Non-Chemical Creating gold foil from karat gold

[Smitty]

Here is something I remember reading a while back, but can't remember where the source came from. It also included pictures. I am sure that I read this article way before I came across this site.

It was an article in which they were demonstrating a method in which they were attempting to refine gold without the use of agua regia. What they did was take karat gold and flatten it down with a hydraulic roller, decreasing the thickness with every pass thru the rollers. When it finally got to a certain thickness they would pour acid on the foil. I really don't remember which acid, but from what I've been reading lately Nitric is probably the logical choice. The Idea is similar to what we do when we harvest gold from fingers. Removing metals that can be removed with Nitric first. You're probably asking yourself if they were using the inquartation method, the picture was of a sheet of yellow karat gold, not silver or copper. The article also mentions other steps before they decided to assay the sample. I really do not remember whether they mention what methods they used after the nitric bath. I do not remember the final assay quality, but I'm pretty sure it's nice and high; otherwise, the story wouldn't be as juicy.

I just brought up this topic just in case someone comes up with a great idea on working with refining karat gold without inquarting.

 

[Irons]

By rolling it thin, the surface area is increased. If you check the Shor site, the sell the equipment to do it.
Gold assay with Silver inquartation uses this. The Silver/Gold alloy is rolled thin so it digests quicker if I remember correctly.

 

[Harold_V]

The one problem with this method (no inquartation) is that as the fineness of gold increases, the less effective it becomes. It stands to reason that if you have 98% gold protecting base metals from exposure to nitric, it would have to be reduced in thickness to just a few atoms for all of them to be exposed and dissolved. It is for that reason that inquartation is used when assaying. The percentage of gold is low enough to permit 100% penetration of the acid, yet the gold content is high enough to prevent fragmentation of the coronet. That's important in order to prevent the minute particles from being discharged with the solution. Under ideal conditions, it remains 100% intact, but is well honeycombed by the extraction of silver. In the case of assaying, oxides of base metals will have been absorbed by the cupel, along with the litharge that is created by the process.

Bottom line? It is my opinion that if you intend to achieve a high degree of purity, you must be able to dissolve the gold. Inquart, or roll the material thin enough that the base metals can be reduced by the use of nitric, then proceed to AR. Base metals will not be eliminated with the nitric process alone. I routinely processed bench filings by this method. The quality of gold that came from the process was always suspect, never high quality. It always received a second refining.

Harold