsorption rate of naturalα-FeOOH is slightly higher than the syntheticα-FeOOH's, both kinds of FeOOH reach the adsorption-desorption dynamic equilibrium in 2.5 hours, after the adsorption treatment on PCP solution with the initial concentration of 10mg/L, it found that the removal rates of synthetic and naturalα-FeOOH were 53.4% and 61.3% respectively. The concentration of treated PCP solution reduced to less than 5mg/L from 10mg/L that upgraded from third class to first class by (GB8978-1996) integrated wastewater discharge standard. The maximum adsorption capacity of synthetic ofα-FeOOH, 0.534mg/g, took place as the pH=6.0, for naturalα-FeOOH, it is 0.613mg/g at 6.0. The causal factor was that, comparing with syntheticα-FeOOH, naturalα-FeOOH had a larger BET surface area and higher surface site density. The adsorptions dynamics of natural and syntheticα-FeOOH on PCP in line with the first-order kinetics, the fitting kinetic equations were lgC = 1-0.1645t and lgC = 1-0.1325t respectively; the adsorption of naturalα-FeOOH on PCP accorded with the Freundlich isothermal equation; and with Langmuir isothermal equation for naturalα-FeOOH; the major adsorption mechanism forα-FeOOH on PCP was that adsorb PCP as hydrogen bond pattern by forming charge-dipole between >FeOH₂⁺ and C₆Cl₅O^-; after adsorption on PCP, natural and syntheticα-FeOOH could change toα-Fe₂O₃ by 500℃thermal regeneration, which with the adsorption capacity was better thanα-FeOOH's, and good effect remained after times of 500℃thermal regenerations.The research on adsorption performance of naturalα-FeOOH on organic pollutants in papermaking wastewater indicated that, naturalα-FeOOH had a higher adsorption rate on COD in papermaking wastewater, and adsorption equilibrium took place in 60 minutes, when the concentration of COD in the wastewater was 394mg/L, 68.89% of COD changed to solid from liquid phase, when the concentration of COD below 150mg/L after mix papermaking wastewater and receiving water, the COD level in the treated wastewater met the demand of surface water quality I in GB3883-2002; the type of adsorption isotherm belonged to Langmuir, saturated adsorption rm=8.006mgCOD/g, adsorption constant k=10.26; phase change was carried out from natural goethite adsorption organic compound toα-Fe₂O₃ by 500℃calcinations, desorption rate was 87% after one time regeneration, good effect for adsorption capacity remained after times of adsorption-desorption.Preparedα-Fe₂O₃ by using homogeneous precipitation, and then testified the composition through X-ray diffract, FTIR and HRTEM, the crystallization of generatedα-Fe₂O₃ was good with no other impurities which belonged to hexagonal crystal, particle radius was less than 300nm, specific surface area was 37.24m²/g, point of zero charge of natural pH_ppzc =7.65.The research of adsorption performance for syntheticα-Fe₂O₃ on PCP indicated that, the adsorption on PCP of syntheticα-Fe₂O₃ reached adsorption-desorption dynamic equilibrium in 2.5 hours, the adsorptions dynamics accorded with the first order kinetics; fitting by Langmuir equation was preferred, the active group number in unit area ofα-Fe₂O₃ was larger thanα-FeOOH's, better effect on PCP ofα-Fe₂O₃ by searing under 500℃for 60 minutes after the first time of adsorption, the adsorption performance could still remain 99.8% after 6 times of regenerations. The maximum adsorption capacity 6.5 mg/g occurred at the time when the pH value was 6.0, adsorption mechanism mainly belonged to electrostatic adsorption and with hydrogen bond as assistant, when the pH value at point of zero discharge reached7.65, the main adsorption method depended on hydrogen bond.Prepared magnetite by using coprecipitation, the synthetic sample was approved to be high purity Fe₃O₄ by X-ray diffraction, and then calculated the average particle radius to be 25nm by formula Debye-Scherrer, the laser particle analysis showed that average radius was 27.2nm. The adsorption rate of Fe₃O₄ on PCP was lower than goethite and hematite's, when the pH value was 5, the adsorption capacity was the highest, 0.35mg/g, and the minimum adsorption capacity was lower than