Synergistic Effect of EDTA and HEDP on the Crystal Growth

Mar 23, 2015 - (13, 25-27) EDTA is reported to retard the crystal growth of calcite and aragonite. ... Aquasoft 330) was obtained from Satyajith Chemi...
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Synergistic Effect of EDTA and HEDP on the Crystal Growth, Polymorphism, and Morphology of CaCO3 Shanmukha Prasad Gopi, V.K. Subramanian,* and K. Palanisamy Department of Chemistry, Annamalai University, Annamalainagar-608002, Tamilnadu, India S Supporting Information *

ABSTRACT: Polymorphic compositions of CaCO3 synthesized under the influence of a blended system of EDTA and HEDP between 60 and 230 °C using a controlled precipitation technique from CaCl2 solution using Na2CO3 has been investigated. The phases and structures of the samples were characterized by Raman, FTIR, and powder XRD techniques. The morphological studies were carried out using SEM, field emission scanning electron microscope (FESEM), and TEM. Usually, at higher temperatures vaterite and aragonite are transformed into stable calcite. Here, we report the stabilization of metastable aragonite and vaterite in the presence of a blended system of EDTA and HEDP at 200 and 230 °C. We also report a novel morphology, roselike structure for vaterite at 230 °C, which is not reported earlier.

1. INTRODUCTION In recent years, design and synthesis of calcium carbonate (CaCO3) one of the most abundant natural inorganic mineral has gained much importance due to its wide range of applications in cosmetics, medicines, controlling biomineralization, and so forth.1−3 It is also one of the most predominant components of scale found in boiler tubes and in heat exchangers.4−7 Generally, CaCO3 exists in three crystalline polymorphic forms, in the order of increasing stability: vaterite, aragonite, and calcite. The crystalline structures of these phases are rhombohedral, orthorhombic, and hexagonal for calcite, aragonite, and vaterite, respectively.8,9 Traditional strategies for the control of polymorphs often involve changing solvents, temperature, pH and other growth conditions, usage of polymer additives, and so forth.10,11 Because different polymorphic forms of same substance have different properties, polymorphism plays an important role in controlling the scale formation using chelating agents or other chemicals used in internal treatment. For example, it is obvious from literature that the predominant polymorphic form of calcium carbonate in scale is calcite and vaterite is seldom present.12−14 Polymorphism of CaCO3 precipitated in a constant composition environment has been reported by Tai et al. They have reported that the solution pH and temperature are the most important factors that determines which polymorphs are obtained.15 However, one of the longstanding challenges of crystallization is the ability to predict and control polymorphism. Reports suggests that, in the presence of scale inhibitors, a substantial amount of vaterite and aragonite occur in scale, whereas in the absence of scale inhibitors, calcite is almost the only crystal form. Moreover, for the scale inhibitor with higher inhibition efficiency, more vaterite and aragonite are present in scale.13,14 Appearance of a phase is based on the supersaturation of that phase under that particular environment and how the dissolution and recrystallization/transformation takes place. The supersaturation “σ” proposed by Nielsen and Toft16 is given by σ = (IP/Ksp)1/2 − 1 (where IP is the ionic product, defined as IP = aCa2+ × aCO32− for this system, and Ksp is the solubility product of © 2015 American Chemical Society

CaCO3). Similarly, the mechanisms of crystallization and transformation of calcium carbonates has been reported by Swada. The study revealed that the transformation from vaterite to calcite proceed by a recrystallization process.17 Many studies have investigated the influence of additives on the crystallization of CaCO3.18−20 Most of the methods reported in the literature employed precipitation of CaCO3 under the influence of a single chelating agent/additive.21−24 To the best of our knowledge, study on the synergistic effect using a blended system of two or more additives to control the CaCO3 scale at higher temperatures has not been reported yet. As a prelude to this exercise, we have chosen a combination (blended system) of two additives ethylenediaminetetraacetic acid disodium salt (EDTA) and commercial grade1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). Ethylenediaminetetraaceticacid (EDTA) and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) are well-known complexing agents and are widely used as a chelating agent in internal water treatment formulations.13,25−27 EDTA is reported to retard the crystal growth of calcite and aragonite.27 Aquasoft 330, a commercial grade HEDP is widely used in industries in India and reports are available on its ability to control the morphology of CaCO3 and calcium oxalate.27−29 The purpose of this study is to understand the effect of a blended system of EDTA and HEDP (Aquasoft 330) on the crystal growth, polymorphism and morphology of CaCO3 between 60 and 230 °C.

