Doping birnessite as a method for synthesizing an ion exchanger selective to strontium and repeatedly working in sorption-desorption cycles

Manganese oxides represent an environmentally friendly and industrially scalable class of materials exhibiting sorption properties for Sr2+. However, there is a critical challenge of the drop in the exchange capacity in the processes of sorption and desorption. In the paper, there are proposed and have experimentally been tested the routes for enhancing stability of manganese oxides in the cycled ion exchange processes. There were analyzed the properties of the doped and “pure” birnessite in Sr-form and H-form. The strontium exchange capacity of doped Fe, Co, Ni samples increases with increasing cycling, whereas that of an undoped sample decreases. The samples doped with Fe and Co at 150°С proved to be most stable during cycling, with those doped with Ni and Co being such at modification temperature 360°С. Introduction of Ni and Co was evinced to favor preserving both the strontium exchange capacity and selectivity.