Synergistic effect of sulfosalicylic acid and polyaspartic acid as an effective inhibitor of calcium phosphate scale

In this work, we address the critical challenge of calcium phosphate scaling in seawater desalination by developing a hybrid scale inhibitor composed of polyaspartic acid (PASP) and 5-sulfosalicylic acid (SSA). The static scale inhibition experiments and the electrochemical measurements are used to investigate its scale inhibiting properties. Compared to single component of PASP and SSA, the blends demonstrate a significantly improvement for the scale inhibition performance, achieving a maximum inhibition rate of nearly 85 % at 12 mg/L PASP + 6 mg/L SSA. The mechanism of scale inhibition is investigated by surface analysis and the molecular dynamic (MD) simulation. The results suggest that the hybrid PASP/SSA is an effective inhibitor of calcium phosphate crystal formation through an increase in chelation and repulsion of negative charges on the crystal surface. Additionally, MD simulations demonstrate that the combination of PASP and SSA enhances the interaction energy between functional groups and the calcium scale surface. The formation of calcium phosphate decreases by lowering the coordination number of calcium ions and phosphate ions.