Extraction and separation of Fe(Ⅲ) from heavy metal wastewater using P204 solvent impregnated resin
来源期刊：Rare Metals2018年第10期
论文作者：Qi Sun Li-Mei Yang Li Zhang Song-Tao Huang Zheng Xu
文章页码：894 - 903
摘 要：The extraction and separation of Fe（Ⅲ） from heavy metal wastewater generated in zinc smelting process were studied using solvent impregnated resin containing CLP204. The influence of pH and temperature on absorbing heavy metal cations by static adsorption was investigated.The batch tests on adsorption equilibrium, kinetics and elution efficiency were carried out to evaluate the performance of CL-P204. Column operations for extraction and separation of Fe（Ⅲ） by CL-P204 were performed for further optimization of process parameters and feasibility evaluation. The reaction mechanism of Fe（Ⅲ） and CL-P204 was analyzed through saturation capability, slope analysis and infrared spectroscopy （IR）. The results show that the separation of Fe（Ⅲ） from heavy metal wastewater using CLP204 can be achieved through process of adsorption and desorption at a flow rate of 1.53 ml·min-1·cm-2, pH 0.8 and temperature of 25℃. The experimental data of Fe（Ⅲ）adsorption by CL-P204 have a satisfactory fit with Langmuir adsorption equation and Freundlich adsorption isotherms.The probable molecular formula of extracted complex is Fe[R2（R2H）],and the adsorption reaction equation is concluded as following:Fe3++4RH KexFe[R2（R2H）]+3H+(Kex, extraction equilibrium constant). This study will supply the fundamentals for treatment of heavy metal wastewater.
稀有金属(英文版) 2018,37(10),894-903
Qi Sun Li-Mei Yang Li Zhang Song-Tao Huang Zheng Xu
National Engineering Laboratory of Biohydrometallurgy,General Research Institute for Nonferrous Metals
The extraction and separation of Fe(Ⅲ) from heavy metal wastewater generated in zinc smelting process were studied using solvent impregnated resin containing CLP204. The influence of pH and temperature on absorbing heavy metal cations by static adsorption was investigated.The batch tests on adsorption equilibrium, kinetics and elution efficiency were carried out to evaluate the performance of CL-P204. Column operations for extraction and separation of Fe(Ⅲ) by CL-P204 were performed for further optimization of process parameters and feasibility evaluation. The reaction mechanism of Fe(Ⅲ) and CL-P204 was analyzed through saturation capability, slope analysis and infrared spectroscopy (IR). The results show that the separation of Fe(Ⅲ) from heavy metal wastewater using CLP204 can be achieved through process of adsorption and desorption at a flow rate of 1.53 ml·min-1·cm-2, pH 0.8 and temperature of 25℃. The experimental data of Fe(Ⅲ)adsorption by CL-P204 have a satisfactory fit with Langmuir adsorption equation and Freundlich adsorption isotherms.The probable molecular formula of extracted complex is Fe[R2(R2H)],and the adsorption reaction equation is concluded as following:Fe3++4RH KexFe[R2(R2H)]+3H+(Kex, extraction equilibrium constant). This study will supply the fundamentals for treatment of heavy metal wastewater.
