That is just the theory. I'm sure if u do some digging you will come across that reference.

But you're absolutely right. There is no unrefutable evidence that NCD is an effective chelator. But there are enough real life cases to indicate that it IS in fact doing something.
There are studies which demonstrate the ability of zeolite to bind heavy metals in industrial application and there have been informal studies demonstrating its ability to enhance heavy metal excretion in children. I could E-mail these studies to you if you would like that.
But, like you, I'm skeptical. And I will be until I see some hard evidence of zeolites ability to chelate mercury.