2. EXPERIMENTAL SECTION Analytical grade CaCl2, Na2CO3 were obtained from Himedia chemicals, disodium salt of EDTA (C10H14N2Na2O8.2H2O) from Qualigens Chemicals and commercial grade 1-hydroxyethylidene- 1,1-diphosphonic acid ((HEDP (C2H8O7P2), Aquasoft 330) was obtained from Satyajith Chemicals Pvt Ltd., Received: Revised: Accepted: Published: 3618

August 28, 2014 March 20, 2015 March 23, 2015 March 23, 2015 DOI: 10.1021/ie5034039 Ind. Eng. Chem. Res. 2015, 54, 3618−3625

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Industrial & Engineering Chemistry Research

study. For a system at 60 °C, the sample was aged for 10 h. In practice, it was necessary to provide more time at elevated temperatures. Hence, for experiments at all other temperatures the samples were aged for 72 h. After digestion, the samples were filtered through (Whatman 40) filter paper and washed 6−7 times with hot distilled water to remove any residual chelants and dried at 45 °C in a hot air oven. The details of reaction conditions are provided in Table 1. The initial and the final pH of the solution were measured after adding Na2CO3 and after the digestion time, respectively. 2.2. Characterization. The composition of the samples was confirmed by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and Powder XRD methods and the morphological studies were done using scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM). FTIR spectra were taken in the range 500 to 4000 cm−1 using Avatar-330 and JASCO-5300, after KBr pelletization. Raman spectra of the samples were obtained with the WI Tec Confocal Raman Microscope alpha 300 R Raman spectrometer, excited by laser lines having a wavelength of 488 nm, provided by an argon laser of 2 mW with an acquisition time of 1 min. The X-ray diffraction (XRD) patterns were recorded on a Bruker D8 Advanced XRD diffractometer with Cu Kα radiation at λ = 1.5406 Å with step size of 0.091063. Microscopic morphological images were taken using Philips XL30-ESEM using a beam voltage of 20 kV and FESEM CARL ZESIS with in lens detectors. Transmission electron microscope (TEM) imaging and selected area electron diffraction studies were carried out on a Tecnai G2 FEI F12 TEM at an accelerating voltage of 200 kV. TEM images were recorded by placing the sample on carbon-coated copper grids.

Table 1. Reaction Conditions, Initial and Final pH of Solutions at Various Temperatures sample no.

temperature (°C)

digestion time (h)

initial pH

final pH

1 2 3 4 5

60 100 130 200 230

10 72 72 72 72

8.10 8.10 8.10 8.10 8.10

8.31 8.45 8.48 8.49 8.62

Mumbai. The above chemicals were used as supplied without further purification. Double distilled water was used to make all aqueous solutions. A rotamantle with temperature controller, manufactured by Remi was used for experiments below 100 °C. A programmable autoclave with digital temperature and pressure controller manufactured by Everflow Scientific Instruments, Chennai was used for synthesis at 100 and 130 °C. A programmable autoclave with digital temperature indicator and automatic controller, manufactured by Thermocon was used. 2.1. Synthesis of Samples. CaCO 3 samples were synthesized using a method similar to the one described by Gopi et al.27 In a typical synthesis, 50 mL of 0.1 M CaCl2 and 10 mL of 0.1 M EDTA, 10 mL of 0.1 M HEDP were taken in a round-bottom flask and heated to 60 °C using rotamantle with constant stirring. After attaining the temperature 75 mL of 0.1 N Na2CO3 was added slowly drop by drop until the precipitation. Experiments 100 °C and above were carried out in auto clave and hydrothermal bombs due to the difficulty in addition of Na2CO3 at reaction temperature, it was also added along with EDTA and HEDP. Preheating to a temperature 10 °C below the reaction temperature for 2 h and filtration of the precipitate was done to remove any CaCO3 formed during the course of heating and to ascertain that the sample is formed at that temperature under

