On February 21, 2017
the Copper Development Association (CDA) held a summit where ASA along with
other stakeholders gathered to discuss the recycling of lead-free brass
products. As introduced on January 2014, EPA requires the maximum lead content for
the wetted surfaces of plumbing products used in potable water to be 0.25
percent. Prior to the January 2014 amendment, the maximum lead content was 8
percent. To comply with the amendment,
manufacturers, rod and bar stock producers replaced the lead in the material with
other elements like bismuth, silicon, tellurium, etc. Due to the many types of
lead-free alloy products in the market, it is becoming a challenge to identify
what type of lead-free alloy products are being recycled. If this issue is not
addressed, it may create the process of material difficult and eventually
create materials containing larger amount of impurities.
According to the CDA,
it is important to keep leaded brass
scrap separate from scrap used to produce lead-free brasses which should not contain
lead by definition. Even within lead-free scrap, strict segregation is needed
to keep scrap containing certain elements such as silicon and bismuth separate.
These elements can irreversibly concentrate up over time in the metal stream
and are impossible to remove from the melt with economic production technology.
The presence of any undesirable impurities can cause problems such as hot shortness
which causes expensive failures during casting and hot extrusion.
According to an article written by Scrap Magazine, elements like bismuth
has a negative effect on “several physical characteristics of the copper,
making it useless for applications that are really widespread such as wire,”
Goris writes. According to the CDA’s report, bismuth is a “potent embrittler of
high-copper alloys,” which means it is “critical to avoid mixing bismuth brass
scrap with the cast engineering alloys such as the aluminum bronzes or
copper-nickel alloys.”
If
the bismuth content in smelting operations exceeds the desired level for
certain applications, the only solution is dilution. “Some scrap contaminated
with undesirable impurities can sometimes be diluted so that the impurity level
is reduced to an acceptable range for smelting,” Goris writes. Alloys that
contain 1.5- to 3.5-percent bismuth would require a dilution of at least 150 to
300 times with bismuth-free scrap to reduce the bismuth content of the copper
anodes to the target level of 1 part per million. “In practice,” he adds, “a
much higher dilution is required since some bismuth is already present in the
common copper scrap.”
At the CDA summit, many
ideas were circulated and discussed such as the possibility of a universal marking
to identify lead-free products containing bismuth, silicon, etc. It was also
discussed that the industry already marks brass products as lead-free (“LF”) or
no-lead (“NL”). Also, that the product may contain compliance labels such as
NSF 372. However, the consistency is lacking and marks do not indicate what
type of alloy is used.
Markings on products
are intended to inform the consumer that the product is safe and that it meets
the minimum safety standards. The consumer, at the end of the day, is not
concerned on whether the product contains silicon or bismuth; all the consumer
is concerned about is that the product is safe for use and that it is lead free. Therefore, the recycling of lead-free products may be an issue that can
be solved between the mills, suppliers/manufactures and the scrap industry; and
not involve a universal marking.
Automated sensor-based
sortation technologies were also discussed. Two viable methods for sorting mixed
brass scrap are laser induce breakdown spectroscopy and X-ray fluorescence. These
methods can be used by the scrap industry to sort and identify materials prior
to sending to manufacturers or mills. This solution seems attainable since sensor-based
sortation technology is commercially available and is likely capable of
segregating different alloy types in mixed primary and secondary brass scrap. While
sorting solutions are available, an additional processing step is required
which, will eventually, add cost to the consumer.
Though no
concrete recommendations came from the CDA summit, it is an important issue and
ASA appreciates the opportunity to participate. ASA plans to continue
participating in the CDA discussions and to be fully involved so that the
interest and concerns of ASA members are heard. In the meantime, CDA
indicated, that they will continue to look at the benefits and barriers
discussed at the summit to determine the next steps. A copy of the slides used
during the CDA stakeholder summit can be obtained
here. ASA members wishing to voice
their opinions on this issue and for questions pertaining to the recycling of
lead-free brass products, please contact Hugo Aguilar, P.E. at
engineer@asa.net.