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Today, toxic rare earth metal ions contamination and huge volume of waster acrylic fibers (WAFs) have caused serious environmental problems, which make the development and implementation of feasible and sustainable methods to recycle the wastes of high practical significance. Herein, we propose, for the first time, that using WAFs as a poly(amino-phosphonic acid) (PAPA) precursor to functionalize graphene oxide (GO) based on the excellent chelating ability of PAPA and remarkable properties of GO. In this study, four novel PAPA modified magnetic graphene oxide (MGO) composites (PAMGOs) with different PAPA concentrations (PAMGO-1, PAMGO-2, PAMGO-3, and PAMGO-4) were fabricated by a facile one-pot sequential reaction method, and used as adsorbent for capturing Gd(III) from aqueous solutions. The prepared materials were characterized by various technologies. Batch adsorption results demonstrate that Gd(III) capture relies upon the content of PAPA grafted onto MGO and the pH of solution. In addition, PAMGO-3 not only shows the best Gd(III) sorption performance among tested adsorbents with the maximum uptake capacity of 499.42 mg/g at 298 K, but also demonstrates a high selectivity of Gd(III) ion over various coexisting ions, these results are attributed to the synergistic effect of MGO and PAPA in PAMGO-3. Moreover, the adsorption isotherm is in better agreement with the Langmuir model, and kinetics data follow the pseudo-second-order equation. The thermodynamic studies indicate the uptake of Gd(III) on PAMGO-3 is spontaneous and endothermic. Furthermore, recycling experiments confirm that no obvious loss of adsorption capacity occurred for the PAMGO-3 after six consecutive cycles. This study provides a new perspective to prepare PAMGO-3 from WAFs and shows its use as a promising adsorbent for Gd(III) elimination in aqueous solutions.