Waste Treatment of Black Oxide Baths

Using Heatbath’s Nitri-Neut and Alkineut

Spent solutions and sludges from black oxide are highly caustic and contain nitrite. These are both hazardous but can be treated safely and rendered harmless if the proper safety precautions are adhered to. Spent solutions must be diluted with a large volume of water. Sludge should be dissolved in enough water to make a thin liquid mixture.

Heatbath Nitri-Neut and Heatbath Alkineut can be used to simplify the procedure, but caution must be used. Nitrites liberate a toxic gas when neutralized; Nitri-Neut will decrease the amount of toxic gas produced by 90%. (Most of the evolved gas will be harmless nitrogen and carbon dioxide). But the procedure still must be carried out in an extremely well ventilated area. Workers must not breathe fumes.


Basis: 100 Gallons Solution to be Disposed

  1. Dilute the solution to be disposed with four times its volume of water. Therefore, 100 gallons is diluted to 500 gallons. A steel tank may be used. It should have a capacity of 800 gallons minimum.
  2. In a separate container, make a slurry using 80 lbs. of Nitri-Neut and 40 gallons of water.
  3. Add this slurry to the diluted black oxide bath and mix well to dissolve.
  4. Add Heatbath Alkineut until pH is 7.5 – 8.5. For 100 gallons of Black Oxide bath, approximately 120 gallons of Alkineut will be required. But this should be added in increments, mixing well and taking frequent pH measurements. pH (not volume) is the determining parameter.Care should be taken not to get localized pH’s below 6 or to go below 6.5 finally. Either of these conditions will cause attack on a steel neutralizing container. Some frothing and bubbling may occur.Alkineut must be added slowly and cautiously. Some spattering may occur and heat will be generated. Workers should wear protective clothing, especially face and eye protection and must not breathe fumes. A mechanical mixer is recommended to get good dispersion of reacting the chemicals.
  5. When pH has stabilized at 7.5 – 8.5, reaction is complete and mixer should be stopped. Allow sludge to settle.
  6. The supernatant liquid contains sodium sulfate and sodium nitrate. It should be acceptable for disposal in most treatment plants. The sludge contains iron oxide and sodium sulfate. Consult with authorities for local, state and federal waste disposal requirements.
  7. The above procedure does not address any hazardous metal contamination accumulated through the processing of steel alloys through the blackening tank over time. A sample should be analyzed by a certified laboratory.

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