Cation exchange properties of a layered manganic acid

There has been a great deal of research in developing highly selective Li⁺ exchangers which can extract Li⁺ from sea water and other brines because of the increased use of lithium in batteries. In a search for highly selective Li⁺ exchangers based on MnO₂ composition, a new layered manganic acid of the rancieite structure with a (001) 'd' spacing of 0.742 nm and a chemical composition of H₂Mn₄O₉ · 3·7 H₂O has been synthesized. The cation selectivity order of this phase was found to depend on the pH and the extent of loading in batch experiments. Below pH 4, the selectivity order increased with increasing ionic radius as follows: Li⁺ < Na⁺ < K⁺ < Cs⁺. Above pH 4, the selectivity was found to be as follows: Na⁺ < K⁺ < Cs⁺ ≪ Li⁺. These selectivity results show that the layered manganic acid reported here may be useful for selective separation of Li⁺ from sea water and assorted brines.