May 23, 2019: Scientists at the National University of Science and Technology in Russia announced on May 21 they had developed a way to recycle silver from silver-zinc military batteries even when it has had lead added to it.
Some batteries made for the Russian Navy are colossal, 14-tonne alkaline batteries that contain seven tons of silver plate, the scientists said.
To save some of the expensive silver, a decade ago manufacturers began adding lead to them as it did not affect performance — yet ultimately saved nearly 500 million Russian roubles ($7.8 million) per battery.
However this almost completely prevented recycling the silver — until now.
Working with JSC Shchelkovo Plant of Secondary Precious Metals, the procedure is a cascade method that purifies the silver from spent batteries used in military submarines and aircraft so it can be re-used.
The technology is a two-stage melting of silver, as a result of which the melt is separated from the slag,” said Sergey Rogov, associate professor of the university’s MISIS Department of Non-Ferrous Metals and Gold.
“Subsequent rapid cooling enables the capture of oxygen, which oxidizes the lead in the composition of the silver material. In the second melting under the coating layer of flux (magnesium and sodium salts) oxidized lead is separated and goes into the slag.
“As a result of this two-stage process, lead is removed, and a commercial product of 99.99% purity is obtained from raw materials with 85% silver content. The pure product is suitable for the manufacture of a new battery.”
Rogov said the technology had been used at JSC Shchelkovo and no additional equipment had been required apart from a high-speed melt cooling unit.
“The use of the new technology has allowed involving previously non-recyclable waste of silver-zinc batteries in the production, increasing the volume of products manufactured by the plant by 7.5%,” said Aleksandr Savisko, director for production at JSC Shchelkovo.
Using silver in military batteries is ideal because volumetric energy density is very high, says Zoe Adamedes, business development manager at BST Systems, a US designer and manufacturer of power systems including silver zinc batteries for military and deep sea applications.
“They’re ideal in places where there’s not a lot of room, especially underwater, where the space is very small,” she said. “Often the machines are designed and just an odd-shaped space left for the battery.
“Lithium ion has very good energy density and lots of cycles but it needs lots of control circuitry and when it goes, it goes suddenly. Larger applications can work and work then suddenly blow up.
“With silver zinc you always get a warning when something’s going to happen. It can’t be fully cycled more than 50 to 100 times, but then neither can lithium be fully cycled as many times as we are led to believe.
“Once the silver zinc batteries reach their end-of-life they are collected and everything is reclaimed to come back to us.”
Adamedes said BST also sometimes used lead as an additive along with other elements such as mercury.
“Everything is sent off to our reclamation people and it all comes back,” she said.