In this study, the removal of nitrate NO À 3 À Á ions from aqueous streams with liquid membrane technique has been investigated. Among the other parameters (temperature, pH, acceptor phase type and medium concentration), the stirring speed was chosen as process parameter. From the experimental results, it has been determined that the reaction was diffusion controlled. The transport ef®ciency of nitrate ions increased with increasing stirring speed. The membrane entrance and exit rate constants (k 1d , k 2m and k 2a respectively) were linearly dependent on the stirring speed ratios of 100 to 250 rpm.Coupled transport of nitrate ions through a liquid membrane in 85% n-hexane-15% tricloromethane as diluent, containing tetraoctyl ammonium chloride (TOACl) as a carrier was examined at various stirring speeds. Membrane entrance (k 1d ) and exit rates (k 2m and k 2a ) increase with increasing the stirring speeds. The diffusion of the nitrate ion-carrier complex through the narrow stagnant layers was found to be rate determining step. The membrane was stable during the transport experiments. There is no leakage of carrier or nitrate ion-carrier complex to both aqueous phases and also, no supplementary water penetration into the membrane. This favours interfacial reaction of nitrate ion and carrier.List of symbols C a nitrate ion concentration in acceptor phase, (mol/l, M) C d nitrate ion concentration in donor phase, (mol/l, M) C m nitrate ion concentration in organic (membrane) phase, (mol/l, M) C d0 initial nitrate ion concentration in donor phase, (mol/l, M) k 1 membrane entrance rate constant, (min )1 ) k 2 membrane exit rate constant, (min )1 ) k 1d membrane entrance rate constant, (min )1 ) k 2a membrane exit rate constant, (min )1 ) k 2m membrane exit rate constant, (min )1 ) R a reduced nitrate concentration in acceptor phase, (dimensionless) R d reduced nitrate concentration in donor phase, (dimensionless) R m reduced nitrate concentration in organic (membrane) phase, (dimensionless) R m,max maximum reduced nitrate concen. in membrane phase, (dimensionless) R reduced nitrate ion concentration, (dimensionless) S dp/mem interface surface of donor phase over per unit of membrane, (cm 2 ) S ap/mem interface surface of acceptor phase over per unit of membrane, (cm 2 ) t time, (min) T max time which nitrate ions concentration becoming maximum, (min) T temperature, (°K) TOACl tetraoctyl ammonium chloride l i distance between phases, (cm) k wave length of UV spectrum e extinction coef®cient of UV spectrum x stirring speed (rev/min, rpm) x a stirring speed of acceptor phase (rev/min, rpm) x d stirring speed of donor phase (rev/min, rpm) x m stirring speed of organic (membrane) phase, (rev/min, rpm)
In this study, the removal of nitrate ions from aqueous solutions with liquid membrane technique has been investigated for different organic solvent types in which solubilized tetradecyl trimethyl ammonium bromide (TDTMABr) as carrier. n-butyl alcohol, chloroform, and mixture of chloroform + n-hexane (n-hexane 85% + chloroform 15%) were used as organic solvent. Kinetic parameters (k 1d , k 2m , k 2a , t max , R m max , J m max , J a max ) were calculated from obtained data. time R a values of mixture, butyl alcohol, and chloroform are 0.81, 0.78, and 0.55, respectively. Similarly R d , R m , and t max values of the mixture equal to 0.14, 0.04, and 87.92 min, respectively. This behavior of the system shows the organic solvent type is an effective parameter on separation yield. It can be concluded that the mixture is the most effective organic solvent type among the investigated ones, because liquid membrane systems should be operated within the range of having the R m , R d , and t max values are minimum while R a values are maximum.Keywords Liquid membrane AE Nitrate removal AE Organic solvent typeList of symbols C a nitrate ion concentration in acceptor phase (mol l À1 , M) C carrier carrier concentration (mol l À1 , M) C do nitrate concentration in the donor phase at t = 0 moment (mol l À1 , M) C m nitrate concentration in organic (membrane) phase (mol l À1 , M) D QNO 3 mean diffusion coefficient of the complex in the membrane of thickness l (m 2 s À1 ) J a max maximum value of membrane exit flux (min À1 ) J d max maximum value of membrane entrance flux (min À1 ) k 1 membrane entrance rate constant (min À1 ) k 2 membrane exit rate constant (min À1 ) k 1d membrane entrance or leak to membrane rate constant (min À1 ) k 2a acceptor phase entrance rate constant (min À1 ) k 2m membrane phase exit rate constant (min À1 ) K equilibrium constant (-) R reduced nitrate ion concentration (-) R a reduced nitrate ion concentration in acceptor phase (-) R d reduced nitrate ion concentration in donor phase (-) R m reduced nitrate ion concentration in membrane phase (-) R m max maximum reduced nitrate concentration of membrane phase (-) S d/m interface surface of donor and membrane phases (cm 2 ) S a/m interface surface of acceptor and membrane phases (cm 2 ) t time (min) t inf time corresponding to inflection point of the function (min) t imax time which nitrate concentration reaches maximum (min) l i distance between phases (cm)
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