An emulsion liquid membrane (ELM) containing Cyanex 302 has been successfully used for the recovery of cadmium from synthetic phosphoric acid solutions containing 30% wt. P205. The ELM formulation was optimised for high extraction rate and stability. Cyanex 302, and a mixture of NaC1 (3M) and HC1 (1M), were selected from a set of possible reagents and stripping phases, following equilibrium and kinetic experiments in two-phase systems. Under chemical control the rate of Cd2 extraction was pseudo first order with respect to Cd2 and Cyanex 302 concentration. Arlacel C was found to be the most suitable surfactant for emulsion stability. The dependence of the ELM rate of Cd 2 extraction on the concentrations of cadmium, Cyanex 302, and surfactant, as well as on phase and treat ratio, and homogeniser and stirrer speed, was investigated. Cadmium extraction levels were found to be above 90% for most conditions. The influence of operating variables on emulsion swelling and rupture was also evaluated as a function of time. Swelling of the internal phase of the emulsion reached values greater than 50%, whilst emulsion rupture was below 2%. Emulsion globule size distributions in the stirred tank were measured for different impeller speeds and diameters, reagent concentrations, and emulsion hold-up, using an endoscope attached to a high-speed video camera. A correlation for globule size, accounting for swelling and rupture phenomena, changes in viscosity and hold-up, was proposed and found to be in good agreement with experimental results. This allowed the effect of the stirring speed on the specific interfacial area and the mass transfer coefficient to be decoupled, and led to the conclusion that the overall rate of Cd 2 recovery was controlled by diffusional resistances in the continuous phase. A time- dependent model, and a quasi-steady state model were proposed for the extraction of cadmium with the ELM. Simulations with both models were found to be in good agreement with experimental results.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:392615 |
| Date | January 1998 |
| Creators | Lizon, Tatiana Gallego |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/7634 |
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