Silver Nitrate and Base Metals Solution Useage

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Goldenrod757

Member
Joined
Jun 30, 2012
Messages
24
Im sure this was discussed somewhere but iv been off the forum for a while until recently. In refining carat gold waste, nitric acid is generally used to extract base metals , primarily copper and silver. The silver is easily recoverable from the blue solution by adding HCl and collecting the white precipitate of insoluble Silver Chloride. The remaining solution should have Copper Chloride and possibly chlorides of Iron and other base metals. So my question is , of this liquor remaining , are the nitrate ions and HCL mix present, useable as some kind of weak AR ? What is the advised use of this liquid remaining?
 
The copper nitrate will not convert to copper chloride i think.
If you cement the silver out on copper instead of the HCL additions you could recover the nitric acid and the copper.
Nurdrage video:
https://youtu.be/l8uQWibpRYk

Not sure if it would work with HCL in the mix.

Martijn.
 
Goldenrod, if you choose to drop your silver as silver chloride, and you'd like to get further use from the remaining solution, I'd suggest using just a bit less HCl than needed to convert all of the silver. By doing so, you won't have any Cl- ions in solution, as they'll all be dropped from solution as AgCl. It will leave you with a solution of HNO3, CuNO3, and a bit of AgNO3. You can use the solution to digest more silver and base metal in your next refine.

Dave
 
Thanks Frugal, Iv started treating a batch of nitrates with careful additions of HCl at the moment. A some ago i had some spent solution that had been sitting and probabably dried out a bit(either nitrates from this stage or after dropping gold from the rich AR that boiled and treated with metabisulphite ) and found two sets of crystals at the bottom. One was blue and so was obviously suspected to be a copper salt. The lesser amout however was some beautiful violet crystals , which i thought to be some kind of precious metal or transition element crystals. I was much more busy with other thing and less organised as a refiner and it got lost somewhere along the way.
Any idea what those likely were?
 
Butcher.
How do we know when we are almost there with the AgCl?
Are there any telltales or is it just done by the seat of our pants?
 
The one reason to cement the silver out with copper is it will also cement any PGMs from the solution which can be recovered by refining the silver in a cell once there is enough to bother with, the silver cement visibly becomes more grey as it contains more and more PGMs.
The only real use I can see for re using the acid is to use it to dissolve low grade materials prior to proper recovery, I’m struggling to see any other use but perhaps butcher has better ideas for its use.
 
copper nitrate can be used in many different ways, I never consider it a waste.

metal nitrates are normally very good oxidizers,.

Copper nitrate can easily be converted into copper chlorides or copper sulfates or converted to other metal nitrates, that can have other uses in recovery or refining or for other uses around the home or lab.

Copper nitrate is a reagent many labs buy to use for many different chemical processes or to make other chemical reagents out of, it can be just as useful in our labs.

As Nick said you can always use copper nitrate and heat to remove base metals (just like using nitric acid).

After cementing silver out of the solution using copper, consider re-using the copper nitrate solution like poor man's nitric, and or like poor man's aqua regia.
The copper nitrate and HCl heated will act like aqua regia to dissolve gold...

Copper nitrate makes a good electrolyte for cells, which can be used as a silver recovery process such as recovering silver from sterling, or copper refining...

Much of the copper can be removed from the copper nitrate using electrolysis, making the solution more ready to dissolve more metals.
Using an inert carbon graphite anode and a copper cathode we can remove much of the copper from the electrolyte, and then reuse the electrolyte solution will be ready to dissolve more metals such as copper. in theory, you could dissolve much more copper with the same solution.

Distillation for those who have studied the dangers and can do it safely, adding sulfuric acid and your copper-based gold plated items (cut into small pieces), adding the copper nitrate, you can distill off NOx gases that if bubbled through the water with a little added H2O2 will make nitric acid out of that water.
The copper dissolves, leaving you gold foils, in a water-soluble pretty blue copper sulfate solution (which can also be saved to use in a copper cell or for some silver recovery project or used as a reagent for some other purpose around the home or lab.
 
