Ian18206 said:
hello everyone i just processed some gold filled and plated through the sulphuric cell and filtered the solution with coffee filters.
all the black powder is in coffee filters and i was wondering on how to get the gold off the coffee filters without losing any.
i was going to melt the filters and all but i don't want to risk losing any gold because i use torches to melt. any help would be greatly appreciated.
thanks
Paper coffee filters will dissolve if you attempt to filter sulfuric acid through them. Matter of fact, you should not use any organic material around sulfuric acid unless your intent is to dissolve the organic material.
I use fiberglass to filter sulfuric acid, or polypropylene felt.
Here is the brand of fiberglass and item number I use...
You can either make what is called a charmin plug, which basically is fiberglass stuffed into the neck of a funnel. By pulling just a little out of the end and allowing it to hang out of the bottom, it will help to pull the solution through. Using a filtering flask and a vacuum pump will work even better. I use the fiberglass, and line a plastic colander with the fiberglass to filter the bulk of the black sand from the sulfuric acid. Then I process through a funnel with a charmin plug, using a filter flask and vacuum pump. Then I take all the fiberglass and immerse it in AR to dissolve the filtered material. It will look something like this.
The white material in the beaker is the fiberglass. here is a picture closer up.
What is interesting about doing this, is that if you turn the fiberglass upside down so the filtered black material is facing the bottom, and the fiberglass that has none is on top, it actually suppresses the NOx from evolving outside the beaker, so that it can be re-absorbed back into solution. You can see I do this under a fume hood because some gas will escape, but the majoring stays in solution doing it in this way. Here is another picture closer up. If you can tell, the brown color is NOx gas, and the bubbles are gas still trapped in solution under the fiberglass.
Now you might be asking yourself the question, how do you get all the solution out of the fiberglass. Good question by the way. Because you want to expand your solution anyway, I simply pour DI water through the fiberglass. I have processed the fiberglass a few times after this process, and have never recovered any more values. But I would still attempt a second digest just to make sure your process is down pat.
So far as filtering using paper coffee filters, if that is what you are intending to do, it just simply will not work. Not if you are using sulfuric acid. Anything that is biodegradable will be eaten up by sulfuric acid.
Scott