United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-90/032 Sept. 1990
\yEPA Project Summary
Recovery of Metals Using
Aluminum Displacement
Steven C. Meyers
Metal finishing operations generate
waste streams containing heavy metals
such as copper, lead, tin, and nickel.
Standard pretreatment practice has in-
volved removing these metals from the
effluent before discharge using a variety
of techniques, primarily precipitation as
a sludge that must be disposed of as a
hazardous waste. This project investi-
gated aluminum displacement as a pre-
treatment process for selected waste
streams. The process has the potential
of producing not only effluent suitable
for discharge but also nonhazardous
pure metal suitable for recovery.
Testing of copper sulfate solutions at
various flow rates showed copper re-
moval in a range of 85% to 97%. The pH
was determined to have an insignificant
effect on copper removal when held in a
range of pH 2 to 3.5. Recirculation test-
ing of copper sulfate solutions reduced
copper concentrations from 200 to 1.5
ppm. Recirculation testing of tin/lead
fluoborate solutions reduced lead con-
centrations from 104 to 0.65 ppm. Eight
other waste streams were evaluated to
determine metal removal efficiency.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Waste streams containing copper and
lead are common in the printed circuit in-
dustry. Printed circuit fabrication processes
such as cleaning, microetching, etching,
electroless plating, and electroplating all
generate rinsewater containing low con-
centrations of these and other regulated
heavy metals. Standard pretreatment prac-
tice often generates a sludge that must be
handled and disposed of as a hazardous
waste.
Removal of copper from etching solu-
tions using displacement with aluminum
was reported in the mid-1960's. Because of
aluminum's position in the electromotive
series, metal ions with lower oxidation po-
tentials such as copper and lead will be
reduced to their metallic state if brought into
contact with aluminum metal under certain
conditions. The aluminum is consumed
stoichiometrically based on the input of more
noble metal ions. The process holds the
promise of yielding a nonhazardous prod-
uct suitable for metal recovery.
The project objective was to study the
variables that affect the recovery of copper
and lead metal from printed circuit and
metal finishing waste streams using dis-
placement with aluminum metal. The vari-
ables include aluminum configuration, waste
stream composition, flow rates, contact
times, solution pH, and aluminum surface
activity.
Procedure
Reactor Design
Test equipment for this project included
a 15-gal aluminum exchange reactor, input
holding tank, metering pump, and output
holding tank (Figure 1).
Air agitation produces mechanical mo-
tion in the reactor to assist in removing
metal particles from the surface of the alu-
minum as displacement occurs. Metal par-
ticles, which are displaced from solution,
settle to the bottom of the tank and are
collected by pumping the solution through a
cartridge filter. Strips of aluminum are sup-
ported above this screen. Solution flow in
the reactor is from a bottom distribution
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PH Adjusted
Solution Inlet
Agitation Air
Aluminum Exchange
Media
I k
* I
Figure I. Aluminum exchange reactor for metal recovery.
IT
F//fer Sag
for Copper
Particles
Treated Solution Outlet
to Final PH Adjust
sparger up through the aluminum and out
through a fitting near the top of the reactor.
Solutions were evaluated both on "flow
through" and on a recirculation basis, al-
though not every solution was evaluated
under recirculation. Recirculation has po-
tential for use with low-volume waste streams
where a holding tank could be used to
accumulate waste for treatment.
Flow-through operation is more appropriate
for the majority of metal finishing shops
because of a lack of holding-tank capacity.
Solutions
Common metal finishing waste streams
were fabricated for testing aluminum dis-
placement. These solutions and their func-
tion in printed circuit fabrication are listed in
Table 1.
All analyses for metal concentrations
employed atomic absorption spectropho-
tometry; accepted procedures for accurate
analysis at the application concentrations
were, of course, used. Solutions fabricated
for testing were at metal concentrations of
approximately 200 ppm and pH of 2.5.
Results and Discussion
Flow-through Testing
The flow rate for all flow-through testing
was 0.15 gpm using 25 gal of solution.
