Think Tank: Lead-free Copper Alloys

UNITED STATES September 10 2015 4:05 PM

By Kent Kiser 

When the U.S.  government mandated the removal of lead-containing plumbing components from the  nation’s potable water supply, manufacturers and their metal suppliers turned to  lead-free copper alloys—primarily brasses and bronzes as binary alloys or  containing bismuth or silicon. By meeting the federal lead-free requirements,  fixtures made of those alloys could find use in the U.S. drinking water system  for decades to come. To some, that’s the end of the story. To others, it’s the  beginning of a future catastrophe. These latter parties say the lead-free alloy  components—principally bismuth—will have disastrous consequences when they reach  the end of their service lives.

The problem, they say, is there’s no  easy way to distinguish the alloys from each other or from traditional  lead-containing brasses, so they’ll get mixed together and create contamination  problems for secondary copper smelters, brass and bronze ingotmakers, and some  copper mills. Is this a cautionary tale of unintended consequences? Competitive  gamesmanship by alloy producers promoting their commercial interests? A market  shift requiring adaptability and cooperation among the stakeholders? Or all of  the above?

Getting the Lead Out
The driving force  behind this copper alloy shift is the federal Safe Drinking Water Act, passed in  1974. A 1986 amendment to the SDWA established that only lead-free pipe, solder,  and flux can be used in the installation or repair of U.S. public water systems,  or in any plumbing in a facility connected to a public water system that  provides water for human consumption. The 1986 amendment defined as “lead-free”  solders and flux containing no more than 0.2 percent lead and pipes and pipe  fittings containing no more than 8 percent lead. Since 1996, the SDWA has made  it unlawful for any company to introduce into commerce plumbing products for  drinking water that are not lead-free.

In January 2011, Congress passed  the Reduction of Lead in Drinking Water Act, which modifies Section 1417 of the  SDWA regarding the use and introduction into commerce of lead pipes, plumbing  fittings or fixtures, solder, and flux. That amendment, which took effect Jan.  4, 2014, lowers the maximum lead content allowed in the wetted surfaces of  plumbing products for potable water from 8 percent to a weighted average of 0.25  percent. The level for solder and flux remains no more than 0.2 percent lead.  

Why all the regulatory concern about leaded plumbing components?  According to the U.S. Environmental Protection Agency (Washington, D.C.), lead  can enter tap water through the corrosion of plumbing materials. “The most  common problem is with brass or chrome-plated brass faucets and fixtures which  can leach significant amounts of lead into the water, especially hot water,” the  EPA says on its website.

Faced with this regulatory requirement,  plumbing product manufacturers and their metal suppliers have turned primarily  to lead-free brasses and bronzes containing bismuth and silicon, which are  effective replacements for the previous leaded alloys. In metal production  operations, bismuth “acts very much like lead in many respects,” according to an  alloy data sheet from the Copper Development Association (New York). “Its  melting point is 101 degrees F lower than that of lead, making its behavior  during casting and solidification similar to that of lead. Like lead, bismuth is  nearly insoluble in copper and copper alloys.

Furthermore, it causes  machining chips to break up into small, easily removed particles, similar to  lead.” Silicon brasses and bronzes—as well as other lead-free alternatives, such  as tin bronze and sulfur bronze—have comparable beneficial characteristics,  those in this market say, giving them a place in the U.S. potable water  market.

It’s important to note that ingotmakers continue to produce and  manufacturers continue to use leaded copper alloys for numerous  non-potable-water applications, thus those alloys will continue to appear in the  copper scrap stream.

Poison in the System
As the use  of lead-free copper alloys grows in the U.S. drinking water sector, the amount  in the copper scrap stream will increase. In its report titled “Plumbing Alloys  in the Scrap Stream,” the CDA calls this material “a significant new factor in  the U.S. secondary copper alloy scrap mix.” Some fear this trend will create  major problems for copper scrap consumers such as brass and bronze ingotmakers,  secondary copper smelters, and certain copper mills. That’s because the various  alloying elements—including bismuth, silicon, zinc, and lead—can be  contaminants, depending on the situation.