Figure 1. PXRD patterns of the samples showing characteristic peaks of different polymorphs of CaCO3present in samples prepared between 60 and 230 °C. 3619

DOI: 10.1021/ie5034039 Ind. Eng. Chem. Res. 2015, 54, 3618−3625

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3. RESULTS AND DISCUSSIONS 3.1. Characterization and Quantitative Estimation Using Powder Diffraction Technique. Figure 1, depicts the

powder XRD pattern and Table 2 represents the polymorphic compositions of the samples determined by Kontoyannis equation.30 It could be observed that a binary mixture of vaterite and aragonite formed initially at 60 °C transformed into pure vaterite at 100 °C and to a ternary mixture of calcite, vaterite, and aragonite at 130 °C. The samples corresponding to 200 and 230 °C showed peaks corresponding to vaterite with very little aragonite. A significant amount of aragonite was found only at 60 °C. The data indicated that, the trend from aragonite to vaterite is obvious at 60, 200, and 230 °C (JCPDS-741867). Appearance of aragonite at 200 °C and gradual decrease in its mole fraction with increase in temperature and the steady increase in mole fraction of vaterite between 130 and 200 °C demonstrated that the blended system favors the formation of vaterite at 100, 200, and 230 °C. Calcite was formed only at 130 °C and the mole fraction indicated that its presence is insignificant. The diffraction peaks well matched with JCPDS cards 862339, 760606, and 741867 for calcite, aragonite, and vaterite, respectively. For the phase identification of respective polymorphs, individual XRD spectra are provided with peak values as Supporting Information (Figure S1). 3.2. FTIR and Raman Spectroscopy. It is well known that different crystal forms of CaCO3 show different bands in FTIR spectrum.31−33 Hence, the polymorphic compositions of CaCO3 crystals were primarily identified by FTIR and represented in Figure 2a. The reference bands observed around 700−745, 856− 874, 1435−1480 cm−1 were assigned to the ν4 in-plane bending, ν2 out-of-plane bending, and ν3 asymmetric stretching modes of CO32−, respectively. The principal bands corresponding to aragonite (A), vaterite (V), and calcite (C) are highlighted, and wherever necessary, the FTIR were deconvoluted (660−800 cm−1) to distinguish calcite from aragonite (713 and 700 cm−1) as shown in Figure 2b. The individual FTIR spectra with band values are provided in Figure S2 as Supporting Information. The results demonstrated that, in the presence of EDTA and HEDP formation of vaterite and aragonite is facilitated with a decrease in calcite on increasing the temperature from 130 to 230 °C. This phenomenon is abnormal and against the Ostwald rule of stages. Although most reports about CaCO3 agree with this rule, our earlier studies also reported similar observations.34,35 Similarly, Raman spectra of the samples were also taken and compared with already reported values.36−38 Appearance of Raman band at 745 cm−1 along with bands at 300 and 330 cm−1 in lattice modes, 881 cm−1 (ν2 out of plane bending), 1090 cm−1 (ν1 symmetric stretching), and 1441 and 1480 cm−1 (ν3 asymmetric stretching) modes in all the samples categorically confirmed the occurrence of vaterite in the entire temperature range (Figure 3). The presence of both calcite and aragonite was confirmed by observing bands at 1462 and 1435 cm−1 (ν3 asymmetric stretching), respectively. Bands at 217 and 284 cm−1 (lattice modes), 701 and 717 cm−1 (ν4), 1085 cm−1 (ν1), and 1464 cm−1 (ν3) confirmed the absence of aragonite in all the samples except at 100 °C. The Raman results were in good agreement with above XRD and FTIR data and the individual Raman spectra are provided in Figure S3 as Supporting Information. 3.3. Morphological Studies Using SEM. To analyze the detailed morphology, SEM and FESEM were performed and are presented in Figure 4. It is evident from Figure 4a,b that the sample prepared at 60 °C consisted of three different morphologies: spherical, flower with elongated prolate spheroid-like petals, and elongated prolate spheroids. Our earlier studies have resulted similar morphological combinations in the

