# Iron/pm alloy separation



## black sands

Hello, this is a wonderful forum you have here. I have been researching precious metal recovery on and off for two years now. Mostly dealing with prospecting. I have recently taken a sample of local black sand and processed it so that the iron has been reduced into one 330 gram solid iron chunk, similar in size to a hockey puck. Some patents I've run across indicate that iron will readily collect gold and some pgm's. 

So I need to dissolve away the iron. The obvious answer would be to use an acid like nitric, HCl, or sulphuric. I would like to use sulphuric acid. The problem is that I want to maintain efficiency. And I don't want to waste large amounts of acid and time on lengthy dissolutions. 

I have seen the use of the sulphuric cell here to de-plate gold. My question is can I use the same idea to dissolve my iron nugget, plate the iron, and leave any possible gold and pgm's in the form of a powder on the bottom of the acid container?


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## butcher

Iron will dissolve easily in dilute sulfuric acid, a 10% H2SO4 solution will form ferrous sulfate (a chemical that can be used to precipitate gold from solution), I normally use heat to dissolve iron in the dilute sulfuric acid.

Electrolysis can force a reaction to occur that would not normally occur with a metal and a solution, or speed a reaction that would normally occur.

I do not think the concentrated sulfuric cell for what your trying to do would work very well.

If you want all of the iron in solution leaving your gold then you would have to use a certain amount of chemical (acid)to dissolve the iron putting it into solution and leaving the gold , a dilute sulfuric electrolytic cell can force the reaction to progress, and could break the bar down to gold and iron powders (once electrolyte solution is saturated with iron no more would stay in solution at that pH or temperature), unless you had enough acidic solution for the iron to go into it would not separate the gold from the iron powders (but then you could easily dissolve the iron powders in a dilute sulfuric acid solution) and recover the gold.


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## black sands

Thank you for the reply butcher!

So as long as I use enough acid, the iron bar could be dissolved much faster with a battery charger lead connected to it...
I was hoping that the iron would plate out on the opposing electrode allowing the acid to avoid saturation, and letting us use a much smaller volume of acid.


I have dissolved the iron ingot using warm dilute sulfuric in a crock pot. Took about half a gallon of concentrated sulfuric to dissolve the entire nugget. I may have gone overboard with the acid because I was impatient and regularly replacing the used acid with fresh. Now I am left with a significant amount of blackish grey powder which will not dissolve in fresh batches of dilute sulfuric.

I am currently treating the powder with HCl. It looks like I will be left with much material that doesn't dissolve in sulfuric or HCl. Should I send this material out for analysis...or try to process it myself using hcl/cl and selective precipitation?


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## butcher

The sulfuric acid will work better to dissolve iron, if it is about 10% H2SO4, if the iron solution is evaporated and crystallized to green ferrous sulfate FeSO4:10H2O we see in this formula for one mole of iron it will take one mole of sulfuric acid H2SO4, and since our solution we dissolve the iron in is 90% water, we are really not using that much acid to dissolve the iron.

Using a stronger concentration of acid can waste acid, some metals dissolve better in some acids better if dilute than if you were using concentrated acid, and the water in the reaction actually helps the reaction to proceed. (This usually depends on what metals and what acids are used)

After the straight HCl will not react on the powders, rinse them, add some water and sodium hydroxide, this will form a salt water solution as the powders give up the chloride to the sodium, any base metals will become hydroxides or oxides or elemental metals as the pH is brought to neutral, rinse the salt from solution well, the reason for this is that gold in salt or chlorides is somewhat volatile at high temperatures, now we can add heat to these gray powders slowly at first to dry them, then after dry crush them to powder and roast them to a red hot glow, stir while hot to get good exposure to air, this will drive off any previous acid used and any base metals will be oxidized by the high temperature and the oxygen in the air, if using a torch you can adjust the flame to an oxidizing flame, and play oxygen over the red hot powders, oxidizing will also help the base metals dissolve in acids easier, let these cool then rinse with water.

At this point you can now use heat and a dilute nitric acid 70%HNO3 mixed with equal volume of water, to remove any remaining base metals from your gold, I would use the nitric acid in small volumes or batches, heating until it dissolve all of the metals it can and the reaction ceases, give it plenty of time to work, letting powders settle and decant solution loaded with base metals, if the solution is highly colored repeat with another batch of nitric to dissolve more base metals, until decantation’s are clear indicating they are not picking up more base metals, (if silver was involved the nitric will dissolve it, you can recover silver from the decanted nitric acid solution using a copper buss bar).

After rinsing these gold powders the gold can now be put into solution or dissolved.
If using aqua regia you can use it without further treatment.
But if you’re not familiar with the procedure for aqua regia, the HCl/NaClO (bleach) method is easier.

If using the HCl and sodium hypochlorite method, you should dry the rinsed gold powders and heat them to red hot again to drive of any nitrate salts, as you can not eliminate nitrates from the HCL/bleach solution easily or by evaporations as the solution is so dilute with water you will form salts long before any nitric would leave this solution.

After the gold is dissolved into solution, the oxidizer is removed using heat (aqua regia use the three evaporation or gold button method), (with HCL/NaClO method bringing to almost a boil will easily remove oxidizer, a much simpler process).

And then solution is filtered.

If aqua regia is used solution is diluted with 4 parts water and left to sit overnight so any silver chloride would settle before decanting and filtering of solution.