Lead, for instance, is anathema  to lead-free alloys. “When we’re making silicon-, bismuth-, or sulfur-based  alloys, we need a much cleaner charge because the lead maximum is 0.09 percent,  so you can’t afford to be too cute with what goes in,” says Chris Greenfield,  vice president of purchasing for The Federal Metal Co. (Bedford, Ohio), a brass  and bronze ingotmaker. On the flip side, lead-free alloys can contaminate heats  of leaded brass or bronze. “The biggest problem we’ve had with our leaded brass  stream,” Greenfield says, “is the increase in the amount of zinc in it, and  that’s a function—at least in part—of the silicon-based alloys in the scrap  stream.” (The zinc content of silicon brass and bronze alloys can range from  zero to 20 percent, depending on the metal producer, he explains.)

One  U.S. brass and bronze ingotmaker interviewed for this article already has  received—and had heats ruined by—lead-free alloys in its purchased copper scrap.  “And it’s not just the bismuth,” the company’s president says. “The problem is  more complex. Just as bismuth is a real problem as a contaminant in a leaded red  brass heat, so is silicon bronze because that doesn’t work in red brass,  either.” If those elements throw a heat of metal out of spec, an ingotmaker must  pour out that heat and feed the off-spec metal into other heats in small  increments to dilute the undesired element.

Lead-free alloys also affect  secondary copper smelters, with bismuth the principal contaminant in their  production of secondary cathode. Secondary smelters attempt to remove impurities  from their infeed material primarily through high-temperature pyrometallurgy and  low-temperature hydrometallurgy, explains Dirk Goris of secondary smelter  Metallo-Chimique (Beerse, Belgium) in a report titled “The Application of  Bismuth Versus Silicon in Copper Alloys From a Sustainability Perspective.” The  pyrometallurgical process removes impurities based on their affinity for oxygen:  They bond with oxygen and collect in the slag. The oxidation process, however,  cannot remove certain elements—including antimony, arsenic, bismuth, lead,  nickel, and tin—to a low enough concentration to achieve certain copper purity  levels, so smelters must resort to the hydrometallurgical step called  electrorefining, which purifies the copper anode to copper cathode.  

According to Goris, antimony, arsenic, and bismuth have a standard  electrochemical potential close to copper, so they will report partially to the  insoluble anode slime and will partially dissolve in the electrolyte. Bismuth,  he writes, plays an important role in the formation of floating slimes—fine,  floating particles that can be entrained at the cathode. And floating slimes are  “probably the most detrimental category of compounds leading to cathode  contamination.” Some bismuth also can contaminate the copper cathode by physical  phenomena such as electrolyte entrapment or occlusion of floating slime on rough  cathode surfaces, Goris says.

Why is the bismuth content in copper  cathode such a concern? 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.”

Copper sheet and strip mills and copper rod and bar  producers also consume copper scrap, and they likewise face potential problems  if certain elements—including bismuth, silicon, and lead—contaminate their  products. “If you put lead in sheet, it degrades the rolling characteristics,”  notes Jim Michel, CDA’s manager of technical services. “If you get bismuth in a  sheet alloy and you hot-roll it in a mill, it can actually shatter like glass.”  In the same vein, “if you add a bismuth-containing alloy to rods and bars in  production, they fall apart in hot-rolling. If the silicon alloys are mixed in,  rod and bar producers can’t stand that, either. That also poisons their  stream.”

The takeaway, Greenfield says, is that “all of us that consume  metal have issues, no matter what it is we’re getting. Silicon hurts us in  certain areas; bismuth hurts us in other areas; lead hurts us in all areas,  except leaded alloys.”

