Photo Engineer and I are both chemists.

When you add a less noble metal to a solution of a silver salt, an oxidation-reduction reaction takes place. The less noble metal is oxidized into solution and the silver salt is reduced to silver metal, which appears as a black sludge.

I've done this many times by adding steel wool to fixer. After a day or so, the steel wool has partially dissolved and there is silver present as a black suspension or sometimes a "mirror" on the wall of the container. The overall reaction is 2Ag(I) + Fe -> 2Ag(0) + Fe(II). There may also be some Fe(III) present. The principle with aluminum is similar, in that case the reaction goes as 3Ag(I) + Al -> 3Ag(0) + Al(III). Depending on the pH of the solution, your Al(III) will precipitate spontaneously and mix into the Ag sludge.

It is not a great idea to ingest huge amounts of aluminum salts, but small amounts are okay. Aluminum hydroxide is one of the ingredients of Mylanta, and it dissolves in the stomach to produce soluble Al(III). Aluminum hydroxide flocculation is a major method of wastewater treatment.