03 – HYDROTHERMAL SYNTHESIS OF SODALITE FROM BAUXITE WASHING CLAY AND ITS TRANSFORMATION INTO BETA-HEXACELSIAN-TYPE MATERIAL

Ano 12 (2025) – Número 3 – Mineral Synthesis Artigos

10.31419/ISSN.2594-942X.v122025i3a3BAMF

 

 

Bruno Apolo Miranda Figueira^1*, Kauany Figueira Bastos², Nayara Aparecida Fonseca Couto¹_, Renata de Sousa Nascimento³_, Igor A. R. Barreto³

 ¹Instituto Federal do Pará, IFPA-Campus Belém, Programa de Pós-Graduação em Engenharia de Materiais – PPGEMAT, figueiraufpa@gmail.com

²Universidade Federal do Oeste do Pará, UFOPA-Campus Santarém, Instituto de Engenharia e Geociências-IEG, Santarém, Pará, Brasil.

³Universidade Federal do Pará, UFPA-Campus Belém, Instituto de Geociências – IG, Belém, Pará, Brasil.

 *To whom it should be sent a correspondences

 

ABSTRACT

In this work, b-hexacelsian (BaAl₂Si₂O₈) type material was successfully obtained from the bauxite washing clay (BWC) from Amazon Region (Brazil), which was converted into zeolitic material type Na-sodalite. The route involved cation exchange of zeolite with Ba²⁺ ions, its subsequent thermal decomposition to form an amorphous barium aluminosilicate material from which b-hexacelsian recrystallized at higher temperatures (above 900º C).

INTRODUCTION

Celsian, ideally BaAl₂Si₂O₈, is a rare barium aluminosilicate that occurs in metamorphic environments and was first reported by Igelström (1867) from manganese mines of Jakobsberg (Sweden) as “red feldspar, occurring in veins a few lines wide in a dense, light-colored, which itself is barite-containing” (Sjogren, 1895). It stands out in the felspar group due to its polymorphic diversity (Fig. 1), which is basically made up of TO₄ tetrahedron units (T = Al, Si) connected by corners in a [Al₂Si₂O₈] framework, large size of Ba²⁺ as out net cations and monoclinic symmetry with I2/m space group (Hoghooghi et. al., 1994; Skellern et al., 2002; Marocco et al., 2011; Radosavljevic-Mihajlovic et al., 2012; Radosavljevic-Mihajlovic et al., 2017). Another naturally occurring polymorph reported is monoclinic paracelsian with P2₁/a space group (Chiari et al., 1985). There are also two other polymorphic structures of BaAl₂Si₂O₈, consisting of double layers of [Al₂Si₂O₈] and Ba²⁺ ions interlayers with orthorhombic and hexagonal symmetries, known as a and b-hexacelsian, respectively (Dondur et al., 2005; Lopes-Badillon et al., 2013). It is important to emphasize that other cations can replace Al³⁺ and Si⁴⁺ (i.e., Ge⁴⁺ and Ga³⁺) in the TO₄ units of the framework, as well as out net cations (i.e., Li⁺, Na⁺, K⁺, Co²⁺, Pb²⁺, Ca²⁺ and Sr²⁺), which makes it possible to obtain new structures of technological interest (Wang et al., 2016; Gorelova et al., 2024).

 

Figure 1- Illustration of the structure celsian (left) and b-hexacelsian (right) obtained by Vesta^® software.

 

Due to its unique properties of corrosion resistance, very high thermal stability, mechanical strength, electrical and dielectric properties, this mineral phase has been widely investigated in terms of obtaining its synthetic analogue in the laboratory, modifications to its chemical composition, characterizations, and noble applications such as advanced ceramic, electrical insulation, materials for aeronautical applications and aerospace (Radosavljevic-Mihajlovic et al., 2015; López-Badillo et al., 2015).

