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silver refining with nitric acid

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jankriel

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Post October 7th, 2012, 1:19 pm

silver refining with nitric acid

can someone please help me .
I submerge my silver concentrate ore in nitric acid and stirr it several times for a period of 24 hours.
I then remove the acid and put it through a coffee filter until the acid is clean.
I then use NaOH to neutralise the acid to a PH of 6 to presipitate the other metals out of the acid solotion.
I then use CaCl (salt) to presipitate the silver chloride at a ph of 8 and above.
The presipitate is white and then adding baking soda to neutralise any acid still in the solution.
When I ad NaOH to the white presipitate the colour did not change to black and when adding
sugar it also did not change to grey.
Due to the number of metals in the concentrate I will have to presipitate the other metals first.
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butcher

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Post October 7th, 2012, 6:20 pm

Re: silver refining with nitric acid

Well I do not know if I can help, first I have a few questions about the process you are trying to use to recover silver from ore.

Why try to neutralize to pH 6 with NaOH this solution to precipitate base metals before recovering the silver?
I do not understand and would be afraid this would also precipitate most of the silver.


Why use calcium chloride?
Calcium is one of the most insoluble compounds, or forms very insoluble compounds (some hard as a rock).


Why raise the pH to 8 or above making solution very caustic before using the CaCl to try and precipitate silver chloride.
Why do you say use backing soda to try and neutralize any acid?
What acid could possibly be left in this solution at this point?
Why do you think these white powders remaining are silver?
Why do you think the NaOH would oxidize any silver if it did happen to be in solution (after all of the caustic added in the above process)? I would think any silver if it made it this far through the process would already be an oxide or hydroxide.
Why do you think you could precipitate other metals from solution before precipitating silver? This is backwards to me.

Well I do not know where to begin to help, beside maybe saying I would not try and reclaim silver from ore using that process.
First nitric on ore could be very dangerous, costly How much silver have you recovered using this process? Will it pay for the nitric acid, how are you dealing with toxic waste and gases?

I thought about asking why you did not cement the silver out of solution using copper, instead of using all of the bases trying to get silver chloride, but then you would still be trying to recover silver from ore using nitric acid , (which I feel at this point is just a terrible idea).

My suggestions learn how to treat what you have for proper waste disposal, if you’re not sure how read about it in our safety section dealing with waste.
How many tons of this silver ore do you have and plan to recover silver from.
Look into silver mining and maybe froth floatation, smelting or other methods.
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4metals

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Post October 7th, 2012, 8:16 pm

Re: silver refining with nitric acid

I completely agree with Butcher.

Unless your concentrates are a high percentage of silver acid is not the method of choice for ore, but perhaps you are not using the proper terminology so I will say this;

If your nitric acid did digest the silver from the ore and the assay you performed on the residues showed no other precious metals, then you should follow Butchers advice and leave it acidic and cement the dissolved silver with copper. The copper will selectively drop all of the precious metals it dissolved as well as mercury if you used an amalgam to concentrate.

Most of the base metals will remain in solution and the relatively pure silver is metallic already so easily handled. (If you used mercury it will still be in there)

Using caustic on the solution will drop your base metals and quite possibly form silver oxide which will drop as well. Keep it acidic and forget about forming a chloride, cement it on copper.
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butcher

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Post October 7th, 2012, 8:26 pm

Re: silver refining with nitric acid

Really without more details of how this silver ore concentrate was recovered or what it contains now or what steps you have done to prepare it up to dissolving it in nitric acid, it is really hard to give advice.
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jankriel

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Post October 8th, 2012, 12:40 am

Re: silver refining with nitric acid

butcher,
I realy appreciate it that you want to assist me.
With an XRF the readings are as follows: Ag 10.73, Pd 11.62, Rh 14.34, Ru 7.67, Pt 2.58,Fe 54.80.
As the refining of silver is not so costly and more simple I want to extract the silver first and refine it
and leave the rest.
I mill the rock with a ball mill to 75 micron and put it through a screen and then remove the Fe with an electro magnet.
The ore is then put through a knelson concentrator to catch small amounts of Au as we have placer Au and which
is nearly undetactable.
The concentrator is unable to catch the silver which is very light and this is done by hand by washing the ore and catching the silver which is very fine.
the silver ore is then heated to remove the sulfates which is very high in this area and submerged in nitric acid for
silver refining.
Itried many times but to date was unable to refine one ounce of silver.
can you please assist futher
thanks jan
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nickvc

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Post October 8th, 2012, 2:33 am

