Quote Originally Posted by Jordan View Post
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.
This is an easy way to remove some silver out of the solution, but the efficacy of such treatment is known to vary hugely depending on the exact composition of the steel, shepe of the cartridge, and the forced flow mechanism. The regulation for residual silver content in many areas is very low, and the steel wool method often does not meet the standard. In small scale amateur darkrooms, steel wool method is better than doing nothing, but don't assume this is the satisfactory solution in all situations.

Best silver removal method in terms of efficacy and cost is electrolytic system using stainless steel and moving carbon electrodes. The SS electrode will corrode very unevenly if the carbon electrode is not moving circularly around the SS disk.

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.
Although I don't like to heat acidic food in non-anodized aluminium cookware, the whole "aluminium-pan can cause Alzheimer's disease" thing was a malicious rumor made by stainless steel industry in the past. In reality, alum is used in pickling (tho I don't use it), and some baking powders contain aluminium compounds as well. (Note that baking powder is a mixture containing baking soda, but not by itself.)