There are several synthetic routes to produce celsian based on commercial reagents, including sol-gel, solid-state and hydrothermal reactions. Since the mid-1990s, there has been an extension to raw materials of natural origin (clay minerals), which after zeolitization process converts into celsian at high temperatures (> 1000 ºC). Among the most notable works are synthesis of celsian from faujasite and zeolite A-type zeolites, after heating at 1200º C.  In addition, Sr-celsian has also been obtained from the zeolite described above, based on the feldspar slawsonite, which has the formula, (Sr,Ca)Al₂Si₂O₈ SrAl₂Si₂O₈, a monoclinic mineral (Ptáček et al., 2016, Wang et al., 2016).

This paper presents a study on the production of b-hexacelsian from Ba-rich sodalite material. It is worth noting that the zeolitic material was obtained from bauxite tailings from Amazon by Bayer-type conditions.

 

MATERIAL AND METHODS

The following reagents were used to produce the materials obtained in this work: NaOH (Neon reagent grade), BaCl₂ (Neon reagent grade) and bauxite washing clay (BWC) collected at the Miltônia mine in Paragominas county, Pará state, belonging to the Hydro^® mining company. For the synthesis of the sodalite phase, the methodology of Melo et al. (2017) was used, who synthesized sodalite from Bayer process conditions. Initially, an acid leaching experiment of BWC with 0.5 mol.L^-1 of H₂SO₄ was used to remove hematite and gibbsite phases. After filtering and washing, the solid material (BWC-LIX) obtained was pulverized, mixed with NaOH and heated at 350º C/4h to obtain a fused material, which was then hydrothermally treated with 30 mL of deionized water at 90ºC/4h. The product was washed with deionized water, dried and coded as Na-ZEO. For the synthesis of Ba-sodalite, a simple cation exchange process was used by adding 1 g of Na-ZEO in a 1 mol.L^-1 of BaCl₂ solution at room temperature for 24 hours. The solid obtained was filtered, washed with deionized water, dried and coded as Ba-ZEO. Finally, b-hexacelsian was synthesized by heat-treating of Ba-sodalite (Ba-ZEO sample) at different range temperature (100 to 900º C), with a heating rate of 50° C min^-1.

The chemical composition of BWC was analyzed by X-ray fluorescence (Axios Minerals, from Panalytical) spectrometer. X-ray diffraction (XRD) was measured in a D2 Phaser diffractometer (Bruker), copper tube (CuKa = 1.5406 Å) at 30 kV and 10 mA. FT-IR analysis was performed by using a spectrometer Vertex 70 (Bruker). SEM analysis (TESCAN Vega) was employed to obtain the morphology of the starting materials and synthetic products.

 

RESULTS AND DISCUSSIONS

The chemical and mineral composition of BWC (Tab. 1 and Fig. 2a) showed that the starting material consisted of high levels of Al₂O₃ (43.6% m/m), SiO₂ (29.2% m/m), Fe₂O₃ (22.3% m/m) and TiO₂ (3.17% m/m). And is composed of gibbsite (PDF 00-012-0460), hematite (PDF 00-013-0534), anatase (PDF 01-078-2486), quartz (PDF 01-082-0512) and kaolinite (PDF 00-006-0221) were identified. A complementary FTIR spectroscopic characterization of the starting material was also carried out (Fig. 2b) and showed characteristic bands of Si-O stretching at 1101 and 789 cm^-1 well correlated to the quartz mineral. The bands at 1033 and 913 cm^-1 corresponded to the Si-O and Al-OH stretching in kaolinite structure, while the band at 537 cm^-1 could be ascribed to the Fe-O vibrations of hematite (Fe₂O₃). Fig. 2c shows the XRD pattern of BWC-LIX, which indicates the absence of the hematite and gibbsite phases. Only kaolinite and anatase were identified in the sample, as also observed by the presence of FTIR bands of Al-O-H stretching at 3660 cm^-1, Al-O-H at 914 cm^-1, Si-O-Si at 670 cm^-1 (Fig. 2d). The bands at 604 and 470 cm^-1 were well correlated with the Ti-O vibrations of anatase (Iriarte et al., 2005; Saikia and Parthasarathy, 2010; Chougala et. al., 2017; Ahmad et al., 2021).

 

Figure 2 – XRD pattern (a) and FTIR spectra (b) of BWC. XRD pattern (c) and FTIR spectra (d) of BWC-LIX. (Kln = kaolinite, Gbs = gibbsite, Ana = anatase, Hem = hematite).

