Residual fines as potential raw materials for M-S-H cements: processing and characterization

Finos residuais como potenciais matérias-primas para cimentos M-S-H: beneficiamento e caracterização

Abstract

This study presents the characterization and a strategy for processing residual fines for their application in the production of magnesium silicate hydrate (M-S-H) binders. Quartzite mining waste (QW), soapstone waste (SW), and sugarcane bagasse ash (SCBA) were evaluated. Initially, the raw materials were characterized by XRF, XRD, FTIR, SEM/EDS, and thermogravimetry. The samples were then subjected to a grinding study and characterized by laser granulometry and SEM/SE. The processed QW and SW samples exhibited high fineness (D₉₀ of 13.5 and 42.9 µm, respectively) and a well-graded and continuous particle size distribution. The processed SCBA presented a high SiO₂ content (60.1%), predominance of amorphous phase (53.7%), and a high specific surface area (49.9 m²/g). Based on the results, the QW and SW are expected to perform effectively as fillers, reducing costs and contributing to the microstructure and mechanical performance of the matrices. The SCBA, in turn, stands out as a potential source of reactive silica (SiO₂) for the synthesis of M-S-H cements. The study aligns with circular economy principles and offers alternatives for utilizing industrial waste in the Brazilian construction industry, opening new possibilities for research on eco-efficient M-S-H systems.

Keywords
Magnesium silicate hydrate; Magnesium-based cements; Industrial waste; Sugarcane bagasse ash; Quartzite mining waste; Soapstone waste

Resumo

Este estudo apresenta a caracterização e uma estratégia de beneficiamento de finos residuais para aplicação na produção de ligantes de silicato de magnésio hidratado (M-S-H). Foram avaliados resíduos da mineração de quartzito (RQT) e pedra-sabão (RPS) e uma cinza de bagaço de cana-de-açúcar (CBCA). Inicialmente, as matérias-primas foram caracterizadas por FRX, DRX, FTIR, MEV/EDS e Termogravimetria. Em seguida, as amostras foram submetidas a um estudo de moagem e posteriormente caracterizadas por granulometria a laser e MEV/SE. As amostras beneficiadas de RQT e RPS exibiram elevada finura (D₉₀ de 13,5 e 42,9 µm, respectivamente) e distribuição granulométrica bem graduada e contínua. A CBCA beneficiada apresentou elevado teor de SiO₂ (60,1%), predominância de material amorfo (53,7%) e elevada superfície específica (49,9 m²/g). A partir dos resultados obtidos, pode-se estimar um comportamento adequado do RQT e do RPS como fíleres, reduzindo os custos e contribuindo na microestrutura e no desempenho mecânico das matrizes. A CBCA, por sua vez, se destaca como potencial fonte de sílica reativa na síntese de cimentos M-S-H. O estudo alinha-se com os princípios da economia circular e oferece alternativas para o aproveitamento de resíduos industriais na construção civil brasileira, apresentando novas possibilidades para o desenvolvimento de sistemas M-S-H ecoeficientes.

Palavras-chave
Silicato de magnésio hidratado; Cimentos magnesianos; Resíduos industriais; Cinza de bagaço de cana-de-açúcar; Resíduo de quartzito; Resíduo de pedra-sabão

1 Introduction

The elevated rate of CO₂ emissions and the massive consumption of non-renewable raw materials intrinsic to the production of ordinary Portland cement (OPC), have driven the development of low-carbon cementitious composites and the utilization of industrial waste in the construction sector (Scrivener; John; Gartner, 2018). In this context, the development of magnesium silicate hydrate (M-S-H) cements using residues from agribusiness and mining emerges as a promising alternative for the Brazilian scenario (Bernard, 2022; Lopes et al., 2023).

1.1 M-S-H binders

The production of M-S-H cements involves the in situ mixing of a magnesium oxide (MgO) source and a reactive silica (SiO₂) source, typically silica fume, with the potential inclusion of a filler (Tran; Scott, 2017; Walling; Provis, 2016). The precipitation of M-S-H (MgO-SiO₂-H₂O) occurs upon mixing these binders with water, leading to MgO hydration and the formation of magnesium hydroxide [Mg(OH)₂], also known as brucite, followed by the partial dissolution of SiO₂ and its gradual reaction with Mg(OH)₂ (Szczerb et al., 2013; Temuujin; Okada; MacKenzie, 2005).

M-S-H gels are poorly crystalline phases with a high capacity for particle agglomeration (Mármol et al., 2016; Szczerb et al., 2013), similar to the calcium silicate hydrate (C-S-H) formed during OPC hydration. The lower alkalinity of M–S–H systems (pH < 11), compared with C-S-H systems, represents an advantage for incorporating plant fibers as reinforcement (Mármol et al., 2016; Mármol; Savastano, 2017) and for immobilizing hazardous waste and heavy metals (Walling et al., 2015; Zhang; Vandeperre; Cheeseman, 2012). Additional benefits of these binders include their potential for CO₂ capture (Abdel-Gawwad et al., 2020) and their suitability for emerging manufacturing technologies such as 3D printing (Panda et al., 2021).

1.2 Sugarcane bagasse ash

Brazil is the world’s largest producer of sugarcane, with a harvest of 713.2 million tons in the 2023/2024 season (CONAB, 2024). The plant is primarily utilized by the sugar-ethanol industry, whose processes generate a fibrous by-product known as sugarcane bagasse. The bagasse is commonly burned (300-900°C) in thermoelectric power plants, producing a residual ash with properties of interest to the construction sector, particularly for the production of cementitious composites (Cordeiro et al., 2008; Khalil; Aslam; Ahmad, 2021; Paris et al., 2016).

