Synthesis and evaluation of phosphate-free antiscalants to control CaSO 4 ·2H 2 O scale formation in reverse osmosis desalination plants

Ali, Shaikh A.; Kazi, Izzat Wajih; Rahman, Faizur

doi:10.1016/j.desal.2014.11.006

Cited by 67 publications

(25 citation statements)

References 23 publications

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“…Among these, polycarboxylates (polyacrylates, polyaspartates, etc.) and phosphonates are found to be highly efficient [6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

“…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. The gypsum scale was taken as a model of a sparingly soluble salt due to: (i) its importance for the RO and other water treatment technologies [10][11][12][13][14][15][16]; (ii) its poor dependence on pH; (iii) its easily detectable crystal shapes; and (iv) the nucleation of gypsum has been investigated extensively in the past [10,11,14,[16][17][18][24][25][26][27][28][29][30][31][32][33]. On the other hand PAA-F1 is expected to be a better antiscalant for CaSO4·2H2O deposits relative to HEDP-F.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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Gypsum scaling in reverse osmosis (RO) desalination process is studied in presence of a novel fluorescent 1,8-naphthalimide-tagged polyacrylate (PAA-F1) by fluorescent microscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS) and a particle counter technique. A comparison of PAA-F1 with a previously reported fluorescent bisphosphonate HEDP-F revealed a better PAA-F1 efficacy, and a similar behavior of polyacrylate and bisphosphonate inhibitors under the same RO experimental conditions. Despite expectations, PAA-F1 does not interact with gypsum. For both reagents, it is found that scaling takes place in the bulk retentate phase via heterogeneous nucleation step. The background "nanodust" plays a key role as a gypsum nucleation center. Contrary to popular belief, an antiscalant interacts with "nanodust" particles, isolating them from calcium and sulfate ions sorption. Therefore, the number of gypsum nucleation centers is reduced, and in turn, the overall scaling rate is diminished. It is also shown that, the scale formation scenario changes from the bulk medium, in the beginning, to the sediment crystals growth on the membrane surface, at the end of the desalination process. 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. 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 trace...

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“…Among these, polycarboxylates (polyacrylates, polyaspartates, etc.) and phosphonates are found to be highly efficient [6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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“…Naturally, an increase in the antiscalant dose led to an increase in the amount of adsorbed antiscalant and a decrease in the rate of crystal growth. The same applies to the conclusions about the patterns of adsorption of antiscalants on seed crystals in experiments in a closed volume [22][23][24][25][26][27]. A number of researchers are currently using the concept of induction period (the time of nucleation of crystals of a visible size in the presence of an antiscalant at high values of supersaturation) to evaluate the effectiveness of antiscalants [24].…”

Section: Introductionmentioning

confidence: 99%

Use of a Fluorescent Antiscalant to Investigate Scaling of Reverse Osmosis Membranes

Oshchepkov

Первов

Golovesov

et al. 2019

Membr. Membr. Technol.

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Knowledge of the scaling mechanism makes it possible to develop effective means to control scaling and improve the membrane performance, increasing the recovery. This paper presents new approaches to the study of the mechanism of scaling in the presence of polymeric inhibitors (antiscalants); the adsorption of antiscalant molecules on the crystal and membrane surfaces has been investigated. The relations of the antiscalant adsorption rates to the antiscalant dose and the calcium carbonate scaling rate have been revealed. For the first time, the inhibition process was "visualized" by using a fluorescent antiscalant containing a fluorescent moiety-a copolymer of N-allyl-4-methoxy-1,8-naphthalamide and acrylic acid (PAA-F1). The examination of the surfaces of crystals and membranes by scanning electron and fluorescence microscopy showed new unexpected results: the antiscalant is adsorbed on the membrane surface and on the surface of calcite crystals formed. Fluorescence turned out to be more intense and noticeable on the surface of crystal faces than inside the crystal. During the nucleation phase, the "dark" part of the crystal lattice is formed and then begins to be covered with a "luminous" layer of the fluorescent antiscalant, which blocks further crystal growth. During experiments with antiscalant solutions in distilled water, the antiscalant was found to be adsorbed on the membrane surface in the absence of calcium ions. In experiments in which the antiscalant was added into the original tap water, it was adsorbed on the surface of the resulting crystals, not on the membrane. The visualization of the crystal growth inhibition process opens up new possibilities for studying the mechanism of scaling and developing of new technologies to control scaling.

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“…This does not allow the efficient use of newly developed antiscalants [14][15][16][17][18][19][20]. The substantiation of the use of antiscalants and comparison of their effectiveness should be based on tests under conditions corresponding to those created in membrane channels during the operation of membrane devices [18][19][20][21][22][23]. In some cases, the introduction of already formed seed crystals into a supersaturated solution is used [7,12], after which the crystal growth rates in the presence of various antiscalants are determined.…”

Section: Introductionmentioning

confidence: 99%

“…In other experiments, an antiscalant is added to a supersaturated solution, and the effectiveness of the antiscalant is determined by the value of supersaturation, at which the nucleation onset becomes "visible" (instrumentally detected concentration "jumps" of calcium or colloidal particles) [15]. Therefore, it is extremely important to determine the true conditions for the formation of crystals in dead areas [23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Investigation of the Scaling Mechanism in Membrane Modules and the Influence of Antiscalants on This Process

Первов

Andrianov

Golovesov

et al. 2019

Membr. Membr. Technol.

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Knowledge of the mechanism of deposition of sparingly soluble salts (scaling) in reverse osmosis membrane devices is extremely important for the selection of means of controlling the scaling and increasing the recovery. This study has made it possible to take a fresh look at the mechanism of scaling and the role of antiscalants in the inhibition of this process. The development of the experimental procedure is based on the idea that the first phase of crystallization-nucleation-is homogeneous; that is, it occurs in the "dead" areas in the bulk of the concentrate at high values of calcium carbonate supersaturation. After formation, the crystals are removed from the "dead" areas and deposited on the membrane surface, like other suspended particles contained in the feed water. The paper also presents the results of a study of the adsorption of polymeric antiscalants on crystal surfaces during nucleation and crystal growth on the membrane. The experimentally revealed relations of the adsorption rates of antiscalants to the antiscalant dose, the calcium carbonate formation rate, the nucleation rate, and the total surface of the seed crystals formed are presented. An experimental procedure is described that makes it possible to determine the concentration of dissolved salts in the dead areas and calculate the supersaturation values corresponding to the onset of crystallization from antiscalantfree water and water in the presence of scale inhibitors in various amounts.

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Synthesis and evaluation of phosphate-free antiscalants to control CaSO 4 ·2H 2 O scale formation in reverse osmosis desalination plants

Cited by 67 publications

References 23 publications

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

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

Use of a Fluorescent Antiscalant to Investigate Scaling of Reverse Osmosis Membranes

Investigation of the Scaling Mechanism in Membrane Modules and the Influence of Antiscalants on This Process

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