Gypsum Scale Formation Research Articles

Enhancement of Polyacrylate Antiscalant Activity during Gypsum Deposit Formation with the Pretreatment of Aqueous Solutions with Spruce Wood Shavings.

Considerable efforts are made worldwide to reduce inorganic scale in reverse osmosis plants, boilers and heat exchangers, evaporators, industrial water systems, geothermal power plants and oilfield applications. These include the development of new environmentally friendly antiscalants and the improvement of conventional ones. The present report is dedicated to the unconventional application of spruce wood shavings in combination with polyacrylate (PAA-F1) in a model case of gypsum scale formation. The electrical conductivity of freshly prepared gypsum solutions with a saturation SI = 2.3 and a concentration of 0.05 mol·dm-3 was analyzed over time at 25°C. It is demonstrated that the small amounts of wood shavings (0.1% by mass) alone, after being in contact with CaCl2 and Na2SO4 stock solutions for 15 min, increase the induction time tind by 25 min relative to the blank experiment (tindblank). In the presence of PAA-F1 (0.1 mg·dm-3), the difference Δtind = tind - tindblank constitutes 110 min, whereas the sequential treatment of the stock solutions with the shavings followed by PAA-F1 injection gives Δtind = 205 min. The observed synergism is associated with the selective removal of colloidal Fe(OH)3solid and Al(OH)3solid nanoimpurities from the stock solutions via their sorption to the well-developed surface of wood. Wood shavings therefore represent a very promising and environmentally friendly material that can significantly improve the effectiveness of conventional antiscalants.

Gypsum scale formation and inhibition kinetics with implications in membrane system

Water desalination using membrane technology is one of the main technologies to resolve water pollution and scarcity issues. In the membrane treatment process, mineral scale deposition and fouling is a severe challenge that can lead to filtration efficiency decrease, permeate quality compromise, and even membrane damage. Multiple methods have been developed to resolve this problem, such as scale inhibitor addition, product recovery ratio adjustment, periodic membrane surface flushing. The performance of these methods largely depends on the ability to accurately predict the kinetics of mineral scale deposition and fouling with or without inhibitors. Gypsum is one of the most common and troublesome inorganic mineral scales in membrane systems, however, no mechanistic model is available to accurately predict the induction time of gypsum crystallization and inhibition. In this study, a new gypsum crystallization and inhibition model based on the classical nucleation theory and a Langmuir type adsorption isotherm has been developed. Through this model, it is believed that gypsum nucleation may gradually transit from homogeneous to heterogeneous nucleation when the gypsum saturation index (SI) decreases. Such transition is represented by a gradual decrease of surface tension at smaller SI values. This model assumes that the adsorption of inhibitors onto the gypsum nucleus can increase the nucleus superficial surface tension and prolong the induction time. Using the new model, this study accurately predicted the gypsum crystallization induction times with or without nine commonly used scale inhibitors over wide ranges of temperature (25–90 °C), SI (0.04–0.96), and background NaCl concentration (0–6 mol/L). The fitted affinity constants between scale inhibitors and gypsum show a good correlation with those between the same inhibitors and barite, indicating a similar inhibition mechanism via adsorption. Furthermore, by incorporating this model with the two-phase mineral deposition model our group developed previously, this study accurately predicts the gypsum deposition time on the membrane material surfaces reported in the literature. We believe that the model developed in this study can not only accurately predict the gypsum crystallization induction time with or without scale inhibitors, elucidate the gypsum crystallization and inhibition mechanisms, but also optimize the mineral scale control in the membrane filtration system.

