The effect of crosslinking additives and molecular weight of starch depressants on pyrrhotite and pentlandite floatabilities

•Synthesized starches (paste starches and crosslinked starch) can depress hexagonal pyrrhotite and pentlandite at pH 9.2.•Paste starch with higher molecular weight and crosslinked starch showed a certain selectivity in a binary mineral system.•The presence of metal hydroxylate species on both minerals allowed their chemical interaction with starch groups according to surface analysis.•Crosslinking additives within starch structure promoted a mixed interaction with mineral surfaces via chemisorption and electrostatic attraction.