Re: silver refining with nitric acid

Jan I would be very wary basing anything on an xrf reading, especially when it shows a very high percentage of values present. If the area your extracting the ore from has a history of high PGMs that may be slightly different but even so I would suggest a proper assay before you spend lots of time and money trying to recover something that may or may not be there, the other problem is that when dissolving silver in nitric if PGMs are present some of them will also dissolve and palladium is fully dissolvable in nitric with or without silver present. If values really are present then the way forward may well be to remove the Fe first and if a concentrate of values can be achieved perhaps using silver to collect them by creating a 97%+ silver anode to recover the values through a silver cell in the slimes, the benefit would also be the recovery and refining of the silver at the same time.
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jankriel

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Post October 8th, 2012, 2:56 am

Re: silver refining with nitric acid

nickvc
The area I am living in is a rich mineral area and around me is a number of mines.
The geology type is the bushveld ingeneous complex in south africa.
The mineral type is mainly: cooperite, bragite,malanite and laurite.
i hope this will also assist.
thanks
jan
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nickvc

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Post October 8th, 2012, 3:17 am

Re: silver refining with nitric acid

Jan I'm not an expert on minerals, ores or mining but I know South Africa does have a lot of mineral wealth but I would get an assay done to determine what exactly to expect, many things in ores and minerals can form toxic and even deadly gases and ompounds if not treated correctly, you need to be aware of what your likely to create by treating your ores! We stress safety first and last on the forum, no values are worth your life or health, your neighbours or the potential damage to the environment. You really need to get a full assay to be able to make the right and safe decisions to treat your ores and be able to recover what values they contain, without a good assay how are you sure your recovering all the known values or even all the values in them. With the right information we have some very clever members on the forum who could point you in the right direction to try and get you to your desired result.
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butcher

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Post October 8th, 2012, 5:52 am

Re: silver refining with nitric acid

jan,

Nickvc, and 4metals give very good advice pay close attention to it.

I am not a professional miner, or any kind of expert on anything, and as you know recovery of these metals from ore can be difficult, there can be several approaches and you may have to experiment with different methods to find the best approach.

At this point we really still do not have enough information to make a decision of which way to go, and in the end you will be the one to make this decision by what you find when dealing with your ore.

From your description:
Ag 10.73, Pd 11.62, Rh 14.34, Ru 7.67, Pt 2.58,Fe 54.80.

I do not see mention of Iridium doesn’t malanite contain this? There are probably many more metals involved like cobalt, nickel and who knows what, like arsenic or mercury or some other metals that may pose dangers in the processes or become problems with certain processes, a good assay can help you to make the decision of what way may be better to try and what to be careful of.

Besides iron and the free gold you seem to be reclaiming, you seem to have a fairly high content of PGM along with silver, in a sulfide ore.

You are grinding the ore in a ball mill, screen, and removing the iron with magnet, concentrating with a centrifuge to recover free gold and heavy material.
You did not go into details of what your process is with this more valuable material (please give more detail here).

We will look at silver more later, in this post,

Here your process sounds good, I would also check the iron removed with the magnet for values.
The concentrated material is should be where the main value is, these are sulfide minerals high in sulfur and PGM like I said I am no professional and only play miner as a hobby, but from what I can tell the possible metals in the ores you listed are Pt, Pd, Ir, Ru, high in sulfides. You also mention recovery of free gold (so I would also assume there to be gold locked up in the iron sulfide\ore also.

Valuable sulfide can be froth floated in oils and air as a recovery method, if using this method you would want to concentrate them as sulfide before roasting, silver sulfide can also be concentrated using this method as well as gold.

Roasting to drive off the sulfur and sulfide, this is important before leaching, elemental iron metal added to this roast can be beneficial, as the iron metal will collect the sulfide and release the valuable metals bond with sulfur, possibly releasing gold silver and PGM's, once the sulfide is removed the iron in the roast can also give these metals back an electron the sulfide had when it was bonded to them, and convert them back to elemental valuable metal powders, the heat and air will drive off SO2 gas as the sulfur burns adding fuel to the roast, and as the sulfide’s are heated iron collects the sulfide (from the valuable metal powders in the ore), and releases it as SO2 gas as the iron forms oxides of iron in the oxygen rich environment, oxygen is also beneficial here, good exposure of powders to air by stirring and raking of the red hot ore, not only will help to remove sulfides but also help to oxidize the base metals which are much easier to oxidize than the more valuable more noble metals, this will help when leaching and removing base metal from the more valuable metals in a leach process later, depending on choice of process.

