On the role of sequestration and chelation in scale inhibition

• K. Popov¹, S. Prorekhin^1,2, E. Vishnikina¹, E. Afans’eva¹, E. Ovchinnikova¹, M. Trukhina¹, M. Oshchepkov³ and O. Yegoshina⁴

¹ JSC “Fine Chemicals R&D Centre” Krasnobogatyrskaya str. 42, b.1, 107258 Moscow, Russia
² R&D Company “Travers”, Electrozavodskaya str. 24, build.3, 107023 Moscow, Russia 3Mendeleev University of Chemical Technology of Russia, Miusskaya sq. 9, 125047 Moscow, Russia
³ Mendeleev University of Chemical Technology of Russia, Miusskaya sq. 9, 125047 Moscow, Russia
⁴ National Research University “Moscow Power Engineering Institute”, Krasnokazarmennaya str., 14, build. 1, 111250 Moscow, Russia

Abstract: The chemical speciations approach is applied to aquatic systems, including laboratory samples within a common NACE TM0374-2007 test, industrial samples and municipal TAP water of several cities. It is confirmed that chelation of calcium always takes place when polycarboxylates and phosphonates are used for scale mitigation. However, calcium sequestration is shown to have no relevance to the substoichiometric scale inhibition phenomenon. Chemical speciations analysis indicated the presence of calcite and barite nanoimpurities in some water samples and the lack of such solids as MgCO₃^solid, MgSO₄^solid, Gypsum, BaCO₃^solid and Al(OH)₃^solid. The presence of iron(III) nanohydroxyoxide impurities in all TAP water and laboratory samples is predicted due to chemical equilibria modeling. The ability of 1-hydroxyethane-1,1-bis(phosphonic acid) to dissolve selectively iron(III) nanohydroxyoxides in industrial and TAP water is demonstrated. Chelation of such trace cations as iron(III) is shown to change drastically the composition of nanoimpurities (dissolution of corresponding nanohydroxyoxides) in any water sample, and therefore to impact indirectly the rate of calcite and gypsum macroscale nucleation and deposition. Besides, chelation has been shown to reduce sufficiently the overall negative charge of antiscalants and their ability to prevent these particles from agglomeration. Advantages and limitations of chemical speciations application in water treatment and scale inhibition are discussed. The reliability of chemical equilibrium constants and of corresponding databases is critically analyzed.

Keywords: sequestration, chelation, chemical speciations, antiscalants, scale formation, chemical equilibrium data, stability constants, TAP water

Int. J. Corros. Scale Inhib., 2026, 15, no. 4, 1-39
doi: 10.17675/2305-6894-2026-15-4-1

Download PDF

Back to this issue content: 2026, Vol. 15, Issue 4 (pp. 1-... (in progress))