Samples were taken at half-hour intervals
Table 1. Aluminum Displace-
ment Solutions and
Their Function
Metal
Solution
Function
Copper
sulfate
Copper
ammonia
chloride
Copper/
EOT A
complex
Hydrogen
peroxide/
sulfuric
acid
Copper
nitrate
Tin/lead
fluoborate
Solder
brightener
Nickel
sulfate
Most common
electroplating solution
Alkaline etchant used
to remove copper
from bare or
copper-plated printed
circuit boards
Very common
electro/ess plating
solution
Etchant used to clean
copper surfaces
Solution resulting
from use of nitric acid
to strip racks used to
hold work during
processing
Common
electroplating solution
Solution used to
remove small
amounts of tin and
lead from printed
circuit boards as part
of post-processing
cleaning
Electroplating
solution
after reactor outflow began. Contact time
was 75 min. Results of this testing are given
in Table 2.
The flow-through system did not effi-
ciently remove copper complexed with
EDTA. Recirculation might improve these
results. Copper nitrate and nickel sulfate
showed no displacement activity under
these conditions. The nitric acid component
of the copper nitrate solution may interfere
with the reaction, reversing it as quickly as
it proceeds. Due to its position in the electro-
motive series, nickel may not be effectively
removed using a system of this type.
Recirculation Testing
Tin-lead fluoborate solution was reduced
from 104 to 0.65 ppm with a contact time of
3-1/2 hr. Copper sulfate solution was re-
duced from a concentration of 200 to 1.5
ppm with a contact time of 24 hr. All
recirculation testing was done at 0.15 gpm
using 25 gal of solution.
Aluminum Exchange Material
The best configuration forthe aluminum
is shredded foil produced with a heavy-duty
shredder using 5/8 x 12 x 0.012-in. alumi-
num entry foil, twisted to eliminate parallel
surfaces. The aluminum was a 3003 alloy
containing 1.5% maganese and .05% to
0.2% copper.
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Table 2.
Test Results for Metal Removal
Waste Streams
Copper sulfate
Copper ammonia chloride
Copper EDTA
Peroxide sulfuric etchant
Copper nitrate
Lead fluoborate
Tin chloride
Nickel sulfate
Metal Removed
Copper
Copper
Copper
Copper
Copper
Lead
Tin
Nickel
Percent Removed
96
90
51
89
0
90
85
0
Other Results
• A regeneration process was devel-
oped to cleanse aluminum exchange
material. This involved lowering the
pH of the input solution to 0.5 for
approximately 1 hrto create an accel-
erated mild etch.
The chloride ion present during the
displacement process was of no im-
portance.
Thorough air agitation is critical to
displacement efficiency but will vary
by input flow and waste stream char-
acteristics.
Conclusions and
Recommendations
Results of this project indicate that the
aluminum displacement process holds
promise as a pretreatment and recovery
technology for certain applications. Cop-
per, lead, and tin were removed at effi-
ciencies of 85+% with a single pass through
the aluminum exchange reactors.
Recirculation shows even higher removal
efficiencies.
The low equipment cost and simplicity
of operation makethis an attractive technol-
ogy for many smaller metal finishing opera-
tions. Aluminum exchange material is readily
available. Metal is recovered in a form ame-
nable to management as a resource rather
than as a waste.
Efficient use of this technology requires
segregation of metal-bearing, non-
metal-bearing, and complexed metal
streams. Care should also be taken to re-
duce rinsewater flow to the minimum with
the use of dragout rinses and countercur-
rent flow rinses. The resulting low volume
waste streams should be suitable up to a
metal concentration of 200 ppm.
Further research is needed on the appli-
cation of recirculation to complexed waste
streams and to those with lower metal re-
moval efficiencies. The pH and concentra-
tion optimization of these streams may also
yield further expansion of the application of
this technology.
This study was conducted through the
Minnesota Technical Assistance Program
(MnTAP) and the Minnesota Waste Man-
agement Board. The full report was submit-
ted in partial fulfillment of Cooperative
Agreement CR 813437-01 underthe spon-
sorship of the U.S. Environmental Protec-
tion Agency.
S. GOVERNMENT PRINTING OFFICE: 1990/748-012/20101
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Steven C. Meyers is with Circuit Chemistry Corporation, Maple Plain, MN 55359.
James. S. Bridges is the EPA Project Officer (see below).
The complete report, entitled "Recovery of Metals Using Aluminum Displacement,"
(Order No. PB 89-222 590/AS; Cost: $1500, subject to change) will be available only
from:
National Technical Information Seivice
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental
Research Information
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-90/032
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