Study On The Emulsion Liquid Membrane With Carrier Extracting Cr～(3+) From Wastewater

The mass transfer with Emulsion Liquid Membranes with activity carrier can bemade up of the extraction and back extraction on the external phase and internalphase comparatively. The extraction with carrier and back extraction of Cr³⁺ fromartificial Wastewater and the mathematics models of Emulsion Liquid Membranewith carder extracting Cr³⁺ be studied in this paper.In the extraction experiment, On the basis of the investigation of a series ofcalixarenes and their derivatives extraction abilities for Cr³⁺ studied, it was foundthat the extraction selectivity for Cr³⁺ with p-tert-butylcalix[4]arene acetate(H_nL_(o)) isoutstanding. From the influences of major factors upon the extraction process includepH value, initial concentration of Cr³⁺ and activity carrier, temperature and rate ofrotation, The effect laws of the extraction distribution ratio of Cr³⁺ can be obtainedrespectively: The distribution ratio increases linearly with pH value, when the initialpH value is less than 5.3; With the increasing initial concentration of Cr³⁺, theextraction distribution ratio decreases firstly, then increases rapidly. When the initialCr³⁺ concentration is about 20mg/L, the distribution ratio achieves a minimum; Theextraction distribution ratio decreases rapidly as the carrier concentration in organicsolution raises in the extraction system, but later decreases slowly; The distributionratio increases linearly with the temperature; With rotation rate increasing, thedistribution ratio decreases firstly, then increases rapidly.Based on the molecular structure of the cup aromatic hydrocarbon and itsderivative, the mechanism of the p-tert-butylcalix[4]-arene acetate (hydrolisis of cup [4]) extraction of Cr³⁺ from the wastewater was predicted. By the slope method, itwas confirmed that the extraction of Cr³⁺ performed via the hydrolysis of cup [4]obeyed the positive ion exchange mechanism: Cr³⁺+H_nL_(o)→[CrH_n-1L_(o)]²⁺+H⁺; and it is obtained that the enthalpy is 69.89[kJ/mol],the free energy is-18.601 [kJ/mol] and the entropy is 294.97J/[mol·K].In the back extraction experiment, The NaOH is employed as back extractant toextract of Cr³⁺ from the organic phase. From the influences of major factors upon theback extraction process include pH value, temperature and rate of rotation, the molarratio,the effect laws of the back extraction distribution ratio of Cr³⁺ could beobtained respectively: The distribution ratio decreases linearly with pH value ofNaOH and decreases linearly with temperature and the rotation rate; With theincreasing the molar ratio, the extraction distribution ratio decreases firstly, thenincreases rapidly.By the slope method, the mechanism of extracting [CrH_n-1L_(o)]²⁺with theNaOH is [CrH_n-1L_(o)]²⁺ +8OH^-+3H₂O₂→2CrO₄^2-+2H_nL_(o)+8H₂O, and theenthalpy is 69.89[kJ/mol], the free energy is-18.601[kJ/mol]and the entropyis 294.97J/[mol.K].Studied on the mathematics models of Emulsion Liquid Membrane(ELM)system with carrier extracting Cr³⁺ from wastewater, three sets of equations weregained by resistance assumptions based on the advancing front model; Parameters ofthe mathematics models were gained from the designed experiments; Three solutionsof the mathematics model were gained by Matlab software, and the advancing frontmodel agrees well the mass transfer process in ELM system, It showed that,the majorresistances of the whole mass transfer process in this ELM system are theresistance of foreign boundary layer, the diffusion resistance in membrane, and theresistance of membrane broken., and the whole mass transfer process in this ELMsystem is controlled by the resistance of foreign boundary layer.