The production of sugarcane bagasse ash (SCBA) in Brazil is estimated at approximately 4 million tons per year, with most of this output concentrated in the Southeast, Midwest, and Northeast regions of the country (Cordeiro, 2006; Lopes et al., 2023; Andrade Neto et al., 2021). The material exhibits a predominantly amorphous structure and is composed mainly of SiO₂ and the presence of various other oxides, including Al₂O₃, CaO, and Fe₂O₃ (Li et al., 2022). The reactivity of SCBA has been demonstrated to be associated with its fineness, amorphous content, and notably, its specific surface area (Figueiredo; Pavía, 2020). To optimize these properties, its processing for use as a raw material in construction typically involves a series of steps, including oven drying, grinding, and recalcination. Mechanical activation aims to refine the particles and increase the ash’s surface area (Cordeiro et al., 2009), whereas secondary calcination enhances amorphicity and reduces the material’s loss on ignition (Yadav et al., 2020). This process, however, increases the carbon footprint and cost of SCBA and may be omitted without significant loss in performance, depending on the raw material used and the initial burning conditions (Cordeiro et al., 2008, 2009; Cordeiro; Tavares; Toledo Filho, 2016; Figueiredo; Pavía, 2020; Sousa et al., 2022).

Several studies have evaluated SCBA as a partial replacement for OPC. In addition to reducing costs (França et al., 2023), the incorporation of SCBA in mortars and concretes enhances mechanical performance and refines the pore structure of the matrices (Amin, 2011; Ganesan; Rajagopal; Thangavel, 2007), also contributing to improved durability (Le; Sheen; Lam, 2018; Mello et al., 2020). The presence of amorphous silica imparts pozzolanic properties to the material, as it reacts with calcium hydroxide [Ca(OH)₂] during cement hydration, leading to the supplementary formation of C-S-H (Cordeiro; Toledo Filho; Fairbairn, 2009).

Studies have also demonstrated the feasibility of using SCBA as an alternative precursor in alkali-activated binders (Castaldelli et al., 2016; Sousa et al., 2022; Yadav et al., 2020). As in OPC-based matrices, the reactivity of SCBA is a determining factor in the alkali-activation process (Yadav et al., 2020). In addition to being a sustainable alternative, the residue can enhance the physical and mechanical properties of the composites when incorporated at optimized dosages (e.g., appropriate SiO₂/Al₂O₃ ratio) (Sousa et al., 2022). In this regard, the high SiO₂ content and predominantly amorphous structure of SCBA, combined with its already demonstrated performance in reactive systems, suggests its potential use as a SiO₂-rich precursor for the development of M-S-H binders.

1.3 Quartzite waste

Quartzite, a metamorphic rock, is frequently utilized in civil construction as an ornamental stone for countertops and coating (Martins; Peixoto; Mendes, 2023). The extraction process entails the removal of the soil cover, the extraction of the friable quartzite, and the implementation of blasting techniques (Santos, 2015). Following the extraction process, the material is then fragmented into slabs or blocks and subsequently processed for commercialization (Santos, 2015). These operations generate granular and powdery wastes, which can account for more than 90% of the extracted material (Collares; Francklin; Motta, 2012). When these materials are deposited in the environment, they accumulate and alter the original landscape, potentially silting watercourses and polluting the atmosphere (Reis; Ribeiro; Reis, 2020).

In Brazil, quartzite extraction occurs primarily in the state of Minas Gerais, with notable production centers in the regions of Alpinópolis, Diamantina, São Thomé das Letras, and Ouro Preto (FEAM, 2015). Despite the compositional variability among these regions, quartzite mining waste (QW) consists mainly of SiO₂. This characteristic is attributable to the elevated quartz content in its mineralogical composition (Martins; Peixoto; Mendes, 2023). The material may also contain other oxides (e.g., Al₂O₃, K₂O, CaO, and MgO), which are associated with different minerals such as feldspar, mica, dolomite, muscovite, and kaolinite (Carvalho et al., 2021; Dantas Júnior; Barros; Neves, 2018; Martins et al., 2024; Martins; Peixoto; Mendes, 2023).

Due to its chemical stability and low amorphous content, QW aggregates exhibit structural and performance similarities to conventional aggregates when incorporated into cement-based matrices (Martins; Peixoto; Mendes, 2023; Mendes et al., 2019). Furthermore, the waste generated during quartzite extraction and processing can be used as a partial replacement for OPC in cement-based composites. Carvalho et al. (2021) evaluated the performance of processed QW as a filler in mortars. In their study, the material was obtained through high-efficiency grinding (180 min in a 200-rpm horizontal ball mill followed by 45 min in a 400-rpm planetary ball mill). As a result, the mortar produced with 25% volumetric replacement exhibited mechanical strength and setting time equivalent to those of the reference mortar. This performance was attributed to the nucleation effect promoted by QW, which enhanced the hydration of cement particles (Carvalho et al., 2021). Li et al. (2021) also highlighted processed QW filler as a sustainable alternative for OPC-based matrices. A replacement level of 30% was adopted, and the powder with the highest specific surface area led to greater mechanical strength and improved pore structure refinement (Li et al., 2021). In both studies, mechanical activation by grinding was crucial for optimizing the material’s performance. In this context, considering that fillers commonly incorporated into conventional cement-based matrices have demonstrated satisfactory performance in M-S-H systems (Capelo; Mármol; Rossignolo, 2023; Tran; Dhakal; Scott, 2020; Tran; Scott, 2017), QW represents a promising component for this class of magnesium-based cements.