HCl/NaClO method let sit to settle any AgCl then filter decanted solution (no dilution needed).

Now precipitate the gold from solution using SMB or ferrous sulfate, or precipitant of your choice.

Wash this precipitated gold per Harold’s instructions (found in getting your gold pure and shining found in help needed section).

For a high purity beautiful button of gold, re-refine your gold again, it is very easy to repeat the process, and the results will be well worth it.

There are minor details of the process not stated here; this is just to give you the general overview.
(Details can be found in Hoke’s book and reading the forum)

As they say some times the devil is in the details (like GSP’s trick of using minimum nitric needed to dissolve the gold in an aqua regia solution, so de-noxing time can be cut way down and using Harold’s trick of adding a gold button to use up un-reacted nitric acid).

Details can be found in Hoke’s book and reading the forum.


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## g_axelsson

I would recommend you to incinerate your black powder before doing any other step.

When smelting ore and reducing iron oxides to iron, some carbon is usually dissolved in the iron. That carbon would be left behind by the acid as a black powder when dissolving the iron. Incinerating will burn away any carbon in your powder and then you will have an easier concentrate to work with.

/Göran


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## black sands

Butcher you just summed up in one post something that took me over a year of searching to learn. I didn't know about the sodium hydroxide step though. Great job, thanks!

What would happen if the nitric wash was omitted? HCl and sulfuric are much easier for me to get. Although there are some interesting plasma arc nitric generator designs floating around the internet. Making nitric acid from atmospheric nitrogen, just like lightning. :shock: 




> I would recommend you to incinerate your black powder before doing any other step.


Thank you axelsson, I have just incinerated the powder and it became a very light ashy color. I have added this powder to fresh muriatic acid, at which point the powder resumed its dark charcoal color. The HCl is not reacting much visibly, but has picked up a shade of yellow, so there is new material dissolving. 

When I hold a flask of the slurry to a light, I can see thousands of microscopic specks glittering within the charcoal colored powder. They look metallic, but may just be crystalline compounds reflecting light.


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## nickvc

You can dissolve values if in powder form using hydrochloric acid and adding bleach, be careful doing this, use a fume hood or work with a fan behind you to dispel the chlorine gas away from you. You need to then warm the solution after all the powders have dissolved to remove the excess chlorine you can then precipitate your gold, make sure to test with stannous after precipitating to ensure all the gold is down and to see if other values are present.


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## black sands

nickvc said:


> You can dissolve values if in powder form using hydrochloric acid and adding bleach, be careful doing this, use a fume hood or work with a fan behind you to dispel the chlorine gas away from you. You need to then warm the solution after all the powders have dissolved to remove the excess chlorine you can then precipitate your gold, make sure to test with stannous after precipitating to ensure all the gold is down and to see if other values are present.




Thank you, I have actually worked with the acid chlorine process some in the past. It is also the current plan of attack on this charcoal colored powder, after I rid it of as much iron as possible. I don't have a proper fume hood with scrubber, so volatile reactions like this are done outside away from neighbours.


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## irishmick

black sands,
How did this turn out for you recovery wise? I've got some black sands I wouldn't mind trying this on and I'm curious how you did.
Thanks


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## black sands

irishmick said:


> black sands,
> How did this turn out for you recovery wise? I've got some black sands I wouldn't mind trying this on and I'm curious how you did.
> Thanks



Didn't work. Guess there weren't any values in my sample. Oh well, on to other experiments.


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## Geo

black sand concentrates have a large percentage of iron in the form of pyrites and magnetite's and sulfates along with a couple more forms.iron will precipitate values almost as fast as they go into solution. if you dont remove the iron first, your solution will always test barren.


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## butcher

I usually pan the black sand out of the pan and just process the gold,
I will usually pan off the black sand after concentrated into a tub, so it can be re-panned just incase I missed a small flake the first time panning. 

Grinding roasting removing magnetic iron, and leaching iron from magnetite and hematite for a grain or two of gold seems like a waste of time when I could be out digging down to bedrock and getting more gold in my pan (dumping that black sand back into the river and seeing gold in the pan).


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## ashraf25ac

Hi 
I have work shop for plating iron by gold for holy mosq in Saudi Arabia , we use iron for Haung piece this wire covered by gold layer . I make test to recover gold by dissolving iron and gold remining as leaf . 
I am using mix of dilute sulphuric acid 10 % with conc. Nitric acid 68% where iron dissolve rapidly but more heat 
If you have any good way to perform this process . 

Sorry my English very weak


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## butcher

ashraf25ac,
If I understand you correctly, you are recovering the gold using the dilute sulfuric (with some nitric as an oxidizer) to dissolve the iron to recover the gold.

I say this would work just as well as most any process, as long as the gold (plating) does not protect the acids from getting to the iron. cutting the wire into small pieces to expose the iron to the acids.
(the spent solution could also be a good source of iron sulfate (copperas).

I may cut up the wire and add it to the stock pot to recover gold.

Another option that I may try, is using my old copper II chloride solution (as I normally have plenty of used CuCl2 from other processes) to dissolve the iron to recover the gold, heating this solution strongly as it become copper I chloride and an iron chloride will dissolve the iron, leaving me with gold foils in a copper I chloride precipitate, that I can regenerate back to Copper II chloride for reuse as I recover my gold foils from the copper powders.

I have made some posts that may give you a better idea of what I am talking about here.
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=60&t=19838


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