How rare is platinum? Imagine that making an ounce of it is so difficult that even exploding stars called supernovae, the crucibles whose high energies forge most chemical elements, can’t do it. In fact, if the latest theories are correct, it takes a collision of two massive neutron stars – objects so dense that a teaspoon of their matter weighs 100 million tons - to manufacture the metal.
But the silvery element also happens to be incredibly useful. It helps scrub pollutants from car exhaust, generate power in fuel cells, and even fight cancer. No wonder scientists have been trying to reclaim every gram they use. “We want to minimize waste and maximize the return,” says Lawrence Kool, a chemist at GE Global Research. “Every ounce we recover is an ounce we don’t have to buy.”
One major consumer of platinum working to improve its recovery record is the aviation industry. Aircraft engine makers use the metal as a kind of Super Glue that binds special thermal barrier coatings to the blades that go inside the high-pressure turbine (HPT). The coating helps protect the blades from corrosion and the infernal heat inside.
The blades, however, do not stay inside the engine forever. Maintenance crews take them out periodically for inspection and repair. But the platinum is really hard to take off. “One method that involves grit-blasting is so harsh that we lose all of the platinum,” Kool says. “We classify the used grit as waste material and it ends up in cement somewhere. Since each blade contains about 1.0 grams of platinum and we go through 50,000 HPT blades a year, we had an expense there.” (Chemical recovery methods vary in yields between 68 and 91 percent.)
Every year, GE Aviation scraps about 24 tons of high pressure turbine blades. Rather than throwing out the valuable metal removed from their surface, the company commissioned Kool to find a way that would strip the layers selectively one by one.
He invented a method that dissolves the coating and leaves a platinum residue on the blades. The deposit can be easily rubbed off with water to form a muddy substance called platinum black “smut.” The smut, which is 49 percent pure platinum, can be easily processed and refined. “I got pretty deeply into the science,” Kool says.
His work could lead to the recovery of as much as 93 percent of platinum that is normally used to coat the blades. “We currently use third-party vendors who employ traditional methods, which we do not believe recover as much platinum or conserve as much of the other valuable elements in the parts, for example, rhenium, that GE’s technology does,” says Denis Oliver, the aerospace business development manager at the high-tech recycling company ELG Metals. “GE’s technology should also be more cost-effective.”
It took several years before Kool could move the technology from the lab into an industrial setting. “We started with ultrasonic baths and filter papers,” he says. “But we needed to scale the process to centrifuges and vibrating barrels.”
ELG, the first company to license Kool’s platinum recovery technology, is currently preparing it for its commercial debut. After stripping the coatings from GE’s blades, ELG will send the smut to a platinum refinery, which will give GE a gram-for-gram credit for all the platinum the black paste holds.