1.4 Soapstone waste

As with quartzite, the state of Minas Gerais also stands as a major producer of steatite, popularly known as soapstone. The Ouro Preto-MG microregion contains numerous deposits of soapstone, particularly in the district of Santa Rita de Ouro Preto, where approximately 4,800 tons of the rock are extracted annually (Rodrigues; Lima, 2012). This metamorphic material is extensively utilized as an ornamental stone in civil construction and in the production of handicrafts (Huhta; Kärki, 2018; Rodrigues; Lima, 2012).

Soapstone is composed primarily of talc, a hydrated magnesium silicate mineral that has the lowest hardness on the Mohs scale (Sudalaimani; Shanmugasundaram, 2014). This characteristic contributes to the material’s high softness and workability, which is reflected by its elevated SiO₂ and magnesium oxide (MgO) contents. According to Rodrigues and Lima (2012), only about 40% of the extracted soapstone is recovered, resulting in a disposal of approximately 60% of the original rock. Additionally, handicraft production generates significant amounts of fine dust, which poses risks to both the environment and the health of artisans (Carneiro et al., 2010; Santos, 2009). An alternative to mitigate these impacts and support the economic development and production chain of these workshops is the use of these residual fines in the construction industry.

Sudalaimani and Shanmugasundaram (2014) incorporated 0-25% of a soapstone powder as a partial replacement for OPC in mortar production. Mortars containing up to 20% powder exhibited higher mechanical strength than the unmodified mortar (Sudalaimani; Shanmugasundaram, 2014). In studies conducted by Gnanaraj and collaborators (Gnanaraj et al., 2021; Gnanaraj; Chokkalingam; Thankam, 2020), a soapstone powder was evaluated as a mineral addition in self-compacting concrete. Replacement levels of 0-25% by mass and fixed water-to-fines ratio were adopted. As a result, the incorporation of soapstone increased mechanical strength up to the 20% dosage and improved durability-related properties (e.g., water absorption, porosity, and chloride penetration) across all replacement levels. The pore refinement promoted by the powder was attributed to its filler effect and the formation of M-S-H (Gnanaraj et al., 2021). Studies have also demonstrated the feasibility of using soapstone waste (SW) powder in the production of soil-lime bricks (Ferreira; Reis; Lima, 2015), red ceramic bricks (Souza et al., 2016), and epoxy resin-based polymer composites (Alves et al., 2020). However, its use in the manufacture of M-S-H binders has not yet been reported in the literature.

1.5 Research aim

Although the incorporation of waste materials into conventional cement matrices has been extensively documented in the extant literature, the utilization of these materials within M-S-H systems remains underexplored. Studies addressing this topic to date have focused primarily on the total or partial replacement of commercial silica fume with alternative SiO₂ sources such as metakaolin (Shah; Scott, 2021), fly ash (Zhang et al., 2016), ground glass (Liang et al., 2023), and rice husk ash (Capelo; Mármol; Rossignolo, 2023; Sonat; Unluer, 2019). The latter has emerged as an abundant and effective source of amorphous silica, reinforcing the potential for utilizing other agricultural ashes produced on a large scale in Brazil, such as that derived from sugarcane bagasse combustion.

In addition to their use as alternative precursors, industrial wastes may also be incorporated into M-S-H cement-based composites as fillers within the mixtures. The incorporation of fillers has been demonstrated to reduce production costs, refine the microstructure, and enhance the mechanical performance of M-S-H matrices (Capelo, 2021; Tran; Dhakal; Scott, 2020; Tran; Scott, 2017). Such benefits can be achieved by valorizing inert industrial wastes generated from mining and the processing of natural stones, such as quartzite and soapstone.

This study aims to characterize industrial residues and propose a processing methodology for their use in the production of M-S-H cement-based binders. To this end, a SCBA sample was evaluated as a prospective SiO₂ source, while QW and SW samples were investigated as potential filler materials through a grinding study and a comprehensive characterization of their chemical, mineralogical, physical, and morphological properties. The study considers the social, environmental, and economic context of Brazil, with emphasis on the micro-region of Ouro Preto-MG. It also presents alternatives for the valorization and optimized use of agro-industrial and mining residues, aiming at the development of more eco-efficient cement-based composites.

2 Materials and methods

2.1 Materials

The industrial residues used in this study are Illustrated in Figure 1. The SCBA was supplied by the sugar-ethanol plant BEVAP Bioenergia Company (João Pinheiro, Minas Gerais, Brazil). The QW was obtained from Sulminas Sílicas Company (Três Corações, Minas Gerais, Brazil), and the SW was provided by Ouro Preto Pedra-Sabão Company (Ouro Preto, Minas Gerais, Brazil).

