Purification–concentration process. Studies on the transport mechanism of a chromium (VI)–sulfuric acid– tri-n-octylamine (TOA)–ammonium carbonate system

A combined system has been devised with a liquid–liquid extraction–re-extraction reactor where the extraction compartment and the re-extraction compartment are put in contact with one another through the organic phase composed of an extractant and a diluent. We have applied this process to a system of chromium–sulfuric acid–tri-noctylamine–kerosene–ammonium carbonate. Interesting results were obtained for diluted solutions (100 ppm). A physical modelling of the extraction–re-extraction reactor demonstrated the existence of transfers that find their origins, on the one hand, in a gradient of potential chemicals, and, on the other hand, in the active transports bound to the coupled processes. The modelling of the reactor identified three phases: the first phase, where the transferred quantities are weak; the second phase, where the transferred quantities are important, such as pumping; and a third phase, which was much slower. The membrane works due to the “activation” by the co-solute of the transporter at one interface and to the “deactivation” at the other interface. Both of these active transport mechanisms created a real “chemical agitation”.

Fig. 6. Influence of time. Aqueous phase: pH = 1 and [SO4 !] = 2 M; organic phase: [TOA] = 5×10!2 M. A purification–concentration process for very dilute solutions has been developed with the conception of a static liquid–liquid extraction combination characterized by the extraction–reextraction process. We have applied this process for the system: Cr(VI)–sulfuric acid–tri-n-octyl amine–kerosene–ammonium carbonate. The results obtained were very good for extraction as well as for re-extraction.