Abstract: 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 wherein R1 is C9-C22 alkyl or alkenyl, which is linear or branched, R2 is H, C1-C4 alkyl, which is linear or branched, R3 is —X—NH2, H or C1-C4 alkyl, which is linear or branched, and X is C2-C4 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 1-X wherein R1 is C9-C15 alkyl, which is linear or branched, R2 is H, R3 is —X—NH2 and X is C2-C4 alkylene, which is linear or branched, is disclosed.