Figure 1
Images from SCBA, SW, and QW

2.2 Chemical and mineralogical characterization

For the chemical and mineralogical characterization tests, the samples were dried at 100 °C to constant mass and then comminuted in a porcelain mortar until passing through a 45 µm sieve. The proposed industrial residues (SCBA, QW, and SW) were chemically characterized by X-ray fluorescence (XRF; PANalytical Epsilon3x) and Fourier transform infrared spectroscopy (FTIR; Thermo Scientific Nicolet iS5). For the XRF analysis, the samples were placed in a polymeric sample holder covered with a 5 µm polypropylene film. The loss on ignition test was performed in a muffle furnace at 1200 °C for 3 h. For the FTIR analysis, the samples were prepared as KBr pellets (1:120 ratio). The spectra were recorded by accumulating 50 scans at a resolution of 8 cm⁻¹ over the range of 400-4000 cm⁻¹. The preparation of the pellets and the measurements were carried out under ambient temperature and relative humidity conditions. The data were processed using the “automatic baseline correction” function in OMNIC software.

The mineralogical profiles of the materials were determined by X-ray diffraction (XRD; Bruker D2 Phaser). To reduce the preferential orientation of residual fines, the samples were loaded into a PMMA sample holder using the back-loading method. The analyses were performed using CuKα radiation at 40 kV and 40 mA, with a step size of 0.02° 2θ over a 6-80° 2θ range. Mineralogical quantification by XRD (QXRD) was performed using Rietveld refinement with PANalytical X’Pert HighScore Plus V3.0 software and the 2024 Crystallography Open Database. For this purpose, 20 wt.% of zincite (ZnO, analytical grade, 99% purity) was added to the samples as an internal standard.

The analysis of the material composition was complemented by scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS; TESCAN Vega3) and thermogravimetry/derivative thermogravimetry (TG/DTG; Shimadzu DTG-60H). For the SEM/EDS analysis, the powder samples were deposited onto metal stubs coated with carbon tape and sputter-coated with gold (Quorum Q150R ES). For the TG/DTG analysis, the powder samples were placed in alumina crucibles and analyzed under the following conditions: heating rate of 10 °C/min, an isothermal step at 25 °C for 30 min, followed by heating from 25 to 1100 °C under an N₂ atmosphere (50 mL/min).

2.3 Grinding study

The materials were dried in an oven at 105 °C for 24 h and then subjected to a high-energy grinding program (Restch PM 100 planetary ball mill; 400 rpm) based on the procedure proposed by Carvalho et al. (2019). The grinding process was conducted for up to 60 min, with samples collected at 5 min intervals. Table 1 presents detailed information on the grinding program and the configuration parameters adopted.

Table 1
Grinding program and setup parameters

Parameter	High-energy program
Jar and balls (material)	Zirconia (ZrO2)
Jar volume (cm³)	250
Input material volume/cycle (cm³)	80 (32%)
Rotation speed (rpm)	400
Balls volume (cm³)	64.3 (26%)
No. of balls/diameter (mm)	99/10 e 191/5

• Source: adapted from Carvalho et al. (2019).

The raw samples and the samples collected during the grinding studies were characterized by laser diffraction using a Bettersize 2000 analyzer (dispersion medium: distilled water), applying the Fraunhofer model. Since mineral comminution is an energy-intensive process (Deniz, 2013), continuing the grinding process after the stabilization of the characteristic diameter (D₉₀) can potentially result in increased energy consumption without substantial gains in particle size reduction. Consequently, as a technical criterion, the optimal grinding times were defined as the points at which the reduction observed between two consecutive grinding intervals was less than 2 µm.

2.4 Physical and morphological characterization

The specific densities of the SCBA, QW and SW samples were determined by vacuum pycnometry (adapted from ABNT, 1984). The specific surface areas of the fines obtained at the optimal grinding times were measured using the BET method (Anton Paar Nova 600; N₂ adsorption). Finally, the morphological characteristics of the processed residues were analyzed by scanning electron microscopy in secondary electron mode (SEM/SE; TESCAN Vega3), using gold-coated samples.

3 Results and discussion

3.1 Chemical and mineralogical properties

Table 2 presents the chemical compositions of the SiO₂ source and the residual fillers evaluated in this study. SCBA is predominantly composed of silicon and aluminum, with other elements in smaller proportions, such as iron, calcium, and magnesium. Its reactivity is directly related to the amorphous SiO₂ content (Zhang et al., 2020). These results are consistent with studies that have assessed the material as a pozzolanic agent in Portland cement matrices (Frías; Villar; Savastano, 2011; Andrade Neto et al., 2021) and as an alternative precursor in alkali-activated matrices (Sousa et al., 2022). The QW evaluated in this study originates from a rock composed predominantly of quartz, which explains the high SiO₂ content in its composition (Martins; Peixoto; Mendes, 2023). The SW, in turn, contains high levels of silicon and magnesium. This is due to the fact that steatite is a rock rich in talc [Mg₃Si₄O₁₀(OH)₂], a hydrated magnesium silicate mineral (Luukkonen et al., 2019; Souza; Silva; D’Almeida, 2021). The material analyzed also exhibits notable amounts of iron, calcium, and aluminum, likely associated with the presence of dolomite [CaMg(CO₃)₂] and phyllosilicate minerals from the chlorite group [(Mg,Fe)₃(Al,Si)₄O₁₀(OH)₂.(Mg,Fe)₃(OH)₆] (Rodrigues; Lima, 2012). Overall, the contents of the compounds identified in the compositions of the studied residues fall within the ranges reported in the literature.

