Impact of boron hybridization types on polyborates scale inhibition in circulating water systems

Abstract

Mineral deposits in circulating water circuits impair thermal efficiency and restrict fluid flow, thereby threatening production safety. The excellent performance of traditional scale inhibitors, such as phosphonates, is accompanied by nitrogen and phosphorus loads in concentrated water, emphasizing the necessity for sustainable alternatives. This study proposes that polyborates have the potential to serve as a new generation of sustainable scale inhibitors, however, their structural optimization lacks theoretical guidance. Therefore, this research examines the electronic distribution and bonding characteristics of different boron hybridization types, specifically [BO₂], [BO₃], and [BO₄] units, and their effects on the scaling inhibition process. The results reveal that sp-hybridized [BO₂] units are resistant to hydrolysis, and their chemical stability leads to unsatisfactory scale inhibition performance. In contrast, sp²-hybridized [BO₃] units exhibit affinity for calcite, inducing the transformation of calcite into vaterite, thereby suppressing scale deposition. The hydrolysis of oxygen-bridged sp²-hybridized boron to form sp³-hybridized [BO₄] units represents a precursor step in the complete hydrolysis and dehydrogenation of polyborates. The resulting borate ions complex with calcium in the form of CaBO₃, effectively inhibiting calcite crystal nucleation. When a solution contains 0.03 mmol/L of B₅O₆(OH)₄⁻, which includes four [BO₃] units, it can reduce the growth rate of calcite crystals by up to 65.4 %. Understanding the relationship between boron hybridization types and inhibition mechanisms provides critical insights for designing optimal polyborates, representing a significant advancement in the development of sustainable water treatment solutions.