The first step is to get the hydrogen in the crystal. It's easy -- you just have to wash the mineral with a little bit of acid. Even a strong vinegar would likely be enough to prepare the mineral for the exchange treatment, but I used about 1% hydrochloric acid. The hydrogen spontaneously replaces the sodium in the crystal, and now the mineral is primed for cesium exchange. It's that simple.
When hydrogen is in the crystal, it forces the water molecules in the tunnels to adopt a unique bonding geometry that remarkably forces the tunnels to expand. In the case of porous tunnel structures like gaidonnayite (
and other minerals we have studied), hydrogen forces the water molecules that are already in the tunnels to adopt a chain-like pattern (sometimes called
quantum water wires), which has a linear pattern because the tunnels are linear. The resulting water wires expand the tunnels just enough to accept an unusually large atom.
For gaidonnayite, it turns out that cesium could now get in.
Once the tunnels are propped open, cesium is allowed to rapidly enter the crystal. After a cesium atom enters the tunnel, the hydrogen atoms is pushed out, and the tunnel closes behind it. This locks in the cesium inside the crystal. It's entombed -- and cannot get back out -- even when we try to wash the mineral with acid and other substances!
Being able to selectively lock toxic elements inside the crystals, and have them safely stored in the crystals for the long-term, is a big advancement. This process can separate the high-level waste from the low-level waste efficiently, and also keep the toxic elements locked away from from interacting with the environment or living organisms. Because gaidonnayite has no known toxicity to humans, there could interesting ways to use it to absorb cesium, when other methods of safe containment, or soil/water remediation, fail. I am currently looking for more minerals that are selective for other radioactive elements.