Problem with gold reduction from iodine-iodine mixture

[domus1212]

Hi,

I started with iodide-iodine method. I bought 500g of KI. Than add 80 ml of HCl and 70 ml of H2O2. I prepare 1000ml solution.

Then the gold dissolved in 40 second.

So I want to precipitate it. I add about 90 g of sodium bisulfate. Then I add ascorbic acid in small portions. I add 300g and Nothing Happened.
So I add more sodium bisulfate, the solution turn brown and reddish. After an hour it turned black again. Then I poured it to another beaker. I remove the sodium bisulfate that didn't dissolved.

Later I try with smb, so I add HCl to ph about 5 and add 100g of smb also nothing happened. So I add 1 g of zinc, also the same.

I came with an idea to add thiosulfate. I add 300g of 5 watered thiosulfate. I left it for a day. Also nothing.

Next I try with the oxalic acid. I add about 80g of 2 watered oxalic acid. The solution was heated to boiling and turn sandy. Later I add about 50g of sodium bisulfate. All goes well but when I came to check the results the solution is black again.

Please help me so much! I don't know what to do now.

The solution contain Gray powder on the bottom which is hardly soluable. Also there are some oxalic acid. And there are now 4000ml of water not 1000ml so it is 4 times diluted

Thanks you in advance, Dominik

 

[domus1212]

I didn't know what I do wrong.

But, I think that this red powder I got after first spoon of Ascorbic Acid was gold. So as I observed the solution could be black, but the precipitate was gold.

I lost a lot of money, cause when I want to rejuvenate it with H2O2 it completly bumped off.

Maybe my case could be some info for other.

Anothee problem is I tried 4 diffrent methods but no one was good. Only the fecl2 and AR was quite good, but we all know how it goes.

 

[Lino1406]

Iod-iodide solution is made by mixing iodine and KI, not what was done. If only gold was there it can be precipitated with caustic soda solution to absorb part of the iodine, giving gold iodide. Then another part of caustic soda with heat to decompose gold iodide to gold + NaI

 

[domus1212]

I think you know something about it. Could you help me with iodine-iodide method with automation?

About the method I made 10% I2 in 40% KI, it was this what I read here.

I think it is not for me or I did something wrong.

After making the solution gold was taken in 40 seconds. And it worked good.

Later I have a problem. If you can help me please give me the info about the color of the solution. I have in school the quantative analysis the reduction of I2 with thiosulfate. The solution turned colorless always. What happened here? What about the pH?

Please write me all you know about the method. I'm thinking about the automation method with stirring, heating and dosing liquids.

I trash all of my reductors and stayed only with thiosulfate and zinc. I think I can order ascorbic acid and of course KI.

Thanks in advance

 

[Lino1406]

Colors: lodine- black, gold, gold iodide-brown. Gold iodide with HNO3- violet iodine vapors. Thiosulphate reduces iodine to iodide - colorless. Gold may link to thiosulphate - colorless. About automation- this is not chemistry but a separate field, talk to automation people

 

[domus1212]

So you could understand it to me that after I add a lot of reducers I got black again?

What are the proportions of KI, HCl, O2 firsty?

How to adjust the pH? What it need to be?

Is the reduction of ascorbic acid or zinc or smb better?

To rejavuate the solution the proportions of 2 question could be used?

How to control the solution volume, so the concentration will be the same every leach?

If you know something more useful please write me

 

[Lino1406]

What is the source material?

 

[domus1212]

Only e-waste. I have a cheap source of pins that have 17 g/kg.

 

[Lou]

17 g/kg of gold is pretty rich. I think you are expecting much more than what you are likely to see. Do you have any pictures of the pins? How do you know they're over half ounce / kg?

 

[domus1212]

I got the analysis. Do you know something about the method?