Trace metals continuous leaching

Fedotov, P. S., Wermrich, R., Stark, H.-J., and Spivakov, B. Ya. (2005b). Continuous-flow fractionation of trace metals in environmental solids using rotating coiled columns some kinetic aspects and applicability of three-step BCR leaching schemes. J. Environ. Monit. 7, 22-28. 

Based on this discussion, it is possible to clarify some aspects of the literature interpretations on the nature of the active species. Lunsford and coworkers [49, 93] published many papers indicating that the active species is colloidal palladium, which implies the easy dissolution of Pd in solution. An analysis of patents clearly reveals that this is not the case for active catalysts and various patents explicitly indicate that there is no leaching of Pd. On the other hand, a colloid would be difficult, if not impossible, to manage in a commercial process and its recovery would be not viable at the very low concentrations of dissolved metal employed. In addition, the presence of even traces of Pd in commercial H202 could be extremely dangerous in terms of the possibility of explosion. Finally, if the solid is a simple reservoir for Pd going into solution, a deactivation is expected with time-on-stream in continuous operations. 

Confirmation of this explanation is unequivocally provided by the presence in the reactor zones of at least half of the more than 30 fission products of uranium. Although soluble salts, such as tho.se of the alkali and alkaline earth metals, have been leached out, lanthanide and platinum metals remain along with traces of trapped krypton and xenon. Most decisively, the observed distribution of the various isotopes of these elements is that of fission products as opposed to the distribution normally found terrestrially. The reasons for the retention of these elements on this particular site is clearly germane to the problem of the long-term storage of nuclear wastes, and is therefore the subject of continuing study. 

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