EPi How-To: Clean Out Your Black Oxide Tank

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Hot Black Oxide tanks need to be de-sludge of iron hydroxide break down product. The Ultra Blak 400/400-L rectifier package floats more iron than other black oxide formulations. This means you do not have to de-sludge an Ultra Blak 400 tank as often. It can go 1.5 to 2 times longer before having to de-sludge the tank; saving you time and money. A rectifier floats the iron hydroxide to the top of the tank and will drag out onto parts and barrels. Ultra Blak 400 customers have stated they use less energy than with other black oxide chemistry. Why? There is less sludge at the bottom which acts as insulation.

How do you de-sludge a tank?
  1.  Turn off all energy sources. Let bath cool to room temperature (typically 2 days). The tank should be cooled between 100-140F. The cooler the better. This will create less sweat working in the tank.
  2.  Turn on exhaust for hot black oxide tank. Be sure to suit up the entire body and wear appropriate PPE including boots, goggles, and gloves (make sure to tape ends of gloves to Tyvek suit). Black oxide solution  causes burns. Be sure to read SDS!
  3.  Decant off liquid using a pump that can handle the viscosity of solution into the rinse tank or containers. You may re-use decanted solution once after de-sludge. 
  4.  Shovel out the wet sand-like iron hydroxide into 55-gallon drums.

      *Note 1: A 55-gallon drum of sludge can easily weigh over 700 pounds. Do not over-fill. Make sure the drum is built for heavy sludge.

      *Note 2: Sludge is like wet sand. There is a mucky interface layer on top of the sludge that is too thick to pump and too thin to shovel.

*Suggestion: add a few bags of oil-dry (clay absorbent) after decanting to tighten up the muck so it can be easily shoveled. You can use any absorbent as long as it is non-reactive with the alkaline sludge.


 To clean iron sludge stuck on pipes, burners, and tank walls:
  1. For best cleaning results, fill tank with water and turn on heat. Boil for 2-8 hours at 212° F depending on the sludge thickness.
  2. Turn off energy source and let solution cool. The iron hydroxide from tank walls will sink to the bottom of the tank. Decant liquid off and send to waste water for ph adjustment.
  3. Shovel out iron hydroxide into 55-gallon drum. Clean out tank.
  4. Add the decanted Ultra Blak 400 solution back into the tank using the same pump that emptied it out.
  5. Add more Ultra Blak 400 powder and water, Ultra Blak 400-L (liquid formula), or Ultra Blak Ox / liquid sodium hydroxide (50% by weight) to operating level.
  6. Energize the tank and bring back up to temperature.