In this article we will demonstrate how to recover precious metals Palladium and Silver out of Monolithic ceramic capacitors, note, that recovery process is not a refining process. This is the prepping for the refining stage.
What are Monolithic Ceramic Capacitors (MLCC)?
Monolithic Ceramic Capacitors (MLCC) are a surface mount device (SMD) and can be found in almost all electronic applications now days and they have two main roles. They support the power supply for semiconductor devices and keep electrical "noise" at a low level. Usually found around chips and CPU's.
Picture Source - murata
Basically, MLCC is an array of electrodes encapsulated within a dielectric material, this material is usually Barium titanate (BaTiO3) and electrodes are made of Nickel and Palladium or Palladium/Silver alloy.
The exterior connection points, for the most part are Tin plated on Nickel.
The color of MLCC is usually light brown but it can be black, white, deep red and more, and it is important to look at the component marking next to it on the PCB, we want to remove from the board and process only those that are marked " Cxxx " .
MLCC's ware made with Pd or Pd/Ag alloy from the mid 90's all the way to this days, although the trend is try and use as less precious metal as possible do reduce costs.
WARNING!! – The process of recovering Palladium and Silver from MLCC's involves hot acids and dangerous fumes. Process most be performed outside or under a suitable fume hood. Safety gear such as gloves and goggles must be worn at all time. Please read chemicals MSDS before dealing with them.
Equipment and chemicals needed:
SAFETY GEAR – Gloves and Goggles
Waste solution container
Paper Filters and Funnel
Stannous Chloride (test solution)
Q-Tips (for testing)
Aluminum or Zinc chunks (1/8-1/4 in" size)
Hydrochloric Acid (HCL) 32%
Nitric Acid 70%
A. Base metals elimination.
B. Palladium & Silver dissolution.
C. Palladium & Silver cementation.
D. Palladium & Silver separation.
A. Base metals elimination MLCC's will be first treated with straight HCL 32% to remove Tin and Nickel. Weight the MLCC's and add acid at a 1 to 5 weight to volume ratio, meaning, for 100 grams of capacitors add 500 ml of HCL.
Place the MLCC's in a suitable Erlenmeyer flask and pour in the acid, once done place the flask on a hot plate. Bring the solution to a boil and maintain boiling for at least 1 1/2 hours.
Compensate evaporation by adding water when needed.
Tip1: Using sand underneath glass vessels distributes heat better and helps prolong glass life.
Tip2: Using a moist cloth cork help prevent some evaporation without pressure build up.
When done, double the solution volume with tap water, and allow settling and cooling down for at least one hour.
At this point most of the capacitors will disintegrate and the solution will turn to a purple suspension, which is the reaction between the Tin chloride, Nickel and other compounds.
Siphon the purple liquid to the waste solution container and test it for precious metals presence.
Add same amount of water as before and let it settle again for one hour and siphon again to the waste solution container leaving only the solids in the flask.
B. Palladium & Silver dissolution.
Using the same weight to volume ratio 1 to 5 as before, prepare a dilute Aqua Regia (AR) solution. Meaning, for every 100 grams of capacitors use 500ml of AR to get full digestion.
Dilute AR composition:
2 pars Hydrochloric Acid 32% (HCL)
1 part H2O2 3%
1 part Nitric Acid 70%
Pour in the calculated volume of HCL to the solids followed by the H2O2 and place the flask onto hot plate and bring to a boil.
Add the Nitric Acid in small increments during the boiling until you reach the respective amount that you calculated before. Please be careful, when adding Nitric Acid to a boiling solution it might foam over, therefore any Nitric Acid addition should be done slowly.
Compensate evaporation to maintain liquid level with more H2O2 or plain water, boiling time recommended is 1-3 hours.
When done, allow settling and cooling down for at least one hour.