作者简介：*Li-Mei Yang e-mail: yanglm@grinm.com;
收稿日期：9 February 2015
基金：financially supported by the International S&T Cooperation Program of China(ISTCP) (No. 2014DFA90920);
Qi Sun Li-Mei Yang Li Zhang Song-Tao Huang Zheng Xu
National Engineering Laboratory of Biohydrometallurgy,General Research Institute for Nonferrous Metals
Abstract：
The extraction and separation of Fe(Ⅲ) from heavy metal wastewater generated in zinc smelting process were studied using solvent impregnated resin containing CLP204. The influence of pH and temperature on absorbing heavy metal cations by static adsorption was investigated.The batch tests on adsorption equilibrium, kinetics and elution efficiency were carried out to evaluate the performance of CL-P204. Column operations for extraction and separation of Fe(Ⅲ) by CL-P204 were performed for further optimization of process parameters and feasibility evaluation. The reaction mechanism of Fe(Ⅲ) and CL-P204 was analyzed through saturation capability, slope analysis and infrared spectroscopy (IR). The results show that the separation of Fe(Ⅲ) from heavy metal wastewater using CLP204 can be achieved through process of adsorption and desorption at a flow rate of 1.53 ml·min-1·cm-2, pH 0.8 and temperature of 25℃. The experimental data of Fe(Ⅲ)adsorption by CL-P204 have a satisfactory fit with Langmuir adsorption equation and Freundlich adsorption isotherms.The probable molecular formula of extracted complex is Fe[R2(R2H)],and the adsorption reaction equation is concluded as following:Fe3++4RHKexFe[R2(R2H)]+3H+(Kex, extraction equilibrium constant). This study will supply the fundamentals for treatment of heavy metal wastewater.
Keyword：
Extraction; Separation; Fe(Ⅲ); CL-P2O4; Heavy metal wastewater;
Received： 9 February 2015
1 Introduction
With the rapid development of mining and smelting industry,heavy metals pollution originated from metallurgy and acid mine drainage has become a serious problem in recent years.The heavy metal wastewater has a negative effect on environment and mankind if discharged without further treatments.Thus more attention should be paid to solve contamination produced from heavy metal wastewater
However,solvent extraction process is affected seriously by low concentration and iron impurity,especially Fe(Ⅲ).It can be extracted easily by most extractants,such as organic carboxylic acid,phosphoric acid,amine agents and neutral extractants,and comes into organic phase prior to other metals while stripping Fe(Ⅲ) from organic phase is difficult because of high bond energy of Fe(Ⅲ) and extractants
Increasing industries are seeking replacement of traditional metal recovery and separation techniques.Extraction chromatography is a category method combining characteristics of ion exchange with solvent extraction
There are also many researches on separation of heavy metals from wastewater using SIR for high efficiency.The concentrations of heavy metal cations,such as Cd(Ⅱ) and Cr(Ⅵ),are low after wastewater treatment using SIR
Above all,extraction chromatography not only have a good selectivity to cations and ease phase separation due to dealing with problem of stable emulsions formation,but also can accelerate the extraction and stripping of Fe(Ⅲ) during solvent extraction process for its multistage property
In current literature researches,much heavy metal wastewater contains rich metal cations such as iron,copper,nickel,cobalt,zinc and cadmium (Table 1)
Table 1 Concentration of heavy metal cations of zinc smelting wastewater in different manufacturers (mg·L-1)
*LD,lower than detection limit,0.1 mg·L-1
2 Experimental
2.1 Reagents and equipment
A synthetic sulfate solution was prepared to simulate zinc smelting wastewater by dissolved analytical reagent or technical grade sulfates of nickel,cobalt,copper,zinc,manganese,magnesium,cadmium,calcium and iron.The concentration of various heavy metal cations were shown in Table 2.The initial pH of simulated solution was adjusted to 0.8 by diluting H2SO4 and NaOH.P204 was supplied by Luoyang Zhong Da Chemical Co.,Ltd.The CL-P204 supplied by Division of Rare Metal Materials&Metallurgy was composed of 30 wt%P204,30 wt%porous material synthesized by styrene and pinylbenzene and 40 wt%deionized water.The particle size was149-301μm.
All batch tests were carried out in a beaker immersed into a temperature controlled bath.IKA RW20 digital motor stirrers and 50 or 55 mm diameter impeller was used for mixing.The pH value was measured using a Mettler Toledo electrode (InLab Routine Pro) coupled with a Seven excellence pH meter (S700-B).All column operations were conducted in a chromatographic column (Φ2.1 cm×25.0 cm)with a longer pump (YZ115IX-A) purchased from Bao Ding Longer Precision Pump Co.,Ltd to provide adequate power.The samples of aqueous solution were collected by automatic sampling instrument (BSZ-100) for assay.
