Being close to Eternium removes or nullifies Black Adam's powers - and interestingly, does the same for Shazam as well.

Savant in his attempts to rid the universe of all magic. First appearing in Legion of Super-Heroes (Volume 4) #110 in 1998, Eternium is the name given to shards of matter that were cast when the Rock of Eternity was destroyed by Dr. That Eternium can weaken or harm Black Adam much like Kryptonite does Superman is taken right from comics. Think of it as Superman's Kryptonite in a sense. But what ends up being truly interesting about it is that it's shown in the film that Eternium is the only thing that can harm Black Adam. It's also shown that, in modern times, Intergang has been oppressing the people of Kahndaq and mining for Eternium for their own weapons and purposes so it's definitely a very useful element. Eternium is introduced pretty early on in Black Adam, where it's shown that King Anh-Kot enslaved the people of Kahndaq and forced them to mine for the element so that he could create the Crown of Sabbac.

Eternium elbans scepter