Hayrapetyan, S.S., et al. “ON SORPTION OF POTASSIUM IONS BY MEANS OF SILICA–MANGANESE DIOXIDE SYSTEM”. Proceedings of the YSU B: Chemical and Biological Sciences, vol. 49, no. 1 (236), Apr. 2015, pp. 29-32, doi:10.46991/PYSU:B/2015.49.1.029.