Geochemical Assessment of Gypsum Scale Formation in the Hydrated Lime Neutralization Facility of the Daedeok Mine, South Korea

Scale is widely observed in the hydrated lime mine drainage treatment plant of the Daedeok Mine in South Korea. In order to understand the environment in terms of the formation of scale minerals, scale and water were collected from the AMD treatment facility and analyzed. In addition, the saturation index was calculated based on geochemical modeling to predict the minerals that could be produced in the AMD treatment facility, and the results were then compared with an analysis of onsite scale minerals. Furthermore, the onsite mine drainage was neutralized from pH 3 to pH 9 in the laboratory, and the precipitates produced were identified. The changes in the Ca2+ and SO42− concentrations were also identified over time for each pH. The results of geochemical modeling predicted the possible precipitation of gypsum, anhydrite, and bassanite after AMD neutralization. Scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS) analysis results showed that the main mineral in scale formed at the AMD treatment facility was gypsum, produced by the reaction of SO42− and Ca2+ from lime during AMD. The laboratory neutralization experiment showed that gypsum was produced in all neutralization ranges from pH 3 to pH 9, and the higher the neutralization pH, the greater the amount of gypsum produced. It was demonstrated that simulated amounts of 2 g/L and 7 g/L gypsum at pH 5 and 9 were well matched with the experimental results. Iron (Fe), a major pollutant in the mine drainage system, was rapidly precipitated in the form of iron hydroxides after neutralization. As gypsum is produced slowly and continuously for a long period of time, it results in the growth of scale throughout the flow path. As a method of minimizing gypsum production in the AMD treatment facility using hydrated lime, it is recommended that the facility should be operated at the lowest pH possible, which will also enable the removal of major pollutants, such as iron and aluminum.

Inhibitory effect of novel green polymer (Aspartic-citric acid) on the process of nucleation during gypsum scale formation

The presence of metal salts in the process fluid in industries leads to scale deposition over the heating or cooling surfaces and causes an significant increase in the overall process and product cost of the product. This further reduces the efficacy of the equipment and the quality of the product is compromised. Hence, in order to avoid this various conventional additives containing nitrogen, phosphorous and sulphur are used as antiscaling agents due to their superior scale inhibition properties. However, excessive use of these antiscalants has created an imbalance in the ecosystem. Hence, there is a necessity to look for more reliable compounds that are as equally efficient as the conventional ones and are eco-friendly, biodegradable and cost effective. In the present study, homo and hetero polymers of aspartic acid and citric acid have been synthesized using condensation method and their antiscaling properties against gypsum deposition is been evaluated. Characterization of the synthesized polymers and deposited scale was performed by FTIR, GPC, SEM and XRD. The polymer showing the highest efficiency in the preliminary screening test was further evaluated to study its effect on the process of nucleation and crystal growth. The synthesized polymers were found to be efficient in inhibiting the scale deposition process at additive concentration as low as 3 ppm. The presence of additive (PAS-co-CA2) increased the induction time, surface free energy of formation, critical nuclei size and number of molecules per critical nuclei. Hence, rate of nucleation was reduced. Molecular weight and functional groups were the crucial factors in determining the scale inhibition properties of the polymer. The process of crystal formation and deposition was significantly retarded in presence of the additive with a change in the crystal morphology of the deposited crystals.

Fluorescent‐tagged Antiscalants: A New Look at the Scale Inhibition Mechanism and Antiscalant Selection

AbstractSolid deposits onto equipment surfaces represent a serious problem all over the world. Mitigation of this process is provided by chemical inhibitors. However, irrespective of successful antiscalant application, the mechanisms of scale inhibition are still not very clear. Thus, the present review summarizes recent advances in novel fluorescent‐tagged antiscalants (polyacarboxylates, phosphonates) application for scale inhibition mechanisms study. Some paradoxical effects, detected during gypsum and barite scale formation visualization are described and interpreted within the “nanodust” concept. It is demonstrated, that the solid nanoimpurities, naturally occurring in both industrial and deionized water samples, are definitely playing a key role in any crystal nucleation process. Such nanoimpurities are responsible for the bulk heterogeneous nucleation in a supersaturated salt solution. Scale inhibitor molecules block and isolate exactly these “nanodust” nucleation centers and therefore retards crystallization process on the whole. The advantages of fluorescent antiscalants to provide a new look at scale inhibition phenomenon and inhibition mechanisms are discussed. Among these, there is a possibility to distinguish particular scale inhibitors in their blends, and an opportunity to track an antiscalant location along the process of scale formation and deposition. Besides, a need of antiscalants testament procedure unification is considered, and a possible role of fluorescent reagents in such a procedure elaboration is indicated.

