Carbon can absorb values under the proper conditions. Activated charcoal, for example, is one of the stripping methods in recovering values from cyanide.
I suggest you incinerate the material by heating in a shallow pan--such as an old stainless fry pan. You can find them at any of the Goodwill type stores.
The carbon will burn much the same way charcoal does in a barbeque. Heat the pan to a dull red heat and allow the material to burn until it is exhausted. Screen the ash to remove large pieces, which may need inquartation, then process in nitric to recover the silver. Once the silver has been removed, AR should dissolve the remaining values.
Harold