This is a description of how I'm doing silver and palladium recovery from MLCC:s. It is based on various procedures here on the forum, put together in a mix that suits me with the limitations I have in my access to chemicals and the fact that I can't incinerate without a whole lot of work.
As I like to do some experimenting myself and not just follow a receipt that wouldn't suit my situation, I have read a lot about palladium recovery and refining during the winter. Then I put together a procedure that should work for me, given my circumstances. It might differ from common procedure and I'm in the middle of testing it out, but so far so good...
I started with a batch of 145g mixed MLCC:s and I wanted to recover silver and palladium powder for later refining. This is the steps I took. I'm not in a hurry so I can do one step, put it away for a while and then continue weeks later if so. Most steps are not time critical and even benefits from being left alone for some time to let the chemicals react to the end.
Any solutions that were filtered off were checked for values before proper disposal. Any reaction that gives off fumes were done outside. Safety precaution should always be in place when working with strong acids and bases, the pictures are taken outside of the plastic bin I normally use as a catch basin.
1. Soak the MLCC:s in hydrochloric acid to remove tin, lead and other base metals. As I didn't heat it I just left it in acid for several days before switching to new acid. Stopped it when it seemed there were no more reaction. Eventually many of the MLCC:s breaks up into separate metallic foils but it can take a week or longer.
2. Wash and decant the broken down MLCC:s with water to get the chlorides and HCl out, quite some foils in it.
3. Add NaOH to transform any AgCl that formed in the HCl treatment into Ag2O. I don't know if this is necessary or even works.
4. Wash and decant off the NaOH solution
5. Add nitric acid to dissolve the silver, silver oxide and palladium. Some chlorides will remain but they get locked up in silver chloride that forms.
6. Filter off the dissolved values. I decanted and filtered. It was apparent that there were some silver chloride in the reaction vessel as the filter clogged up with silver chloride that turned purple.
7. add NaCl solution to the filtered tea colored solution, it precipitates the silver as white silver chloride. Stop when additional NaCl doesn't make any precipitation.
8. Decant and filter off the palladium solution, I reused the filter from above as it caught all silver chloride. Multiple washes was used to get most of the palladium out from the silver chloride.
9. Treat the silver chloride with NaOH and sugar to get silver powder.
10. Add zinc shavings to the palladium solution to cement out the palladium.
11. Decant off the liquid from the cemented palladium and then wash it with HCl to remove excess zinc and eventual base metals that the zinc precipitated.
... collect, dry and weigh the result. The fluids goes to the proper stockpot and the metal powders are put into respective storage beaker with other powders awaiting final refining when I have enough to do it.
Right now I'm at step 9 and 10.
Some pictures....
Step 5, leaching palladium out of MLCC:s
Step 7, NaCl added and the silver chloride drops to the bottom. The palladium solution is coloring it yellow.
Step 8, decanting the palladium solution from the silver chloride. Pour along a glass rod for better control of the liquid.
Step 8, after two washes. There is still some palladium mixed in with the silver chloride but it is getting paler. I think I made five washes totally.
The minute amount of palladium I didn't wash out will follow the silver until it is separated in the silver cell I'm going to build some day.
Between step 8 and 10, the filtered palladium solution, free from silver.
(Continued below)
As I like to do some experimenting myself and not just follow a receipt that wouldn't suit my situation, I have read a lot about palladium recovery and refining during the winter. Then I put together a procedure that should work for me, given my circumstances. It might differ from common procedure and I'm in the middle of testing it out, but so far so good...
I started with a batch of 145g mixed MLCC:s and I wanted to recover silver and palladium powder for later refining. This is the steps I took. I'm not in a hurry so I can do one step, put it away for a while and then continue weeks later if so. Most steps are not time critical and even benefits from being left alone for some time to let the chemicals react to the end.
Any solutions that were filtered off were checked for values before proper disposal. Any reaction that gives off fumes were done outside. Safety precaution should always be in place when working with strong acids and bases, the pictures are taken outside of the plastic bin I normally use as a catch basin.
1. Soak the MLCC:s in hydrochloric acid to remove tin, lead and other base metals. As I didn't heat it I just left it in acid for several days before switching to new acid. Stopped it when it seemed there were no more reaction. Eventually many of the MLCC:s breaks up into separate metallic foils but it can take a week or longer.
2. Wash and decant the broken down MLCC:s with water to get the chlorides and HCl out, quite some foils in it.
3. Add NaOH to transform any AgCl that formed in the HCl treatment into Ag2O. I don't know if this is necessary or even works.
4. Wash and decant off the NaOH solution
5. Add nitric acid to dissolve the silver, silver oxide and palladium. Some chlorides will remain but they get locked up in silver chloride that forms.
6. Filter off the dissolved values. I decanted and filtered. It was apparent that there were some silver chloride in the reaction vessel as the filter clogged up with silver chloride that turned purple.
7. add NaCl solution to the filtered tea colored solution, it precipitates the silver as white silver chloride. Stop when additional NaCl doesn't make any precipitation.
8. Decant and filter off the palladium solution, I reused the filter from above as it caught all silver chloride. Multiple washes was used to get most of the palladium out from the silver chloride.
9. Treat the silver chloride with NaOH and sugar to get silver powder.
10. Add zinc shavings to the palladium solution to cement out the palladium.
11. Decant off the liquid from the cemented palladium and then wash it with HCl to remove excess zinc and eventual base metals that the zinc precipitated.
... collect, dry and weigh the result. The fluids goes to the proper stockpot and the metal powders are put into respective storage beaker with other powders awaiting final refining when I have enough to do it.
Right now I'm at step 9 and 10.
Some pictures....
Step 5, leaching palladium out of MLCC:s
Step 7, NaCl added and the silver chloride drops to the bottom. The palladium solution is coloring it yellow.
Step 8, decanting the palladium solution from the silver chloride. Pour along a glass rod for better control of the liquid.
Step 8, after two washes. There is still some palladium mixed in with the silver chloride but it is getting paler. I think I made five washes totally.
The minute amount of palladium I didn't wash out will follow the silver until it is separated in the silver cell I'm going to build some day.
Between step 8 and 10, the filtered palladium solution, free from silver.
(Continued below)