Environmental Engineering Reference
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of Mastny et al. [601] , the decoked catalyst containing Pt and Re was treated either with 5M
HCl/HNO 3 acids or ammonia. The temperature had a pronounced effect on metals dissolution.
For example, using HCl at 90 C, almost complete dissolution of Pt and Re was achieved after
2 and 4 h, respectively. When aqua regia was used, the rate of dissolution was higher. When
diluted ammonia was used at 60 C, after 1 and 2 h, 80 to 85% and 85 to 91% of Re,
respectively, was dissolved, while almost all Pt remained in the catalyst. An alkaline cyanide
solution was found to be suitable for the recovery of Pd from spent catalysts [602] . Once in the
solution, precious metals can be isolated in the pure form by precipitation [603,604] , solvent
extraction [605] , and membrane separation [606] .
Other metal reclamation process is based on the gas phase volatilization of precious metals
using the Cl-containing agents such as AlCl 3 , CCl 4 , mixture of CO+ Cl 2 , and phosgene [599] .
In this method, Pt and Pd are selectively chlorinated to volatile products, which on cooling
condense. Apparently, main constraints of this method are the handling of toxic agents, and
products.
The pyrometallurgical process patented by Japanese inventors is based on the mixing spent Pt
containing catalyst with the mixture of metallic copper and copper oxide, as well as a flux and
reductant components [605] . The melt of this mixture consisted of two layers, i.e., one
containing Pt and copper metal, and the other containing slag. These layers could be readily
separated. The Pt enriched mixture was heated in air to partially oxidize copper metal to
copper oxide. This resulted in the formation of two layers, one containing oxide and the other
consisting of copper metal significantly enriched with Pt. These two layers could be readily
separated for further processing.
For noble metal catalysts supported on carbon, the total oxidation of carbon and carry-overs
may be the method of choice for noble metals recovery from spent catalysts [607] . For this
purpose, a two-stage method may be suitable. In the first stage, reactive carry-overs are
removed by controlled oxidation. This follows by a prolonged oxidation of carbon support,
which is much less reactive than carry-overs. After removal of all carry-overs and carbon
support, the remaining material was very homogeneous. Also, its volume was substantially
decreased.
This chapter was incorporated in anticipation of more advanced hydroprocessing catalysts
containing precious metals and acidic supports entering the market in a near future. As it has
been indicated, the information on development and testing of such catalysts is rather
extensive, whereas the properties of the corresponding spent catalysts (e.g., regenerability,
toxicity, flammability, leachability, etc.) are unknown. Additional research is necessary to fill
this gap.
 
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