Table 2
Chemical composition of the proposed residues and ranges of occurrence according to the literature data

Compound/Content (%)	Measured			Literature data
	SCBA	QW	SW	SCBA	QW	SW
SiO2	60.1	91.9	44.5	55.1-78.3	55.2-96.5	38.4-58.9
MgO	1.4	0.2	29.9	0.6-6.4	0.1-1.7	27.8-38.0
Al2O3	14.9	5.4	4.1	1.1-29.2	7.8-18.0	1.6-3.7
Fe2O3	4.3	0.8	5.3	0.9-12.3	0.4-2.7	5.0-16.6
CaO	2.6	-	2.7	1.0-12.6	0.8-19.4	0.1-3.0
K2O	2.6	0.9	-	2.0-8.3	0.8-16.1	-
P2O5	1.7	-	-	-	-	-
Others	1.6	0.8	0.8	-	-	-
Loss on ignition (%)	10.8	0.4	12.7	0.4-21.0	1.2-1.9	5.1-21.3

• Source: adapted from Khalil, Aslam and Ahmad (2021), Martins, Peixoto and Mendes (2023), Cota et al. (2012), Ferreira, Reis and Lima (2015), Luukkonen et al. (2019), Souza et al. (2016) and Strecker et al. (2010).

Figure 2 and Table 3 present the results of the XRD analysis and the mineralogical quantification by Rietveld refinement (QXRD), respectively. In the QW sample, quartz (SiO₂) accounted for 96.8% of the identified phases. Minor amounts of biotite [K(Mg,Fe)₃(AlSi₃O₁₀)(F,OH)₂] and kaolinite [Al₂Si₂O₅(OH)₄] were also detected, which justify the presence of MgO, Al₂O₃, Fe₂O₃, and K₂O in its chemical (Table 2). As expected, SW sample presents significant contents of phyllosilicates such as talc, chlorite, and clinochlore [(Mg₅Al)(AlSi₃)O₁₀(OH)₈]. The QXRD analysis also confirms the presence of dolomite, as well as measurable amounts of magnesite (MgCO₃) and tremolite [Ca₂Mg₅Si₈O₂₂(OH)₂]. The mineralogical heterogeneity of steatite has also been reported in previous characterization studies (Ilyina; Klimovskaya; Bubnova, 2023; Luukkonen et al., 2019; Rodrigues; Lima, 2012). It's worth mentioning that, despite its predominantly crystalline structure and inert nature, studies have reported that mechanical activation can promote amorphization of talc (Andrić et al., 2014; Liao; Senna, 1992), which includes the formation of amorphous silica in its composition and the potential reactivity of SW in M-S-H systems. Finally, the only crystalline phase identified in the SCBA sample was quartz (SiO₂). Although the composition of SCBA is influenced by the combustion process, the material exhibits a predominantly amorphous structure (53.7%), evidenced by the halo observed between 20° and 30° 2θ (Capelo; Mármol; Rossignolo, 2023; Cordeiro; Toledo Filho; Fairbairn, 2009; França et al., 2023). The presence of crystalline quartz in SCBA can be attributed to impurities adhered to the material during harvesting, such as sand (Pereira et al., 2018).

Figure 2
Diffractograms of the proposed residues

Table 3
Mineralogical composition of the proposed residues

Phase/Content (%)	SCBA	QW	SW
Quartz	46.3	96.8	-
Chlorite	-	-	30.3
Talc	-	-	25.7
Clinochlore	-	-	21.9
Magnesite	-	-	8.1
Dolomite	-	-	7.5
Tremolite	-	-	6.6
Biotite	-	1.8	-
Kaolinite	-	1.1	-
Amorphous	53.7	0.2	0.0

Figure 3 presents the FTIR spectra of SW, QW, and SCBA. All samples present peaks at 3436-3444 cm-1 and 1618-1638 cm-1 in the FTIR spectra. In previous studies related to SCBA (Frías; Villar; Savastano, 2011; Pantongsuk et al., 2026), as well as for talc (Yang et al., 2006), similar bands near those observed in the present study were related to water. Based on this, the observed bands may be derived from sample preparation and measurement, considering exposure to humidity, which may increase the water content in the samples and influence the FTIR spectra.

Figure 3
FTIR spectra of the proposed residues

The bands at approximately 1168, 1081, 795, 779, 693, and 459 cm^-1 identified in QW and SCBA correspond well to characteristic quartz bands in the ranges 1080-1175, 780-800, 695, and 464 cm^-1 associated with Si–O (Saikia; Parthasarathy; Sarmah, 2008). Similar bands (1086, 798, 778, 695, and 468 cm^-1) have also been attributed to quartz in a clay characterization study (Jozanikohan; Abarghooei, 2022). The presence of quartz in SCBA has already been reported in previous studies (Cordeiro et al., 2009; Soares et al., 2016; Frías; Villar; Savastano, 2011; Pereira et al., 2018). The assignment of quartz-related bands in the FTIR characterization of SCBA shows consistency with findings from other studies on Brazilian SCBA. For example, in the FTIR analysis of SCBA conducted by Frías, Villar and Savastano (2011), the bands at 1176, 1106, 1093, 798, 696, and 472 cm^-1 bands were correlated to quartz. The presence of quartz is further supported by good correspondence with the reference FTIR bands reported for mineral quartz (SiO₂) (RRUFF, 2025a).

Regarding QW, the bands at 3694, 3617, 1034, 796, and 459 cm^-1 may be associated with kaolinite, as they show good correspondence with the reference bands reported for this phase (3693, 3620, 1031, 792, 471 cm^-1) by Van Der Marel and Beutelspacher (1976), in agreement with the QXRD results (Figure 2). Additionally, the bands at 459 and 519 cm^-1 are close to the bands at 451-462 and 520 cm^-1, also present in the biotite spectra (Van Der Marel; Beutelspacher, 1976).

