what is happening???

[rickbb]

Having small bits of gold left when the digestion reaction stops indicates that the nitric acid was used up and not enough left to finish off all the gold. Just add a small amount more to dissolve the leftover gold. The act of dissolving gold uses up the nitric. The goal is to use only the amount of nitric that you need for the amount of gold you want to dissolve. In this case you were just a bit shy of that goal.

This is what's meant when others have suggested you read up and study some more. It seems that even though you have had some successes, you, (as I do too), still need more knowledge of the process steps and what it means when you get some unexpected activity.

And, please, don't take it outside when you get heat and fumes, start and keep it outside. Please. The white smoke could have been just water vapor, but maybe not.

 

[solar_plasma]

He had intentionally 2g left! Boys... :lol: , I think, Vicke has not done anything definitely wrong. He had just a strange observation and asked for possible explanations. And I am with Jon, there are good chances, there's more gold in solution, still or redissolved. That's why I said, drive off SO2 and stannous test it.

 

[solar_plasma]

I have a theory....you used a more concentrated acid, which was hot, you added all smb in one portion.... yap, like Jon already said: add in small increments! Under the hot exotherm reaction most of your SO2 was gone before it could reduce any gold. That is why you only precipitated 22g gold. There is more gold in solution.

 

[solar_plasma]

By the way, you need some excess HCl to convert the smb. If your stannous test is positive and if you add more smb, you could need more HCl ...just a thought.

 

[solar_plasma]

And my last advice... I would let it sit overnight, now, maybe the rest will precipitate by itself.

 

[bswartzwelder]

Where were you doing this that you had to take it outdoors to cool? This is not normally a reaction you do indoors.

Listen to the sage advice given. First, test with stannous chloride to be certain all the gold dropped. If it hasn't, you need to precipitate what is left in solution. Second, when making AR, I believe the accepted process is to measure out what you think you will need, and then add it in small increment until all the gold disappears. Then you add the SMB in small increments until it stops reacting.

TEST, TEST, TEST. Without testing your solution at every step, you really don't know what you have.

 

[Harold_V]

TEST, TEST, TEST. Without testing your solution at every step, you really don't know what you have.

Don't you find it rather strange that many readers don't seem to understand this simple concept?

Harold

 

[bswartzwelder]

I had to learn the value of testing. Sometimes it was the hard way and cost me. I learned that lesson and it cannot be stressed enough.

A little off topic, but I mixed up stannous chloride test solution over a year ago. I added stannous chloride crystals with HCl and a little water. Put the solution in a brown bottle with a dropper and keep it in the fridge. A week ago I took it out and put a Q-tip in my gold chloride solution and dropped 1 drop of the stannous onto it. The Q-tip turned black indicating the stannous was still working. Only my wife and I here at home and the grand kids aren't tall enough to reach it. It is well marked.

 

[rickbb]

I keep mine in one of those small dorm room fridges in the shop. Not comfortable with it in the food fridge in the kitchen. Although many kitchen products are just as dangerous I suppose.

 

[Vicke]

I had to take it out becous i had it in my lab so i never do stuffs like this close to my house.
I have no test solution bevous i not want to keep it in my fridge but i will get someting i can store in my lab.
Ive got out everything and it seems like i had iron in it, i am using some sort of steel tols for handling stuffs in acids and i have no idea of the material but it only builds up a thin layer of something black on it when used in strong acids then i just wash it and looks new again.
I beleve thats where the iron comes from.

 

[g_axelsson]

If you are using steel tools in acids where you have dissolved gold or other precious metals the black could be gold cementing out on the steel.

Use glass stirring rods or plastic tools to not add contaminants to your gold.

Göran