2.2 Chemical analysis
Concentrations of heavy metal cations in aqueous solution were all determined by inductively coupled plasma optical emission spectroscopy (ICP-OES,Agilent 725) made in Agilent Technologies Inc.
The capacity of P204 in CL-P204 was measured by acid-base titration.According to the theory that similar structure agents are solvable easily each other,P204 can be dissolved so easily in ethanol that P204 can be transferred from the resin.The concentration of P204 in ethanol was measured by acid-base titration,while phenolphthalein was used as an indicator
Table 2 Theoretical concentration of heavy metal cations in syn-thetic solution (g·L-1)
2.3 Static adsorption
Static adsorption was a basic experiment method in which a certain amount of resin was prepared to mix simply with aqueous solution containing target cations in a vessel.Then the target cations pure solutions were obtained after the resin was scrubbed and eluted in a way similar to adsorption process.This method was suitable to make a trial at the beginning of the experiment.Equilibrium constant and capacity of SIR could be obtained easily.
2.3.1 Influence of pH on adsorption of heavy metal cations by CL-P204
To determine adsorption isotherms,a group of synthetic solutions (40 ml) were mixed adequately with 10.00 g CL-P204 in beakers at 400 r·min-1,25℃for 60 min until the equilibrium was achieved.The equilibrium pH values were adjusted to0.5-3.0 by diluting H2SO4 and NaOH,respectively.The amount of heavy metal cations absorbed on SIR was calculated by determining the amount in the supernatant after sorption.
Formulas for calculating adsorption and distribution coefficient of the cations are shown in Eqs.(1) and (2),respectively:
where E and D,respectively,represent the adsorption and the distribution coefficients,C0 and C are,respectively,initial concentration and equilibrium concentration of heavy metal cations in aqueous solution (g·L-1),M denotes the mass of resin (wet weight,g),and V is the volume of aqueous solution (ml)
2.3.2 Influence of temtperature on Fe(Ⅲ) adsorption by CL-P204
To analyze temperature effect on Fe(Ⅲ) adsorption by CL-P204,a group of single solutions (40 ml) containing 5 g·L-1Fe(Ⅲ) were prepared and mixed adequately with 5.00 g CL-P204 in beakers at 400 r·min-1 and pH 0.8 for 60 min.The system temperature was adjusted in the range of 20-50℃controlled by thermostatic water bath until the equilibrium was achieved.The amount of Fe(Ⅲ) absorbed on the resin was calculated by determining the amount in raffinate.
2.3.3 Adsorption distribution isotherm of Fe(Ⅲ) by CL-P204
To determine adsorption distribution isotherms,CL-P204with different mass were prepared and mixed with single solutions (40 ml) containing 5 g·L-1 Fe(Ⅲ) in beakers at400 r·min-1,pH 0.8 and 25℃for 60 min until the equilibrium was achieved.The amount of Fe(Ⅲ) absorbed on SIR was calculated by determining the amount in raffinate.
2.3.4 Elution efficiency of Fe(Ⅲ) absorbed on CL-P204
To analyze the elution efficiency of Fe(Ⅲ),some single solutions (40 ml) containing 5 g.L-1 Fe(Ⅲ) were prepared and mixed adequately with 5.00 g CL-P204 in beakers immersed into a temperature controlled bath at 400 r·min-1and 25℃for 60 min.After separated by filtering,the resin was washed with some deionized water and eluted with1-3 mol·L-1 H2SO4 and 0.1-6.0 mol·L-1 HCl,respectively.The raffinates were taken for assay.
2.3.5 Adsorption kinetics of Fe(Ⅲ) on CL-P204
To determine adsorption kinetics of cations,a certain amount of CL-P204 was mixed with single solution containing 5 g·L-1 Fe(Ⅲ) in a beaker at 400 r·min-1,pH 0.8and 25℃.Stirring time was recorded when stirrer worked.The samples were taken at a series of time interval for assay.