Interfacial interactions between scale-brine and various reservoir rocks

The efficiency of water injection, as a conventional approach to enhance oil recovery, can profoundly be compromised due to detrimental impacts of scale formation. The present study discerns the interfacial interactions of brine with anhydrite, calcite, dolomite, and sandstone rock surfaces leading to gypsum scale formation. This was fulfilled using experimental jar tests at different salinities of 3000, 6000, and 9000 mg/L of [Ca2+] at T=363 K and P=1 atm. The interactions were also investigated using geochemical PHREEQC simulation as well as XDLVO theory. The experimental results showed that higher salinity of the brines the greater would be the mass of gypsum particles and as such, sandstone is more prone to formation of gypsum scale. Additionally, the theoretical basis of gypsum-brine-rock interactions would overwhelmingly be influenced by the Lewis acid-base energy. Consequently, the results demonstrated that decreased electron donor sub-component of surface energy of the rocks would be more influential than other surface energy sub-components which dominants the affinity of the rocks to scale formation.

Predominant Effect of Material Surface Hydrophobicity on Gypsum Scale Formation.

Scale formation is an important challenge in water and wastewater treatment systems. However, due to the complex nature of membrane surfaces, the effects of specific membrane surface characteristics on scale formation are poorly understood. In this study, the independent effect of surface hydrophobicity on gypsum (CaSO4·2H2O) scale formation via surface-induced nucleation and bulk homogeneous nucleation was investigated using quartz crystal microbalance with dissipation (QCM-D) on self-assembled monolayers (SAMs) terminated with -OH, -CH3, and -CF3 functional groups. Results show that higher surface hydrophobicity enhances both surface-induced nucleation of gypsum and attachment of gypsum crystals formed from homogeneous nucleation in the bulk solution. The enhanced surface-induced nucleation is attributed to the lower nucleation energy barrier on a hydrophobic surface, while the increased gypsum crystal attachment results from the favorable hydrophobic interactions between gypsum and more hydrophobic surfaces. Contrary to previous findings, the role of Ca2+ adsorption in surface-induced nucleation was found to be relatively small and similar on the different SAMs. Therefore, increasing material hydrophilicity is a potential approach to reduce gypsum scaling.

Visualization of a novel fluorescent-tagged bisphosphonate behavior during reverse osmosis desalination of water with high sulfate content

Gypsum scaling during reverse osmosis desalination process is studied in presence of a novel fluorescent-tagged bisphphosphonate antiscalant: 1-hydroxy-7-(6-methoxy-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)heptane-1,1-diyldi(phosphonic acid), HEDP-F, by fluorescent microscopy, scanning electron microscopy (SEM) and a particle counter technique. A case study of gypsum scale formation revealed a nonconventional mechanism of antiscalant efficacy. It is found that scaling takes place in the bulk retentate phase via heterogeneous nucleation step. Herewith, the background solid particles (“nanodust”) play a key role as gypsum nucleation centers. It is demonstrated that contrary to popular belief, an antiscalant interacts not with gypsum nuclei, but with “nanodust” particles, isolating them from calcium and sulfate ions sorption. Therefore, the number of gypsum nucleation centers gets reduced, and in turn an overall scaling rate becomes diminished. It is demonstrated that the fluorescent-tagged antiscalants may become a very powerful tool in membranes scaling inhibition studies. 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 desalination process.