Sizing Up the  Problem
Lead-free copper alloys aren’t showing up in significant  quantities in the scrap stream yet for the simple reason that plumbing  components have a long service life. Fixtures installed today won’t be scrapped  en masse for decades. Projections about the potential volume of lead-free alloys  in the scrap stream vary widely, with most focusing on bismuth. One ingotmaker  estimates that more than 50 percent of the metal used for U.S. potable water  plumbing components now is copper-bismuth alloys.

Metallo-Chimique’s  Goris, for one, writes, “While no detailed and accurate data are available, it  is expected that large amounts of new lead-free bismuth-bearing articles will be  manufactured every month. This means every faucet, fire hydrant, valve, water  meter, etc. produced will contain up to 3% bismuth. These materials will  eventually find their way to the secondary copper smelters for  refining.”

CDA paints two possible scenarios for copper-bismuth alloys in  its report: In one, the alloys will remain limited to the “tightly regulated  plumbing products,” which could amount to 2,000 to 20,000 tons a year,  “depending on the extent of use by the in-line plumbing product manufacturers.”  In the other scenario, the alloys could expand into a broader range of products  currently cast in leaded red and yellow brass. “We are now seeing foundries  adopting, or considering adopting, the bismuth-modified alloys for a variety of  cast products unrelated to drinking water, even including cast bronze bearings,”  CDA says. “In this case the upper bound is uncertain.”

Foundries could  embrace lead-free alloys “to meet U.S. lead-in-air regulations and to avoid the  expense of disposal of lead-contaminated foundry sands,” the association says.  If that shift gains momentum, “some parts of the markets for cast copper alloys  would presumably be lost to competitive materials including plastics due to the  increased cost.” Either way, the CDA expects annual production of  bismuth-containing alloys to be “somewhere within the lower range; i.e., not  greater than 20,000 tons [40 million pounds].”

Others see a much bigger  storm brewing. One West Coast brass and bronze ingotmaker maintains that North  America manufactures about 100 million pounds a year of potable water components  for municipalities, not including components sold directly to consumers. “This  means that the 100-million-pound figure is very conservative,” the ingotmaker  says.

Despite their diverse projections, all parties agree that the  volume of lead-free copper alloys in the U.S. scrap stream will grow. Given that  copper scrap is traded internationally, the material will reach melting  operations the world over, making this a global issue. “The problem is still in  its infancy, but in the next four or five years, you’re going to see a lot of  this material coming in,” the U.S. ingotmaker says. “Ten years from now it’s  going to be a complete nightmare.” Others—such as Mike Buyarski, Federal Metal’s  chief operating officer—acknowledge the challenge without alarm. “It doesn’t  keep us up at night, but it’s something we have to address.” Michel supports  taking action sooner rather than later. “Some people have said, ‘It’s early in  the game, so why are we worrying about this?’ I say, maybe we ought to start  talking about it because it may turn into a flood. We have to be aware of  it.”

Scrutinizing the Scrap Stream
Ingotmakers such  as Federal Metal certainly are aware of the potential problem and already are  taking steps—some internal and some external—to address it. “As these different  alloy options have popped up, we’ve had to improve our internal processes for  sorting and allocating scrap to the right type of furnace,” Greenfield says.  “We’ve also had to work with our suppliers to make sure they understand what our  challenges are so they can help us overcome them. We’ve worked pretty hard with  our supplier base to make sure they’re educated as to how to segregate out the  silicon and bismuth alloys from the leaded brass.”

The problem, in the  U.S. ingotmaker’s view, is that most scrap dealers “really aren’t even aware of  this problem yet,” he says. Since lead-free alloys aren’t appearing in large  quantities in the scrap stream, processors “aren’t super receptive to have that  discussion right now. The problem is off in the distance for them, so they’ll  say, ‘Well, I’ll ship the material somewhere else, and when it becomes a  problem, it’s a problem.’”

