Green Descaling of Gypsum Deposits in Industrial Pipelines: A Chelant-Free Approach

Gypsum scale (CaSO₄·2H₂O) is a persistent and costly problem in industries such as oil and gas, power generation, and water treatment. Conventional removal strategies rely heavily on aminopolycarboxylate chelants such as EDTA, which, despite their effectiveness, present significant environmental drawbacks due to their persistence, potential for heavy metal mobilization, and high treatment costs. This study introduces a fully chelant-free gypsum remediation method based on potassium carbonate (K₂CO₃) combined with biodegradable carboxymethyl cellulose (CMC). Using in situ FT-IR spectroscopy, SEM/XRD characterization, and geochemical speciation coupled with microkinetic modeling, we elucidate the kinetics, mechanisms, and polymorph-selective pathways governing gypsum conversion. Carbonate bases, particularly K₂CO₃, achieved up to 96% conversion under ambient conditions, predominantly forming vaterite, which exhibited a markedly slower transformation to calcite compared to bicarbonate systems. The addition of CMC at optimized dosage prevented secondary blockages by maintaining converted particles in suspension, with only minimal impact on conversion efficiency. By integrating a chelant-free K₂CO₃ conversion process with mechanistic control over CaCO₃ polymorphism and a biodegradable polymer-assisted dispersion step, this study delivers the first unified gypsum scale remediation strategy that achieves substantial cost savings, offering a promising chelant-free alternative for sustainable industrial flow assurance.