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)