2.3.6 Batch tests on CL-P204 recycle
A certain mass of the resin was prepared to absorb Fe(Ⅲ)by multiple cycle courses,including adsorption,washing,desorption,and washing in beakers at 400 r·min-1 and25℃to evaluate the recyclability of CL-P204.The capacity of P204 and adsorption exchange capacity of Fe(Ⅲ) on CL-P204 after multiple cycles were measured by acid-base titration.
2.4 Column operations
Some CL-P204 was transferred into a chromatographic column using filter paper and some deionized water.The synthetic solution was prepared and flowed through the column with a peristaltic pump.The solutions from outlet were collected by BSZ-100 automatic sampling instrument and determined by ICP-OES.
2.4.1 Colummn operations on adsorbing Fe(Ⅲ)
To study adsorption properties of the metals in column,the CL-P204 (30 g in wet weight) was transferred into chromatographic column (Φ2.1 cm×25.0 cm).A feed solution was fed at a flow rate in a downward direction from top of the column.The residual metal aqueous solutions were taken for assay.
The breakthrough capacity and saturated exchange capacity can be calculated through Eqs.(3) and (4),respectively.
where M1 and M2 are,respectively,breakthrough capacity and saturated exchange capacity of CL-P204,V1 and V2 are bed volumes,respectively,when the resin is penetrated and saturated,and m is mass of the resin in the column.
2.4.2 Column operations on scrubbing impurities and stripping Fe(Ⅲ) from CL-P204
After adsorbing tests,the resin in the column was washed at a flow rate with 1 mol·L-1 H2SO4 and 2 mol·L-1 H2SO4successively and eluted subsequently by feeding 6 mol.L-1HCl solution at the same condition.The samples from the outlet were collected for assay.
3 Results and discussion
3.1 Metals adsorption isotherms
The CL-P204 is further tested for metals adsorption isotherms.The metal adsorption isotherms are shown in Fig.1.The results show that the adsorption of Fe(Ⅲ),Cu(Ⅱ),Ni(Ⅱ),Co(Ⅱ),Zn(Ⅱ) and Cd(Ⅱ) increases gradually with the increase of equilibrium pH.When the equilibrium pH is between 0.5 and 1.5,the adsorption of Fe(Ⅲ) is much higher than those of other cations.Therefore,separating Fe(Ⅲ) from other cations can be achieved at equilibrium pH range of 0.5-1.5.The equilibrium pH 0.8 is regarded as the best condition in this experiment.
Fig.1 Metals adsorption isotherms with simulation solution and CL-P204 at 25℃
3.2 Effect of temperature on Fe(Ⅲ) adsorption by CL-P204
A series of adsorption curves are obtained with singleFe(Ⅲ) solution (Fig.2).The adsorption and distribution ratio of Fe(Ⅲ) increase gradually as system temperature rises.57.75%Fe(Ⅲ) is absorbed at 52℃.The reason why adsorption of Fe(Ⅲ) is lower,compared with 100%mentioned above,is that Fe(Ⅲ) is so excessive that CL-P204 has been saturated.According to the thermodynamic equation of Clapeyron-Clausius in Eq.(5):
where T is system temperature,ΔH is reaction enthalpy,p is pressure of thermodynamic system and R is thermodynamic gas constant.Based on experimental data,the plot of T-1 versus lgD is linear (Fig.3).The reaction enthalpy is 266.48 kJ·mol-1,showing that the process is an endothermic reaction.
3.3 Adsorption distribution isotherm and its verification
Adsorption distribution isotherm of Fe(Ⅲ) is obtained(Fig.4).The results show that the concentration of Fe(Ⅲ)on resin goes up with the increase of concentration of Fe(Ⅲ) in aqueous solution.Initially,the isotherm upward tendency changes dramatically,then it begins to flatten even if the concentration of Fe(Ⅲ) in aqueous solution still increases.It is proved that CL-P204 has been saturated when the concentration of Fe(Ⅲ) in aqueous solution is greater than or equal to 1.5 g·L-1.The static exchange capacity of Fe(Ⅲ) absorbed on CL-P204 is 11.89 mg·g-1.
