Metastannic Acid Experiment

[Yggdrasil]

Nice experiment man thank you.
I have encountered this metastannic acid so many times, I once cried because of its problem.
I have also discovered a simple way to avoid with an easy method I will like to share here. But unlike yours, this method will prevent it from forming by eliminating the tin before reacting the pins, or PCBs in nitric acid.
To do this simply cover the the pins or PCBs in water, the add a few drops of nitric acid 67% to the solution, then give it some heat and a few hours (at least 1 hour). Assuming you covered your pins in 400ml of water, you will need only 25ml of nitric to do this.
As the solution is heated with time, it will turn from clear color to green. Sometimes the metastannic acid can even precipitate out.

The acid will be strong enough to attack the less reactive metals like tin while the more reactive metals from copper above are not attacked, therefore the acid is so weak it will not strip any gold foil. When you're comfortable you've eliminated all the tin, pour off and discard the waste solution.

If you do this properly, when you add nitric acid to eliminate base metals, no metastannic acid will form.

Better use HCl, no risk of Metastannic acid then.
Or better yet, use AP directly.
If you use Nitric it will create Metastannic acid with Tin, you just throw it away.
Wasteful and depending on how you treat your waste, it may be bad for nature.

 

[Saddiq NG]

Better use HCl, no risk of Metastannic acid then.
Or better yet, use AP directly.
If you use Nitric it will create Metastannic acid with Tin, you just throw it away.
Wasteful and depending on how you treat your waste, it may be bad for nature.

No doubt HCl may be the best for eliminating tin but it is also good that we also discuss alternatives because there are several factors that affect the availability of resources for refining across the world like price, availability, regulations etc.
It takes only a few drops. But maybe I'm thinking it's not that wasteful because nitric acid is available and affordable in my country.

 

[Ayham Hafez]

I have been doing some low grade pins in HNO3(nitric), as we know it creates Metastannic Acid and it is hard to get the gold foils. I have found an easy way to rid the Metastannic and its works for me. Here is the process i used today along with pics, The steps are as follows,

Put the gold bearring Metastannic into the reaction vessel.
Add water to just above the material about 1/2 inch.
Add 1/2 teaspoon of lye.
Heat solution(DO NOT BOIL) you will see a reaction of the lye change colors it will cheese up to a fluff and then change to a brown material and settle to the bottom.
While warm decant and filter the solution as much as you can. It will be Brown.
Add water to the remaining solution NOT MUCH.
Add HCL to the solution, this will change to a yellow / green.
Decant and filter - your trapped gold will be free and settle in the filter. Use the same vessel and filter as before to decant in.

Hope this helps someone.
Ken

update; Using the procedure above will put gold into solution, just done a test with stannous and its positive, Done a bigger amount and it works for a leach solution on Metastannic for micro gold removal. More tests are needed to confirm.

I tested this method couple times, yes its work very well, it's better than incineration specially that incineration need to be filter the metastannic acid first but with this method you just wait the metastannic acid to drop down the beaker then add NaOH solution (like 50% NaOH with water to avoid boiling) then after solution been alkaline add water and wait to settle couple times then add HCl, am sure no gold will be missed with NaOH, I tested it with gold powder and with foils, both work very well, thanks for the author

 

[Shark]

Sorry to say Ken (Jeneje) died a few years ago. Thankfully the forum carries the information forward.