A new insight into the mechanism of the scale inhibition: DLS study of gypsum nucleation in presence of phosphonates using nanosilver dispersion as an internal light scattering intensity reference

Abstract

Scaling in reverse osmosis facilities, boilers, heat exchangers, evaporation plants, and oilfield applications is a serious problem worldwide. A widely used solution for controlling scale deposition is an application of chemical inhibitors. However, irrespective of the broad and a long-term antiscalant application, the mechanisms of scale inhibition are still the matter of discussions.In order to provide a new insight into the mechanism of the scale inhibition, a novel dynamic light scattering (DLS) special technique is used to study the bulk supersaturated gypsum aqueous solutions during the induction period. It is based on the standard Ag nanoparticles (ARGOVIT) injection into the supersaturated gypsum solution. These nanoparticles act as an internal indifferent light scattering intensity reference, and provide a semiquantitative measurement of a relative gypsum particles content in a blank solution and in the system treated with phosphonates: amino-tris(methylenephosphonic acid), ATMP; 1-hydroxyethane-1,1-bis(phosphonic acid), HEDP; 2-phosphonobutane-1,2,4-tricarboxylic acid, PBTC. It is found that ATMP sufficiently reduces the number of gypsum nuclei, spontaneously formed in the supersaturated solutions. The less effective inhibitors of gypsum scaling HEDP and PBTC also reduce the gypsum nuclei number, but to a less extent. A tentative nonconventional mechanism of scale inhibition in the bulk supersaturated aqueous solutions of gypsum is proposed.