Name of toxic liquid product that can be cleared with flocking agent
If your impurity is tritium, it can not be purified, whatever the method used. If your impurity is another substance, it can be purified by adding aluminum sulfate. Aluminum sulfate is slowly hydrolyzed in dilute solutions. And this phenomena produces a light and insoluble substance called aluminum hydroxide $\ce{Al(OH)3}$. The particles of this substance look a bit like snow flakes and have the property of fixing impurities on its surface, between its branches. So after a couple of hours, this aluminum hydroxide will be deposited on the ground of the river or the lake, with the impurities fixed inside its particles.