Table 2. Molar Fraction of CaCO3 Polymorphs in the Presence of EDTA + HEDP and Absence of Additive at Various Temperatures without any additive27

in the presence of EDTA + HEDP

temperature (°C)

calcite

aragonite

vaterite

calcite

aragonite

vaterite

60 100 130 200 230

81 12 45 95 97

19 88 55 05 03

00 00 00 00 00

04 02 13 05 03

46 04 22 14 09

50 94 65 81 88

Figure 2. (a) FTIR spectra showing characteristic bands of different polymorphs of CaCO3 present in samples prepared between 60 and 230 °C. (b) Deconvoluted FTIR of sample 3 synthesized at 130 °C represents 700 cm−1 (aragonite), 712 cm −1 (calcite) and 744 cm −1 for vaterite.

3620

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Figure 3. Raman bands of different polymorphs of CaCO3 present in samples prepared between 60 and 230 °C.

presence of EDTA at 230 °C, where we had confirmed the flower and spherical morphologies to vaterite and the elongated prolate spheroids as aragonite.27 Here, in the presence of EDTA and HEDP at 60 °C, the SEM images have spherical vaterite at the end of the flower petals where as sharp edged petals were resulted when reactions were conducted at 230 °C in the presence of EDTA alone. The XRD, FTIR, and Raman spectra confirmed almost similar composition of vaterite and aragonite in both samples. This confirms that the reaction environment is similar to that of EDTA at 230 °C, which could be created at 60 °C by the addition of HEDP. SEM images of samples at 100 °C showed only spherical morphology that accentuated the FTIR, XRD, and Raman data: the presence of only vaterite (Figure 4c). Figure 4d depicts the FESEM image of sample prepared at 130 °C. Both spherical and rhomboidal morphologies are present in the SEM image confirming a binary mixture of vaterite and calcite in the sample. The XRD, FTIR, and Raman studies revealed presence of aragonite in this sample. There can be two reasons for the absence of morphologies corresponding to aragonite. First, the molar fraction of calcite and aragonite in this sample were too low and might not have been covered in the scan area. The second reason could be a possibility of an almost similar morphology as that of vaterite. The chance for the second possibility is more because the spherical morphology of vaterite in this sample is not uniform and contains some elongated prolate spheroids (Figure 4d), a morphology already reported for aragonite.27 The FESEM images of sample prepared at 200 °C are presented in Figure 4e,f. The morphology resembled like a closely packed bed of roses. However, it is obvious that the individual roses are not clearly distinguishable. Interesting morphological changes were observed on raising the reaction temperature from 200 to at 230 °C (Figure 4g,h). The highly

thickly packed bed of roses secede to give individual roselike structures having size 400 to 500 nm and petals ranging from 200 to 250 nm. It is evident from this image that the sample at 200 °C is like a closely packed bed of roses. The FTIR, Raman, and XRD results confirmed the presence of vaterite with very little aragonite in this sample. However, the molar fraction of aragonite in this sample is found to be negligible (Table 2) and hence this morphology is assigned to vaterite. 3.4. Confirmation of Vaterite Structure by TEM Studies. Figure 5a depicts the TEM image of sample prepared at 230 °C. Results displayed a self-assembly of many petals/flakelike nanoparticles developed into a roselike structure. From Figure 5a it is obvious that the average size of the rose is about 350 nm. The corresponding TEM-EDAX spectrum (Figure S4, Supporting Information) indicates that the particles are indeed made of pure CaCO3. The composition of CaCO3 for this structure is C, 53.31%; Ca, 28.67%; O, 18%. Figure 5b depicts the selected area electron diffraction of (SAED) of Figure 5a. The SAED image exhibits the orthorhombic diffraction pattern which can be indexed for vaterite. The corresponding inter planar distance had good agreement with powder diffraction results with plane values of (111) confirming orthorhombic structure of vaterite vide JCPDS-741867 for the rose morphology. 3.5. Thermal Stability of EDTA, HEDP, and CO32−. In order to understand the thermal stability of EDTA and HEDP at 230 °C, CaCO3 samples were prepared at 230 °C and evaporated to dryness and the FTIR was taken without washing. The FTIR spectra of unwashed samples (Figure 6) exhibited a number of new bands and they were compared with reported FTIR values of EDTA and HEDP. The FTIR bands for EDTA and its salts was clearly reported by Lanigan et al. and for HEDP Zenobi et al.39,40 Figure 6a represents the unwashed samples of EDTA at 230 °C. The strong absorption/transmittance bands due to the COOH 3621

