Removal of Co2+, Sr2+ and Cs+ from aqueous solution by phosphate-modified montmorillonite (PMM)

► Phosphate-modified montmorillonite (PMM) was highly effective in Co2+, Sr2+ and Cs+ removal. ► Cs+ sorption on PMM was higher than Co2+ and Sr2+ in single-solute sorption. ► Co2+ and Sr2+ sorption were synergistic, but Cs+ sorption was antagonistic in bi-solute sorption. ► Sorptions of Co2+ and Sr2+ were dependent on initial solution pH but not Cs+. ► Sorptions of Co2+ and Sr2+ were endothermic but that of Cs+ was exothermic.