FTIR analysis of SW reveals bands at 3676 and 3660 cm^-1, which may be associated with -OH group (Karagöz et al., 2025; Pinto et al., 2018). Bands in the spectra of tremolite (3675 and 3653 cm^-1), talc (3680, 3658 cm^-1), chlorite (3670 cm^-1), and clinochlore (3678 cm^-1) are similar to those identified in this region (Van Der; Beutelspacher, 1976). The band at 3567 cm^-1 is likely related to chlorite and clinochlore as well, given the 3560-3572 cm^-1 bands reported for spectra chlorite minerals (Van Der Marel; Beutelspacher, 1976).

QXRD analysis of SW revealed 15.6% carbonate phases associated with dolomite and magnesite (Table 3). The FTIR bands identified at 2527, 1443, 884, and 728 cm^-1 show good similarity to those reported by Manni et al. (2022) and associated by the authors to the carbonate group (CO₃^2-). These bands also correlate well with the FTIR bands of the dolomite (728, 882, 1432 cm^-1) and magnesite (748, 886, 1445 cm^-1) based on Van Der Marel and Beutelspacher (1976). Other identified bands also approximate those attributable to talc, including 1045 (Si-O), 1017 (Si-O-Si), 673 (Si-O-Mg), 463 (Mg-O), and 451 (Si-O-Mg) cm^-1 (Van Der Marel; Beutelspacher, 1976). The occurrence of the clinochlore phase in a previous study on a steatite sample (Pinto et al., 2018) was reported with the presence of a shoulder at 951 cm⁻¹, which is also observed in the present study. This band may be associated with the Si–O–Mg (956 cm⁻¹) of clinochlore, further supported by the identification of bands at 1045 (Si-O), 665 and 451 (Si-O-Mg), and 463 (Si-O) cm^-1 (Van Der Marel; Beutelspacher, 1976). Some bands in the FTIR spectrum of SW also approach 437,640, 683, 945, and 3672 cm⁻¹, which correspond to bands reported in the tremolite spectrum (RRUFF, 2025b), a phase that was likewise identified by QXRD. Overall, the results show good compatibility with the phases identified through QXRD analysis. However, given the multiphase characteristic of the samples, overlapping bands associated with different minerals are expected.

As with the FTIR data, the thermogravimetric behavior of the raw materials, shown in Figure 4, aligns with the QXRD results. The SW exhibited an initial mass loss of 7.9% between 540 ºC and 710 ºC, followed by a secondary mass loss of 2.9% between 850 ºC and 1080 ºC. The first range of mass losses is possibly related to the dehydroxylation within the brucite layer of chlorite and the decarbonations of dolomite and magnesite (Demir et al., 2003; Ilyina; Klimovskaya; Bubnova, 2023). The second range can be mainly associated with the dehydroxylation of talc and its transformation into enstatite and amorphous silica (Liu; Liu; Hu, 2014; Ward, 1975; Wesolowski, 1984). The SCBA presented an initial mass loss of 2.0% between 30 ºC and 150 ºC, attributed to moisture evaporation, followed by a mass loss of 13.0% between 410 ºC and 640 ºC, associated with organic matter volatilization (Tabish; Zaheer; Baqi, 2025). The mass losses of the SW and SCBA samples below 1000 °C justify their loss on ignition values indicated in Table 2. Finally, the analysis of QW indicated that the specimen did not exhibit a defined mass loss peak within any temperature range, with a total mass loss of 3.0%.

Figure 4
TG/DTG curves of the proposed residues

Figures 5 and 6 present the results of the SEM/EDS analysis. Point P1 in the SCBA sample indicates a predominance of silicon and oxygen and is therefore attributed to a quartz grain. At the second point (P2), the presence of various elements is identified, including silicon, aluminum, oxygen, potassium, calcium, and phosphorus. Given that quartz was the sole crystalline phase identified SCBA (see Table 3), the presence of aluminum can be attributed to amorphous alumina (Al₂O₃) (Zhang et al., 2020). In addition, phosphorus, magnesium, potassium, and calcium are likely present in the form of soluble salts (e.g. potassium phosphate) and are related to the vegetal ash nature of the material (Lyra et al., 2021; Zhang et al., 2020). With respect to QW, the first point (P1) indicates the predominance of silicon, aluminum, and oxygen and can thus be associated with kaolinite [Al₂Si₂O₅(OH)₄]. Point P2, in turn, indicates only the presence of silicon and oxygen, representing quartz grain. Finally, point P1 in the SW sample mainly identifies silicon, oxygen, and magnesium, corresponding to a talc grain [Mg₃Si₄O₁₀(OH)₂]. At the second point (P2), silicon, magnesium, calcium, and oxygen are predominantly detected and may be associated with tremolite [Ca₂Mg₅Si₈O₂₂(OH)₂]. It is worth noting that the identification of gold in all points is due to the gold coating applied to the samples during preparation. The color-based elemental identification (Figure 6) corroborates the point analysis results and is consistent with the chemical compositions of the studied residues (Table 2), as well as with the other characterization tests performed.

Figure 5
SEM/EDS images with element identification by points

Figure 6
SEM/EDS images with element identification by color

The differences in the composition of the residues are also reflected in their visual appearance (Figure 1). SCBA presents a dark color, typically associated with the presence of unburned carbon and iron oxides. In contrast, QW displays a very light color, consistent with its high quartz content. The SW residue shows a light greenish tone, which is characteristic of minerals commonly found in soapstone, such as talc and chlorite.

