United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-90/035 Aug. 1990
&EPA Project Summary
Metal Recovery/Removal Using
Non-Electrolytic Metal
Recovery
Vance G. Leak
Radiator repair shops most
commonly use hot caustic solutions
to clean radiator sections before
resoldering. These "boil-out"
solutions become contaminated with
dirt, rust, paint, and metals such as
lead, copper, zinc, and tin. Metal
levels as high as 18,000 ppm lead, 500
ppm copper, 1,000 ppm zinc, and
2,500 ppm tin have been reported.
The project summarized here
investigated onsite recovery of these
metal values as an alternative to
current disposal practices.
Cooling the used solutions allowed
dissolved metals to settle along with
other solids and allowed reuse of up
to 80% of the solution. This settled
material was effectively stripped of
metal hydroxides by using sodium
sulfide. The hydroxide precipitate
was then treated with two leachants
to remove copper and leave a lead-
rich sludge suitable for recovery by
smelting. Ammonium carbonate was
an effective copper leachant;
ammonium persulfate was ten times
less effective than ammonium
carbonate.
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
The "boil-out" tank using hot caustic
solutions is one of the prime components
of the repair line in radiator repair shops.
In the United States and Canada over
8,000 facilities use boil-out tanks for
radiator preparation. These radiators are
almost entirely composites of copper,
lead, zinc, and tin, and also alloys that
can be dissolved to a considerable extent
during the boil-out treatment. One study
found that wastewater from these
treatments commonly exceeded
discharge standards and that bulk
discharge of used solutions is commonly
practiced (Figure 1).
Wastes generated from the radiator
repair process include rinsewater from
the rinse booth and sludge that settles to
the bottom of the boil-out tank. Some
rinses are configured so that, they
discharge directly to the sewer, whereas
others rinse in a closed loop using; water
from a reservoir. Sludge generation with
either mode of operation ranges>from 30
to 300 gal per yr. In Minnesota (where
shops in this study are located), disposal
costs for this material range from,$175 to
$225 per 55-gal drum. Hazardous waste
haulers consider the material to be
primarily a strong caustic solution and
«yQ Printed on RecycledJRSper
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Evaporation
Evaporation
Radiator In
Radiator Out
4 F
Draining
and
Physical
Cleaning
4
Waste Oil
andlor
Radiator
Fluids
4 I If 41
Boilout
Tank
t
Make-up
Water
-.
Rinse
Booth
Test Tank
t T
Make-up Make-up
Water Water
-------
concentrations of earthy and sandy solids
as well as metals.
Leaching and Precipitation
Cooled caustic liquids and sludges
were treated with sodium sulfide in a 1 to
20 weight ratio, stirred thoroughly, and
then allowed to settle. Precipitation of
ionic metals was done with sodium
sulfide. Ammonium persulfate and
ammonium carbonate were used to
separate the copper and lead fractions.
The purpose was to put the copper into
solution in its ionic form. This solution
could then be decanted and the copper
precipitated. Bench-scale leaching tests
were performed in 1-L plastic jars, and a
"U.S. Stoneware" jar mill provided
agitation, mixing, and blending between
the leachate solution and the sludge
sample.
In the case of copper solutions
"stripped" from sludges, copper was the
major component of the precipitate.
Precipitation of all ionic metals in the
liquid portions of sludges B and C was
tested. The objective was to determine
the efficiency of sodium sulfide in
yielding an easy-to-settle precipitate and
a supernatant low in heavy metal
concentrations.
Results and Discussion
Testing showed that a significant
amount of copper could be leached into
solution and that sodium sulfide would
precipitate the ionic copper to leave a
nearly copper-free filtrate. Ammonium
carbonate was found to be the most
efficient leachant for this leaching
procedure. Eighty percent of the copper
was extracted without neutralization or
optimization of the leachant/copper ratio,
an important factor for a process
performed onsite by available labor.
Ammonium persulfate attained a
maximum copper concentration of only
1,280 ppm in the leachate, as opposed to
10,600 ppm using ammonium carbonate.
The precipitate produced by treatment
with sodium sulfide proved difficult to
filter, but settled readily. Metal
concentrations were reduced by as much
as 800:1. Only tin concentrations were
not significantly reduced; however, this
metal is not currently regulated as
hazardous.
Conclusions and
Recommendations
Tests showed that ammonium
carbonate efficiently leached ionic copper
into solution and that sodium sulfide
precipitated the ionic copper to leave a
nearly copper-free filtrate. The results of
this project indicate that copper can be
effectively separated from radiator boil-
out tank sludge by a single leaching with
ammonium carbonate. Although some
equipment and labor would be
necessary, shops with large volumes of
waste could justify this procedure to
provide an acceptable feedstock for
secondary lead refining. Smaller shops
using ultrasonic boil-out tanks could
precipitate all metals from their solution
using sodium sulfide to either reduce
waste volumes or provide a lead-rich
material for secondary smelting, if copper
concentrations are low enough.
Because ammonium carbonate
leaching of boil-out solutions from
standard equipment seems to involve
more steps and procedures than would
be cost-effective for a small radiator
shop, further research is needed to
develop this method as an intermediate
step preformed by a collector/processor.
This study was conducted through the
Minnesota Technical Assistance Program
(MnTAP) and the Minnesota Waste
Management Board. The full report was
submitted in fulfillment of Cooperative
Agreement CR 813437-01 under the
partial sponsorship of the U.S.
Environmental Protection Agency.
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Vance G. Leak is with the University of Minnesota-Duluth, Natural Resources
Research Institute, Duluth MN 55811.
James S. Bridges is the EPA Project Officer (see below).
The complete report, entitled "Metal Recovery/Removal Using Non-Electrolytic
Metal Recovery," (Order No. PB90-250 1501 AS; Cost: $17.00, subject to
change) will be available only from:
National Technical Information Service
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
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use S300
EPA/600/S2-90/035
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