A process for producing superabsorbent particles by polymerizing a monomer solution or suspension comprising a) at least one ethylenically unsaturated monomer which bears acid groups and may have been at least partly neutralized, b) at least one crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned under a) and e) optionally one or more water-soluble polymers, comprising the steps of i) polymerizing the monomer solution to give a polymer gel, ii) optionally comminuting the resulting polymer gel, iii) drying the polymer gel, iv) grinding and classifying the dried polymer gel to give polymer particles, v) thermally surface postcrosslinking the classified polymer particles, vi) optionally reclassifying the surface postcrosslinked polymer particles, vii) optionally recycling polymer particles removed in step iv) upstream of step iii) and viii) optionally recycling polymer particles removed in step vi) upstream of step iii), which comprises adding to the monomer solution prior to step i) at least 0.75% by weight of a hydroxyphosphonic acid or salts thereof, calculated on the basis of the total amount of monomer a) used, and adding to the polymer particles between step iv) and step vi) at least 0.09% by weight of aluminum cations, calculated on the basis of the total amount of polymer particles used, and using the aluminum cation in the form of aluminum sulfate. a) at least one ethylenically unsaturated monomer which bears acid groups and may have been at least partly neutralized, b) at least one crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned under a) and e) optionally one or more water-soluble polymers, comprising the steps of i) polymerizing the monomer solution to give a polymer gel, ii) optionally comminuting the resulting polymer gel, iii) drying the polymer gel, iv) grinding and classifying the dried polymer gel to give polymer particles, v) thermally surface postcrosslinking the classified polymer particles, vi) optionally reclassifying the surface postcrosslinked polymer particles, vii) optionally recycling polymer particles removed in step iv) upstream of step iii) and viii) optionally recycling polymer particles removed in step vi) upstream of step iii), which comprises adding to the monomer solution prior to step i) at least 0.75% by weight of a hydroxyphosphonic acid or salts thereof, calculated on the basis of the total amount of monomer a) used, and adding to the polymer particles between step iv) and step vi) at least 0.09% by weight of aluminum cations, calculated on the basis of the total amount of polymer particles used, and using the aluminum cation in the form of aluminum sulfate. i) polymerizing the monomer solution to give a polymer gel, ii) optionally comminuting the resulting polymer gel, iii) drying the polymer gel, iv) grinding and classifying the dried polymer gel to give polymer particles, v) thermally surface postcrosslinking the classified polymer particles, vi) optionally reclassifying the surface postcrosslinked polymer particles, vii) optionally recycling polymer particles removed in step iv) upstream of step iii) and viii) optionally recycling polymer particles removed in step vi) upstream of step iii),