Effectiveness of Green Additives vs Poly(acrylic acid) in Inhibiting Calcium Sulfate Dihydrate Crystallization

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%

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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“…Therefore, environmentally-friendly and biodegradable “green” inhibitors that are phosphate-free and nitrogen-free have recently gained more attention. Rabizadeh et al, [ 100 ] studied the alternative green inhibitors poly(epoxysuccinic acid) and poly(aspartic acid) to control BaSO 4 scaling. Yu et al, [ 101 ] reported the green anti-scalant, carboxymethyl cellulose, to prevent BaSO 4 scaling.…”

Section: Reverse Osmosismentioning

confidence: 99%

Frontiers of Membrane Desalination Processes for Brackish Water Treatment: A Review

et al. 2021

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Climate change, population growth, and increased industrial activities are exacerbating freshwater scarcity and leading to increased interest in desalination of saline water. Brackish water is an attractive alternative to freshwater due to its low salinity and widespread availability in many water-scarce areas. However, partial or total desalination of brackish water is essential to reach the water quality requirements for a variety of applications. Selection of appropriate technology requires knowledge and understanding of the operational principles, capabilities, and limitations of the available desalination processes. Proper combination of feedwater technology improves the energy efficiency of desalination. In this article, we focus on pressure-driven and electro-driven membrane desalination processes. We review the principles, as well as challenges and recent improvements for reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and membrane capacitive deionization (MCDI). RO is the dominant membrane process for large-scale desalination of brackish water with higher salinity, while ED and MCDI are energy-efficient for lower salinity ranges. Selective removal of multivalent components makes NF an excellent option for water softening. Brackish water desalination with membrane processes faces a series of challenges. Membrane fouling and scaling are the common issues associated with these processes, resulting in a reduction in their water recovery and energy efficiency. To overcome such adverse effects, many efforts have been dedicated toward development of pre-treatment steps, surface modification of membranes, use of anti-scalant, and modification of operational conditions. However, the effectiveness of these approaches depends on the fouling propensity of the feed water. In addition to the fouling and scaling, each process may face other challenges depending on their state of development and maturity. This review provides recent advances in the material, architecture, and operation of these processes that can assist in the selection and design of technologies for particular applications. The active research directions to improve the performance of these processes are also identified. The review shows that technologies that are tunable and particularly efficient for partial desalination such as ED and MCDI are increasingly competitive with traditional RO processes. Development of cost-effective ion exchange membranes with high chemical and mechanical stability can further improve the economy of desalination with electro-membrane processes and advance their future applications.

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“…The first studies were focused on the inhibition of the crystallization, testing additive compounds that can effectively slow nucleation and growth [11,12]. Investigating the effect of various inhibitors and reaction conditions is a popular topic even today [13][14][15][16][17][18]. However, to fully understand the mechanisms of the crystallization of gypsum in presence of various inhibitors, the crystallization kinetics from pure (inhibitor-free) solutions is needed to be understood and described.…”

Section: Introductionmentioning

confidence: 99%

The kinetics of the precipitation of gypsum, CaSO4·2H2O, over a wide range of reactant concentrations

Ziegenheim

Peintler

Pálinkó

et al. 2020

Reac Kinet Mech Cat

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In this work, the precipitation kinetics of gypsum was studied over a wide range of degree of supersaturation at 25 °C in the reaction Na 2 SO 4(aq) + CaCl 2(aq) + 2 H 2 O → 2 NaCl (aq) + CaSO 4 ⋅ 2 H 2 O (S) with the aim of constructing a comprehensive kinetic model for CaSO 4 •2H 2 O (s) formation that is valid from the lowest (0.04 M) to the highest (0.20 M) feasible initial reactant concentration. To monitor the variation of reactant concentrations during the precipitation reaction, conductometry was employed. For reasonably slow reactions (where the establishment of the equilibrium potential on the indicator electrode was possible), the measurements were supplemented by a Ca-ion-selective electrode. The structure and morphology of the precipitating solids was characterized by XRD and SEM. The induction period was found to decrease about two orders of magnitude with the increasing reactant concentration. It was experimentally established that the influence of the so-called wall effect is of secondary importance. Using the data collected, a kinetic model have been suggested that can describe the entire precipitation process of gypsum simultaneously, incorporating nucleation and crystal growth, in a wide concentration range. Our calculations strongly suggest that the inclusion of the CaSO 4(aq) ion pair is necessary for the appropriate kinetic description of gypsum precipitation.

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Effectiveness of Green Additives vs Poly(acrylic acid) in Inhibiting Calcium Sulfate Dihydrate Crystallization

Abstract: This is a repository copy of Effectiveness of Green Additives vs Poly(acrylic acid) in Inhibiting Calcium Sulfate Dihydrate Crystallization.

Cited by 44 publications

References 61 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

Frontiers of Membrane Desalination Processes for Brackish Water Treatment: A Review

The kinetics of the precipitation of gypsum, CaSO4·2H2O, over a wide range of reactant concentrations

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