Mechanistic study of the synergetic inhibiting effects of Zn2+, Cu2+ and Mg2+ ions on calcium carbonate precipitation

Water Res. 2020 Nov 1:186:116323. doi: 10.1016/j.watres.2020.116323. Epub 2020 Aug 20.

Abstract

This research work investigates the Zn2+, Cu2+ and Mg2+ inhibiting effects on CaCO3 precipitation. The results demonstrate a synergetic effect of the Cu2+-Zn2+-Mg2+ mixture by a long (infinite) induction time. The individual inhibition action of Cu2+, Zn2+ and Mg2+ is well-established, but it is much lower than the effect of the mixture. A dual mechanism is suggested, where the inhibition effect is attributed to the cation interaction with hydroxide anions (OH-) to form the corresponding CuOH+, ZnOH+ and MgOH+ hydrocomplexes. This, in return, prevents and delays the CaCO3 precipitation. The pH range plays a crucial role in the effect where Cu2+ prevents the precipitation below a pH of 7.5. Zn2+ reacts in the pH range of 7.5 - 8.8, while Mg2+ completes the synergy by inhibiting the precipitation at high pH values. The results indicate that the inhibition efficiency by Mg2+ is improved in the presence of both Cu2+ and Zn2+ ions. These predictions were verified by theoretical calculations of thermodynamic equilibria.

Keywords: CaCO(3) precipitation; Induction time; Scale formation; Scale inhibition; Synergetic inhibition mechanism.

MeSH terms

  • Calcium Carbonate*
  • Copper
  • Hydrogen-Ion Concentration
  • Thermodynamics
  • Zinc*

Substances

  • Copper
  • Calcium Carbonate
  • Zinc