Gold cell success to failure

[oldtimmer]

Last week when I used my gold cell to strip the gold from some small gold plated metal plates, I was successful and produced a nice small button. This week I finished up the metal plates and did a batch of pins.

The gold cell worked just like the video from Steve. Copper screen basket, pins, stir until all of the gold is removed. I then decanted the acid and diluted the remaining acid and gold. I washed the gold after decanting. I then did a hot HCL wash and the HCL came off looking very clean. I then did another two wash to remove the last of any acid. The water from the last wash looked very clear. I decanted the water off and poured the gold into an evaporating dish to dry.

One thing that I noted that was different this time, is that during the drying stage the gold looked more like a batch of tar, thick and very shinny black. It also took longer to dry that the first batch and did not want to really dry all of the way. In weighing the dried gold power, it was heavier than I had expected. But I went ahead and fired up the oven and melted it.

When I took off the top of the oven, I knew that something was wrong as the gold button did not have that nice glow it and seen to loose it color and harden. The flux in the melting dish ended up a nice black color, almost the same as the color of the gold that I had started with. Below is a picture of the button setting on the side of the melting dish.

So, the question, is, what did I do wrong this time? The color is somewhere between good silver and that of gold. The unknown button weighs in at 5.8 grams. I had expected to recover around 4.5 to 5 grams of gold. What is the possible source of the contamination?

How best to reprocess? Flatten it out or inquart and make flakes?

 

[lazersteve]

Oldtimer,

The contamination could have been anything from a base metal that was protected from the wash acid by the tarry black gold powder to a sulfuric acid compound.

The fact that it was stubborn to dry leads me to believe it had some sulfuric trapped in the black powder. Incineration of the black tar (without melting) would have driven of any trapped sulfuric acid.

It's always best to dissolve all the powder from your cell in HCl-Cl or AR after washing, then precipitate and wash a second time for the best purity.

I would suspect you may have carried some silver over into the button from the color. Inquart, cornflake, and dissolve in 35% nitric should do the trick.

Steve

 

[leavemealone]

I can help with the tar issue.You definitely had contaminants in your gold.When your gold powder has base metals in it,the powder tends to be a finer consistency,you mentioned that it weighed more than you expected and thats why.When you run the pins in the "basket",the added time it takes to dissolve all of the gold allows the rest of the pins to be exposed longer hence dissolving more base metals than normal.And because the powder was "finer" than you are used to it would be more dense.And Im sure you know the oily consistency of sulfuric,that would explain the lack of the powder drying.The leftover sulfuric becomes almost gelatin like and can inhibit water and muratic(even if boiling) from penatrating ,hence the need to incinerate,and dissolve.

Steve I'll get that stuff out tomorrow around 2.Talk to you later,
Johnny

 

[goldsilverpro]

I agree with Steve that it's always best to dissolve the powder and purify it. In fact, I consider it absolutely necessary in 100% of all cases. It would have been much easier to do this before you melted it.

 

[leavemealone]

yeh chris I agree 100% too.I only wanted to help explain to oldtimmer why it looked the way it did.Sorry steve if it sounded like I was stepping on your toes,you know I would never do that.

 

[oldtimmer]

Thanks to all for the help and information provided. It was fun and interesting doing the inquarting and silver recovery as well as getting the gold back.

Attached is a photo of the newly arrived little gem.

She weighs in at a whopping 2.9 grams.

 

[butcher]

nice hunk