Study On The Kinetics Of Transportation Of Cadmium Ion With Liquid Membrane

Liquid membrane technology is a kind of potential separation technology with membrane. Liquid membrane has better selectivity and flux than organic macromolecule solid membrane in separating. And liquid membrane technology displays directional characteristic similar with biologic membrane. The transportation of cadmium ion through bulk liquid membranes and supported liquid membranes containing tributylphosphate as carrier has been investigated and the kinetics of this transportation also have been studied. The influence of the concentration of nitric acid in the feed phase, the concentration of ammonium in the stripping phase, the concentration of tributylphosphate in the membrane phase and the species of negion in the feed phase for transportation of cadmium ion through bulk liquid membranes has been investigated in the experiment. The results show that:(1) Transportation of cadmium ion will be obstructed when the concentration of nitric acid in the feed phase is higher or lower than the fit. (2) Transportation rate of cadmium ion increase with the increasing of the concentration of ammonium acetate in the stripping phase. (3) Increasing the concentration of tributylphosphate in the membrane phase is beneficial to the transportation of cadmium ion. (4) The cadmium ion can be transferred through bulk liquid membranes only iodic ion presence in the feed phase. The kinetics of transportation of cadmium ion through bulk liquid membranes was studied and the results indicated that:(1) Transportation of cadmium ion follows the co-transport mechanism. (2) The driving force of the transportation is differences of concentration of hydrogen ion between feed phase and stripping phase. (3) The transportation is a complicated process that includes the complexing reaction and diffusion. Neglecting the influence of diffusion and referring to the kinetics equation of concatenation reaction, the kinetics equation of the transportation is obtained. But the result of this equation is different from the result of experiments. Considering the transportation of cadmium ion is a diffusion process that is facilitated by the complexing reaction and supposing the reaction rate is very higher than the diffusion rate, the mass transfer equation of the transportation is obtained. According to this equation, the flux of cadmium ion is determined by the differences of the product of the concentration of cadmium ion and the concentration of hydrogen ion between the feed phase andstripping phase. The influence of the concentration of nitric acid in the feed phase, the concentration of ammonium in the stripping phase, the porosity of supported membranes and the concentration of tributylphosphate in the membrane phase for transportation of cadmium ion through supported liquid membranes has been investigated in the experiment. The results show that: (1) Transportation of cadmium ion is obstructed with increasing the concentration of nitric acid in the feed phase. (2) Transportation rate of cadmium ion increase with increasing the concentration of ammonium acetate in the stripping phase. (3) Transportation rate of cadmium ion increase with the increasing of the porosity of supported membranes. (4) Transportation of cadmium ion will be obstructed when the concentration of tributylphosphate in the membrane phase is higher or lower than 30 percent (volume ratio).The kinetics of transportation of cadmium ion through supported liquid membranes was studied and the results indicated that: (1) Mechanism of transportation of cadmium ion through supported liquid membranes is the same with the mechanism of transportation of cadmium ion through bulk liquid membranes. (2) The steady state approximation method is applicable for the transportation of cadmium ion through supported liquid membranes. (3) The logarithm of the ratio of concentration of cadmium ion to original concentration of cadmium ion in the feed phase is linear with time.