The interaction between CaOH+ ions and pyrite, marcasite and pyrrhotite surfaces was studied using density functional theory (DFT) calculations. The calculated results show that the adsorption energy of CaOH+ on the marcasite surface is the largest, -384.65 kJ/mol; then pyrrhotite, -346.61 kJ/mol; pyrite, -276.62 kJ/mol. After CaOH+ adsorption, oxygen atom is bonded to one iron atom, calcium atom is bonded to two sulfur atoms of pyrite surface. And there exists a Ca-Fe2 anti-bonding on the pyrite surface. For marcasite, oxygen atom is bonded to one iron atom, calcium atom is bonded to two sulfur atoms of marcasite surface. As for pyrrhotite, calcium atom is only attached to three sulfur atoms of pyrrhotite surface. The charge transfers occur from CaOH+ to sulfides surfaces. The value of charge transfer from CaOH+ to marcasite surface is the largest, then pyrite, pyrrhotite in order. However, formation of Ca-Fe2 anti-bonding on the pyrite surface weakens the reaction of CaOH+ with pyrite. (c) 2015 Elsevier B.V. All rights reserved.