Extraction of cadmium (II) from phosphoric acid media using the di(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA): Feasibility of a continuous extraction-stripping process

The extraction of cadmium from phosphoric media has been Studied. The D(2)EHDTPA 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% 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% 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%). 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 mu g 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. (C) 2008 Elsevier B.V. All rights reserved.