The invention concerns a process for enriching an iron mineral from a silicate containing iron ore by inverse flotation comprising the addition of a collector or collector composition comprising at least one of the compounds of formulae RC(O)N(Z—O—X—NH2)2 (Ia); RC(O)N(Z—O—X—NH2)2H+ Y− (Ib); in which X is an aliphatic alkylene group containing 2 to 6 carbon atoms; Z is an aliphatic alkylene group containing 2 to 6 carbon atoms; Y− is an anion; and R is a saturated or unsaturated, linear or branched, aliphatic or aromatic moiety having between 7 and 23 carbon atoms. The invention also relates to the novel compounds according to formulae (Ia) and (Ib), compositions comprising said compounds and the use of compounds and formulations as collectors for enriching of iron mineral.