glondor said:
Just a curious question. I know the methods for dealing with filters are incineration or a wash with A/R.
Would dissolving the filters in sulphuric be a viable option also? What would the drawbacks be? Seems it would be an easy option ( just drop them in a small pail of sulphuric as used ) but if no one is doing it there must be a reason.
I would say no! Bad idea! It's not as easy or nearly as safe as you would think. If you just put the papers into concentrated sulfuric cold, the organic material is quickly attacked, leaving a lot of black carbon. About the only way to get rid of the carbon is by small additions of nitric to the sulfuric and, the sulfuric would have to be quite hot, probably above the boiling point of water - very easy to break the glassware. Not a pleasant task, especially in any quantity larger than a few 100 ml. Also, when the nitric is added to the hot solution, mini eruptions occur and drops of hot sulfuric will fly out of the container. And, even when hot, it's a slow process.
When I did this, I processed, at the most, 2 small filter papers. I used about 200 ml of conc H2SO4 in a 500 ml erlenmeyer flask, inside of a Pyroceram Corning Ware dish. The nitric was added a drop at a time, although some people add about 5% nitric, by volume, before heating the solution. The shape of the erlenmeyer helps prevent most of the drops from flying out when adding the drops of nitric, but it still happens. It probably took 45-60 minutes, with constant watching, before the solution cleared up and the gold was clumped on the bottom. The endpoint is reached when copius amounts of white toxic fumes emanate just above the mouth of the flask. It must be very, very hot to do this. Before the white fumes appear, some or all of the gold will often be dissolved, but don't ask me to explain the chemistry of this. Also, the white fumes don't appear until any traces of water is cooked off. At this point, the strength is probably higher that reagent grade sulfuric.
I'm sure one could do this on a larger scale, but it would require a lot of expensive equipment and a closed system, I'm sure.
Burn the papers or pulp them in aqua regia. Much, much safer.
The method is called "wet ashing."
http://www.goldrefiningforum.com/phpBB3/search.php?keywords=wet+ashing&terms=all&author=&sv=0&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search
