Gold Plate Question - Why refine further after AP?

[starzfan0211]

Thanks again for the useful info about trimming fingers. Since I am new, I have been reading the posts, downloading all the texts that I see you guys post and trying to watch the videos. Extremely helpful.

We will start trimming fingers and pulling pins this weekend to hopefully soon try our first batch and I will let you know how we do. Now for the question.

From what I have read, gold plating such as on the fingers and even on other materials like china, I seem to understand that is 24k. Please correct me if I am wrong. If it is 24k, why the need to refine it further after the AP? It seems if I get flakes from the AP that I should just be able to rinse per your instructions and melt down. Am I missing something?

BTW, I have to say that the experience and knowledge from all of you is invaluable. I have learned way more from this forum than months of web research. Thanks to the administrator for setting this up.

 

[banjags]

The gold is not totally pure 24k

ap is used to remove all the metals buy the gold... eg the copper that the gold is bonded to on the finger leaving the gold flakes.

hcl and bleach is used to dissovle the gold thus removing all impurities. Then you can melt the resulting powder and you would then have 24 or 99.9% pure gold.

 

[Harold_V]

While some of the plating you recover may be 24 karat, it is well contaminated by the substrate and other metals that manage to find their way into the process. Gold that has been dissolved, precipitated and well washed is still not pure, although it may be close.

If you're familiar with industry standard, typical gold that is purchased is warranted to be 9995 pure. That allows for 5 parts in 10,000 parts to be contamination. Electrolytically refined, gold leans towards a higher degree of purity-----and is often represented as 9999 fine. That still allows for 1 part in 10,000 to be contamination.

Getting gold truly pure is not easy. Depending on the contaminant, even traces can render gold unsuitable for many applications. Lead, for example, destroys gold's ductility.

You may have to do some experimenting in order for this to make sense to you. You can start by simply melting some of the recovered gold you have. Wash it well in water, them melt to form a small button. I think you'll find that the gold will have an oxide coat, and the flux in your dish will discolor. When it freezes, it's unlikely it will form a deep pipe, which is characteristic of pure gold. It also may not form a shiny surface in that some contaminants cause gold to cool with a fine frosty surface, dull in appearance.

Pure gold, when melted, will discolor the flux only a light purple. color, a sign of colloidal gold particles getting absorbed by the flux. Any discoloration of the flux, black, blue, green, are evidence of included base metals.

When your gold solidifies, it should remain bright of color, with no signs of oxides forming on the surface. Pure gold does not oxidize, only the base metals contained within do.

Those of us that strive (I used to, I no longer refine) for high purity often re-refine our gold to insure quality. The gold in the picture that is attached is just such gold. While it appears very bright, I doubt it is 9999 quality, although very close. It was refined at least two times, and some of it had been through as many as three refinings. It takes that to achieve a high degree of purity when gold is recovered from dirty solutions, or from highly contaminated sources, where base metals are not removed completely. Recovering gold from electronic scrap is a good example. There is far more base metal than gold present, and all of it is not eliminated, in spite of considerable effort. Drag down of the base metals when gold is precipitated is often the source of the contamination, and it's difficult to eliminate once the gold is precipitated. It is for that reason that you should adopt a very good washing procedure, assuming your are intent on achieving industry standard with your gold.

Unless your objective is to concentrate the gold you collect, with no regard for purity, it should be refined after recovery, at least once. I highly recommend a second refining if you desire high purity.

Do not confuse the recovery of gold from base metals with refining. While it's true that you do concentrate the gold by stripping it from base metals in various ways, refining it involves further processing. It's virtually impossible to produce gold of high quality without further processing.

Hope some of this helps.

Harold

 

[starzfan0211]

That helps a lot. It definitely explains and I kind of figured that was why. We (my son and I) will be trying it in the pretty near future to see how it goes and I will let you know. I will admit that I am a little nervous especially dealing with the chemicals. We will try a small batch first to experiment. Thanks a bunch.