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Industrial & Engineering Chemistry Research

Figure 4. SEM images (morphology) of CaCO3 synthesized at different temperatures (a, b) at 60 °C; (c) at 100 °C; (d) at 130 °C; (e, f) at 200 °C; (g, h) at 230 °C, self-assembly of nano roses (vaterite).

carboxylic group stretching are identified at 1700−1550 cm−1, 1340−1330 cm−1, and 950−800 cm−1. The bands around 1630− 1640 cm−1 showed the ionized carboxyl groups and symmetric stretching bands typically noticed at 1410−1420 cm−1, which

confirmed the stability of EDTA in the sample. Similarly, in the presence of HEDP (Figure 6b), the occurrence of bands at ∼1099, 1077, and 968 cm−1 were assigned to asymmetric and symmetric stretching’s of PO32− respectively and the bands 3622

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Figure 5. (a) Magnified TEM image of roselike vaterite nano structure of about 350 nm; (b) SAED for vaterite as orthorhombic structure (phase taken along the (111) direction).

Figure 6. FTIR of CaCO3 sample prepared at 230 °C and evaporated to dryness (a) with EDTA (b) with HEDP.

around 1130−1144 cm−1 were also assigned to asymmetric and symmetric stretching’s of HPO3−. The important bands for identification phosphonate groups fall between 900−1200 cm−1, especially bands at ∼925 cm−1, 970−1000 cm−1 corresponds to ν (P−OH), ν (PO32−) vibrations, respectively. The simulations occurrence of all these bands in Figure 6b confirmed the stability of HEDP at this temperature. From these FTIR observations it was confirmed that both EDTA and HEDP are thermally stable at 230 °C. Bilton et al.41, reported the thermal stability of CO32− between 25−800 °C and the studies confirmed that CaCO3 was more stable below temperature below 600 °C. 3.6. Mechanism. Our previous experiments without any additive resulted into a binary mixture of calcite and aragonite below 170 °C. At 200 and 230 °C, calcite was the only polymorph which was stable. Vaterite was not observed in any of the sample. When EDTA was used, we found a considerable amount of vaterite at various temperatures particularly at 130 and 230 °C.27 Similarly, our experiments with HEDP at various concentrations have shown presence of vaterite at different temperatures.28 Both EDTA and HEDP have shown different morphologies for vaterite. Although EDTA favored threedimensional sprouts-like morphology, HEDP favored twodimensional growth leading to a sunflower like morphology.

Keeping the experimental data of individual chelating agents and the blended system side by side, the probable mechanism of synergistic effect could be drawn as follows. When both of the additives are added together, the Ca2+ ion present in the system will form complex with both EDTA and HEDP. At room temperature (30 °C) the TDS of the solutions showed 3260 ppm after addition of EDTA and HEDP. On addition of Na2CO3 the TDS came down to 2760 ppm. The amount of Ca2+ present in the solution before addition of EDTA and HEDP could be about 4000 ppm. This requires 100 mL of 0.1 M EDTA or HEDP or both put together to form 100% complex with all Ca2+ ions. On addition of 20 mL each of EDTA and HEDP, which is only 40% of the stoichiometric the concentration of Ca2+ ions are supposed to be 2400 ppm. When Na2CO3 is added and heated to a temperature 10 °C below the reaction temperature and aged for 2 h, the free Ca2+ ions present in the system and those which could not be released at that temperature are reacted with CO32− ions present in the system. Filtration of sample after cooling can redissolve a small portion of CaCO3, but could be significant only, if additives/chelating agents are absent. Because a sufficient quantity of EDTA and HEDP is present in the system, they can easily complex the redissolved Ca2+ ion. HEDP, being a pentadentate ligand and having less affinity toward Ca2+ than 3623