Sometimes salting the ore in the roast is beneficial other times it may cause trouble, salt NaCl in a roast sometimes can help to form chlorides in the roast, making a chloride leach later more easy, but if too much salt is used or the chemistry of the ore is such that this method would not be combatable, you can also make values more volatile and lose values in fumes, and could fume off values in a valuable chloride gas leaving the roast. (With your ore I would not try this method).

Now that we have this concentrated material roasted we can more easily remove the oxidized base metals and as our valuables will be mostly elemental metal powders at this point, and most of the other base metals are oxidized, some of the non magnetic iron may become magnetic (caution collecting iron with a magnet can also pick up some values so check this material later), many of the valuable powders may also be more easily separated from the oxidized base metal powders using water and gravity methods (maybe experiment with gravity separation again at this point and see if there is any benefit, water may also help to remove some of the more soluble oxides here, and the powders no longer being sulfide salts of metals but elemental valuable metal powder and lighter base metal oxides, you may find it beneficial to use gravity again.

Now to separate base metals further from the oxidized base metals, choosing or experimenting with which leach to use for the base metal leach is important, or if we are using a leach more selective for values, you probably have access or experience with chemicals that I do not have access or experience with, but if you discuss your methods, there are members here that may help.

Also depending on how well we can separate the base metal from the valuable ore can also determine what method of further recovery or refining or separation of these valuable metals we may try.

With high PGM content I tend to think smelting the PGM and gold, with silver metal as a collector is a good idea.

Your silver ore can also be used here, and recovered also, (your silver sulfide ore that was converted to elemental silver metal powder in the roast with elemental iron as described above, it could be used as the roasted powders, or if you can get a good separation of the silver powders after the roast, melting the silver powders with elemental iron metal, you could get silver metal silver which will not alloy with iron (like gold will),and any unconverted silver sulfide left after roasting would convert to silver metal in the melt, again iron taking the remaining sulfide and forming SO2 gas, the iron oxide reporting to the glass slag from flux) this silver could now be used as a collector.

Depending on how much silver you used as a collector to the amount of platinum or platinum group and gold in the ore, can make a big difference in how these would react to some acids later, or if you used enough silver to make very high silver percentage of silver anode, the PGM and gold could be collected in an electro-refining cell as anode mud’s as you recovered silver in the cell, then you could further treat the anode slime for recovery separation or refining of gold and the platinum group or selling to a refiner.

Like I said mining is not easy and there can be several ways to go some ways will get you there, some ways you could just get lost, and other ways would get you to where your going faster and better, also you may have to experiment on which way works better than others with small experiments before you commit to which direction you will go in this journey, there are many members here on the forum more experienced than I am, I only play with mining on a very small scale, but I am sure the forum can help you in some way to come up with a method that will work for you, we could use more details of how you are processing and maybe we can give you a few more ideas, to decide which direction you wish to try.

You will find reading Hokes book and the forum very beneficial in helping you develop and improve your processes.
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jankriel

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Post October 8th, 2012, 12:33 pm

Re: silver refining with nitric acid

butcher
thanks again for your information above which is very valuable to me.
What I find with the Knelson concentrator is that particle sizes above 25 micron the concentrator is very helpfull but when the particles are smaller it did not recover Au.
With regard to particles smaller than 25 microns the concentrator cannot concentrate it and one may loose most of the PMG and all of the Ag and Au.
In fact the Knelson concentrator is only for Au.
What I will do is to make a fire assay and send it to a laboratory for testing to determin exactly the metals present.
In fact I have a furnace which can go to a temperature of maximum 1300Celcius.
as i plan to move away from accids can you perhaps help me with the details on flotation.what chemicals are used
and how the process works.
I live on my own farm and have a large number of game which I love and will never use chemicals which will endanger the environment.
To answer your other question,the other valuable material which is still in solution is stored in a safe store room which is locked 24 hours.
This is my first batch I am doing of about 500 kilogram.
Can you also please advice me on the process to use copper to cement the silver.
You also asked previously the number of tons of this ore I have,which is thousands of tons ontop of the ground and underground.
thanks for everything so far
jan
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g_axelsson

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Post October 8th, 2012, 1:40 pm

Re: silver refining with nitric acid

I'm feeling that something is missing from the discussion.

