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In this paper, original thermosensitive copolymers bearing phosphonic acid groups, namely the poly(N-n-propylacrylamide-stat-2-(methacryloyloxy)methylphosphonic acid) (P(NnPAAm-stat-hMAPC1)) were synthesized, and their sorption properties for three divalent cations (Ni(2+), Ca(2+), Cd(2+)) and one trivalent cation (Al(3+)) have been investigated. The sorption experiments were performed with increasing relative amount of cationic pollution compared to the amount of sorption sites (C(n+)/P ratio) in mono and multi-component solutions to investigate the sorption mechanisms. C(n+)/P proved to strongly affect the sorption capacity and high capacities were obtained for all cations at highest C(n+)/P ratios, reaching one mole of C(sorbed)(n+) per phosphonated moiety. For divalent cations, sorption mechanisms were likely to be described by electrostatic interactions only, whereas for aluminum trivalent cation the sorption not only resulted from electrostatic interactions but also from the formation of coordination binding. The selectivity of the phosphonic acid moieties for aluminum cations was demonstrated, highlighting the interest of P(NnPAAm-stat-(h)MAPC1) for their use for the treatment of metallic pollution from wastewater.