Features and Capabilities of New DNPDSE Method

Dissolved Nitrogen Predispersed Solvent Extraction (DNPDSE) is a new method devised for improving the performance of equipment utilized in the solvent extraction (SX) method, especially for dilute solutions. In this method, for mixing the two phases, bubble dispersion of the organic phase (colloidal gas aphrons [CGAs]) is used instead of its drop dispersion in the aqueous phase. Through increased contact area and enhanced buoyancy force of organic phase, this performance mode leads to more satisfactory phase disengagement, less extraction time and more recovery of metal ions in high aqueous/organic (A/O) ratios. The results of experiments conducted on dilute (128 mg Cu/l) and dense (2000 mg Cu/l) synthetic solutions indicated 22% and 2.5% (on average) increased recovery, respectively in the DNPDSE method compared with the SX method. This increase in recovery was only due to the difference between the performance modes of these two methods, and copper ion flotation (IF) by cationic (dodecytrimethyl ammonium bromide) and anionic (sodium dodecylbenzene sulphonate) surfactants was not involved in this promotion. On the other hand, there is the possibility of applying this method combined with the precipitate flotation (PF) and IF methods to produce environmentally-friendly raffinates. Comparison of raffinate pictures from the DNPDSE and PF methods with both ferrous sulfate and aluminum sulfate coagulants indicated increased transparency of raffinate after PF due to elimination of the organic phase from it. Moreover, the flotation of residual copper ions in raffinate using ethyl xanthate resulted in complete removal of copper from it. Finally, the flow sheet representing the combination mode of the three methods (DNPDSE-PF-IF) was presented.