| Iron is one of the most common impurities in chemical and metallurgical processes.Currently,the traditional iron removal methods,including chemical precipitation,solvent extraction and ion exchange,are only used to remove iron impurities in high content from aqueous solutions.However,for the aqueous solutions containing trace amount of iron impurities and large amount of coexisted ions,it is difficult to deeply remove iron impurities through the traditional methods.Ion imprinted polymers(IIPs),due to the selectivity of functional groups and the imprinting effect of template ions,have exhibited good performance in selective recognition of target ions and became one of the most promising methods for deep removal of impurity ions.The preparation and regulation of IIPs are the key factors affecting the separation efficiency of this method.In this paper,several Fe(?)-IIPs were synthesized through different methods by using the template of Fe(?)ions and corresponding functional monomers.The prepared polymers were analyzed and characterized,and their adsorption performance was also evaluated.The Fe(?)-IIPs were applied to remove trace iron impurities from aqueous solutions containing chromium or vanadium and high iron removal efficiencies were achieved.The main innovative progress is summarized as follows:(1)An Fe(?)-IIP with carboxylic groups was synthesized by bulk polymerization.The synthesis conditions and adsorption behaviors of the Fe(?)-IIP were studied,and the prepared Fe(?)-IIP was used to deeply remove trace Fe(?)ions from Cr(?)-containing solutions.The experimental results indicated that the suitable molar ratio of functional monomers to template ions was 9:1.The selectivity coefficient and relative selectivity coefficient of the prepared Fe(?)-IIP for Fe(?)ions were 492.18 and 50.87 in the binary solution containing Fe(?)ions and Cr(?)ions,respectively,and the maximum adsorption capacity could be 114.25 mg g-1.The adsorption processes could be well fitted by the Langmuir isotherm model,the Freundlich isotherm model and the pseudo-second-order equation.The carboxylic groups were showed to combine the Fe(?)ions through electrostatic interactions,and the selectivity was derived from the functional groups and the three-dimensional pore structure of the polymer.Under the optimized adsorption conditions,94.43%of iron impurities could be removed by the Fe(?)-IIP in solutions containing 1.5 g L-1 of Cr(?)ions and the concentration of the residual iron was only 0.053 mg L-1.(2)Fe(?)-IIPs with amino or carboxyl functional groups were prepared on the surface of silica gel by surface imprinting method and their adsorption performances were studied.For the Fe(?)-IIP with amino groups,the content of amino groups on silica gel was 4.46%,and the values of selective coefficient and relative selective coefficient for Fe(?)ions were 81.88 and 8.06 in the binary solution containing Fe(?)ions and Cr(?)ions,respectively.However,its adsorption capacity was only 0.94 mg g-1.For the Fe(?)-IIP with carboxylic acid functional groups prepared by surface initiation method,the adsorption rate was much faster than the Fe(?)-IIP prepared by bulk polymerization method.(3)An Fe(?)-IIP with monophosphonic groups was synthesized and characterized and its adsorption behaviors in high concentration of Cr(?)solutions were studied.The results showed that the selectivity coefficient and relative selectivity coefficient for Fe(?)ions were 701.10 and 2.44 in the binary solution containing Fe(?)ions and Cr(?)ions,respectively.The monophosphonic groups were showed to combine the Fe(?)ions in the stoichiometric ratio of 3:1 through electrostatic interactions,and the selectivity was derived from the functional groups and the three-dimensional pore structure of the polymer.Under the optimized adsorption conditions,the adsorption capacity could reach 15.71 mg g-1 in solutions containing 10 g L-1 of Cr(?)ions.The adsorption processes could be well fitted by the Freundlich isotherm model and the pseudo-second-order equation.(4)The deep removal process of iron impurities from industrial basic chromium sulfate by using the Fe(?)-IIP with monophosphonic groups was studied.The results showed that under the optimized conditions,the iron impurities could be deeply removed from solutions containing 180 g L-1 of basic chromium sulfate.The content of iron impurities in basic chromium sulfate could be reduced from 111.31 mg kg-1 to 4.33 mg kg-1,and no obvious change of other quality indexes was found after the iron removal process.Compared with the Tulsion CH93 ion exchange resins,the prepared Fe(?)-IIP could achieve a better performance on iron impurity removal,a lower loss of trivalent chromium and an easier process for desorbing the removed iron.(5)The removal of iron impurities from vanadium-containing solutions was studied through a continuous adsorption process by using the Tulsion CH93 cation exchange resins and the Fe(?)-IIP with monophosphonic groups in order.The results showed that under the optimized adsorption conditions,96.39%of the iron impurities could be removed by using ion exchange method and the content of iron impurities could be reduced from 1 g L-1 to 30 mg L-1.Subsequently,92.70%of the iron impurities could be deeply removed by using the selected Fe(?)-IIP,and the content of iron impurities could be reduced from 30 mg L-1 to 2 mg L-1.Therefore,by using these two methods in order,the total iron removal rate could be as high as 99.74%. |
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