 

Table 1- Chemical composition of BWC.Table Tab. 1_Celsiana

Chemical elements as oxides	SiO2	Al2O3	Fe2O3	TiO2	SO3	K2O	ZrO2
Contents (Wt. %)	29.2	43.6	22.3	3.17	0.227	0.134	0.251

 

The XRD patterns of Na-ZEO and Ba-ZEO are shown in Fig. 3. For the Na-ZEO sample, the XRD pattern was characterized by well-defined peaks at 13.81°, 24.04°, 34.27°, 42.31°, 51.41° (2 theta), which corresponded to the (110), (211), (222), (330) and (431) planes of cubic sodalite (PDF 01-082-1812). The average crystallite size calculated using the Scherrer equation was 58 Å. On the other hand, the XRD pattern of Ba-zeo indicated disordering in the sodalite framework after ion exchange treatment with Ba²⁺ ions, as observed by the low intensity and definition of the peaks. In addition, amorphous material may be present in the Ba-ZEO sample.

Figure 3 – XRD pattern of Na-ZEO and Ba-ZEO. SO: sodalite.

 

The thermal transformations of Ba-sodalite into celsian were monitored by XRD analysis and shown in Fig. 4. The results revealed that even at a relatively low temperature (100º C), the barium-doped sodalite structure showed a broadening of its main peaks with low intensity, suggesting an intense decrease in the ordering of the zeolitic structure. As the temperature increased, this disorder became more pronounced, and the structure probably transformed into a quasi-amorphous phase between 300-700º C. Up to 900º C, the XRD pattern revealed the presence of peaks at 11.48, 22.66, 30.26, 33.96 and 41.16º (2 theta), which were well correlated with the (001), (101), (012), (110) and (11-2) reflections of the hexacelsian phase (PDF 01-088- 1050). For the sample heat-treated at 1000º C, in addition to the hexagonal celsian phase, mullite (01-088-1050) was also identified. It is worth noting that these results for the thermal behaviour of Ba-sodalite are like those described for zeolite A and 13 X doped with Ba, which were synthesized to obtain celsian (Radosavljevic´-Mihajlovic et al., 2015; López-Badillo et al., 2013; Wang et al., 2016).

 

Figure 4 – XRD pattern of BaZEO heated at 100, 300, 500, 700, 900 and 1000º C for 1 h. (SO = Sodalite, HC = hexacelsian, MU = Mullite).

 

A morphological characterization of the starting material leached by H₂SO₄ (BWC-LIX), zeolitic precursor (Na-ZEO) and its product heated at 900 ºC (Ba-ZEO-900) were carried out by using scanning electron microscopy (Fig. 5). A pseudo-hexagonal plate morphology could be identified with an average size of 1 mm and thickness of 0.32 mm (Fig. 5a, b). This morphology is common in clay minerals and showed that kaolinite has preserved its plate morphology, despite of acid treatment over 12 h. For sodium sodalite sample (Fig. 5c), aggregates of sticks-shaped morphology with an average size of 15 mm and 1 mm thickness were observed. It is worth noting that this morphology differs from that in wool ball reported for sodalite obtained from kaolin tailings (Paz et al., 2010; Sousa et al., 2020), suggesting that pre-treatment by alkaline fusion may interfere the morphology of the final product. After the sintering process at 900 ºC, it was possible to observe a complete transformation of the sticks into aggregates with an undefined shape of hexagonal celsian (Fig. 5d).

 

Figure 5 – SEM analysis of BWC-LIX (a), Na-ZEO (b, c) and Ba-ZEO heated at 900º C (d).

 

CONCLUSIONS

The conversion of bauxite washing clay (BWC) from Amazon Region (Brazil) into b-hexacelsian-type material was proposed. Initially, the BWC was transformed into Na-sodalite, which presented sticks-shaped morphology. After ion exchange with Ba²⁺ ions, the sodalite structure underwent intense structural disorder, collapsed into amorphous barium aluminosilicate material, and recrystallized as pure b-hexacelsian up to 900º C. Our results have shown that a new and abundant raw material can be used to synthesize a product of great value to the ceramics industry.

 

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