CFD modeling of gypsum scaling in cross-flow RO filters using moments of particle population balance

Abstract Gypsum scaling over a RO membrane significantly reduces the permeate flux. Since, the phenomenon is linked to concentration polarization; the present study aims to understand the effect of high shear rates over the membrane in reducing gypsum scaling of cross-flow RO filters. We have proposed an integrated CFD and moment-based population balance (MPB) formulation which is less complex than tracking the growth of individual particles. Most of the previous studies on modeling of scaling and permeate flux decline employing MPB formulation were limited to dead-end filters. The present numerical model for cross-flow RO filter has been verified by comparing the precipitate mass and permeate flux decline with the published results for channel filter. This model has been employed for different cross-flow conditions and geometries. We have demonstrated that scaling can be mitigated by increasing the shear rate over the membrane surface. In roto-dynamic RO filters, a 50% increase in the initial permeate discharge can be achieved, and permeate flux decline in time can be restrained if the shear rate is increased by rotating the disk. For a channel of identical membrane area, a similar improvement of permeate discharge requires an approximately two orders of magnitude higher feed discharge. In a channel, gypsum scale formation is significant at larger distances from the inlet. While for roto-dynamic filters, scaling occurs at the stagnation zone near the axis of rotation, the scaling potential decreases with radius. Additionally, we have also discussed some striking differences between fouling and scaling patterns in cross-flow RO filters.

Evaluation of gypsum (CaSO4·2H2O) scale formation and its inhibition by different antiscalants by static and dynamic test

ABSTRACT Deposition of calcium salts or scaling on heat transfer surfaces is a major industrial problem around the globe. Scales get deposited in industrial process equipments severely affecting its life span, operating cost and adversely altering the process. Antiscalants are widely used for inhibition of metal salts formed in this water. In this study, chemical species like phosphates, various vinyl monomers and polymethacrylic acid are tested for their scale inhibition properties under static condition as per NACE standard and dynamic condition using SS and MS metal Strips. The performance of the compounds like Acrylic Acid, Malic acid, Succinic Acid and Polymethacrylic acid, studied during this working was found to be increasing with an increase in the number of a carboxylic (-COOH) group attached to its molecule. The presence of a negative charge over the carboxyl group plays an important role in the formation of ionic bond with the Ca2+ ions present in the liquid bulk. The carboxyl group attaches itself on the active sites of the crystal lattice and changes the crystal morphology significantly by blocking the active sites for its possible future growth.

Gypsum scale formation on graphene oxide modified reverse osmosis membrane

Graphene oxide (GO) coatings on membranes can improve antifouling performance against a variety of microorganisms and organics. However, the effects of GO coatings on mineral scaling were not investigated. Here gypsum scaling on bare (ESPA2) and GO-modified thin-film polyamide membranes (ESPA2-GO) followed by cleaning with deionized (DI) water were investigated with a bench-scale reverse osmosis setup. The flux decline caused by gypsum scaling on ESPA2-GO was slightly reduced than on ESPA2. This is because the ESPA2-GO membrane is more hydrophilic than ESPA2, indicating a higher energy barrier for heterogeneous nucleation and/or the deposition of gypsum on it. Moreover, the more negatively charged ESPA2-GO membrane lead to stronger electrostatic repulsive forces between the membrane and the negatively charged gypsum particles and thus further inhibiting gypsum deposition onto membranes. Interestingly, during the cleaning process, smaller flux recovery was observed for ESPA2-GO. This is because ESPA2-GO surfaces have higher densities of carboxyl (–COOH) groups, which form complexes with Ca2+, building strong bonds between GO coatings and gypsum. This study provided unique insights on the physicochemical interactions among membrane, the scaling mineral, and aqueous species, which can help the rational design of coatings for better simultaneous anti-scaling and anti-fouling performances.