Fig.2 Effect of different temperatures on Fe(Ⅲ) adsorption by CL-P204 at pH 0.8
Fig.3 T-1 versus lgD for Fe(Ⅲ) adsorption by CL-P204 at pH 0.8
It can be seen obviously in Fig.4 that adsorption distribution isotherm of Fe(Ⅲ) by CL-P204 is fit perfectly with Langmuir equation.The Langmuir adsorption isotherm is shown in Eq.(6):
where qmax is the maximal adsorption capacity of monomolecular layer on the surface of resin particles,Caq is initial concentration of Fe(Ⅲ) and KL is the Langmuir constant.The higher the KL is,the larger the maximum adsorption amount of Fe(Ⅲ) on CL-P204 is
Fig.4 Adsorption distribution isotherm of Fe(Ⅲ) by CL-P204 at pH0.8 and temperature of 25℃
Fig.5 Caq Q-1 versus Caq for Fe(Ⅲ) adsorption by CL-P204 at pH0.8 and temperature of 25℃
Meanwhile,according to Freundlich equation shown in Eq.(7):
By taking the logarithm of Eq.(7) and rearrangement:
where k is adsorption equilibrium constant of Freundlich model,n is adsorption strength,Q (mg·g-1) is adsorption capacity before the resin is saturated,and C (mg·L-1) is the concentration of Fe(Ⅲ) in aqueous solution after the adsorption reached to equilibrium.The plot of lgC versus lgQ is linear,as shown in Fig.6.After calculated,n is 5.71and k is 10.75,and the Freundlich equation is shown in Eq.(9):
As to n>1,absorbing process is easy to be achieved
Fig.6 lgC versus lgQ for Fe(Ⅲ) adsorption by CL-P204 at pH 0.8and temperature of 25℃
As discussed above,RL and RF which are fitting degrees with Langmuir and Freundlich adsorption isotherm models are up to 0.99 and 0.95,respectively,showing that the experimental data of adsorption Fe(Ⅲ)by CL-P204 fit with Langmuir adsorption isotherm and Freundlich adsorption isotherm well.Both isotherms prove that adsorption process can be achieved easily.The adsorption parameters are shown in Table 3.
3.4 Elution efficiency of Fe(Ⅲ)
A series of tests on elution efficiency of Fe(Ⅲ) absorbed on CL-P204 were conducted with 1-3 mol·L-1 H2SO4 and0.1-6.0 mol·L-1 HCl.It can be seen from Fig.7 that Fe(Ⅲ) absorbed on CL-P204 is difficult to be stripped by H2SO4.Only 20.13%Fe(Ⅲ) can be stripped even3 mol·L-1 H2SO4 is used.However,with the increase of HCl concentration,the stripping of Fe(Ⅲ) rises sharply.The stripping rate is 99.56%when HCl concentration is up to 6 mol·L-1.Thus the recycle of resin can be achieved with 6 mol·L-1 HCl,while H2SO4 as diluent can be used to remove impurities.
3.5 Adsorption kinetics of Fe(Ⅲ) on CL-P204
CL-P204 is further tested for Fe(Ⅲ) adsorption kinetics.The curve of adsorption kinetics of Fe(Ⅲ) on CL-P204 is attained at pH 0.8 and temperature of 25℃(Fig.8).It can be seen that adsorption kinetics of Fe(Ⅲ) is fast and over87.3%Fe(Ⅲ) is adsorbed within 10 min.
Table 3 Equilibrium data of Fe(Ⅲ) adsorption by CL-P204
Fig.7 Elution efficiency of Fe(Ⅲ) on CL-P204 with different concentrations of H2SO4 and HCl
Fig.8 Fe(Ⅲ) adsorption kinetics with CL-P204 at pH 0.8 and temperature of 25℃
3.6 Influence of recycle on capacity of P204
The content of P204 and static adsorption capacity of Fe(Ⅲ) on CL-P204 after several cycle times are shown in Table 4.The loss of P204 and the static exchange capacity of Fe(Ⅲ) on the resin after six cycles reduce less than 5%,which indicates that the cyclic properties of CL-P204 are outstanding.