Sorry about that Butcher.
I think you missed my point and answered Nicks question not mine :)
Are there any telltale signs of that it is close to no more Ag in solution, or is it an experience thing?
 
While I’m not butcher I believe unless you access to assays then it’s an experience scenario as you have no idea how much silver you are looking at to start, if dealing with a large volume perhaps take a known amount of sample and add HCl in very small measured increments until no more chlorides form and then calculate how much you need to recover most of the silver from your larger solution.
 
You can test a sample as Nick has described. Even better is to do a Volhard titration on a sample of the solution to determine its silver content, then process the bulk solution based on that information.

Dave
 
A drop of HCl in a test tube sample, how white the clouds are, less silver less white cloud, no silver no white cloud.

Titration, taking measured volumes in a test, slowly and in intervals adding drops of HCl in increments until an endpoint is reached.
Then measuring how much HCl was used, or measuring how much salt was produced, would give you an indication of how much silver was dissolved in solution or precipitated out.
This can also give you a reference to how much HCl you may need to add to the original solution to precipitate the amount of silver involved from that volume.
Normally you need fairly accurate measurements of solutions volumes and accurate measures of weights, specialized lab glass, or equipment would be helpful with this approach.

A piece of copper wire dangled in samples can also be an indicator of how much silver is left in the solution, as the silver tends to cling to the piece of copper as the silver ions are reduced, you should see less of the copper-covered with gray silver as the silver is depleted from the solution. From memory,I believe Juan or GSP discussed using this method to test as an indicator.

I would not use HCl to remove silver from a copper nitrate solution (I hate dealing with silver chloride if can avoid it.) if possible I would like to keep chlorides out of the nitrate solution if my plan is to use it in the future for silver.

I would use copper to remove silver as the metal from the solution (along with PGMs as Nick noted), adding nothing but copper to the copper nitrate solution.
 
Sorry Butcher..
I mistakenly adressed it to you instead of Frugalrefiner, my bad. :oops:
Anyway I got my answer, but I'll be more careful next time
 
Volhard Titration

How it Works - Potassium thiocyanate reacts with silver ions to create an insoluble precipitate of silver thiocyanate. It also reacts with the ferric (Fe3+) ions of the indicator solution to create a blood/wine red solution. Silver ions have a greater affinity for the thiocyanate than ferric ions, so the thiocyanate will react preferentially with the silver ions until there are no more of them in solution. When there are no more silver ions in solution, the red color will remain, indicating the endpoint of the titration.

Two reagents are needed for the titration, the Indicator, and the Titrant. They are prepared as follows.

Ferric Ammonium Sulfate Indicator - The indicator solution is easy to prepare. Only a small amount (approximately 1 ml.) of the indicator solution is needed for each test, so any convenient amount can be made depending on your needs. Dissolve about 1 gram of ferric ammonium sulfate into about 10 ml. of distilled water. The amounts are not critical. It is only important that there be sufficient ferric (Fe3+) ions in the solution to combine with excess thiocyanate ions at the endpoint of the titration. The ferric ions form a dark red complex with the thiocyanate ions to indicate the endpoint has been reached. For best results, the indicator solution should be prepared the same way each time, and the amount used should be consistent.

Potassium Thiocyanate Titrant - More care is required when preparing the titrant, as the precise concentration is important to achieve accurate results. The solution should be prepared in a volumetric flask to ensure accuracy. The molecular weight of potassium thiocyanate is 97.181 grams per mole. We want a 0.1 molar solution, so add 9.718 grams of potassium thiocyanate to a 1,000 ml. volumetric flask. Add about 500 ml. of distilled water to the flask and swirl the solution in the flask until all the thiocyanate is dissolved. When it is all dissolved and at room temperature, add distilled water to bring the solution up to the mark on the neck of the flask. This creates a 0.1 molar solution of potassium thiocyanate.

Note: Potassium thiocyanate is hygroscopic to the point of being deliquescent. Be sure to keep the bottle tightly capped and work quickly when weighing a sample as the sample will gain weight the longer it is exposed to any moisture in the air.