3.2 Determination of grinding times

Figure 7 presents the results of the grinding studies for SCBA, QW, and SW. The curves demonstrate a correlation between the duration of high-energy grinding and the fineness parameters D₅₀ and D₉₀, which represent the particle diameters corresponding to 50% and 90% of the accumulated volume in the particle size distribution respectively.

Figure 7
Grinding curves of the proposed residues obtained from the high-energy program

The reduction in D₉₀ between 45 and 50 minutes was 1.3 µm for the SCBA sample, suggesting that additional grinding provides limited improvement in particle size refinement. Therefore, considering the diminishing grinding efficiency, an optimal grinding time of 45 minutes was established for material processing, yielding D₅₀ and D₉₀ values of 3.7 and 10.6 µm, respectively. Regarding QW, a significant reduction in the fineness parameters is observed after the first 5 minutes of grinding. However, grinding efficiency becomes marginal after 20 minutes, with a 1.2 µm reduction in D₉₀ between 20 and 25 minutes. Considering the limited additional refinement beyond this point, an optimal grinding time of 20 minutes was established for material preparation. The processed QW exhibited a D₅₀ of 3.6 µm and a D₉₀ of 13.5 µm. Finally, the curves associated with SW demonstrated a plateau from 30 minutes of grinding, indicating that further grinding leads to negligible changes in particle size distribution. Considering the small reduction in D₉₀ (0.3 µm) observed between 30 and 35 minutes, an optimal grinding time of 30 minutes was established, resulting in a material with D₅₀ and D₉₀ values of 6.4 and 42.9 µm, respectively. The reduction in D₉₀ from the raw materials to the processed materials was 90.7% for SCBA, 84.6% for QW, and 69.5% for SW.

3.3 Physical and morphological properties

Table 4 presents the physical properties of the SiO₂ source and the residual fillers after the determination of the optimal grinding times (45 min for SCBA, 20 min for QW and 30 min for SW). SCBA exhibited the highest fineness (D₉₀ of 10.6 µm), followed by QW (D₉₀ of 13.5 µm). The results obtained for these materials were significantly lower than those of SW (D₉₀ of 42.9 µm). Overall, the processed residues evaluated in this study exhibited high fineness when compared with those reported in the literature. Sousa et al. (2022) and Zhang et al. (2020) processed SCBA and obtained D₉₀ values of 64.4 and 22.1 µm, respectively. In addition, Carvalho et al. (2021) and Li et al. (2021) processed QW and used powders with a D₉₀ of 13.0 µm and D₅₀ of 6.3 µm, respectively. For the purpose of comparison, all materials investigated in this study exhibited a fineness equal to or higher than that of OPC, whose D₉₀ typically ranges from 30 to 60 µm (Carvalho et al., 2019, 2023; Costa et al., 2022).

Table 4
Physical properties of the proposed residues

Physical parameters	SCBA	QW	SW
D90 (µm)	10.6	13.5	42.9
D50 (µm)	3.7	3.6	6.4
D10 (µm)	1.1	1.0	1.5
Specific gravity (g/cm³)	2.32	2.61	2.78
Specific surface area (m²/g)	49.9	4.8	14.4

The higher density of SW (2.78 g/cm³) is possibly related to its higher iron content (5.3% de Fe₂O₃), as shown in Table 2. The iron oxide present in the material composition may also have contributed to its lower grinding efficiency (Pan et al., 2016). Although SCBA contains a significant amount of Fe₂O₃ (4.3%), the material exhibits a loss on ignition of 10.8%, which is primarily associated with the release of CO₂ during combustion. Therefore, the higher density of QW (2.61 g/cm³) compared to SCBA (2.32 g/cm³) can be justified by the higher molar mass of SiO₂ relative to CO₂, considering that the loss on ignition of the quartzite residue is considerably lower (0.4%).

The SEM images (Figure 8) complement the results presented in Table 4. The micrographs acquired at 1000x magnification confirm that the processed SW exhibits large particle sizes, whereas the processed SCBA is the finest material.

Figure 8
SEM/SE images of the proposed residues with 1000x and 8000x magnification

The SCBA image, acquired at 8000x magnification, reveals the presence of grains exhibiting irregular shapes and disparate sizes, as reported in previous studies (Pereira et al., 2018; Sousa et al., 2022; Zhang et al., 2020). The finest particles of the material, which are primarily composed of silicon and aluminum oxides, have a propensity to agglomerate around larger and more angular particles, which likely correspond to quartz grains (Cordeiro et al., 2009; Frías; Villar; Savastano, 2011). The high fineness and agglomeration tendency of the material likely contributed to its high specific surface area (49.9 m²/g), a key property for assessing its reactivity (Figueiredo; Pavía, 2020). Regarding the processed QW, its grains, mainly composed of quartz, exhibit angular shape and lower surface roughness, as reported by Li et al. (2021) and demonstrated by the SEM/EDS analysis (point QW-P2 in Figure 5). Additionally, smaller particles with irregular shapes can be observed, indicating a reduced tendency for agglomeration in comparison to the ash. The processed SW, in turn, presents spherical and rough particles, as reported by Kannaiyan et al. (2022). Lamellar and elongated shapes with pointed ends can also be observed, which are characteristic structures of talc (Al-kroom et al., 2024; Ding; Ouyang; Yang, 2016). These filaments were also clearly observed in the SEM/EDS analysis (see point SW-P1 in Figure 5). The differences in morphological characteristics, particularly surface roughness, explain the higher specific surface area of SW (14.4 m²/g) compared to QW (4.8 m²/g).