Table 4 Influence of cycle times on adsorption capacity of Fe(Ⅲ)and capacity of P204 on CL-P204
3.7 Column test on adsorbing Fe(Ⅲ) by CL-P204
The adsorption curves of the heavy metal cations at flow rates of1.53 and 3.06 ml·min-1 cm-2 are shown in Fig.9.It can be seen only when bed volume is less than 700 ml at flow rate of1.53 ml·min-1·cm-2 or 100 ml at flow rate of3.06 ml·min-1 cm-2 can Fe(Ⅲ) be absorbed completely.The breakthrough capacity and saturated exchange capacity at flow rates of 1.53 and 3.06 ml·min-1·cm-2 are shown in Table 5.The results prove that dynamic exchange capacities of Fe(Ⅲ) in CL-P204 at 1.53 ml·min-1·cm-2 are larger than that at3.06 ml.min-1·cm-2.Both dynamic exchange capacities are much lower than static exchange capacity because a small amount of Zn(Ⅱ) replace Fe(Ⅲ) on the resin.The results suggest that the flow rate of 1.53 ml·min-1·cm-2 is more appropriate to adsorb Fe(Ⅲ) by the resin.
3.8 Column test on scrubbing impurities and stripping Fe(Ⅲ)
The column tests for scrubbing and eluting were operated with 1 mol·L-1 H2SO4,2 mol·L-1 H2SO4 and 6 mol·L-1HCl at flow rates of 1.53 and 3.06 ml·min-1·cm-2,respectively.The scrubbing and stripping curves of the heavy metal cations are shown in Fig.10.It is found that impurities are washed off when 1 and 2 mol·L-1 H2SO4 are used.However,a small amount of Cu(Ⅱ),Zn(Ⅱ) and Mg(Ⅱ) exists in elution with 6 mol.L-1 HCl at a flow rate of 3.06 ml·min-1.cm-2compared with 1.53 ml·min-1·cm-2,which proves that the flow rate of 1.53 ml-min-1·cm-2 is more appropriate to scrub impurities and strip Fe(Ⅲ) from the resin.
Table 5 Dynamic exchange capacity of Fe(Ⅲ) on CL-P204 at dif-ferent flow rates
Fig.9 Column tests for adsorbing heavy metal cations at pH 0.8,temperature of 25℃and flow rate of a 1.53 ml·min-1·cm-2 and b 3.06 ml·min-1·cm-2
Fig.10 Column tests for scrubbing and stripping heavy metal cations at pH 0.8,temperature of 25℃and flow rate of a 1.53 ml·min-1·cm-2and b 3.06 ml·min-1·cm-2
3.9 Proposed adsorption mechanism of Fe(Ⅲ) by CL-P204
The content of P204 on CL-P204 contributes directly to adsorption capability of Fe(Ⅲ).The methods that analyze extraction mechanism in solvent extraction can also be applied to SIR.The saturation capability method,slope analysis and infrared (IR) spectroscopy were applied to study adsorption mechanism of Fe(Ⅲ) with CL-P204 in this paper.
The capacity of an extractant is a constant called saturation capability of extractant under certain conditions.It is considered theoretic ally that all extractants bond with metals cations thoroughly and they form extracted complex during mixture of organic phase and aqueous solution.Therefore,the composition of extracted complex was calculated according to molar ratio of extractant and metal cations.The content of P204 on CL-P204 is 0.911 mmol·g-1 through content analysis.The saturation capacity of Fe(Ⅲ) on CL-P204 is 11.89 mg·g-1,that is 0.213 mmol·g-1 through static adsorption.The extraction proportionality is 1.0:4.3,speculating that the molecular formula of extracted complex is Fe[R2(R2H)].
The slope analysis is a frequently used method to study adsorption mechanism of Fe(Ⅲ) with CL-P204.It is generally recognized that extraction reaction of Fe(Ⅲ) and P204 is a cation exchange process and the reaction mechanism is expressed as follows
The distribution ratio (D) is defined as:
where the subscript org denotes the species in the organic phase,the subscript aq denotes the species in the aqueous phase,and Kex is the extraction equilibrium constant.