goethite and hematite's, Freundlich for adsorption isotherm was preferred.Theα-Fe₂O₃ has a effected adsorption on the PCP, however, it is a powder material which is loose, easy hydrolysis and amorphous, and it has a poor permeability performance when used in fixed bed, moving bed reactor during intermittent process, difficult to dehydrate and big loss of adsorbent are its disadvantages, at the same time, it also produces a large amount of sludge and need additional treatment cost, based on previous which loadedα-Fe₂O₃ on quartz sand to prepare filter, this essay firstly, loadedα-Fe₂O₃ on the ceramic filtration ball which has a lager surface area, high porosity and low density through coprecipitation, and used detection technologies such as scanning electron microscope (SEM), BET surface area(BET), X-ray diffraction(XRD), and high-resolution transmission electron microscopy (HRTEM) and so on to take analysis and characterization on loadα-Fe₂O₃, and load iron amount, adhesive performance, anti-acid and anti-base capacity is tested to show the performance of loadα-Fe₂O₃.Took Fe(NO₃)₃.9H₂O as raw materials and urea for homogeneous precipitant, loadedα-Fe₂O₃ on the ceramic filtration ball by coprecipitation. When molar ratio of CO(NH₂)₂ and Fe(NO₃)₃.9H₂O was 1.0 and the weight ratio of Fe(NO₃)₃.9H₂O and ceramic filtration ball was 0.2, heated ceramic filtration at 600℃for 1 hour, after this, the BET surface area increased from 0.973m²/g to 5.639m²/g which was 5.8 times than before, the pH value at point of zero charge increased from 5.8 to 7.8, load absorbentα-Fe₂O₃ had good performances on mechanical stability, anti-acid and anti-base, the weight loss rates were 0.352%, 2.387% and 0.568% respectively.The dynamic process of static adsorption of loadα-Fe₂O₃ on PCP was similar withα-Fe₂O₃'s, but the equilibrium adsorption capacity, 0.19 mg/g, was only 29.23% ofα-Fe₂O₃'s, 0.65mg/g; PCP removal rate presented a good relativity with the BET surface area of loadα-Fe₂O₃, it was clear that, as the incensement of BET surface area, the removal rate increased; the removal rate changed by the different pH values and adsorption mechanism of loadα-Fe₂O₃ on PCP were similar withα-Fe₂O₃ powder's; distributive ratio and thermodynamics temperature regression equation of loadα-Fe₂O₃ on PCP, lnD=2.0577/T-1.8869, adsorption heat of adsorption reaction,â–³H =-17.1kJ/mol. The dynamic adsorption experiment of loadα-Fe₂O₃ on PCP showed that, when the loading height of absorption column was 30cm, empty bed contact time(EBCT) were 8 min, 12min, 16min respectively, the level of out water accorded to GB8978-1996 level 1 treatment time, which were 271min, 516min, 805min, the cumulative water production were 12810.5ml, 16211ml, 18955.6ml, bed rate were 50.28BV, 43BV, 34BV, the absorption capacity were 83%, 71% and 56% of static absorption capacity. Regeneration effect of adsorption of loadα-Fe₂O₃ on PCP was good, and the penetrated curve of PCP almost had no change after three times of regnerations at 600℃.In order to study on the performance of fixed bed honeycomb sorbentα-Fe₂O₃ on PCP, first time used oxygen-consuming corrosion on iron to productα-Fe₂O₃. The X-ray diffraction analysis on the pure iron assisted by oxygen showed that, besides Fe₃O₄, the surface does also includedα-Fe₂O₃, but the Raman Spectraon analysis on surface does indicted that, there was only one component,α-Fe₂O₃; the component in the middle layer of the samples was mainly divided into Fe₃O₄, followed with slight amount ofγ-FeOOH andα-Fe₂O₃; SEM analysis found that the surface oxide presented as dendrite, the pH value on the surface averagely was 7.22, the adsorption equilibrium time of loadα-Fe₂O₃ on PCP generated in-situ was 2.5 hours, peak occurred when the pH value was about 5.5, the maximum adsorption capacity was 0.55mg/cm²; Langmuir isothermal equation was preferred for fitting, it could regenerate by searing under 500℃for 1 hour, and the adsorption performance could still remain 99.9% after 4 times regenerations.As an absorbent on PCP in HIOCs wasterwater for adsorption treatment use,α-Fe₂O₃ will have a potential application prospect.