Abstract: New macroporous alkylaminophosphonic chelating resins which exhibit excellent mechanical stability and strength and good chemical stability are characterized by having an apparent density of 0.35 to 0.425 g/ml, a granulometry smaller than 0.8 mm, a water retention of 50 to 60 percent in the acid form, a porosity of 800 to 1100 mm.sup.3 g, a total theoretical capacity for the fixation of calcium ions of not greater than 31 g/l of resin in the sodium form and an osmotic resistance such that more than 90 percent of the beads are intact after 30 shocks. The high resistance to osmotic shock combined with an adequate exchange capacity exhibited by the new resins makes them particularly suitable for use in highly concentrated solutions, such as concentrated electrolytic brines.