Hey catfish!
Here lately I have come into several pairs through my purchases and scrap hunts. I would like to know more about how to get the most from them.
I'm not convinced you're leaving anything behind, but I'm of the opinion that you're fighting with the stuff a lot more than need be, between your incineration process and filtration of the gold chloride.
When you get involved in quantities, the volume of solution you generate can take a long time to filter, and has a tendency to plug your filter. That can be eliminated entirely, with the benefit of precipitating much higher quality gold. I struggled with the process for a long time until I came up with a concept that really helped.
For starters, I don't recommend dissolving the frames in AR. Gold filled articles are primarily base metals, including soft solders in some instances. Eliminating base metals prior to dissolving the gold is always a good idea, although I'm not suggesting that your approach doesn't work. I realize it does, but it's a process I avoided like the plague.
I tried to make a distinction between recovering gold, and purifying gold. When you dissolve gold filled in AR, both operations are combined, yielding gold of questionable quality, guaranteed! Washing alone won't usually improve the gold to what I considered an acceptable standard.
I processed the frames in nitric, then incinerated the remaining solids to eliminate any traces of nitric, followed by an HCL wash, which removed undesirable contaminants that made filtration of the gold chloride much easier. It also improved the quality of the gold that was precipitated.
After the hard boil, water was added and the contents allowed to settle well. Once settled, the solution was decanted from the beaker, and, if clean enough, the solids were then dissolved in AR. If the solution was quite dirty, I'd rinse a second time before dissolving the gold. The balance of the operation was routine.
One comment I'd make. When you process yellow gold, you're always producing traces of silver chloride. If you'll incinerate the filters and traces contained within, then store the ash, you'll be accumulating some serious value, and it won't take much space, and liberates no fumes. When you process the wastes in the future, you'll be pleasantly surprised to find you'll even have a considerable amount of gold included. The recovery from the ash is beyond the scope of this post, so I won't dwell on that issue. .
I am curious about the incineration process you mentioned and would certainly appreciate any suggestions or recommendations you could furnish me on this process. Harold, please keep in mind that I have a Paragon Oven that is capable of 2300 degrees F. What I have been doing is after cutting them up in small pieces is put them in a crucible and heating them. My question is, how hot should I get them before process them. Any information you could give me would be greatly appreciated.
I'll include a poor picture of the small furnace I used to incinerate the glass frames. It was fired by natural gas, so it burned absolutely clean, with no fumes. I simply dropped full pairs of eyeglasses in the furnace (with the glass removed) as it ran, and made sure they got exposed to the flame such that they were heated to redness. I moved the frames about with a short metal rod to insure all of them were properly exposed. They fall apart when they are hot enough, and the plastics that were included were fully incinerated, along with the oils that are ever present. I wasn't concerned about getting anything too hot, for the entire mass was removed and processed. Hinges and individual components were often all that remained, nothing that resembled a frame. By over heating the frames, the gold surface was usually disrupted to the point where acid would attack the base metal directly, so that was very helpful in penetrating the gold except in rare instances.
I own two electric ovens, one of which is a 23 kw unit, and suited to heat treating steels. It can achieve temps that parallel those of which you speak, but to be brutally honest, there's no way I'd use either of them for gold refining. They're not necessary, and are not headed the right direction for the work at hand. If you were faced with hundreds of frames to process, this would come into focus immediately as you incinerated the frames. The burning plastic would be a serious issue, very unlike burning plastic in a flame. Again, that's not saying that what you're doing doesn't work, but it's not the easiest way to go. Cutting up hundreds of frames, for example, is wasted time, and I'd have more than a little trouble with the fumes from the plastic involved.
If you have a specific question, fire away. I gave you a brief outline of how I processed the frames, but I'm willing to provide greater detail if you feel it would help. There's no doubt you're doing an adequate job---just differently than the way I ran them.
Harold