Figure 9
Particle size distribution of the proposed residues

Finally, Figure 9 presents the particle size distributions of the studied residues. The curves for QW and SW indicate a satisfactory gradation and the absence of discontinuities. Although correlated, higher surface area is commonly associated with the filler effect, as it provides additional nucleation sites for hydration products, whereas particle size distribution and fineness play a key role in improving particle packing and matrix densification (Carvalho et al., 2019; John et al., 2018; Oey et al., 2013). In this sense, despite its lower fineness, the roughness and favorable particle size distribution of SW suggest its potential as a component of M-S-H-based cements. In addition, the processed SW may still exhibit reactivity due to the mechanical activation of talc promoted by high-energy grinding (Andrić et al., 2014; Liao; Senna, 1992), which may further contribute to the formation of M-S-H gel.

4 Conclusion

This study involves the advanced characterization and subsequent processing of quartzite mining waste (QW), soapstone waste (SW), and sugarcane bagasse ash (SCBA), seeking to valorize them as potential raw materials for the production of M-S-H binders. The findings revealed that:

1. the SCBA contains 60.1% SiO₂ in its chemical composition and 53.7% amorphous phase in its mineralogical composition;

2. the physical analyses of the SCBA indicated a high fineness (D₉₀ of 10.6 µm) and specific surface area (49.9 m²/g) after 45 minutes of high-energy grinding;

3. the mineralogical structure of QW is predominantly composed of quartz (96.8%), while SW contains mainly magnesite (8.1%), dolomite (7.5%), and phyllosilicate minerals (30.3% chlorite, 25.7% talc, and 21.9% clinochlore); and

4. the QW and SW samples presented D₉₀ values of 13.5 and 42.9 µm after 20 and 30 minutes of high-efficiency grinding, respectively. Despite its coarser particle size, the SW exhibited a higher specific surface area (14.4 m²/g) compared to the QW (4.8 m²/g), and both presented a particle size distribution without discontinuities after processing.

The advanced characterization techniques employed (XRF, XRD, FTIR, TG/DTG, and SEM-EDS) have enabled a deep understanding of the chemical and mineralogical properties of the residual fines. Additionally, the grinding studies and subsequent physical and morphological characterizations allowed the optimization of material processing in terms of energy consumption, as well as the discussion of the preliminary technical suitability of the materials based on their physicochemical properties.

The results indicate that SCBA is a potential source of reactive silica, being an alternative SiO₂-rich precursor. Its good physical and morphological properties may also promote the filler effect as a secondary mechanism. Regarding the mining residues (QW and SW), both showed potential for application as mineral fillers, also considering their performance in conventional cement-based composites reported in the literature. For future research, the authors suggest determining the amorphous phases of SCBA (e.g., using the PONKCS method) and evaluating the role of mechanical activation of talc on the reactivity of SW in M-S-H systems.

The processing and characterization strategies presented reveal new opportunities for the valorization of agro-industrial and mining residues. The results show that proper treatment of fines and systematic analysis of their physicochemical properties can broaden the applicability of these residues, supporting technically feasible and environmentally relevant solutions. Overall, the study contributes to advancing research on M-S-H binders and highlights the potential of industrial residues as promising raw materials for the construction industry.

Acknowledgements

We gratefully acknowledge the Ministry of Science, Technology, Innovation Communications and the agencies CAPES, CNPq [403545/2020-0; 304108/2022-7], and FAPEMIG [RED-00191-23] for providing financial support. We are also grateful for the infrastructure and collaboration of the Research Groups on Solid Waste (Reciclos/CNPq) and Alkali-Activated Cements (Ative/CNPq), the Federal University of Mato Grosso (UFMT), the Laboratory of Sustainable Innovative Materials (LAB-SIM) at the Federal Center for Technological Education of Minas Gerais (CEFET-MG), and the laboratories of Civil Construction Materials (LMC²) and Electron Microscopy (NanoLab) at the Federal University of Ouro Preto (UFOP).

• CARVALHO, V. R.; MOURA, C. A. M. de; ROSAS, M. H.; BARBOSA, M. A. L.; BRIGOLINI, G. J.; DEFÁVERI, K.; BEZERRA, A. C. da S.; PEIXOTO, R. A. F. Residual fines as potential raw materials for M-S-H cements: processing and characterization. Ambiente Construído, Porto Alegre, v. 26, e152373, jan./dez. 2026. ISSN 1678-8621 Associação Nacional de Tecnologia do Ambiente Construído. http://dx.doi.org/10.1590/s1678-86212026000100983
• Declaration of Generative AI and AI-Assisted Technologies in the Writing Process
  During the preparation of this work the authors used ChatGPT (OpenAI) in order to check grammar issues and to improve readability. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the publication.

Data Availability Statement

Data will be made available on request.

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Edited by

• Editor-in-chief:
  Enedir Ghisi

• Guest editor:
  Lourdes Souza

Publication Dates

• Publication in this collection
  22 June 2026
• Date of issue
  Jan-Dec 2026

History

• Received
  15 Dec 2025
• Reviewed
  27 Feb 2026
• Accepted
  02 Apr 2026