SEPARATION OF MOLYBDENUM SPECIES BY ELECTRODIALYSIS

Lab-scale tests have been carried out in order to assess the possibility of separating molybdenum from aqueous solutions by means of electrodialysis (ED). Mo-containing sodium hydroxide, sulfuric acid, ammonium hydroxide, and hydrochloric acid solutions were tested at 25°C in a five-compartment ED cell. Cell voltages were markedly lower in ammonium hydroxide and chloride solutions, but separation in the latter electrolyte was limited by the low solubility of Mo species. Best results were achieved for Mo separation by ED from an aqueous alkaline solution with 21.8 g L^?1 Mo and 3.4 M ammonium hydroxide and a cell current density of 120 A m^?2. Under these conditions, the Mo transport rate from the working solution was 5.6 mol m^?2 h^?1 and the specific energy consumption for Mo separation was 2.2 kWh kg^?1. These results suggest that this operation should be further studied at pilot scale.