By taking the logarithm of Eq.(13) and rearrangement:
where for constant organic volumes,balance of free active P204 concentration is calculated according to Eq.(15).
A small amount of Fe(Ⅲ) in aqueous solution is controlled during all the experiments,thus[RH]org>>[RH°]org.The plot of lgD versus lg[RH]is linear while taking equilibrium pH and temperature as constant.As seen in Fig.11,the slope of fit linear is 3.96,which proves that extracted complex is composed of 80 at%P204 and 20 at%Fe(Ⅲ) and the molecular formula is Fe[R2(R2H)].The result is consistent with that obtained by the saturation capability method.The adsorption mechanism can be expressed as Eq.(16).
Fig.11 lgD versus lg[RH]for Fe(Ⅲ) adsorption by CL-P204 at pH0.8 and temperature of 25℃
Fig.12 Infrared spectroscopy of a unabsorbed resin and b saturated resin in wavenumber range of 4000-400 cm
Changes of function groups of unabsorbed resin and Fe(Ⅲ) loaded resin were analyzed and compared by aid of IR spectrogram analysis in wavenumber range of 4000-400 cm-1 (Fig.12).It can been found that the hydroxyl radical of P-OH on CL-P204 without adsorbing Fe(Ⅲ) has a strong characteristic peak in wavenumber of 3440 cm-1,which may result from the stretching vibration of O-H.Intensity of O-H characteristic peak becomes smaller after CL-P204 is saturated with a large amount of Fe(Ⅲ) as hydrogen atom of O-H is exchanged by Fe(Ⅲ) through cation exchange process.The hydroxyl radical concentration on CL-P204 decreases.Thus,the intensity of stretching vibration of O-H also decreases.The stretching frequency of P=O for saturated resin moves from 1174 to 1229 cm-1obviously compared with unabsorbed resin.P204 is easy to form two dimers,and it forms hydrogen bond which leads to frequent decline due to electron density averaging in this process.The formation of extracted complex destroys hydrogen bond and makes the stretching frequencies of P=O blue-shift.The characteristic adsorption peaks of P-O-C have no significant moving before and after absorbing Fe(Ⅲ).However,the stretching intensity of P-O-C increases significantly.The probable reason is that the function of Fe(Ⅲ) and P204 can make dipole moment higher and the transition probability increases as well.
4 Conclusion
A series of experiments,composed of batch adsorption tests and column operations,on removing Fe(Ⅲ) from zinc smelting wastewater using CL-P204 were conducted.The results of batch adsorption tests show that the distribution coefficient of Fe(Ⅲ) is much higher than that of other cations and separating Fe(Ⅲ) from the wastewater can be achieved at pH 0.8 and temperature of 25℃.The static exchange capacity of Fe(Ⅲ) is 11.89 mg·g-1.The experimental data of Fe(Ⅲ) adsorption by CL-P204 fit with Langmuir adsorption equation and Freundlich adsorption equation well.The reaction enthalpy is 266.48 kJ·mol-1,showing that the process is an endothermic reaction.The results of Fe(Ⅲ) adsorption kinetics show that it is fast with 87.3%Fe(Ⅲ) being adsorbed within 10 min.The results of column operations show that Fe(Ⅲ) can be separated from the heavy metal wastewater through absorbing,scrubbing impurities two times with 1 mol·L-1H2SO4 and 2 mol·L-1 H2SO4 and eluting Fe(Ⅲ) one time with 6 mol·L-1 HCl at a flow rate of 1.53 ml·min-1.cm-2and temperature of 25℃.The FeCl3 purity of 97.47%is obtained finally.
The study on adsorption mechanism shows that the extraction proportionalities is 1:4 and the molecular formula of extracted complex is Fe[R2(R2H)].The adsorptionmechanism can be expressed as:
Acknowledgments This study was financially supported by the International S&T Cooperation Program of China (ISTCP)(No.2014DFA90920).
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