Kinetic and morphological investigation of calcium sulfate dihydrate (gypsum) scale formation on heat exchanger surfaces in the presence of inhibitors

Kinetic and morphological investigation of calcium sulfate dihydrate (gypsum) scale formation on heat exchanger surfaces in the presence of inhibitors

Synthesis and evaluation of phosphate-free antiscalants to control CaSO4·2H2O scale formation in reverse osmosis desalination plants

Polysuccinimide (PSI) of various molecular weights (MW) was synthesized from aspartic acid. The PSIs were hydrolyzed with NaOH to obtain sodium polyaspartates. Partial hydrolysis of a PSI gave the copolymer poly(SI-co-sodium aspartate). PSIs were treated with one equivalent of cyclic amines: pyrrolidine, piperidine, and azepane to afford the corresponding polyaspartamides in excellent yields. Treatment of PSI with 0.5 equivalents of the cyclic amines led to the formation of 1:1 copolymer poly(SI-co-aspartamide) which on basic hydrolysis gave the corresponding 1:1 copolymer poly(sodium aspartate-co-aspartamide).The antiscalant behavior of the newly synthesized compounds was evaluated at various concentrations (2.5ppm–10.0ppm) for the inhibition of gypsum scale formation. The antiscalant evaluation experiments were performed by measuring conductivity and using concentrated brines. The study revealed the performance of low MW antiscalants to be superior to their high MW counterparts. Thus, a polyaspartate is found to be a better antiscalant than its corresponding copolymer of SI/aspartate, i.e. a partially hydrolyzed PSI. Derivatives of 7-membered cyclic amine azepane performed better than their 5- and 6-membered counterparts. At the same degree of polymerization, performance with decreasing order of effectiveness was found to be: polyaspartate>poly(aspartamide-co-aspartate)>(SI-co-aspartate)>poly(SI-co-aspartamide)>polyaspartamide.

Influence of Flow Rates and Copper (II) ions on the Kinetics of Gypsum Scale Formation in Pipes

Influence of Flow Rates and Copper (II) ions on the Kinetics of Gypsum Scale Formation in Pipes

Influence of Flow Rates and Copper (II) ions on the Kinetics of Gypsum Scale Formation in Pipes

Experiments were performed in a piping system to examine the effects of flow rates and Cu, a common metal ion in wastewater, on the kinetics of gypsum (CaSO4.2H2O) scale formation. The scaling was monitored by measuring the decrease in Ca concentrations, [Ca], of the scaling solution. AAS analysis shows that [Ca] reduces progressively after a certain induction time, during which time the concentration remains steady. Thus, the gypsum precipitation which leads to scaling in pipes does not occur spontaneously. Higher impurity concentrations (0 to 10 ppm Cu) result in longer induction time (26 to 42 min), which indicate that Cu could inhibit the scale formation. Impurity concentrations and the scale mass generated are negatively correlated. Reduction in scale mass was as high as 61% depending on impurity concentrations and flow rates. Data of [Ca] versus time were used to calculate the reaction rate of the gypsum precipitation which led to scaling. It was found that the reaction follows a first order kinetics with respect to [Ca], with rate constants ranging between 5.28 and 7.37 per hour, which agree with most published values for mineral scale formation.

Gypsum scale formation on heated metal surfaces: The influence of polymer type and polymer stability on gypsum inhibition

The deposition of gypsum (i.e. calcium sulfate dihydrate) on brass heat exchanger surfaces in the presence of homopolymers and copolymers containing different functional groups from aqueous solution has been studied. The amount of gypsum deposited on the heat exchanger surface (in the absence of bulk or spontaneous precipitation) is strongly dependent on the polymer architecture and the polymer concentration. Scanning electron microscopic investigations on the deposit show morphological changes to the crystals due to interactive effects of some of the polymers. The effectiveness of the polymers as inhibitors was reduced by thermal treatment (150–240°C), likely due to polymer degradation.

Effects of Process Parameters on Gypsum Scale Formation in Pipes

AbstractScaling often leads to a series of technical and economical problems in industrial plants and equipments by blocking water flow in pipes or limiting heat transfer in heat exchangers. While most contemporary studies are focusing on crystallization at heat‐exchanger surfaces and scaling on nanofilters in desalination plants, very little work has been done investigating scale formation on pipe and vessel walls. A comprehensive investigation of the effects of various process parameters in controlling the formation of calcium sulfate scale in pipes was undertaken. Supersaturation ratio, run time, and operational hydrodynamics were altered systematically to determine their influence on the scale growth rate. The results confirmed that the deposition of gypsum on pipe walls was significantly affected by these process parameters.