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Industrial & Engineering Chemistry Research EDTA, could release the Ca ions first in to the solutions with increase in temperature. As EDTA is sufficiently coordinated with Ca ions, it cannot accommodate the released Ca2+ ions under increasing temperature and pressure. This could increase the number of species in the system and thereby increase the entropy of the system. As the supersaturation is reached, Ca2+ ions are forced to form CaCO3. As the temperature is very high, before this reaction attains equilibrium, the Ca ions coordinated to EDTA are also released in to the system. Now, the presence of HEDP and EDTA in the environment provides two different activation sites that could act individually and favor both the two and three-dimensional morphological growth of CaCO3. Although the HEDPwhich favors sunflower morphology stretches the structure horizontally, the EDTAwhich favors the spiked flowersacts vertically. As a result, the sunflower morphology is crammed resulting into cone shapes. This effect further enhances with the release of chelating agents (EDTA and HEDP) with time, forcing them to get wrapped in concentric circles, one over the other, finally resulting into a rose structure. From the above discussions, it is obvious that the self-assembly of these petals are induced by the synergistic effect of EDTA and HEDP.

(3) Payne, S. R.; Butler, M. H.; Butler, M. F. Formation of Thin Calcium Carbonate Films on Chitosan Biopolymer Substrates. Cryst. Growth Des. 2007, 7, 1262. (4) Yu, J.; Guo, H.; Davis, S. A.; Mann, S. Fabrication of Hollow Inorganic Microspheres by Chemically Induced Self-Transformation. Adv. Funct. Mater. 2006, 16, 2035. (5) Cölfen, H. Precipitation of Carbonates: Recent Progress in Controlled Production of Complex Shapes. Curr. Opin. Colloid Interface Sci. 2003, 8, 23. (6) Braga, D. From Amorphous to Crystalline by Design: Bio-Inspired Fabrication of Large Micropatterned Single Crystals. Angew. Chem., Int. Ed. 2003, 42, 5544. (7) Yang, Q. F.; Liu, Y. Q.; Gu, A. Z.; Ding, J.; Shen, Z. Q. Investigation of Calcium Carbonate Scaling Inhibition and Scale Morphology by AFM. J. Colloid Interface Sci. 2001, 240, 608. (8) Macipe, A. L.; Morales, J. G.; Clemente, R. R. Calcium Carbonate Precipitation from Aqueous Solutions Containing Aerosol OT. J. Cryst. Growth 1996, 166, 1015. (9) Ahmed, J.; Menaka; Ganguli, A. K. Controlled Growth of Nanocrystalline Rods, Hexagonal Plates and Spherical Particles of the Vaterite form of Calcium Carbonate. CrystEngComm 2009, 11, 927. (10) Xiao, J.; Wang, Z.; Tang, Y.; Yang, S. Biomimetic Mineralization of CaCO3 on a Phospholipid Monolayer: From an Amorphous Calcium Carbonate Precursor to Calcite via Vaterite. Langmuir 2010, 26, 4977. (11) Chen, S. F.; Yu, S. H.; Jiang, J.; Li, F. Q.; Liu, Y. K. Polymorph Discrimination of CaCO3 Mineral in an Ethanol/Water Solution: Formation of Complex Vaterite Superstructures and Aragonite Rods. Chem. Mater. 2006, 18, 115. (12) Hart, J. R. Ethylenediaminetetraacetic Acid and Related Chelating Agents. In Ullmann’s Encyclopedia of Industrial Chemistry; Wiley-VCH: Weinheim, Germany, 2000. (13) Zhang, G. C.; Ge, J. J.; Sun, M. Q.; Pan, B. L.; Mao, T.; Song, Z. Z. Investigation of Scale Inhibition Mechanisms Based on the Effect of Scale Inhibitor on Calcium Carbonate Crystal Forms. Sci. China B Chem. 2007, 50, 114. (14) Tang, Y.; Yang, W.; Yin, X.; Liu, Y.; Yin, P.; Wang, J. Investigation of CaCO3 Scale Inhibition by PAA, ATMP and PAPEMP. Desalination 2008, 228, 55. (15) Tai, C. Y.; Chen, F. B. Polymorphism of CaCO3 Precipitated in a Constant-Composition Environment. AIChE J. 1988, 44, 1790. (16) Nielsen, A. K.; Toft, J. M. Electrolyte Crystal Growth kinetics. J. Cryst. Growth 1984, 67, 278. (17) Sawada, K. The Mechanisms of Crystallization and Transformation of Calcium Carbonates. Pure Appl. Chem. 1997, 69, 921. (18) Ketrane, R.; Saidani, B.; Gil, O.; Leleyter, L.; Baraud, F. Efficiency of Five Scale Inhibitors on Calcium Carbonate Precipitation from Hard Water: Effect of Temperature and Concentration. Desalination 2009, 249, 1397. (19) Euvrard, M.; Martinod, A.; Neville, A. Effects of Carboxylic Polyelectrolytes on the Growth of Calcium Carbonate. J. Cryst. Growth 2011, 317, 70. (20) Lee, K. B.; Park, S. B.; Jang, Y. N.; Lee, S. W. Morphological Control of CaCO3 Films with Large Area: Effect of Additives and SelfOrganization under Atmospheric conditions. J. Colloid Interface Sci. 2011, 355, 54. (21) Wang, T.; Che, R.; Li, W.; Mi, R.; Shao, Z. Control Over Different Crystallization Stages of CaCO3-Mediated by Silk Fibroin. Cryst. Growth Des. 2011, 11, 2164. (22) Chakrabarty, D.; Mahapatra, S. Aragonite Crystals with Unconventional Morphologies. J. Mater. Chem. 1999, 9, 2953. (23) Liu, Y.; Cui, Y.; Mao, H. Y.; Guo, R. Calcium Carbonate Crystallization in the Presence of Casein. Cryst. Growth Des. 2012, 12, 4720. (24) Yan, G.; Wang, L.; Huang, J. The Crystallization Behavior of Calcium Carbonate in Ethanol/Water Solution Containing Mixed Nonionic/Anionic Surfactants. Powder Technol. 2009, 192, 58. (25) Altay, E.; Shahwan, T.; Tanoglu, M. Morphosynthesis of CaCO3 at Different Reaction Temperatures and the Effects of PDDA, CTAB,

