When we investigated how this feat was accomplished, we found that is likely some interesting effects with water molecules inside the crystals.
When hydrogen is in the crystal, it forces the water molecules in the tunnels to adopt a unique bonding geometry. Think of when water freeze to ice. As the temperature of water decreases, crystals begin to form in a natural hexagonal pattern. In the case of zeolites and other porous tunnel structures like gaidonnayite, hydrogen forces the water molecules to adopt a chain-like pattern because the tunnels only go in one direction. This effectively expands the tunnels by a large margin, propping the tunnels open for just the right sized atom.
Once the tunnels expand, this allows for cesium to rapidly enter the crystal. After the cesium enters the tunnel, the tunnel closes behind it and locks in the cesium inside the crystal. It's entombed, cannot get back out.
Being able to selectively lock toxic elements inside the crystals is a big advancement. This process can separate the high-level waste from the low-level waste efficiently, and also lock-away the toxic elements from any biological activity.
Not all elements will exchange the hydrogen out of the crystal. For example, when we tried to put sodium back into the crystal, very little migrated into the crystal. When we tried to exchange cesium into gaidonnayite at high temperatures without hydrogen in the crystal, there was a little exchange, but nothing near to the degree of exchange when hydrogen is present.
In the end, I think we found an interesting process t