Sulfuric acid question

[Dougplogan]

I'm looking for a little advice hopefully from someone who has actually processed their old filters. I have a big jar or small bucket of used filters building up. Lots of them still have hydrochloric acid in them and weren't rinsed out well. The ones on bottom I'm sure have a decent amount of gold in them as I was learning and figuring out things. I don't want to burn them when I process them because of the acid still in them several are still green and can actually see crystals on them. What I'm thinking is use small amount of sulfuric acid to eat the paper. Once paper is gone and no more add hcl and small bit of nitric. My question is how will I burn off the sulfuric before filtering. I'll be doing it all in a beaker. More or less dump in all the old aqua regia filters I've used. Put on heat. Add tiny bits of sulfuric till filters are gone. Lots of these filters are from dirty solutions. Alot of escrap I'll just digest copper and gold together and drop the gold then refine the gold again. And a third time in some situations before I'm happy with it. Ultimately I'm afraid the acid in filters will cause the gold to burn up and oxidize and then rinsing away ashes will cause gold to be lost since it never was turned back to metallic gold. I'm not in a rush by any means and would love to hear how others have processed theirs. I suppose it's worth noting that a couple of months ago I processed my waist bucket to see how much gold I've missed since starting this and ended up with 4.8 grams out of it. That waist bucket has had every drop of my waist gone through it since my first attempt. Anyways to anyone that adds to this discussion thank you for your time and knowledge

 

[kurtak]

Ultimately I'm afraid the acid in filters will cause the gold to burn up and oxidize

You can burn the filters (it's actually called "ashing") without "burning off" the values in them - if done right

In other words - yes - the values can "go up" in smoke if you don't do it right

But if you do it right you will reduce & recover the VAST majority of your metal (95 - 98%)

I posted about it a couple years ago here ---------

https://goldrefiningforum.com/threa...nd-pm-salts-recovery.21638/page-2#post-306023
after reading that if you have any questions I am more then glad to help

Kurt

 

[nickvc]

You can also just process as is in hot AR and if as you suspect you have chloride crystals start by adding some water and then slowly adding doses of nitric until you get no reaction and then add a little HCl and see if the reaction kicks off , if you use too much nitric it doesn’t really matter if you add sulphamic to neutralise it as the sulphuric created will eat some of the filter paper.

 

[Geo]

If the container the filters are in is durable, Mix a few spoons of sodium hydroxide in water until it's dissolved. Slowly add this to the filters while stirring. It will neutralize any acid present in the filters. After a short time to ensure all the acid is neutralized, dry and roast the filter material. You will wind up with oxides of the metals in the filters and a little carbon depending on how well you roast the material. After neutralizing the acid, there little chance of of losing any values as a chloride in the smoke or fumes.

 

[Dougplogan]

If the container the filters are in is durable, Mix a few spoons of sodium hydroxide in water until it's dissolved. Slowly add this to the filters while stirring. It will neutralize any acid present in the filters. After a short time to ensure all the acid is neutralized, dry and roast the filter material. You will wind up with oxides of the metals in the filters and a little carbon depending on how well you roast the material. After neutralizing the acid, there little chance of of losing any values as a chloride in the smoke or fumes.

Thank you. That's actually what I'd started thinking. It's way to many filters to try and process straight into aqua regia. And many of the filters I never rinsed the acid through. Basically after pouring acid through them just let them dry. Some are completely covered in crystals and break up when touched. Plus alot are from AP solutions as well. Not just aqua regia. I believe there is alot of gold in them especially the ones from the beginning. I recently processed an old waist bucket that I'd run AP solutions through and was able to get back almost 7 grams of gold alone.