Here are my 20 Argentine pesos on silver extraction from film fixer.
As you already know, a big variety of light sensitive emulsions contain silver salts that form the image through development and fixing procedures. When you create black and white photographic image (just one to mention), a part of the silver halides remains on the film to form the image but a bigger one migrates to the fixer solution. Depending on the type of film, its quality and date of manufacturing the silver halides may differ by types of crystals and quantity. This post will show you my experience in extracting the silver from exhausted film fixers.
According to a Kodak document, J-215 Recovering Silver from Photographic Processing Solutions (1999), there are 3 methods to desilverize your fixer:
- electrolysis (>90% efficiency);
- metal replacement (>95% efficiency);
- precipitation (>99% efficiency).
Electrolysis is technically tempting, but I decided to check the practical aspects of the metal replacement approach. Here are the steps that I followed and the results.
1. Make sure your fixer’s pH is between 5.5 and 6.5
If you check carefully the Kodak document J-215 I linked above, that’s the major condition for good metal replacement. I mainly use Sodium Thiosulfate (Na2S2O3) based fixers, but its pH differs from process to process. To normalize its pH to my needs, I use vinegar acid and tap water. And pH test strips to control.
If my fixer is alkaline, I add vinegar, if it goes more on acidic side of the pH scale — I add tap water. Normally, few tests are needed to get the fixer’s pH between 5.5 and 6.5.
Though this method for pH control is not very accurate, it gives me a close idea and is economical enough.
2. Use metal wool to replace the silver from the solution
I use normal household metal wool from the convenience store in my neighborhood. When you reach the desired pH just put the metal in the fixer. I use a Beher glass.
If everything goes well, in a matter of hours you will notice that the solution becomes grayer and grayer until it reaches dark, almost black anthracite color.
Of course you may use a normal household jar for this.
You may notice here the silver deposits on the Beher glass. I leave it like this for at least 24 hours.
3. Filter the solution to extract silver from it.
I use normal coffee filters to separate the silver from the solution.
I filter until the remaining solution is clean and clear. The silver metal remains in the filter.
4. Dry the filters up
I leave the filters with the silver in them to dry completely.
Silver dust may look different if you are using different fixers. In this example I was extracting silver from ORWO A-300 (black and white fixer) and ORWO C-71 (color reversal film fixer).
5. Burn the filters to ash
I’ve discovered that if you spend some time to burn the filters to ashes, the next step — melting the silver dust — is much faster and efficient, compared to melting the dry filters.
I burn the dry filters in a Beher glass with alcohol.
To burn completely it takes several minutes. In the ideal situation you will get black ash as this one:
5. Melt the silver dust
Now, when you have the filters with silver dust burned down to ashes, you need to separate the silver.
I do this by melting the metal with jet burner using gas and oxygen.
6. Final result
When the pot cools down you may expect to get something like that:
Now, I use a hammer to knock away borax and soda remains. Then I wash the silver from the dust.
Then measure the metal to calculate your yield.
These 14.58 grams of silver were extracted from around 4 liters of fully loaded fixers. The fixers I desilverized were ORWO A-300 and ORWO C-71.
Economically, with all expenses for filters, vinegar (cheap, yeah!), pH measuring strips, oxygen and gas, alcohol for burning the filters AND TIME SPENT I made around 5 EUROs of silver with doubtful purity. It does not make sense economically, but think about the emotional gain this silver would create if you make a simple jewelry for your loved one, who waited long hours for you being in your dark room.
Photography process has always been emotional.