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Metal Finishing Process
Barrel method electroplating
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Metal Finishing Objectives
List key chemicals associated with metal finishing
Describe basic metal finishing processes
Describe electroplating process details
List major modes of release to the environment
Identify analytical methods useful for detecting metal finishing
contaminants in the environment
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Billion of dollars per year
Tens of thousands of businesses
Both large and small businesses, from steel rolling millsand automotive manufacturing to "mom and pop" job shops
Process Overview
Gold-plated jewelry claspsZinc-plated screws
galvanized
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Metal surface preparation
Surface protection and / or decoration
Focus on electroplating
(Barrel method )
Process Overview
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Metal Finishing Process Video
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Metal Finishing Process Video
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Solvents
Benzene
TCEetc.
Coatings
Cadmium
ChromiumCyanide
etc.
Acids and Bases
HCLCaustic
Key Chemicals
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Solvents 2005 ATSDR Rank
Benzene 6
TCE 16etc.
Coatings 2005ATSDR Rank
Cadmium 8
Chromium 18, 77Cyanide 28
etc.
Acids and Bases 2005 ATSDR Rank
HCL >100Caustic >100
Key Chemicals
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Specialty Electronic Parts - Rack Method
Cu, In, Ga, Se sequentially electroplated onto solar panels
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RM
R
P
B
W
NEUTRALIZED SALTS,
METALS, SOLVENTS,
EMULSIONS
CYANIDE,
METAL SALTS,
SOLVENTS, BASES,
ACIDS
FINISHED METAL
RECYCLED SOLVENTS
METAL SLUDGE, SCALE
UNFINISHED METAL
PRODUCTS
SOLVENT
VAPORS
Standard Process Schematic
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Process Details - Metal Surface Preparation
Physical modification
De-scale, cut, shape, smooth
Surface oil removal
Wipe, dip, vapor degrease
Final cleaning
Detergent, acid, base, anodic, cathodic, ultrasonic
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TYPICAL VAPOR DEGREASER
FREEBOARD
VAPOR
CONDENSINGCOILS AND
COOLING JACKET
BOILINGSOLVENT HEATERS
SOLVENT LEVEL
VAPOR LINE
PART
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Process Details Cleaning / Degreasing
Solvents that are most used:
Trichloroethylene
1,1,1-Trichloroethane
Methylene chloride
Tetrachloroethylene (Perchloroethylene)
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Organic coatings
Solvent based
Water based
100% solids
Process Details - Surface Protection / Decoration
Inorganic / metal coatings
Physical deposition
Chemical deposition
Electrochemical methods
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Process Details Chemical Conversion Coating
Conditions surface for painting or coating
Uses chromates, phosphates, phosphoric acid, and
hexavalent chromium
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Electrochemical process
Converts surface metal to insoluble oxide
Uses chromic, sulfuric, or boric acids
Process Details -Anodizing
Chromic Acid Anodizing vat
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Process Details - Electroplating Process
Electrochemical process
Acid, alkaline, or neutral pH
Uses metal salts, cyanides, brighteners, solid metal anodes
Cyanides keep metal ions in solution
Brighteners make surface more reflective
Fiber drums of ZnCN
concentrate in abandoned
plating shop
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ALKALINE
CLEANER RINSE ACID DIP RINSE
PLATING DRAG-OUT
TANKS RINSE
FINISHING
TREATMENT RINSE
SURFACE PREPARATION
SURFACE TREATMENT
Source: adapted from EPA 1995
Process Details - Electroplating Process
Waste water Discharge
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Source: adapted from EPA 1995
GENERATOR OR
RECTIFIER
ANODE BUS BAR+
CATHODE BUS BAR
CATHODES
VOLTMETER
AMMETER
ANODES
+
Process Details - Electroplating Process
Workpiece
To be plated
Plating
metal
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Plating vat for Chrome Plating
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Source: EPA 1990
Process Details - Common Electroplating Bath Compositions
Bath Name Composition
Brass and bronze Copper cyanide, zinc
cyanide, sodium cyanide,sodium carbonate, ammonia,Rochelle salt
Chromium Chromic acid, sulfuric acid
Cadmium cyanide Cadmium cyanide, cadmium oxide,sodium cyanide, sodium hydroxide
Cadmium fluoroborate Cadmium fluoroborate, fluoroboric
acid, boric acid, ammoniumfluoroborate, licorice
Zinc Zn metal, sodium hydroxide, sodiumcyanide (some non-CN baths too)
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Modes of Release
Air emissions
Solvent vaporsAcid mists
Water releases
Rinse water
Spent plating bath treatment
Washdown liquids
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Metal Finishing Process Video
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Modes of Release
Soil
Washdown liquidsSolvent spills
GroundwaterHexavalent chromium
(more mobile)
Chlorinated solvents(DNAPL)
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Modes of Release
Solid and hazardous wastes
TCLP metals (D006, D007, etc.)
Wastewater (F006)
Spent plating baths
(F007, F008, F009)
Quenching baths, etc.(F010, F012, F019)
Nickel Plating Bath
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Analytical Considerations
Laboratory methods
Metals: AA, ICPSolvents: GC/MS
Field analytical methods
Hazard Categorization
Metals: XRF
Solvents: Portable GC, Portable GC/MS
CN gas: Real time instruments, Draeger
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Summary
Mostly small businesses with limited environmental control
programs
Use a wide variety of chemicals:
Organic solventsMetals, metal salts, and cyanide
Corrosives
Metal finishing wastes can affect all four media: soil,
surface water and sediment, air, and groundwater