problem in dropping down the GOLD out of AP process

[ahmadbayoumi]

Dears,

After finishing 4Ks of clean and depopulated cell phone boards using AP process, I got quite decent amount of gold foils.

After washing the foils with HCL then water, I covered the foils with HCL then added colorox with small increments till all foils dissolved. then I sued a filter to get a clear solution and to remove all dirts.

I tested the solution with stannous chloride. and the color turned into dark purple but I noticed that it was not immediate and it took some seconds to see the dark purple color.

Anyway, I then heated the solution and added about 4 grams of SMB as i was expecting 2.5 to 3 grams of gold.

but seems that there was some free CL exists as gold didn't start to drop at the beginning.

After about 15 mins. of heat the solution started to drop but i not iced it was not as much as I was expecting.

The gold amount was 0.25 grams which is impossible to have such an amount out of 4ks of old cell phone boards.

Now, would you pls help me discover what went wrong and how i can reclaim the missed amount of gold ?

 

[anachronism]

A lot of the gold in cell phones is in the components and chips not just the boards. If you just ran the surface gold you're not going to have the majority of it in your foils.

When you added stannous you saw that the change to purple took a while. This is an indicator that there isn't much gold in solution which backs up the comment above. Have you stannous checked the remaining solution to be sure it is clear? If you have, and you've collected 100 percent of the powder than that is what you have got.

I'm not asking things about remaining metal since you say you had just foils and I'm assuming you let everything dissolve. Also the gas evolved by SMB stays in solution longer if it's colder rather than hot so you might want to bear that in mind for future reference.

Jon

 

[kernels]

As Jon has said, the surface plating on cellphone boards is incredibly thin, there just isn't very much Gold there. Running 4kg of cellphone boards you have probably created a very large amount of hazardous copper solution, the reason why I encourage everyone not to bother with ENIG plating in AP.

Pretty much exactly as Jon described, getting a slow stannous reaction that turns purple is a sure sign of very little Gold in solution. When you have a good amount of Gold for the volume of solution, the reaction is immediate and almost pitch black.

 

[ahmadbayoumi]

Thanks Jon and kernels for your replies

However, PLS note the following:

1- I already processed the IC chips removed from these 4ks of cell phone boards and I managed to recover 1.25 gram of gold out of 270 grams of cell phone IC chips.

2- The amount of foils I got out of the plain cell phone boards was quite decent amount that for sure is greater than only 0.25g of gold. I processed a lot of RAM fingers and I have some experience to know that the foils I got should yield about 2 to 3 grams.

3- For the stannous chloride test, yes it took a while to change the color but it went very dark purple which is an indicator for a decent amout of gold.

I read somewhere here that the PH could affect the process specially when you know that there was no fizzing while adding the clorox.

So inlight of above, would you pls help

 

[anachronism]

The bit you need to consider is that the foils from the fingers are thicker than the majority of the foils on the surface of these boards. The fingers are designed for wear.

 

[kernels]

Yep, Jon beat me to it again, the thickness of gold plating on fingers can be 10x what it is on cellphone boards. Less than 2 micro-inch is common for ENIG plating on Cellphone boards, on ram fingers you expect more like 20-40 micro-inch.

That being said, it is not impossible that some Gold can remain in your solution, have you done another Stannous test ? You can also put a bar of copper in the solution, if there is a few grams of Gold left in there you will see it cement out very quickly.

 

[patnor1011]

Gold foils from AP are one of the most misleading things on earth. You simply can't guess what comes out by just looking at some volume of them. It will be different every time.