The invention relates to a method for manufacturing a concentrate enriched in iron mineral content from an ore, which contains an iron mineral and silicate, by reverse flotation, which method comprises the step of (c) adding a compound of formula I

##STR00001## wherein R.sup.1 is C.sub.9-C.sub.22 alkyl or alkenyl, which is linear or branched, R.sup.2 is H, C.sub.1-C.sub.4 alkyl, which is linear or branched, R.sup.3 is XNH.sub.2, H or C.sub.1-C.sub.4 alkyl, which is linear or branched, and X is C.sub.2-C.sub.4 alkylene, which is linear or branched, or a salt of a protonated compound of formula I and an anion, to a prepared aqueous pulp of the ore and optionally one or more flotation auxiliaries to obtain an aqueous mixture. Furthermore, a method for manufacturing a specific group of compounds of formula I, i.e. compounds of formula I-X

##STR00002## wherein R.sup.1 is C.sub.9-C.sub.15 alkyl, which is linear or branched, R.sup.2 is H, R.sup.3 is XNH.sub.2 and X is C.sub.2-C.sub.4 alkylene, which is linear or branched, is disclosed.