Photographic fixer compositions and method for processing a photographic element

A hardening black and white photographic fixer composition comprising a thiosulfate silver halide solvent, an aluminum salt hardening agent in an amount of at least 0.02 mol/L, a buffering agent and ammonium ions in an amount of at least 0.20 mol/L, wherein said fixer composition also contains at least 0.05 mol per mole of hardening agent of an aminopolycarboxylic acid sequestering agent of formula (I-a) or (I-b) or a water-soluble salt thereof and at least 0.05 mol per mole of hardening agent of a polyphosphonic acid sequestering agent of formula (II-a), (II-b), (II-c), (II-d') or (II-d"):

• wherein X is an unsubstituted alkylene group having 1 to 4 carbon atoms;
• R.sub.3 and R.sub.4, equal or different, each represent hydrogen or --CH.sub.2 --R.sub.1 and R.sub.1 and R.sub.2, equal or different, each represent --COOM, wherein M represents a hydrogen atom, a sodium atom, a potassium atom, a lithium atom, or an ammonium group;
• ##STR10## wherein M is as above and R.sub.5 is an alkyl group, an aryl group, an aralkyl group, an alkaryl group, an alicyclic group or a heterocyclic group;
• ##STR11## wherein M is as above and R.sub.6 is an alkyl group, ##STR12## wherein M is as above and R.sub.7, R.sub.8 and R.sub.9 are hydrogen or an alkyl group, and ##STR13## wherein R.sub.12, R.sub.13 and R.sub.14, equal or different, each represent a hydrogen atom or a --PO.sub.3 M.sub.2 group, wherein M has the same meaning as above, and R.sub.10 and R.sub.11, equal or different, each represent a hydrogen atom, an alkyl group, a --PO.sub.3 M.sub.2 group or a --PO.sub.3 M.sub.2 substituted alkyl group, and Q:
• represents the atoms or chemical bonds necessary to complete a 3- to 6-membered ring, with the proviso that at least two of R.sub.10, R.sub.11, R.sub.12, R.sub.13 and R.sub.14 substituents represent a --PO.sub.3 M.sub.2 group, and wherein said fixer composition has a pH in the range from 4.75 to 6.25.