4. CONCLUSION In summary, exclusive formation of vaterite was attained through controlled precipitation of CaCO3in the presence of a blended system of EDTA and HEDP at 100 and 230 °C. A binary mixture of aragonite and vaterite was obtained at 60 and 200 °C and a ternary mixture of calcite, aragonite and vaterite at 130 °C. At 230 °C, roselike morphology was observed for vaterite, which was a result of the synergetic effect of EDTA and HEDP.

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ASSOCIATED CONTENT

S Supporting Information *

The individual XRD (Figure S1), FTIR (Figure S2), and RAMAN (Figure S3) spectra showing the peak/band values and corresponding polymorphic forms of CaCO3. Figure S4, which is the TEM-EDAX spectrum corresponding to Figure 5a, indicating that the particles are indeed made of pure calcium carbonate. This material is available free of charge via the Internet at http://pubs.acs.org/.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +91 94862 82324. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the University Grants Commission (UGC) for the financial supported through Major Research Project (3740/2009 (SR) dated 12.01.2010). S.P.G. is thankful to Prof. M.V. Rajasekharan and UGC networking Resource Centre, University of Hyderabad, Hyderabad for providing facility for carrying out instrumental analysis.

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REFERENCES

(1) Morse, J. W.; Arvidson, R. S.; Luttge, A. Calcium Carbonate Formation and Dissolution. Chem. Rev. 2007, 107, 342. (2) Gehrke, N.; Cölfen, H.; Pinna, N.; Antonietti, M.; Nassif, N. Superstructures of Calcium Carbonate Crystals by Oriented Attachment. Cryst. Growth Des. 2005, 5, 1317. 3624

DOI: 10.1021/ie5034039 Ind. Eng. Chem. Res. 2015, 54, 3618−3625

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DOI: 10.1021/ie5034039 Ind. Eng. Chem. Res. 2015, 54, 3618−3625