Green Inhibitor Performance against CaCO3Scaling: Rate-Modeling Aided Test Procedure

Abstract

Green inhibitors (GI) are eco-friendly organic molecules capable of inhibiting the nucleation and precipitation of solids, like CaCO3 minerals. Although increasingly used in technical settings, their individual selection and dosage guidelines are hardly available and mostly based on empirical observations. In this study the performance of GI, based on aspartate, maleic, and acrylic acid, in concentrations between 0.5 and 10 mg L-1, was assessed using a newly designed experimental test procedure. The inhibition of CaCO3 scaling introduced by CO2 degassing was quantified by thermodynamic modeling. The coupled CO2 degassing and CaCO3 precipitation rate models and time-resolved experimental data sets show (i) GI performance to be independent of CO2 degassing rates, (ii) an upper supersaturation limit for calcite approaching amorphous CaCO3 solubility, (iii) average efficiencies reaching ∼70-100% and normalized retardation time (delay of precipitation relative to the control test) of ∼3-6 times at a GI concentration of 10 mg L-1, and (iv) polyaspartate being able to modulate calcite to serve as a template for vaterite growth depending on polymer chain-length, d/l ratio, and ion diffusion rate of the GI. Our rate-model-aided test procedure provides a compact and fast tool to assess and quantify GI performances against CaCO3 scaling to be properly selected and individually tuned.