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OAR Box 1814 

Prepped by Ollie Stewart 

Document Number: 

43) ll-B-21 

Docket Number: 

A-88-02 

Printed 11/7/2008 7:22:08 AM Sheet 43 of 63 
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A-88-02 

"j£- & - Z.\ MIDWEST RESEARCH INSTITU 

4505 Creedmoor He 

Raleigh. N C 

Telephone (919) 78 

Date: March 16, 1987 

(Finalized April 2, 1987) 

Subject: Site Visit—Reliable Plating Company 

Chromium Electroplating NESHAP 

EPA Contract 68-02-3817; ESED Project 85/02a 

MRI Project 7717-K 

From: Robin Barkerj^VTo: Al Vervaert 

ESED/ISB/SSS (MD-13) 

U. S. Environmental Protection Agency 

Research Triangle Park, N.C. 27711 

I. Purpose 

The purpose of this site visit was to gather background Information 

about the chromic acid anodizing operation at this plant and to assess 

visually the amount of misting from the chromic ad d anodizing tank. 

II. Place and Date 

Reliable Plating and Polishing Company, Inc. 

Post Office Box 4217 

80 Bishop Avenue 

Bridgeport, Connecticut 06607 

(203) 366-5261 

December 18, 1986 

III. Attendees 

Reliable Plating Company 

Bob Morris, Plant Maintenance 

Auggle Dattolo, Process Engineer 

U. S. Environmental Protection Agency (EPA) 

Al Vervaert, ISB 

Midwest Research Institute 

Robin Barker 

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IV. Discussion 

The plant visit began with a discussion about the chromic ad d 

anodizing operation. The discussion was followed by a tour of the 

facility. 

A. General 

Reliable Plating Company 1s a job shop engaged primarily 1n chromic 

acid anodizing of aircraft and miscellaneous parts. Decorative chromium 

plating and other plating operations are also performed at this plant. 

Reliable Plating Company 1s a certified United States military 

contractor. The plating shop 1s operated 8 hours per day, 5 days per 

week. 

B. Process Description 

The one chromic ad d anodizing tank at this facility 1s configured 

as shown 1n Figure 1. The chromic ad d anodizing process consists of the 

following steps: alkaline cleaning, cold water rinse, nitric ad d dip, 

cold water rinse, anodizing, and nickel acetate sealing and/or hot water 

sealing. The aluminum frequently 1s dyed after sealing. The anodizing 

H n e 1s equipped with an automatic hoist to transfer parts into and out of 

the process tanks. 

The anodizing solution contains chromic acid 1n a concentration of 

approximately 60 to 75 grams per liter (8 to 10 ounces per gallon) of 

water. The operating temperature ranges from 35° to 38°C (95° to 100°F). 

The anodizing tank 1s 3.5 meters (m) (11.5 feet [ft]) long, 0.61 m 

(2.0 ft) wide, and 0.91 m (3.0 ft) deep and has a capacity of approximately 1,893 liters (500 gallons) of anodizing solution. The tank 1s 

equipped with a 4,000-ampere rectifier. The voltage 1s applied step-wise 

until a level of 40 volts is reached. This level 1s applied for the 

remainder of the anodizing time. The current typically ranges from 200 to 

300 amperes, and the anodizing time 1s approximately 1 hour. 

C. Emission Control 

The anodizing tank 1s equipped with a double-sided draft hood to 

capture the chromic ad d mist. The ventilation hood 1s ducted to a wet 

scrubber manufactured by Neihaus Brothers, Inc. The scrubber 1s located 

adjacent to the anodizing tank. 

The Niehaus scrubber 1s a fume exhaust and separating unit developed 

primarily for the electroplating and chemical industries. The scrubbing 

action 1s achieved by a combination of water absorption and centrifugal 

separation. Figure 2 is a schematic of the Niehaus scrubber. Its 

operation is described by Niehaus as follows: 
-=» => 

DRAIN 

LEGEND AIRFLOW 

VENTILATION 

HOODS 

AIR STREAM OUTLET 

AIR STREAM 

INLET 

SCRUBBER 

Figure 1. Schematic of chromic acid anodizing tank. 

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WATER INLET 

INTAKE STACK 

SPRAY CHAMBER 

SEPARATING 

CHAMBER 

BLOWER 

DRAIN 

OUTLET 

Figure 2. Centrifugal-flow scrubber manufactured by Niehaus Brothers, Inc. 

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"... contaminated air is drawn in through the Intake duct Into 

whfch sprays of water are introduced. These sprays, upon Impinging 

on the high speed blower wheel are reduced to fog which Intimately 

mix with the contaminated air, dissolving the contaminants. The 

blower wheel being axlally located within the separating chamber also 

acts as the Impeller of a centrifuge, thereby separating the water 

entrained contaminants which are drained at the bottom of the unit. 

The cleaned air spirals out the discharge located at the top." 

The design gas flow rate of the scrubber 1s 85 cubic meters per minute 

(3,000 cubic feet per minute). The design water flow rate ranges from 7.6 

to 11.4 liters per minute (2 to 3 gallons per minute). The scrubber water 

1s not recycled and the scrubber 1s continuously sprayed with fresh 

water. 

The scrubber wastewater 1s combined with other waste streams and 1s 

drained to a wastewater treatment system. Sulfur dioxide 1s used to 

pretreat the wastewater to reduce the hexavalent chromium to trivalent 

chromium. After pretreatment, the wastewater 1s pumped to a clarifier 

where a polymer 1s added causing the heavy metals to precipitate as sludge 

and settle to the bottom of the tank. Clean water 1s then drawn off the 

top. The sludge 1s pumped to a press where 1t 1s compressed Into a cake. 

V. Observations 

A small amount of gassing occurred at the sides of the tank 

(cathode) and around the workpiece (anode) while the tank was 1n 

operation. However, the gas did not appear to be breaking through the 

plating solution surface. There was no chromic ad d visible on a piece of 

clean white paper that was held over the bath for a short period of time. 

VI. Conclusions 

The Reliable Plating Company plant 1n Bridgeport, Connecticut, 1s 

representative of a small job shop that performs chromic add anodizing of 

aircraft and miscellaneous parts. To determine the desirability of 

performing emissions testing, it 1s recommended that a chromium mass 

balance be performed on the chromic acid anodizing operation by collecting 

samples of the once-through scrubber water to determine 1f the quantity of 

chromic ad d taken up 1n the scrubber water Indicates whether emissions 

appear to be significant. If the results of the mass balance show that 

chromic ad d emissions from anodizing tanks are negligible, no further 

testing would be performed. However, 1f the results of the mass balance 

indicate that chromic ad d emissions may be significant, emissions testing 

on the anodizing bath will be recommended. 

VII. Reference 

1. Niehaus Brothers, Inc., Neihaus Fume Separators, Indianapolis, 

Indiana. 1986.