A comparison of the electrochemical recovery of palladium using a parallel flat plate flow-by reactor and a rotating cylinder electrode reactor

The production of catalytic converters generates large amounts of waste water containing Pd(2+), Rh(3+) and Nd(3+) ions. The electrochemical treatment of these solutions offers an economic and effective alternative to recover the precious metals in comparison with other traditional metal recovery technologies. The separation of palladium from this mixture of metal ions by catalytic deposition was carried out using a rotating cylinder electrode reactor (RCER) and a parallel plate reactor (FM01-LC) with the same cathode area (64 cm(2)) and electrolyte volume (300 cm(3)). The study was carried out at mean linear flow velocities of 1.27 < nu < 11.36 cm s(-1) (120 < Re = upsilon d(e)/nu < 1080) for the FM01-LC reactor and 20 < nu < 140 cm s(-1) (7390 < Re= upsilon d/nu < 51,700) for the RCER. The morphology of the palladium deposits at the entrance and at the exit of the electrolyte compartment of the FM01-LC reactor showed the effect of the manifold distributors during the electrolysis; the manifolds generate micro turbulences, increasing the mass transport coefficient in these areas and favouring rapid recovery of palladium ions. More uniform high purity palladium deposits were obtained on the surface of the RCER. The cumulative current efficiency to recover 99% of Pd(2+) ions in the parallel plate electrode reactor was 35% while the recovery of 97% of Pd(2+) in the RCER was 62%. The volumetric energy consumption during the electrolysis was 0.56 kWh m(-3) and 2.1 kW h m(-3) for the RCER and the FM01-LC reactors, respectively. Using a three-dimensional stainless steel electrode in the FM01-LC laboratory reactor, 99% of palladium ions were recovered after 30 min of electrolysis while in the RCER, 120 min were necessary. (C) 2011 Elsevier Ltd. All rights reserved.