Solubility and scale prevention of gypsum in transportation pipes of well brine with salinities up to 5 M at temperature range of 278–298 K

The results of work performed on reducing gypsum scale formation in transportation pipes of well salt brine are described. Two methods: seeding with calcium sulfate dihydrate and dilution of brine were proposed. With the first method, various mass and size distributions of seeds were introduced into an perspex reactor with well salt brine (NaCl: 300 g/L, Na2SO4: 20 g/L) to investigate the factors that influence crystallization of calcium sulfate dihydrate, such as temperature, mass of seed crystals, and size distribution of seed crystals. The kinetics of calcium sulfate dihydrate growth at temperatures ranging between 5 and 25 °C were obtained. Results showed that the elimination of supersaturation was enhanced with increasing temperature and the dosage of seed crystal. It was also found that the more efficient in scale prevention was obtained when smaller seed crystals were employed. It was seen that the crystal growth of calcium sulfate dihydrate in brine was proportional to the square of supersaturation at the investigated temperatures. With the second method, results showed that a complete elimination of supersaturation was achieved when 4.3% water was added into the brine with the help of solubility determination of calcium sulfate dihydrate.

Effects of feed water temperature on inorganic fouling of brackish water RO membranes

A bench scale RO process simulator was operated in a batch concentration mode to determine the effects of product water recovery and feed water temperature on flux, rejection, and inorganic fouling by gypsum scale formation for simulated brackish water. As feed water temperature increased, salt rejection and concentration polarization decreased (reducing scale formation potential at a given recovery). However, gypsum crystal nucleation and growth rates increased with temperature. Specifically, at 15 and 25°C gypsum scale formation resulted in slow, steady flux decline at recoveries as low as 10–20%. At these temperatures, many small crystals formed over the entire membrane surface. In contrast, at 35°C flux decline was due to the increasing feed solution osmotic pressure — up to a recovery of about 70%. At this recovery, we observed a sudden, rapid loss of flux and a concomitant spike in feed water turbidity. Relatively few (in number), large crystals formed on the membrane towards the brine outlet of the RO simulator, but the entire membrane surface was covered with “needle-like” crystal fragments. The crystal fragments broke off from growing gypsum rosettes and re-deposited uniformly across the membrane forming a “cake layer” that caused the massive flux decline. These results suggest that high temperature operation of brackish water RO processes could enable higher recovery and lower energy consumption, but operating near the limiting recovery (at elevated temperature) creates an increased risk of a catastrophic fouling event.

Kinetics of gypsum crystal growth on a reverse osmosis membrane

The development of calcium sulfate dihydrate (gypsum) mineral scale in reverse osmosis (RO) membrane desalting was investigated by direct real-time observation of crystal growth. Gypsum scaling studies were conducted in a specially modified plate-and-frame reverse osmosis cell fitted with an optical window, with dark-field membrane lighting arrangement within the membrane cell to enhance crystal boundaries and allow recording of digital surface images magnified through an optical microscope. The evolution of the surface number density (SND) of gypsum crystals resembled a sigmoidal population growth process with an increasing rate of crystal formation at higher solution supersaturation (with respect to gypsum) at the membrane surface. The rate of formation of new crystals declined as the surface scale coverage increased, with surface scale progressing by diffusion-controlled growth of existing crystals as the gypsum crystal SND approached its plateau. The apparent crystallization induction time (i.e., observation time for the appearance of surface crystals) decreased with increased supersaturation, with single crystals growth reasonably characterized by a diffusion-growth model and a single crystal fluid mass transfer coefficient that was generalized by a Sherwood number type correlation. The present approach provides a convenient method of characterizing the kinetics of gypsum scale formation via quantification of single crystal mass transfer coefficient and evolution of the crystal SND. Such information can guide the development of comprehensive RO membrane scale formation models and characterization of mineral scaling propensities of RO membranes and source water where mineral salt scaling is of concern.