ELECTRODIALYSIS TECHNOLOGY FOR ANODIZING BATH SOLUTIONS

Revision Date: 8/01
Process Code: Navy/Marines: ID-04-99; Air Force: MMT03; Army: ELE, MTF
Usage: Navy: Low; Marines: Low; Army: Low; Air Force: Low
Alternative for: Hazardous waste generation and the associated disposal costs
Applicable EPCRA Targeted Constituents:
Sulfuric Acid (CAS: 7664-93-9), Aluminum (Fume or Dust) (CAS: 7429-90-5)
Overview: Electrodialysis is a process that will efficiently maintain a low metal ion concentration in the anodizing bath solution by transporting metal ions (for example aluminum) from the bath solution through a selective membrane into a capture media using an electrical current to induce flow.

When anodizing aluminum, for example, the bath solution is required to be changed out and disposed of when the aluminum concentration reaches 80-100 grams/liter. The spent solution contains high levels of sulfuric acid and aluminum, requiring neutralization and metals removal for a typically large volume prior to disposal.

Electrodialysis does not affect the anodizing process. It is simply a process that can indefinitely extend the useful life of the bath solution by maintaining a low concentration of metal ions. The capture media, catholyte, removes the metal ions and forms a concentrated sludge. The sludge must be removed from the unit and the catholyte changed out on a regular basis to ensure effective metals removal from the anodizing bath solution. The recovered sludge is a hazardous waste containing high concentrations of metal that can be reclaimed by an outside company.

 

Compliance Benefit:

The addition of an electrodialysis unit to an anodizing bath system can extend the useful life of the bath solutions and thereby significantly reduce the volume of hazardous waste generated. The reduction of hazardous waste helps facilities meet the requirements of waste reduction under RCRA, 40 CFR 262, Appendix, and may also help facilities reduce their generator status and lessen the amount of regulations (i.e., recordkeeping, reporting, inspections, transportation, accumulation time, emergency prevention and preparedness, emergency response) they are required to comply with under RCRA, 40 CFR 262. In addition, because the useful life of the bath solution is extended (i.e., less sulfuric acid is required at a facility) there is less of a chance that the facility would meet any of the reporting thresholds for hazardous substances/chemicals under SARA Title III (40 CFR 300, 355, 370, and 372; and EO 12856). Other compliance issues include Energy Efficiency and Water Conservation at Federal Facilities - EO 12902, and that additional electricity will be consumed with this technology.

The compliance benefits listed here are only meant to be used as a general guideline 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:


N/A

 

Safety and Health:

Spent sulfuric acid waste can be extremely corrosive to skin tissue. Contact with the body can result in severe burns. 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 any of these technologies.

 

Benefits:
  • Reduction of hazardous waste volume and the associated disposal costs. 
  • Metals reclamation and reduction of liability if sludge is recovered by an outside company. 
  • Indefinite extension of anodizing bath solutions useful life. 
  • Lower annual cost for chemical makeup & replacement. 
  • Improved production quality and consistent reproducibility of manufactured parts due to control of the metal ion concentration in the anodizing bath solution.

 

Disadvantages:
  • Moderately high capital cost. 
  • Increase in the number of possible exposures with regard to the handling of hazardous waste. 
  • Must be able to locate company that will recover and reclaim metals from the sludge.

 

Economic Analysis: The addition of an electrodialysis unit to an anodizing bath system can significantly reduce the volume of hazardous waste generated and the associated disposal costs. Variables affecting the capital cost, operation & maintenance costs, and the hazardous waste disposal costs with regard to the addition of an electrodialysis unit include:
  • The frequency of pre-change bath solution replacement. 
  • Cost to heat the bath solution after replacement. 
  • The metal ion loading rate for the bath solution. 
  • The metal ion removal rate of the electrodialysis unit. 
  • Ability to locate an outside company to recover the generated sludge.

The cost elements for installing an electrodialysis unit to an anodizing bath at a site is provided below:

Assumptions:

  • Estimated equipment cost: $25,000 
  • Estimated hours required for installation: 100 hours 
  • Labor rate: $40/hr. 
  • Installation cost: $4,000 
  • Volume of anodizing bath solution, 5000 gal. 
  • Volume of electrodialysis unit, 55 gal. 
  • Electricity: $0.07/kw-hr. 
  • Annual energy costs for the electrodialysis unit: ($0.07/KW hr)[(400 amp)(12 volt)K/1000](8hr/day)(250 day/yr) 
  • Anodized bath solution replaced once a year. 
  • Anodized bath solution requires 10% vol. sulfuric acid, $200, and 10 oz./gal. chromic acid, $1500, per changeout. 
  • Anodized bath make-up solution volumes and costs are negligible. 
  • Electrodialysis solution, catholyte, is $50 per 55 gal. make-up. 
  • Catholyte replacement during the first six months of operation shall be weekly, thereafter, on a bi-weekly basis. 
  • Hazardous waste volume generated for an Anodizing Bath System using the current technology = 5000 gal. 
  • Hazardous waste volume generated for an Anodizing Bath System using an Electrodialysis Unit = 2145 gal for the first year, 1430 gal/year thereafter. 
  • Hazardous waste disposal costs: $1/gal for anodizing bath solution; $0.28/gal for catholyte and sludge.

Annual Operating Cost Comparison for an Anodizing Bath System using an Electrodialysis Unit vs. using the Current Technology

  Electrodialysis Unit1 Current Technology2
Operational Costs:    
Anodizing Bath Solution Replacement/Make-Up: $0 $1700
Catholyte Solution Make-Up: $1300 $0
Hazardous Waste Disposal Cost: $400 $5000
Total Operational Costs: $2372 $6700
Total Recovered Income: $0 $0
Net Annual Cost/Benefit: -$2372 -$6700

1 57% Hazardous Waste Volume Reduction, 88% Reduction of Hazardous Waste Disposal Costs
2 71% Hazardous Waste Volume Reduction, 92% Reduction of Hazardous Waste Disposal Costs

Economic Analysis Summary

Annual Savings for Systems using Electrodialysis Units: $4,328 
Capital Cost for Systems using Electrodialysis Units: $25,000 
Payback Period for Investment in Equipment/Process: 6.9 years

Click here to View an Active Spreadsheet for this Economic Analysis and Enter Your Own Values. To return from the Active Spreadsheet, click the reverse arrow in the Tool Bar.

 

Approving Authority:

Approval is controlled locally and should be implemented only after engineering approval has been granted. Major claimant approval is not required.

 

NSN/MSDS:
Product NSN Unit Size Cost MSDS*
Electrolysis Membrane 6640-00-884-3321 ea. $30.50  
Electrolysis Membrane 6640-01-023-7852 ea. $70.00  

*There are multiple MSDSs for most NSNs.
The MSDS (if shown above) is only meant to serve as an example.

 

Points of Contact: Navy:
Mr. Michael Viggiano
Naval Facilities Engineering Service Center
1100 23rd Avenue
Code 423
Port Hueneme, CA 93043-4370
Phone: (805) 982-4895 
DSN: 551-4895 
Email: viggianoml@nfesc.navy.mil

 

Vendors: IONSEP Corporation, Inc.
P.O. Box 258
Rockland, DE 19732
Phone: (302) 798-7402 

Technic, Inc.
55 Maryland Ave
Pawtucket, RI 02860
Phone: (401) 728-7081 

This is not meant to be a complete list, as there may be other suppliers of this type of equipment.

 

Sources: None listed.

 

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