You haven't told us how the ore has been treated. Your XRF results states high PGM levels and 50% iron but there is no mentioning of oxygen or sulphur. The minerals you named are sulphides or oxides.
Is the ore in metallic form, reduced by smelting or roasting? Is it a flotation concentrate? Is it gravimetrically concentrated (i.e. panned)?
You must understand that minerals containing chemical components made up by metals and other atoms (sulphides, oxides, ... ) reacts differently on acids compared to the bare metal.

I guess that the result from the XRF is in percent. Then you only have metals and no oxide or sulphide as the percentage is even above 100%, or the results from the XRF is wrong or misleading.

I'm no expert on mining and refining of ores, but I've always seen that the first step in ore processing is to roast the ore, driving off volative compounds as sulphur and arsenic.

I also think it is strange that you have ore that contains so high values of PGM (14% Rh, 11% Pd...) and you are trying to get the silver. I would be more concerned about the PGM:s. It's like recovering silver plate from gold bars and ignoring the gold. The PGM:s would be worth more than 30 times of the silver. Something isn't correct in your XRF data.

I hope I haven't sounded too harsh, I just want to help you but what I see is a lot of vague information and some people that tries to help you blindly.
I look forward to see the assays of your ore, it sounds like an interesting ore and I would like to learn more about it. Do you have any photos of the ore and the concentrate?

/Göran
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jankriel

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Post October 8th, 2012, 4:37 pm

Re: silver refining with nitric acid

g-axelsson
Thank you for your reply and comments which I realy appreciate.
The XRF did not indicate the sulpher content however I know it is considerable high as I wash the ore with 1:12 HCl and water one can smell an egg which is no more fresh also when roasting the ore one get the same smell.
The XRF is in persentage.
I once tested other ore on the farm which indicated the following with regard to sulphates and oxides in Mg/L:
SiO 0.18 ,CaO 0.24,Co 0.0016,As 0.33,MgO0.13, Cl 0.12, Fe2O30.1,Na2O30.05,K2O 0.037,P2o5 0.03,MnO 0.021,
CuO 0.008,SO3 0.0028,TiO 0.0027,Cr2O3 0.0019,bAo 0.01
I hope this will give you an indication of the sulphates and oxides in the ore although it is not the same ore outcrop.
This is the first time I am attempting to extract a mineral from ore on my farm and the silver seems to be the simplest of all.
For sure if i have the knowledge to extract the PGM"S I would have attempted it first.
Thank you for your assistance so far.
jan
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butcher

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Post October 8th, 2012, 6:36 pm

Re: silver refining with nitric acid

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jankriel

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Post October 9th, 2012, 2:44 pm

Re: silver refining with nitric acid

butcher
why are you sending me to search the world.
All I am asking is for help.
I will for sure follow your advice as it is already of great help.
Please just remember I am in Africa and it is not as easy as where you are.
My great grand father imigrated here from Germany, why I dont know.
thanks
jan
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butcher

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Post October 9th, 2012, 11:26 pm

Re: silver refining with nitric acid

Jan,
froth floatiation is a big subject with many varibles, I have not used the process, and the link I provided is a good place for you to begin learning about it, so searhing the world (or information provided by computer) could greatly benifit you, I was trying to help the best I know how, I could of said put some pine oil in a barrel and pump in some air with stirring and float off the sulfide gold and silver ore, but you will do much better reading about it on the google search provided.

did not mean to offend you.
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jankriel

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Post October 10th, 2012, 12:49 am

Re: silver refining with nitric acid

butcher
here is a photo of the ore i promissed to send
regards
jan
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butcher

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Post October 10th, 2012, 10:20 am

Re: silver refining with nitric acid

Jan, the picture did not work.
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jankriel

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Post October 10th, 2012, 1:08 pm

Re: silver refining with nitric acid

butcher sory for this
please find it now attached
thanks
jan
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butcher

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Post October 10th, 2012, 9:53 pm

Re: silver refining with nitric acid

That looks just like the quartz which contains some gold around here, most of the gold in quartz around here is recovered by grinding and gravity methods (it would not be worth leaching to recover other small traces left), but in your case that may be different.

If most of your ore looks like this rock it is good, as the quartz will not dissolve into solution, and a little quartz in a smelt is a good ingredient to flux and can help to make glass in the slag.
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jankriel

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Post October 12th, 2012, 6:39 am

Re: silver refining with nitric acid

butcher
I have taken a clearer photo of the ore indicating the spots and veins more clearly.
The rock is more a dull white as it is a white quartz and much harder than quartz.
when I ball mill this ,the colour of the milled ore is dark grey to blue.
i would like to send you a sample of the rock if you will allow me.
thanks
jan
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