Echoing Greenfield, the U.S. ingotmaker says  educating scrap processors is part of the solution, suggesting that ISRI “needs  to get out in front of this.” The association should initiate a conversation—at  its Commodities Roundtable Forum, the Copper Spot­light at the annual  convention, or some other ISRI event—to acknowledge that “brass and bronze are  going through a revolution, and things are changing.” As the scrap industry’s  trade association, “it’s up to ISRI to take a strong leadership position on that  education.” Then, he says, all ISRI members who handle copper scrap need to  become stewards of this issue and not put their heads in the sand “because  that’s only going to degrade the value of these products going  forward.”

Until scrap dealers are fully up to speed on sorting lead-free  alloys, consumers such as Metallo-Chimique “will be forced to spend more time  and efforts on quality inspection of incoming materials to safeguard their  refining process and final product specifications,” Goris says. These stepped-up  efforts “will result in a significant increase in costs,” he says. Consumers  could penalize their scrap suppliers for the lead-free alloy content in their  scrap to offset the additional costs to sort and/or refine the metal to an  acceptable grade. Some consumers could reject certain scrap loads based on their  concerns about lead-free alloy content, imposing additional transportation and  marketing costs on the processor. In a worst-case scenario, consumers could stop  buying certain types of copper scrap altogether. “If I don’t know what’s in the  scrap,” the U.S. ingotmaker says, “I’m probably going to move toward using  material with a known chemistry.”

For processors, much of the answer lies  in doing more thorough and accurate sorting of copper scrap grades. “It’s not  that the lead-free alloy scrap is bad,” he says. “If it’s kept separate,  entirely free from everything else, and if it’s identified as what it is, it’s  great. There’s no problem with it at all. It can be 100-percent recycled.” This  additional sorting will be more time-consuming and expensive for processors, but  they might be able to earn more for their sorted grades because some of the  alloys—such as those containing bismuth—are worth more than other brass grades.  “They actually make more money on the lead-free alloys than they will on the  leaded ones, so it’s to their advantage to pull them out,” Buyarski  says.

One factor aiding the sorting process: Some manufacturers of  bismuth brass and bronze plumbing components label them “NSF 61” or “NL,” which  helps processors separate them from other alloys. “Our suppliers routinely sort  these units and sell them as identified bismuth brass,” Greenfield says. The  U.S. ingotmaker would like to see such markings expanded and simplified. “It  would be easier if manufacturers would add some sort of identification, such as  S for silicon bronze or B for bismuth brass—something so sorters would know what  the product is,” he says. With silicon alloys, their yellowish color helps  distinguish them from leaded and bismuth red brasses, but processors also can  use a grinding wheel to verify their identity, Greenfield says. If those  identification approaches don’t work, processors might have to use hand-held  metal analyzers to sort these alloys.

Overall, cooperation between scrap  processors and consumers is key to preventing these newer metals from creating  problems in the scrap supply. “If you don’t want to get bounced by your  consumers, and you don’t want your consumers to stop purchasing this material,  we all have to be part of the solution,” the U.S. ingotmaker says. These  cooperative efforts could point to a need for new scrap specifications,  particularly regarding the bismuth or silicon content in copper alloys.  “Everyone’s dancing around all of these issues, but it’s a material  specification issue across the board regardless of the industry and regardless  of the lead-free alternative,” Greenfield says.

In the long run, the  lead-free copper alloy issue has far-reaching business repercussions for scrap  processors and consumers, suggesting it’s in their best interests to find a  resolution that works for all parties. “Change is never easy, and the scrap  industry really isn’t aware of the magnitude of this change,” the U.S.  ingotmaker says. “Scrap dealers need to prepare themselves for the onslaught of  these materials in the future. That doesn’t mean it’s bad. It’s just going to  have to be managed entirely differently. It’s a new deal.”

Kent  Kiser is publisher of Scrap and assistant vice president of industry  communications for ISRI.