ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Optimization of scale inhibitors nitrilotriacetic acid and 1-hydroxyethylidene-1, 1-diphosphonic acid, effect of magnesium ions and temperature on calcium carbonate scale

V. K. Subramanian, M. Nirmala Devi, and K. Sanjiv Raj

Department of Chemistry, Annamalai University, Annamalainagar, India

E-mail: drvksau@gmail.com

Received: 9 July 2022  Accepted: 18 September 2022

Abstract:

The objective of this study was to investigate whether scale inhibitors’ performance vary with operational conditions and if so, how to develop a methodology for the same. Commonly used internal water treatment additive ingredients, nitrilotriacetic acid (NTA) and 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) were used and effect of temperature and presence of magnesium ions were taken to consideration for the optimization studies. Calcium carbonate (CaCO₃) was synthesized from calcium chloride (CaCl₂) solution by addition of sodium carbonate in the presence of NTA, HEDP and magnesium ions (Mg²⁺) between 60 and 100 °C. The samples were characterized using XRD, FTIR, and FE-SEM techniques. The study revealed HEDP is most effective in scale inhibition at 80–100 °C when 5 ml Mg²⁺ ion solution was used. The mechanism of inhibitor’s interaction on the crystallization revealed that the formation of CaCO₃ when its ionic product reach solubility product resulted in the stabilization and depletion of Ca²⁺ ions. This can result into liberation of more inhibitor into the system that can complex with the Mg²⁺. If the ionic product of Mg²⁺ and CO₃²⁻ ions reaches its solubility product formation of MgCO₃ initiates. This is a critical point as the further formation of CaCO₃ causes depletion in CO₃²⁻ ions and this initiates the dissolution of MgCO₃. This facilitated a positive synergistic effect on the stabilization of vaterite at 80–100 °C when 5 ml of Mg²⁺ solution was present in HEDP systems. The data also showed that it is essential to have an empirical investigation to ascertain the efficacy of internal treatment formulation for various operational conditions and feed water parameters.

Keywords: Scale inhibition; Water treatment; Inhibitor; Polymorphism; Morphology

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-022-02503-7

Chemical Papers 77 (2) 719–732 (2023)