lectroplating process.pdf

8/11/2019 LECTROPLATING PROCESS.pdf

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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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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


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

+


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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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

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