| The cyanide wastewater discharged from the gold smelting process has caused huge threat to human health and ecological environment,and the efficient management and comprehensive utilization for cyanide have important scientific significance and utility value to promote the industry development and improve the economic and environmental benefits.Liquid membrane separation technology has the characteristics of high efficiency,energy saving,high permeability,high selectivity and high stability,which has been paid more and more attention in environmental protection and wastewater treatment.In this study,four kinds of liquid membrane separation systems were established for the treatment of cyanide wastewater to study the mass transfer process of cyanide in different liquid membrane systems.The mechanism of cyanide migration in different systems was explored,and the liquid membrane stability and its control mechanism were also analyzed.The results provide valuable theoretical basis and technical reference for the preparation of high performance liquid membrane material and its application in cyanide wastewater treatment.The bulk liquid membrane was prepared by using TOA as the carrier,and the effects of the initial concentration of the feed phase,the concentration of the strip solution,the stirring speed and the concentration of the carrier on the migration of the cyanide were investigated.The migration dynamic mass transfer process and mechanism of the cyanide were also analyzed and calculated.The optimum conditions were as follows: the concentration of the strip solution was 1%;the stirring speed was 250r/min;the carrier concentration was 2%;the migrate rate of the cyanide in low concentration cyanide wastewater was above 90%.After bulk liquid membrane was reused 5 times,the stability is basically same.In order to improve the extraction efficiency of cyanide,the emulsion liquid membrane with water-in-oil structure was used in the treatment of cyanide wastewater.The influence of preparation conditions on the stability of liquid membrane was investigated.Then,the effect of cyanide migration was analyzed from the microscopic parameters,and the suitable preparation condition: surfactant(Span-80)concentration was 3%;the membrane solvent(kerosene)concentration was 93%;the membrane adjuvant agent(liquid paraffin)concentration was 2%;the carrier(TOA)concentration was 2%;oil to inner ratio was 1:1,Rew was 1:7;stirring speed for preparing ELM was 3300 r / min;NaOH concentration was 2% and extraction time was10 min.The effect magnitude order of four factors on the total cyanide removal rate was determined by response surface methodology(RSM): NaOH> Span-80> Rew > TOA.The optimum extraction conditions were also obtained as follows: Span-80 concentration was 4.00%;TOA concentration was 3.91%;NaOH concentration was 1.00%;Rew was 0.27.Finally,the effects of centrifugation and ultrasonic demulsification on the recovery of cyanide were investigated.The optimum emulsion liquid membrane demulsification technology and operating conditions were determined.The supported liquid membrane does not require the complex preparation and demulsification process of ELM.However,the membrane solution of traditional supported liquid membrane was loss easily in operating process.In this way,the dispersion supported liquid membrane was prepared by combined the supporting liquid membrane with dispersion system,and mass transfer kinetics equation was also deduced.The four factors influencing the cyanide migration were studied by using the response surface methodology.The regression model was established to optimize the optimum extraction conditions for cyanide wastewater treatment,and the predicted highest extraction efficiency of cyanide was 98.40%.The maximum of actual extraction efficiency of cyanide was 97.14%,the error was only 0.17%.It was showed that the regression model of RSM was in good agreement with the actual extraction condition.The regression model has a good feasibility for the optimization of dispersion supported liquid membrane.When dispersion support liquid membrane was used to extract cyanide wastewater,compared with the traditional support liquid membrane,the extraction efficiency of cyanide increased by 13%,and stability had two fold increase.Based on the quantum-mechanical theory,the B3LYP/6-31G* method of DFT was used to calculate bindingenergy of [Bmim]+ with CuCN?Cu(CN)2-?Cu(CN)32-?Cu(CN)43-.The results showed that the energy of the four complexes could converge to the minimum value in the optimal binding position of the ionic liquid and the cyanide,and the energy of the four kinds of complexes can be converged to the minimum value.It was showed that the ionic liquid and cyanide could form stable complexes in theory,and the migration mechanism of cyanide in supporting ionic liquid membrane was further analyzed in the perspective of quantum chemistry.The supported ionic liquid membranes was prepared with three methods using the hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate([Bmim]PF6)as the membrane phase immobilized in the polyvinylidene fluoride microporous membrane(PVDF).The performance indexes of differents liquid membranes were investigated,and the optimum preparation method and oprating conditions were determined.The electrochemical impedance spectroscopy(EIS)was used to study the membrane solution loss during the mass transfer process.The electrochemical impedance spectroscopy was analyzed by equivalent circuit method.It was found that the equivalent circuit Rs(RmCm)Q could accurately describe the electrochemical impedance characteristics of the migration pool.It was related to the relationship between the membrane resistance or the membrane capacitance value and physical properties changes of supported ionic liquid membrane,which indicated that the change of the membrane resistance Rm and the capacitance Cm could reflect losslessly the loss of membrane solution in real time.The initial concentration of the feed phase,the concentration of the strip solution and the initial pH of the feed phase were explored and optimized during the cyanide extraction process.It was verified that shearing emulsification should be the main mechanism of membrane solution loss during cyanide extraction process with supported ionic liquid membrane.The optimum extraction conditions were determined as follows: the concentration of feed phase was 468.36mg/L;pH of feed phase was 4,the ionic liquid concentration was 30%;the membrane immersion time was 1h;the NaOH concentration was 3%;the extraction time was 1h;the extraction temperature was 25?;the extraction efficiency of cyanide was 95.31%.Microscopic characterization and physical properties showed that ionic liquid as membrane solvent could inhibit significantly the loss of membrane solution,which overcame the shortcomings of traditional supported liquid membrane.The method was simple and efficient,and it provided a new method and technology for the treatment of cyanide wastewater. |
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