Scale inhibition properties of metallic cations on CaCO3 formation using fast controlled precipitation and a scaling quartz microbalance.

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 components of scaling. In addition, some foreign ions added can considerably modify the scaling rates. In this work, 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 (=1 mg/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 solution containing 5 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 more efficiently than Cu²⁺. SEM and XRD results indicated that both cations affect calcium carbonate nucleation by changing the morphology of CaCO3 crystals. [ABSTRACT FROM AUTHOR]