Few people have ever heard of rhenium—a rare and semi-precious metal—but it is an important material in the aerospace industry. Modern jet engines require rhenium as an alloying element—critical to the performance of commercial, military and even rocket engines used for space exploration. Rhenium also happens to be one of the rarest elements on earth, mined mostly in the United States, Chile and Kazakhstan. All engine manufacturers use it because it allows engines to reach higher temperatures required in jet flight and to consume less fuel when operating.
For the past 10 years, GE Aviation has been working to lessen its dependence on rare minerals, including rhenium. This is being accomplished through a combination of innovative component designs, advanced manufacturing processes and new alloys. Recycling materials from unserviceable engine parts is also being practiced to reduce the need for rhenium as a raw material in jet engine manufacturing. Through the GE Reclamation Program, GE Aviation is producing better outcomes for GE, its customers and the environment, saving millions of dollars by using recycled material.
“The goal of the program is to recycle, reuse and replace this rare metal,” said Ted Grossman, chief manufacturing engineer, GE Aviation. “Not only will it help us reduce our need for rhenium and lower costs, it is reducing the environmental impact associated with mining activities and material disposal.”
Increased Demand Comes at a Cost
When alloyed with other materials from the periodic table, rhenium helps create strong superalloys necessary for the manufacture of high-pressure turbine (HPT) blades used in jet engines today. As early as the 1980s, engine makers discovered that nickel-based alloys containing rhenium were able to retain their strength at extremely high temperatures, providing durability, wear and extended life for certain engine components.
However, the aerospace industry’s reliance on rhenium has placed a premium on this mineral. The continuing demand for commercial and military aircraft has increased the supply-demand imbalance and fueled steep price increases for this rare commodity. The drive for newer, more fuel-efficient engine models has also translated into greater demand. While the introduction of rhenium enabled alloy developers to increase alloy strength and environmental capability, the industry is now faced with the challenge of recycling rhenium to address increased demand and mounting costs.
“Anything that can reduce copper mining and raw-material usage through reclamation, recycling and reuse definitely benefits the aviation industry (and the environment).”
LEE ANN TEGTMEIER OF AVIATION WEEK
GE Aviation began to evaluate ways to reduce its reliance on this rare metal in 2006. That year, the business launched the GE Reclamation Program in response to volatile markets and rising prices. One kilogram of the silvery-white metal today costs around $4,000. But not less than two years ago, booming demand made the price of rhenium surge to more than $6,600 per kilogram, making the semi-precious metal worth almost a third the price of gold and one of the most expensive industrial metals in the world.
Not only is rhenium extremely rare at an average concentration of two parts per billion in the earth’s crust, it is very difficult to extract. Rhenium is not mined, but rather recovered and extracted as a byproduct of copper mining. Very little rhenium is actually processed and isolated each year as compared to the millions of tons of copper and millions of pounds of molybdenum that are extracted from the same copper deposits.
To put this into perspective, consider the following scenario. It takes, on average, approximately 120 metric tons (264,554 pounds)—or the equivalent weight of 44 Cadillac Escalade SUVs—of copper ore to produce 1 ounce of rhenium—or the equivalent weight of five U.S. quarter coins. The production of one HPT blade requires about 0.5 ounces of rhenium. The extraction processes required to mine that material are significant, as are the environmental impacts and carbon emissions that go along with them.
A Three-Pronged Approach
Recognizing the need to incorporate conservation into alloy development, the GE Reclamation Program is an effort to combat costs, curb dependency on this rare element and simultaneously minimize the need for extraction. A three-pronged approach involves the following:
- Recycling metal grindings from the manufacturing process
- Developing alloys that require less or zero rhenium
- Reclaiming rhenium from used engine parts
The first prong of the GE Reclamation Program involves recycling excess material as engine parts are made. During the production process for HPT blades, rhenium-bearing alloys are melted and then poured into a mold, solidified and machined in order to extract the part. Those components are then ground to meet part specification, and the grindings, which were previously discarded, are now being refined to extract rhenium, generating a new supply stream.
The second prong of the GE Reclamation Program is focused on reducing rhenium usage in its alloys. GE Aviation metallurgists and engineers worked to develop new alloys that contain significantly less rhenium. In doing so, they sought, and were successful in obtaining, the same mechanical properties and benefits of the original alloy, while minimizing the amount of rhenium used. That alloy development resulted in reduced-rhenium alloys and no-rhenium alloys. Both went through rigorous certification testing to comply with the requirements of the U.S. Federal Aviation Administration (FAA). Part of the FAA demonstration requirement for engine testing is to understand the behavior of the material in the engine environment and to prove that the new alloys had the same high-temperature properties, endurance, efficiency and performance as the original higher-rhenium content alloys. GE now uses these low- and no-rhenium alloys across all of its jet engines and industrial gas turbines.
