Efficiency of five scale inhibitors on calcium carbonate precipitation from hard water: Effect of temperature and concentration

The effects of temperature and concentration of five scale inhibitors (three polyphosphates, one polyphosphonate and one polycarboxylate) on calcium carbonate (CaCO3) precipitation from hard water are reported in this paper. The CaCO3 precipitation from calcocarbonically pure water was induced by imposed potential and studied on gold electrode by chronoamperometry technique. With this technique, the efficiency of preventing CaCO3 precipitation was determined for all scale inhibitors. The composition of these scale inhibitors were analysed by ICP-AES technique and no or few toxic elements were detected. For each tested inhibitor, the optimal concentration was determined and their efficiency was studied in the range temperature 20-50 °C. SEM/EDS and Raman spectroscopy techniques were used to analyse the microstructure and the elemental composition of the formed scale. Only polyphosphonates remain efficient at 50 °C. All the tested inhibitors were shown to act by threshold effect.