Be meticulous when preparing this solution. Any error in this step will be magnified when the solution is used. My inexpensive scales can drift during use, so I weigh the thiocyanate multiple times to achieve an accurate weight. Always allow all solution to return to the temperature specified on your volumetric flask when topping up the volume to the line on the flask. Be sure to thoroughly mix the final solution to ensure the concentration is consistent throughout.

Performing The Titration - Precision is important in titrations. Pipettes and burettes must be clean and dry. Using a quality measuring pipette, add exactly 1 ml. of the solution to be tested to a suitable, clean container. Erlenmeyer flasks are ideal for this work, as they allow you to swirl the solution in the flask to ensure thorough mixing while minimizing the risk of splashing any of the solution out of the flask. A 250 ml. flask is a good size. A beaker can be used, but extra care must be exercised to prevent any loss of solution which would render the results inaccurate. Add about 1 ml. of the indicator solution, and about 100 ml. of distilled water. These quantities are not critical as they do not affect the accuracy of the results, but be consistent from one test to the next.

Fill a burette with the titrant and adjust the level to the zero mark. Begin adding the titrant from the burette to the flask containing the sample, swirling the flask continuously to mix the solutions. At first, you’ll see a red reaction where the titrant contacts the sample, but the color disappears quickly and a precipitate forms as the solutions mix together. As you approach the endpoint, the color remains longer and the additions of titrant should be slowed to avoid overshooting the endpoint. At the end, you should only add the titrant one drop (or less) at a time, thoroughly mixing between each addition. The endpoint is reached when the last addition of titrant causes the solution to remain a slight pink/orange/purple/red color (the color will vary depending on the colors of any other ions in the solution). Read the amount of titrant that has been used from the burette and use it in the following calculations.

Calculations - The titrant contains 0.1 moles of potassium thiocyanate per liter, or .0001 mole per ml. Multiply the number of ml. of titrant used by .0001 to determine the moles of potassium thiocyanate used. The thiocyanate ions combine with the silver ions in a 1:1 relationship as shown in the formula below.

Ag+ (aq) + SCN- (aq) => AgSCN (s)

So the moles of thiocyanate used equals the moles of silver in the solution.

If you used 10 ml. of titrant, you would have used 10 * .0001 = .001 moles thiocyanate = .001 moles Ag. Since our sample was 1 ml., multiply this result by 1,000 to find the number of moles of silver per liter of solution (or multiply by the number of milliliters of solution to find the number of moles of silver in your solution).

The most common strength of HCl here in the US is 32%. This is a 10.2 molar solution, so in each liter of this HCl there are 10.2 moles of HCl. If your HCl is a different strength, look up or calculate the molarity of what you have available.

So let's say you have a liter of solution that contains 1 mole of silver. You would want to add a little under 1 mole of HCl to react with almost all of the silver.

It is worth noting that the resulting solution will be fairly dilute nitric acid. For a stronger result, evaporate the solution prior to adding the HCl.

NOTE: Palladium, lead, and mercury will interfere with this test as they also form insoluble thiocyanate compounds/complexes.

Dave
 
Thanks Dave for an excellent tutorial.
It is way over my needs in the moment,
but very on topic for the interesting Silver threads running now.
I'll bookmark this one in case I accumulate enough silver to run some decent amounts.
 
nickvc said:
The one reason to cement the silver out with copper is it will also cement any PGMs from the solution which can be recovered by refining the silver in a cell once there is enough to bother with, the silver cement visibly becomes more grey as it contains more and more PGMs.
The only real use I can see for re using the acid is to use it to dissolve low grade materials prior to proper recovery, I’m struggling to see any other use but perhaps butcher has better ideas for its use.

I had hardly ever even bother much about saving silver that much and really in the past had not been thinking about PGMs, partly because they would not have been in amounts to really bother with, me being a part time refiner and all, but I am about to set up a stock pot soon. ( Also Palladium was around $600/oz and is now higher that gold, not that im ready to deal with the tocicity of its/their salts ). Also i was more concerned about solving issues with Au recovery at that time.
 
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