The third prong of the GE Reclamation Program is focused on recovering the rhenium in no longer serviceable HPT blades, generating another supply stream for rhenium. GE Aviation began recycling rhenium in 2007 at its own maintenance, repair and overhaul facilities. Shortly afterward, it extended the program to its military and commercial customers. GE has become a leader in recycling rhenium-bearing alloys, recovering thousands of pounds of the metal in 2009. Through its closed-loop recycling program, GE has successfully rebalanced the supply and demand for this material, directly benefitting its customers and the environment.
Under the program, unserviceable engine parts are re-used in the HPT blade supply chain. Prior to this, scrap material was often sold to vendors, who recycled the material for use in the stainless steel industry. This meant that key, rare elements like rhenium were lost to the production of steel and less high-tech alloys.
“Besides enabling GE to save significant sums of virgin materials, we are also helping to ensure a steady supply stream of minerals for our engines.”
JOHN CAMARDO, SOURCING TEAM LEADER, GE AVIATION
In 2006, GE partnered with a metals-processor to recover engine-run hardware from GE customers around the world. The supplier picks up unserviceable hardware directly from each customer site and processes it at the supplier’s facility. The fully-processed material is then reintroduced into the GE supply chain. With this approach, all of the metals contained in the alloy are recycled and reused. The positive impact of that recovery on the environment and the carbon footprint is substantial.
The process also has numerous benefits for GE customers, who receive significant value for the scrap metal that they return. The U.S. Navy was one of the first participants of the GE Reclamation Program, and has already reaped benefits worth hundreds of thousands of dollars in savings. Approximately 50,000 pounds of material have been picked up from the U.S. Navy’s Fleet Readiness Center in Jacksonville, Florida, and recycled. That includes out-of-use F414, F404 and T700 engines, which are also the models that have the highest rhenium content.
Captain Ted Fink has driven the program for the U.S. Navy, and explained the numerous benefits that the Navy acquires through its participation. “When the Navy was disposing the material, there was a cost for storage, shipping and other costs with rendering the material safe. By collaborating with GE on disposal, we receive payment for the material, which goes toward offsetting the cost of engine materials we will buy in the future.” Captain Fink further elaborated, “The process also gives GE a predictable source of material. In addition to being a cost benefit to both parties, it is a risk reduction effort. Over time as we get more and more material retained in the supply chain, it reduces the risk of supply and provides an offset on the price volatility and the expensive nature of the materials in these engines.”
GE receives certification on each pick-up worldwide. Customers benefit from a controlled environment where GE can manage this material stream and provide certification of where the material is reused. This ensures that parts are disposed of properly and won’t exceed their functional life. “The aviation industry is highly regulated and companies need to ensure that all scrap parts are taken out of service in a documented and controlled fashion to avoid the scenario of unserviceable parts entering the market in any fashion,” said Lee Ann Tegtmeier of Aviation Week. “Properly documented materials benefit the entire industry.”
Reducing the Carbon Footprint
In addition to the cost and safety benefits, the GE Reclamation Program has significant environmental benefits. Greenhouse gas emissions are reduced by using reclaimed rhenium in its new products. By avoiding the processes needed in refining minerals, many of the steps that would have been required to produce pure rhenium are eliminated—from extracting the mineral from the ground to refining it.
“GE is helping to conserve 60 percent of the greenhouse gases that would otherwise be emitted if it had to mine all of these elements directly out of the earth. It is the environmentally responsible thing to do.”
SOS PRESIDENT DON SHADROW, PRESIDENT OF SOS, A METALS RECYCLER
GE Aviation is working to increase the proportion of reverted material used for each part. “Currently, a significant portion of the material used in one casting pour to produce a blade is reclaimed—and that portion is growing,” said Eric Beutel, a financial analyst for GE Aviation.
GE is also working to expand the recycling program to other types of alloys and in encouraging more customers to participate in the reclamation program. Dozens of commercial and military customers are signing up. Participants span the globe and include Air France, ASA, Austrian Airlines, Delta Airlines, KLM, Korean Airlines, Lufthansa, Air Canada, American Airlines, British Airways, Shanghai Airlines, Spring Airlines, Croatia Airlines, Aveos, China Eastern Aviation, ST Aerospace, Shenzhen Airlines, MTU Zhuhai, SR Technics, the U.S. Air Force, the U.S. Navy, Turkish Airlines and Saudi Arabian Airlines.