CASE STUDY # 174
1. Headline: An Experimental Project Using an Electrowinning
Cell and Ion Exchange Unit Minimizes Water Usage and
Hazardous Waste
2. Background: See below.
3. Cleaner Production Principle: New technology
4. Description of Cleaner production Application: This
experimental technology uses an electrowinning cell and
ion exchange system to recover copper and reduce water
usage.
Case Study Summary
Process and Waste Information: The line on which the
experiment was undertaken is composed of a bath for bright
acid copper plating, followed by a "dead" rinse and two
rinses in counterflow. Nothing about pretreatment is
mentioned in the source document. The dead rinse consists
of a tank of 1500 gallons used to replenish the volume
lost from the plating bath. The first running rinse, also
1500 gallons, overflowed to the waste treatment facility.
The second running of 3000 gallons, was fed with 4 gallons
of city water per minute.
In the first stage of the project, an electrowinning
system was introduced in a circulating loop with the dead
rinse resulting in reduction in the copper content and in
drag-out of copper into the running tanks. The
electrowinning cell design consisted of a tank using up to
50 square feet of cathode material and 48 square feet of
insoluble anode. A 300 Amp, six volt rectifier powered
the cell. Current densities could be varied throughout
the study. An air sparger was used to agitate the bath
liquid, although no heating was used. After successful
reduction of copper in the dead rinse, and thus in the
running rinses, an ion exchange unit was installed to
remove copper from the drag-out tank. The deionized water
was returned to the last rinse bath.
The ion exchange system consisted of a pump which supplied
four gallons of water per minute to the system. Two ion
exchange tanks containing 1.4 cubic feet of a strong acid
resin were used. The dual system allowed one tank to be
in service while the second tank automatically regenerated
or was in standby position. The technology resulted in
reduction of the copper concentration from 15 to 6 g/l in
the static rinse tank. In seven months of operation, 360
pounds of salvageable copper have been recovered by the
electrowinner. As a consequence, the concentration in the
first counterflow rinse dropped from over 200 to below 50
mg/l.
The water coming from the ion exchanger has copper levels
well below 0.01 mg/l and is reintroduced into the second
counterflow tank. It was necessary to change from city
water to softened water at the inlet. Regeneration is
necessary every second day and takes about 20 minutes.
The run-off water from the first counterflow rinse
contains 6 mg/l of copper. It is transformed into sludge
in the waste treatment system.
Stage of Development: Implemented, but tests are
continuing.
Material/Energy Balances and Substitutions:
Material Category Quantity Before
Quantity After
Waste Generation:
Sludge, 60% dry, 18.5
2.5 lbs/day
Feedstock Use: N/A
N/A
Water Use (gpm): 4
2
Energy Use: N/A current
density
See "Assumptions" for a discussion of sludge production
calculations.
5. Economics: Information not provided.
6. Advantages: Use of this technology was prompted by
tightening control on discharge limits and waste
production in the U.S. Sludge production and water usage
are reduced and salvageable copper are recovered.
7. Constraints: Copper at low concentrations in the
electrowinner burned while plating. Lowering current
densities also lowers plating to a rate at which the
cell cannot keep pace with the drag-out rate. The running
rinses had to be fed with demi-water.
8. Contacts and Citation
Citation: Reduce Water Consumption and Hazardous
Waste. Jerome Kovach, Kinetico Engineering Systems,
Inc., Newbury, Ohio, United States.
Industry/Program Contact and Address:
Jerome Kovach,
Kinetico Engineering Systems, Inc.,
Newbury, Ohio, United States.
9. Keywords: United States, USA, metal, electroplating, new
technology, plating, electrowinning, ion exchange, copper,
rinsing, sludge.
10. Reviewer's Comments:
Assumptions: No absolute figures on sludge production are
given. It is assumed all wastes of the company are sent
to the same facility.
As copper concentrations in the runoff water decreased by
over 75% (from over 200 to below 50 mg/l) and the runoff
was reduced from 4 to 2 gpm, it is assumed that the amount
of copper entering the waste treatment facility from the
experimental line decreased 87.5%. In the source
document, a 75% reduction was claimed. The sludge
production decreased by 16 lbs/day. From these figures,
the before and after sludge production were computed.
This case study was originally compiled by the UNEP IE
Working Group on Metal Finishing. It underwent a UNEP IE
funded technical review in 1994 for quality and
completeness. It was edited for the ICPIC diskette in
July 1995.
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