Extraction of cadmium (II) from phosphoric acid media using the di(2-ethylhexyl) dithiophosphoric acid (D_2EHDTPA): Feasibility of a continuous extraction-stripping process

摘要

The extraction of cadmium from phosphoric media has been studied. The D_2EHDTPA was used as extractant and dodecane as diluent. No third phase was observed in the investigated conditions. A continuous micro-pilot scale mixer-settler was successfully tested for both extraction and stripping. More than 99 percent extraction rate was obtained in steady-state conditions with a flow rate ratio Aqueous/Organic equal to 1.1. Continuous stripping was performed using HCl 4 M. More than 96 percent of the cadmium was stripped in one continuous mixer-settler stage for flow rate ratio equal to 0.7. Results were in good agreement with the predicted values based on the McCabe-Thiele method. Experimental mixer-settler stages behave as ideal ones (Murphree efficiency >98 percent). An optimal flow sheet is proposed to purify the Wet Phosphoric Acid (WPA) and to recover a relatively concentrated cadmium solution (1 g L~(-1)). Two ideal stages operating at phase ratio A/S equal to 5/1 are required for the extraction step leading to a very depleted raffinate (<0.2 ug L~(-1)). For the stripping step, six stages are required (S/A = 5/1). The recovered organic phase contains less than 2 mu g L~(-1) and could be recycled in the extraction step.