Iron Contamination in Silver

[Buildeddie97]

Hello All!

Brand new to this site and silver working in general. I tried to find some posts that answered this question but couldn't so I'll make my first post.

I am doing silver recovery from a nitric acid solution. I have a dirty nitric acid and silver solution (it is used for silver stripping mostly on stainless steel parts but other some contaminants definitely get in). I pour sodium chloride (table salt) to acquire the silver chloride. I rinse this solution many times with tap water and then distilled water. I now do one of two things.

1. I add the silver chloride to a mixture of water, sulfuric acid, and I stir with an iron rod. This yields silver at the bottom. I then wash the silver with tap water, hydrochloric acid, and then finally distilled water. I finally take the silver and smelt it to a small ingot. I ran an analysis on this ingot and found that it is 99.6% silver and .4% iron. I figured the iron rod may have been the culprit so I cut out the middle step and tried solution 2:

2. I take the silver chloride and put in the crucible. I heat it and the chlorine burns away (I'm in a very well ventilated area, but I do want to know if this is safe regardless) and then continue to heat it until I can pour the silver and get an ingot. The same analysis was done and same results! 99.6% silver and .4% iron.

My guess is that in the nitric acid solution, some of the stainless steel that's dissolved leaves some trace amounts of iron which then react with the nitric acid to form mostly iron nitrate and apparently a trace amount of Fe2O3. Turns out that this Fe2O3 also reacts with table salt and forms a precipitate. This is my guess as to where the extra iron is coming from.

I did do some reading that the sulfuric acid method should have taken care of the iron issue so maybe it's just a coincidence and I should try again, but please let me know what you all think! I'm excited to be here and doing this so any help and thoughts are greatly appreciated!!

Buildeddie97
Edward

 

[nickvc]

Welcome to the forum.
Rinsing silver chloride clean of any contamination uses a lot of water and in some cases is almost impossible.
Try cementing your silver out using either copper sheet or opened up and flattened copper pipe this should help eliminate your iron contamination, once your solution has finished cementing the silver out remove the cement and wash thoroughly in clean water several times agitating it and then vacuum filter and add several more rinses through the filter.

 

[Lino1406]

Some use boiling AgCl with HCl to remove iron. The loss of silver is minimal

 

[Buildeddie97]

Welcome to the forum.
Rinsing silver chloride clean of any contamination uses a lot of water and in some cases is almost impossible.
Try cementing your silver out using either copper sheet or opened up and flattened copper pipe this should help eliminate your iron contamination, once your solution has finished cementing the silver out remove the cement and wash thoroughly in clean water several times agitating it and then vacuum filter and add several more rinses through the filter.

Does cementing work if the silver is bonded with chlorine? Also, what kind of filters are recommended? Should I run this through a small pump or is that overkill?

 

[Buildeddie97]

Some use boiling AgCl with HCl to remove iron. The loss of silver is minimal

Ahh that seems smart and easy! Kind of a related but different question, what is the best concentration of HCl and Nitric acid to use? I buy 63% nitric and dilute it with water, but I'm sure there's "ideal" levels for faster and better dissolving. Gosh there so much to learn.

 

[Lino1406]

Learning is pleasure, when you do not have something new to learn, in any aspect, your life becomes boring

 

[chapitas03]

Hi Buildingdie97. I am not an expert on this subject, but I often recover silver from a dirty nitric acid solution, and the first thing I do is filter the entire solution in a buchner funnel before precipitating it with table salt, this way I remove all the impurities contained in the dirty nitric acid solution.

Carrying out this step I always obtain silver with a purity of .999, free of any contaminant. Greetings and I hope this works for you.

 

[grainsofgold]

Is it reasonable to achieve 999 Ag from AgChloride + Sulfuric Acid and + Iron
Others on here have gotten high purity Ag results from sugar and lye.

Maybe 4metals can chime in on how high the purity can get using iron and sulfuric.


GOG

 

[cejohnsonsr1]

Short answer is no. You can get pretty close, but really the only reliable way to get 999-9999 is with an electrolytic cell.

 

[4metals]

The iron and sulfuric will never generate the high purity silver which is why I only recommend it for dirty silver chlorides that has gold in it from aqua regia refining.
With exceptional rinsing, the caustic sugar method will get you to 999+ purity but it takes a lot of rinsing.
If you have enough silver to feed it, an electrolytic Silver cell is the way to go.