SULFURIC/BORIC ACID ANODIZING

Revision Date: 4/03
Process Code: Navy/Marines: IND-004-99; Air Force: MT03, MT05; Army: ELE, MTF
Usage List: Navy: Medium; Marines: Low; Army: Low; Air Force: Low
Alternative For: Chromic Acid Anodizing (CAA)
Compliance Impact: Not applicable
Applicable EPCRA Targeted Constituents and CAS Numbers: Chromic acid (CAS: 7738-94-5), Chromium (CAS: 7440-47-3)
Overview: The Sulfuric/Boric Acid Anodizing (SBAA) process is a direct replacement for the Chromic Acid Anodizing (CAA) process used on aluminum production pieces. The SBAA process consists of a sulfuric/boric acid anodizing bath and a chromate sealer bath. SBAA is a commercially available and tested process that provides a protective coating meeting all military and industrial specifications applicable to the CAA process.

The CAA process is currently used by all Naval Aviation Depots (NADEPs), Naval Shipyards, and other facilities to apply a protective coating to aluminum parts used by many naval aircraft and ships. CAA generates chrome containing waste streams from the rinsing of parts and ventilation system washdowns. The resulting CCA rinse water requires the removal of metals at the Industrial Wastewater Treatment Plant (IWTP) prior to release to a Public Owned Treatment Works (POTW). The SBAA process doses not use chrome except for a small amount in a separate sealer tank (70 ppm compared to 74.9x103 ppm in CAA) used to dip parts after the SBAA process; therefore, no chrome containing waste streams are generated from the rinsing of the parts and the ventilation system. The rinse waters still contain metals and acids that must be treated at the IWTP prior to release to a POTW.

The SBAA process was tested by the Naval Air Systems Command (NAVAIRSYSCOM) at NADEP North Island and has been approved by NAVAIRSYSCOM as an alternative to the CAA process. The SBAA process has since been implemented at NADEP North Island and NADEP Cherry Point. Mil-C-8625C (the Mil-Spec that governs all anodized coatings) is being revised to include the SBAA process as an option for aluminum anodizing.


Compliance Benefit: The SBAA process does not use chrome except for a small amount in a separate sealer tank (70 ppm compared to 74.9x103 ppm in CAA) used to dip parts after the SBAA process; therefore, no chrome containing waste streams are generated from the rinsing of the parts and the ventilation system. The rinse waters still contain metals and acids that must be treated at the IWTP prior to release to a POTW. The elimination of hard and decorative chromium electroplating from a facility may decrease the need for meeting NESHAP requirements under 40 CFR 63.340 - 63.347 and for an air permit under, 40 CFR 70 and 40 CFR 71. It should be noted that a new air emission may result from the use of this new technology.

The compliance benefits listed here are only meant to be used as general guidelines and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g., the amount of workload involved.


Materials Compatibility: No materials compatibility issues were identified.


Safety and Health: Sulfuric acid can be extremely corrosive to skin tissue. Contact with the body can result in severe burns. Boric acid can be a dermal and mucous membrane irritant. It is also a suspected teratogen and mutagen. Chromic acid can irritate the respiratory tract and mucous membranes, and is a known mutagen. Proper personal protective equipment should be used.

Consult your local Industrial Health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.


Benefits:
  • Replaces a major source of chromic acid in anodizing operations.
  • Significantly reduces the amount of chromic acid to be treated at the IWTP.
  • Reduces toxic air emissions from the chromic acid process.


Disadvantages:
  • Generates a hazardous waste stream requiring pre-treatment.


Economic Analysis: Cost savings will depend largely on the volume of chromic acid contaminated rinse water generated, rinse water treatment costs, and the hazardous waste disposal costs for the heavy-metals-contaminated sludge. The cost to implement the SBAA process is minimal at a facility that currently utilizes CAA. Additional equipment requirements include:
  • Sealer tank.
  • Immersion heater or steam line for the sealer tank.
  • Cooling coils for the SBAA to keep bath temperature below 80 ° F.

The cost elements for installing an SBAA process at a site is provided below.

Assumptions:

  • Estimated equipment cost: $6370
  • CAA, SBAA and sealer bath capacities: 2,800 gal each.
  • Sulfuric/Boric Acid bath : 30-50 g of sulfuric acid per liter of bath fluid, 5-11 g of boric acid /l of bath fluid, 76-84 ° F.
  • Sealer bath: 26 g of chromic acid per 100 gal of bath fluid, 190-200 ° F.
  • No differential in labor, permitting, training, etc. Personnel operating the CAA process can be trained to operate the SBAA equipment.
  • Operating costs are equivalent for both processes with the exception of bath make-up costs.
  • Treatment costs from IWTP are $0.70/gal.

Annual Operating Cost Comparison for SBAA and CAA Processes

 

SBAA Process

CAA Process

Operational Costs:    
Chemical Make Up for SBAA and Sealer Tanks: $6800 $0
Chemical Additions for CAA Process: $0 $2200
Treatment Costs: $21,000 $70,000
Total Operational Costs: $27,800 $72,200
Total Recovered Income: $0 $0
Net Annual Cost/Benefit: -$27,800 -$72,200

Economic Analysis Summary

  • Annual Savings for Implementing an SBAA Process: $44,400
  • Capital Cost for Implementing an SBAA Process: $6370
  • Payback Period for Investment in Equipment/Process: < 1 year

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NSN/MSDS: None identified.


Approving Authority: Appropriate authority for making process changes should always be sought and obtained prior to procuring or implementing any of the technologies identified herein.


Points of Contact: For more information

Vendors: None listed


Sources: None listed