In this paper, The Zn2+ inhibition mechanism on CaCO3 precipitation was investigated. It is well established that Zn2+ delays the precipitation, even at very low concentrations; however, the related mechanism remains not well understood. This paper proposes a novel thermodynamic mechanism to explain the key inhibiting pre-precipitation step of Zn2+ on CaCO3 precipitation. It is based on the hypothesis of the Zn2+/OH-spontaneous complexation reaction to form ZnOH+. This OH- removal by Zn2+, an established Lewis acid, prevents the HCO3-/OH- reaction. These predictions were verified thermodynamically. It confirms the spontaneous formation and predominance of ZnOH+ complex in the 7.0-9.0 pH range. This Zn2+ inhibiting property is strengthened by other complex formation (ZnCO3(aq)center dot, Zn(CO3)(2)(2-), Zn(OH)(2)(center dot)((aq))) and by the absence of any Zn precipitate at low Zn2+ concentrations. Furthermore, the comparison of chemical-electrochemical experimental methods clarified their differences and evidenced more the thermodynamic and stoichiometric inhibition mechanisms. (C) 2016 Elsevier B.V. All rights reserved.