| Abstract |
The recycling of scarce elements such as platinum-group metals is becoming crucial due to their growing importance in current and emerging applications. In this sense, the recovery of palladium and rhodium from a spent auto-catalyst by leaching in HCl/CuCl2 media was studied, aiming at assessing the kinetic performance as well as the influence of some processing factors, and the behaviour of contaminant metals. Based on a kinetic model developed for the present case, the influence of temperature was evaluated and the corresponding values of activation energy were estimated as 60.1 +/- 4.1 kJ mol(-1) for Pd and 44.3 +/- 7.3 kJ mol(-1) for Rh, indicating the relevance of the chemical step rather than diffusion. This finding was corroborated by the non-significant influence of the stirring velocity. The reaction orders were estimated for each leaching reagent: for HCl, values of 2.1 +/- 0.1 for Pd and 1.0 +/- 0.3 for Rh were obtained; for Cu-2+,Cu- the obtained values were 0.42 +/- 0.04 for Pd and 0.36 +/- 0.06 for Rh. Without any significant loss of efficiency, solutions with higher metal concentrations were obtained using lower liquid/solid ratios, such as 5 L/kg. The main contaminant in solution was aluminum, and its leaching was found to be very dependent on the temperature and acid concentration. |
