Barite crystallization in presence of novel fluorescent-tagged antiscalants

Abstract

Formation of barite crystals in a bulk supersaturated aqueous solution at ambient temperature is studied in presence of two novel fluorescent-tagged antiscalants: a bisphosphonate 1-hydroxy-7-(6-methoxy-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)heptane-1,1-diyldi-(phosphonic acid), HEDP-F, and a co-polymer of N-allyl-4-methoxy-1,8-naphtalimide with acrylic acid, PAA-F1 by fluorescent microscopy, scanning electron microscopy (SEM), turbidimetry, dynamic light scattering (DLS) and a particle counter technique. Both scale inhibitors at a 20 mg·dm -3 dosage are found to be effective in supersaturated BaSO 4 solutions with saturation index (SI) 10 at 25°C (0.001 mol·dm -3 ). Herewith PAA-F1 reveals a higher efficacy than HEDP-F. At the same time a dramatic impact of foreign background "nanodust" particles on antiscalant efficacy is detected and interpreted in terms of barite nucleation. It is demonstrated, that barite nucleation takes place exclusively on "nanodust" particles as a bulk heterogeneous process. Thus an antiscalant molecule acts not so much as barite nuclei surface modifiers, but as the modifiers of "nanodust" particles. It is shown that inter alia the lower efficacy of HEDP-F relative to PAA-F1 is associated with insoluble barium salts formation by the former reagent (tentatively by Ba 2 HEDP-F·nH 2 O or BaH 2 HEDP-F·mH 2 O). Thus an efficacy evaluation may be strongly affected by the way of antiscalant introduction into the system. Being initially added to the barium brine both antisclants demonstrate greater difference in barite scale inhibition, than in the case of the sulfate brine. Both fluorescent-tagged reagents reveal perfectly an antiscalant location on barite crystals. Despite expectations they cover BaSO 4 crystal surface uniformly, and indicate no special concentration of antiscalant on crystal's kinks, edges etc. Thus the scale inhibitors affect rather the primary nucleation step of barite solid phase formation than the secondary one (macro-crystal growth phase).

Gypsum Crystallization during Reverse Osmosis Desalination of Water with High Sulfate Content in Presence of a Novel Fluorescent-Tagged Polyacrylate

“…However, the visualization of PAA-F1 molecules indicates clearly that there is no definite interaction between antiscalant and gypsum along the brine RO treatment. The same result was obtained earlier for HEDP-F/gypsum RO desalination process [22] as well as for batch static experiments with gypsum [20] and barite [21] in presence of HEDP-F. A tentative mechanism of gypsum inhibition in RO membrane fouling is proposed [22] and our present data for PAA-F1 give a further approval to this hypothesis.…”

“…It is demonstrated that the fluorescent-tagged antiscalants may become very powerful tools in membrane scaling inhibition studies.However, in spite of numerous relevant studies, some controversy regarding both the dominant scaling mechanism in particular situations and the mechanism of antiscalant activity still exists [12][13][14][15][16][17][18]. Recent reviews on scale formation control in RO technologies [6,19] mention two main hypothetic mechanisms of inhibition: (i) antiscalant molecules adsorb on the active growth sites at the crystal surface of sparingly soluble inorganic salt and retard nucleation and crystal growth by distorting its crystal structure; (ii) antiscalant molecules provide similar electrostatic charge, and thus, repulsion between particles prevents them from agglomeration.Nevertheless, our recent static [20,21] and RO [22] experiments operating gypsum as a model scale in presence of a novel fluorescent-tagged bisphosphonate antiscalant 1-hydroxy-7-(6-methoxy-1,3dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)heptane-1,1-diyl-bis(phosphonic acid), HEDP-F (H 4 hedp-F) revealed a paradoxical effect: an antiscalant does not interact with gypsum at all, but provides nevertheless retardation of corresponding deposit formation. According to the classical crystallization theory [23], this is possible only in the case, when gypsum passes bulk heterogeneous nucleation, and exactly the "nanodust" plays the role of the solid phase template.…”

“…Nevertheless, our recent static [20,21] and RO [22] experiments operating gypsum as a model scale in presence of a novel fluorescent-tagged bisphosphonate antiscalant 1-hydroxy-7-(6-methoxy-1,3dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)heptane-1,1-diyl-bis(phosphonic acid), HEDP-F (H 4 hedp-F) revealed a paradoxical effect: an antiscalant does not interact with gypsum at all, but provides nevertheless retardation of corresponding deposit formation. According to the classical crystallization theory [23], this is possible only in the case, when gypsum passes bulk heterogeneous nucleation, and exactly the "nanodust" plays the role of the solid phase template.…”

“…Indeed, it is demonstrated that HEDP-F molecules being immersed into the stock solution (undersaturated against gypsum) occupy a significant part of "nanodust" crystallization centers and form there their own solid phase Ca 2 hedp-F·nH 2 O. However, polyacrylates are much less sensitive to calcium environment than phosphonates [20,21]. In this way, it was reasonable to study the traceability of phosphorus-free fluorescent polymeric antiscalants in RO process.The present study is focused on the scale inhibitor visualization during RO treatment of model water sample, with high sulfate content, in the presence of a fluorescent antiscalant-1,8-naphthalimide-tagged polyacrylate, PAA-F1, Figure 1.Crystals 2020, 10, x FOR PEER REVIEW 2 of 17…”

“…Indeed, it is demonstrated that HEDP-F molecules being immersed into the stock solution (undersaturated against gypsum) occupy a significant part of "nanodust" crystallization centers and form there their own solid phase Ca 2 hedp-F·nH 2 O. However, polyacrylates are much less sensitive to calcium environment than phosphonates [20,21]. In this way, it was reasonable to study the traceability of phosphorus-free fluorescent polymeric antiscalants in RO process.…”