A synergistic effect of sodium gluconate and 2-phosphonobutane-1,2,4-tricarboxylic acid on the inhibition of CaCO3 scaling formation

Abstract

This study aims to investigate the synergistic effect of sodium gluconate (SG) in conjunction with 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) on the inhibition of CaCO3 formation. The kinetics and mechanism of inhibition were mainly examined based on light scattering spectrometer and characterization of CaCO3 scaling. Pilot tests using a formulation containing SG were also carried out to confirm the possibility of practical use. The laboratory results based on the light scattering spectrometer revealed that the presence of SG, as compared to PBTC alone, slowed down the germination rate of CaCO3 scaling by 4.3 times. The deposition rate determined by chronoamperometry analysis showed that the involvement of SG made a slight improvement to prevent the scaling deposition. The examinations on the obtained CaCO3 scaling by scanning electron microscopy, X-ray powder diffraction, and particle size distribution indicated that the presence of SG promoted the stabilization of metastable aragonite and vaterite phases. An inhibition mechanism is thus proposed that SG could recognize and react with calcium ions, resulting in a slow germination rate of CaCO3 scaling. Moreover, SG also confers more charges to calcite nuclei than PBTC, improving calcite distortion as a result of relatively low surface energy. Pilot tests showed that the corrosion and deposition rates in the presence of SG/PBTC at seven cycles of concentration were 2.33MPY and 0.069MCM, respectively, being better than that with PBTC alone. Sodium gluconate, providing an excellent capability towards scaling and corrosion inhibition with controlled microorganism growth, could be an effective substitute to phosphate-based scaling inhibitor in a chemical formulation for cooling water system.