Electrochemistry How do I filter Sulfuric Acid from my gold cell?

[cobrawearer]

I am using a pickle jar to settle my gold cell acid. At first, the black powder settled out nicely, and I reused the acid. But recently there is another layer of gray liquid above the black powder that takes forever to settle, if ever. Can I recover this acid? I am reverse plating computer pins, so there is some silver, lead, iron, copper, gold in the material.

 

[Geo]

you dont filter. just let settle then decant/syphon solution from the top of the black powder(i use a turkey baster,the kind with a rubber bulb).put solution back in the cell for the next batch or put in a airtight container for later use.when you get ready to harvest the gold from the solution in a glass container just add small amounts of wet powder to water slowly checking the temp,allow to cool when the glass gets warm until all the powder has been added.allow powder to settle and the liquid will turn green,decant this liquid to a clean container for later reclaiming the acid.repeat the water rinse until the water remains clear.this is still very dirty and needs to be refined.when the solution becomes saturated with nickle it stops working so well. slowly add your acid to water to keep the heat down until you have diluted all the acid and let whatever settles settle to the bottom and the liquid becomes clear.then you evaporate the water in a coffee pot till the boiling subsides(water makes the solution boil vigorously) as the water evaporates out the boiling is less intense but be careful because even though the boiling subsides the temperature will rise so be mindful and watch this process closely.when the boiling subsides then the solution should be as close to moisture free as possible,let cool and store for later use.this process will cause most metals to drop out of solution as salts,pour liquid off careful to leave the salts behind.you should be left with a nearly clear version of the liquid you started with.

 

[cobrawearer]

I am using a "turkey baster'' to remove the clear liquid after settling, my problem comes when the gray layer does not seem to want to settle. Just looking for a short cut to possibly speed up the settling of this layer in my jar.

 

[Geo]

no real way to speed it up,use what liquid you can and add some new liquid as needed to keep the cell at operating level and let the other sit is the best advise i can give you.you should keep enough material on hand just in case you need to start over with totally fresh acid. as for me, i never harvested the gold until i had a gallon container full anyway.that's usually about a quart of wet powder. the grey in your solution could be lead(probably is) and you dont need it in your cell.the only way to clean it out of your solution is by the method i described above.

 

[goldsilverpro]

If it doesn't settle 100%, it don't hurt to leave a little stuff in the solution. You'll eventually get it. If you want to re-use the solution, this isn't always a 100% batch process. There are several reasons why people get other types of precipitates besides gold but my guess is that it is mainly due to running it too hot. I always limited it to about 110F.

There are no standard cellulose filter papers that will stand up to the concentrated sulfuric. Glass fiber filter papers (or, circles) would likely work but they're quite expensive.

 

[philddreamer]

Another idea is the "poormans fiber glass filter" & funnel; its the one I use when I run the cell. I have several funnels & when one filter cloggs, I set it on a beaker & add a bit of HCL/CL & it dissolves the sediment collected in the filter. Then I add this to the rest of the batch that's been dissolved. :mrgreen:

Someone once said: "Necessity is the mother of invention!"

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=7034&p=65081&hilit=fiber+glass+filters#p65836

 

[cobrawearer]

I have tried the fiberglass, too much of a mess. I will keep an eye on the temperature from now on.

 

[Geraldo]

Three thoughts:

1. Sulfuric acid isn't that expensive, if that is your primary "recovery" concern.
2. If you have a tall, narrow glass vessel, you can put your slurry in that and do a "column" settling exercise. It should let you recover a higher % of the acid (easier to siphon clear solution off the top) compared to a wide jar.
3. If you have a simple, fairly coarse piece of WOVEN fiberglass (not the hairy mat), you can use that as a filter support, then use fine granular sand as the filtration media - maybe an inch of sand over the fiberglass. This will make it hard to recover solids, however. Make sure to test your sand first with some H2SO4 to make sure it is pure silica sand and doesn't react significantly.

You can also play with cooling the solution (in the fridge or freezer) as that sometimes helps settling for fine particles.

Best Regards, Gerald

 

[cobrawearer]

Thank you much. I have some fiberglass boat repair cloth that will work perfectly. Thanks