Electroless Nickel Tank Clean-Out Procedure
Nitric Acid solutions are commonly used to remove nickel that has plated out onto equipment. Recommended concentration of stripping solution is 30-45% by volume of 67% nitric acid in water. More concentrated solutions are not recommended since they will shorten the life of polypropylene or CPVC components.
1. Turn off heater and remove the used filter bag.
2. Transfer the electroless nickel solution to a clean processing or holding tank using a hose with a filter attached. Use separate hoses for transferring nickel solution and nitric acid solution.
3. Thoroughly wash the plating tank and equipment with tap water. Circulate tap water through the filtration system. This step will prolong the life of the nitric acid stripping solution.
4. Discard the water to waste treat.
5. Make sure heater or heat exchanger is cool, then add nitric acid stripping solution to the plating tank. Fill to slightly above operating level.
CAUTION: Nitrogen dioxide fumes can be generated if nitric acid stripping solution comes in contact with a hot heater or heat exchanger and piping that is partially coated with nickel. Even a cool heavily plated out tank will generate fumes. Adequate ventilation should be used.
6. A hose long enough to reach beneath the surface of the nitric acid stripping solution should be attached to the pump outlet. This will prevent excessive splashing.
7. Recirculate the strip solution through pumps and filtration system until equipment is stripped. This can take 3 hours or more depending on the condition of the tank and age of strip solution.
8. Transfer the strip solution to an appropriate holding tank.
9. Thoroughly rinse the process tank and equipment with tap water. Circulate rinse water through the pumps and filtration equipment.
10. Discard the water to waste treat.
11. Fill tank again with water and add approximately ½ gallon of ammonium hydroxide per 100 gallons of tank volume.
12. Circulate through pumps and filtration equipment for at least 15 minutes.
13. Discard the neutralizing solution to waste treat.
14. Fill with tap water. Circulate through pumps and filtration equipment. Spray down ventilation hood.
15. Discard the water to waste treat.
16. Rinse again using deionized water.
17. Verify nitric acid residues are not present by testing water with nitrate test strips.
18. Discard the deionized water to waste treat.
19. Transfer plating solution back into tank using hose with filter attached, or prepare new bath as necessary. Put on a new filter bag.
NOTE: It is important to make sure all nitric acid residues are removed. Nitrate contamination is detrimental to an electroless nickel bath and can negatively affect plating rate, deposit appearance and adhesion.Return to the List of Articles.