Enhanced Calcium Carbonate Scale Mitigation by Binary Carboxylate-Phosphonate Antiscalant Blends: Formulation Optimization and Mechanistic Insights

Calcium carbonate scaling poses a persistent challenge across diverse industrial water systems. Binary blends of carboxylate-based polymers and phosphonate-based molecules may enhance inhibition through complementary interactions between different functional groups, yet a systematic understanding of the interplay among formulation variables under varying water chemistry remains limited. Herein, we employed response surface methodology (RSM) coupled with a Box-Behnken design (BBD) to investigate and optimize the inhibition efficiency of two representative binary antiscalant systems across varying blend proportions, total dosage, and initial Ca2+ concentration. Second-order polynomial models were established to quantify main and interaction effects. Initial Ca2+ concentration had the strongest main effect in both blend systems. The PESA/PBTCA and HPMA/PAPEMP systems exhibited excellent model fit (R2 > 0.98, predicted R2 > 0.85) and pronounced interaction between blend proportions and total dosage. Binary antiscalant blends could achieve a performance improvement of more than 20% compared to commercial products. Kinetic analysis together with solid-phase analysis provided mechanistic insights into the inhibition behavior of the binary blends. These findings demonstrate that rational combination of phosphorus-free polycarboxylates and phosphorus-containing phosphonates provides an effective strategy for enhancing CaCO3 scale inhibition, while RSM offers a practical tool for formulation optimization under different water chemistry conditions.