Using Nitric Acid prior to AR.

[MiltonFu]

I have read on this board that it is advisable to use nitric acid to remove base metals prior to leaching gold with aqua regia.
I have also read that hydrogen peroxide is capable of reducing nitrous oxide emissions.
Questions:
1. Would the addition of hydrogen peroxide to a diluted nitric acid solution reduce nitrous oxide emissions?.
2. What strength of hydrogen peroxide and what quantity is needed?.
3. Does the addition of hydrogen peroxide to the aqua regia or diluted nitric acid have any material consequence on the recovery process?.

Thank you...thank you very much.

 

[Lino1406]

Does not remove base metals.
You meant Hydrochloric acid

 

[g_axelsson]

Nitric acid does remove base metals and hydrogen peroxide reduces the nitric gases by converting it back to nitric acid again.
I have read some patents on it but I don't have it in front of me and I haven't tested it yet so I can't help with the amount needed.

/Göran

 

[Lino1406]

Pd - yes
Ag - yes
Cu - yes
Pb - yes
Sn - with additional stage needed
Iron - no
Ni - no. I would say Pb, Cu the only relevant base metals
to be removed

 

[goldsilverpro]

Nitric will dissolve nickel. It will dissolve iron when it's weak and hot.

 

[Noxx]

Adding concentrated H2O2 to AR or HNO3 solution will increase its dissolving power but also increase dissolving rate.
I can't remember the numbers but be sure to also add Ethylene Glycol in order to prevent H2O2 decomposition.

 

[61 silverman]

Hi everyone, I am wanting to try adding h202 to my AR, mainly to reduce the toxic fumes and maximize acid efficiency. Has anybody found a proper percentage by volume that works the best, also is 3% h2o2 strong enough?Also how much Ethylene Glycol is needed.
Thank You MARK

 

[butcher]

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=55&t=764&p=6629&hilit=get+rid+of+NOx+fumes+and+get+stronger+nitric+acid#p6629

I can see how the H2O2
reconverts the nitric oxide, and nitric dioxide back to nitric acid
2NO + O2 --> 2NO2
3NO2 + H2O --> 2HNO3 + NO

but I'm still confused on how the antifreeze works in this?

 

[leavemealone]

Hey mark,
I tried it a long time ago but had problems percipitating.I don't remember the amounts that I used at the time,but Im sure the problem had to do with too much h2o2.
Johnny

 

[Irons]

Hey mark,
I tried it a long time ago but had problems percipitating.I don't remember the amounts that I used at the time,but Im sure the problem had to do with too much h2o2.
Johnny

Residual H2O2 will inhibit the precipitation of Gold. You can remove it by boiling, like in getting rid of Nitric or add lots of extra reducing agent.

The Peroxide you buy in the store already has the proper stabilizers and adding Glycol just adds more crap. It's going to break down. That's how the recycling of Nitric works. Nothing is free. If something is oxidized, something else is reduced.

 

[leavemealone]

Residual H2O2 will inhibit the precipitation of Gold.

Thanks irons.I still have a lot of 35% peroxide so maybe I will try it again and see if I can't recieve some better results.
Johnny

 

[Lino1406]

Works (in my opinion) through specific adsorption
to gold, other advantages not so meaningful, therefore
addition of H2O2 is recommended to every acid in contact
with plated gold

 

[asllan]

i m interested to now how to refine gold using the method using aqua regia

 

[leavemealone]

I cant stay but a minute or else I would get you the link to a good thread about poormans aqua regia.That is the method that I primarily use.If you search for poormans AR and my username ....hang on let me try to find it.
Try reading these posts I listed.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=6807&p=60860&hilit=poormans#p60860
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=58&t=6476&p=59588&hilit=poormans#p59588
Im sorry I don't have more time.These are just 2 quick links for you to read.Do a search for "poormans AR" and you will find many other posts about the procedure,but make sure you use the multiple decant and digest procedure like In the links.Steve taught me this a long time ago,and it works very well if done properly.
Johnny

 

[4metals]

The peroxide converts the NO2 back into Nitric so you actually use less. The residual nitric in solution has to be eliminated to drop the gold or it keeps re-dissolving and eventually you get a red cloud when the peroxide is exhausted and you're burning off the residual nitric.

To prevent this use sulfamic acid to kill the excess nitric, unlike urea, it does not generate the red NO2 cloud.

Using the peroxide method makes using a caustic fume scrubber a very viable option as all of the species of nitrogen generated will be effectively scrubbed by a single pass caustic scrubber.