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International audience; Scaling process is the main problem encountered in industrial plants using water. Several factors, (pH, temperature, hydrodynamic conditions, metal surface, and especially, water composition),can affect the scaling kinetics of calcium carbonate (CaCO3), one of the main component of scaling. In addition, some foreign ions added can considerably modified the scaling rates. In thiswork, the inhibiting effects of Zn2+ and Cu2+ cations on CaCO3 precipitation were studied in a 50°F synthetic carbonic solution by using fast controlled precipitation (FCP) and scaling quartz crystal microbalance (SQCM) methods, for homogeneous and heterogeneous scaling deposition, respectively. Results showed that Zn2+ and Cu2+ ions are efficient, at high concentrations (≥ 1mg/L), to delay or even to prevent nucleation/growth of CaCO3. FCP measurements showed a complete inhibition of the homogeneous CaCO3 precipitation after 120 min in synthetic solutioncontaining 5 mg/L and 4 mg/L of Cu2+ and Zn2+, respectively. SQCM measurements showed that the surface coverage of the metallic substrate by a layer of CaCO3 is reduced when the amount of these cations increased. Zn2+ cations inhibited the heterogeneous CaCO3 precipitation moree fficiently than Cu2+. SEM and XRD results indicated that both cations affect calcium carbonatenucleation by changing the morphology of CaCO3 crystals