Murdock Engineering Company
A Hexavalent Chromium Regeneration Unit (HCRU) has been developed and installed on Murdock's sulfuric acid-sodium bichromate deoxidizer process tank which oxidizes trivalent chromium to the hexavalent state and removes extraneous cationic metal contaminants without interfering with production. The HCRU is applicable for eliminating waste streams commonly generated from solutions containing hexavalent chromium in etchants, plating solutions, deoxidizers, anodizing solutions, chem film, and similar processes.
The HCRU utilizes electrodialysis technology whereby an anode cell is fitted on either side with a cationic selective membrane that has an anode suspended inside. The cell is suspended into a tank of catholite solution with a cathode suspended on either side of the anode cell adjacent to the membrane window. The process solution (anolite) is pumped to the bottom of the cell and gravity flows from the top of the cell back to the process tank. As the anolite rises through the cell, a current flow between the electrode plates oxidizes trivalent chromium to the hexavalent state and attracts cationic metal contaminants through the membrane into the catholite solution; thus, the process solution is maintained at a comparable fresh bath state.
The HCRU can be operated intermittently or continuously as needed to maintain solution integrity. It is free standing and is located so as not to interfere with production. All parts are commercially available for ease of servicing.
The environmental impact from use of the HCRU is very significant in that the process solution is never depleted due to normal process contaminants.
Specific benefits are:
* Oxidizes trivalent chromium to the hexavalent state
* Extracts dissolved metal contaminants from the process solution
* Maintains consistency of process solution resulting in uniform processing
* Lowers solution viscosity which reduces rinsewater dragout contamination
* Eliminates downtime due to spent solution change out
* Eliminates fresh bath make-up chemical cost
* Eliminates the ever increasing cost of hazardous waste disposal and associated liabilities
Details of Reductions
Additional Information :
Cost savings associated with use of the HCRU will vary depending on chemical composition, type and quantity of materials processed, and the volume of process solution.
Typical Performance on Deoxidizer Solution (1988 Data)
* Solution: Sulfuric Acid 37.6-39.3 oz/gal Sodium Bichromate 4.1-5.0 oz/gal
* Temperature: 155-160oF
* Tank Volume: 1870
* Trivalent Chromium: 1.9 percent by weight maximum
Cr+6 Cr+3 A1+3 REMARKS
HCRU Start Up 4.22 1.1623 .748 Cr+6 Near low limit
HCRU Shut Down 4.963 .7519 .653 Cr+6 Near high limit
Change (percent) +17.6 -35.3 -12.7 Run Time:74 Hrs.
Cost: Approximately $3.79
Cost prior to HCRU installation: (Low production period)
Chemical Disposal: Approximately $ 9,000
Replacement Chemicals: 2,800
TOTAL $11,800 x an average of twice a year
Production Downtime: Two days
Hazardous Waste Liability: Forever
The HCRU was developed for Murdock's own need and use. After the system was tested and proven in a production environment, Murdock patented the device with the intention of producing HCRUs as a commercial product line.
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