GeeDub said:
Harold_V said:
It's desirable to raise the temperature of the ash near a red heat to insure you eliminate all traces of carbon. Hard to do when you're heating a cast iron pan.
Actually, it's not hard at all. A pile of briquettes will get it dull red if the pan is placed directly on the coals.
For the occasional incineration, perhaps. I refined on a daily basis, processing polishing wastes routinely. Charcoal would have been worthless in my case.
Also, most gas burners such as found on a home stove, will get a small to medium sized pan red hot.
Yes, they will, but only in a given area. I used burners exactly like you describe, taking advantage of 1 pound of natural gas pressure (my natural gas service was installed to serve my refining business----it was not the typical 4 ounce delivery). I adjusted the flame to maximum, strictly for incineration. When the pan was as hot as it was going to get, and burning had subsided, it required torch heating to increase the temperature so remaining carbon would ignite. There were no exceptions. That was with thin pans. Cast iron would have been far worse.
A gas fired barbecue will do it too, if the pan is close to the flame.
From my experience, I'd say that is a poor idea. Incineration causes dusting, and dusting results in losses. To incinerate without some means of capturing potential losses was not a good idea, and proven in practice by having a filtered hood. Cleaning out the hood on about a two year cycle resulted in a recovery of roughly eight ounces of gold. That does not take into account the amount of gold that was trapped in filters.
Use a pan large enough to spread out the sweeps, do not pile them high in a cone. You want an even coat on the pan.
I used the largest diameter pans I could acquire from second-hand stores. Always stainless. It was not unusual to have a yield of a half gallon of ash after incineration.
That being said Harold, stainless is a good idea. I was just suggesting the cheapest way to set up.
That's why I used stainless pans. Not only were they inexpensive ($1.00 maximum), but they are far easier to heat to redness. The amount of energy it would take to heat a cast iron pan is enormous, and playing a torch on one would most likely result in a cracked pan. Cast iron does not enjoy uneven heating, something that is very obvious to anyone that has done any cast iron welding.
A thin stainless pan will warp, and then the bottom can spring upon the next heating, bumping stuff out of the pan
Interesting comment, but not true in practice. Like I said, I used stainless pans for more than twenty years. Never had that problem, although they do tend to deform somewhat.
A heavy stainless pan will cost more but will work fine.
Not likely to be encountered. Stainless is a poor conductor of heat as compared to many metals. When they are thicker, they become less desirable. What you will encounter is stainless pans with copper bottoms, or even aluminum bottoms, on the outside, of course. They were not the best choice, due to the red heat I spoke of.
I guess the best idea is to pick up heavy stainless used stuff from the Salvation Army. In fact, that is what I did 2 months ago for some experiments i am doing.
Indeed! I did exactly that, then when the pans had finally corroded to the point of having a pinhole, they would be transferred to the stock pot, where they slowly dissolved, resulting in recovery of traces of values.
Everything but the squeal was my motto. I was rewarded handsomely for my process methods.
BTW this is only for small lots. Large lots we just burned in out gas fired incinerator.
Depends on what you call small lots. I had only my hood for incineration, and it served me perfectly well for the entire run of my humble refining business (more than 20 years, including processing carpets). I processed thousands of ounces of gold. It's a matter of running more than one pan when necessary. It's like eating an elephant - a bite at a time.
Harold