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Article

Sustainable Utilization of Modified Electrolytic Manganese Residue as a Cement Retarder: Workability, Mechanical Properties, Hydration Mechanisms, Leaching Toxicity, and Environmental Benefits

by
Liang Tang
1,2,
Jan Fořt
2,*,
Robert Černý
2 and
Zhaoyi He
1
1
School of Civil Engineering, Chongqing Jiaotong University, Chongqing 400074, China
2
Department of Materials Engineering and Chemistry, Faculty of Civil Engineering, Czech Technical University in Prague, Thákurova 7, 16629 Prague, Czech Republic
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(10), 1586; https://doi.org/10.3390/buildings15101586
Submission received: 9 April 2025 / Revised: 5 May 2025 / Accepted: 6 May 2025 / Published: 8 May 2025
(This article belongs to the Special Issue Recent Scientific Developments in Cement-Based and Alternative Materials—2nd Edition)
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Abstract

:
This study aims to enhance the sustainable utilization of electrolytic manganese residue (EMR), an industrial solid waste rich in sulfates and pollutants, by modifying it with appropriate proportions of granulated blast furnace slag (GBFS) and carbide slag (CS) and evaluating its potential as a cement retarder. The influence of both the GBFS/CS ratio and the dosage of modified EMR on the performance of cement mortar was systematically investigated, focusing on workability, mechanical properties, hydration behavior, leaching toxicity, and carbon emissions. Results showed that GBFS and CS significantly reduced pollutant concentrations in EMR while improving gypsum crystallinity. Modified EMR exhibited retarding properties, extending the initial and final setting times of cement mortar from 98 min and 226 min to 169 min and 298 min. With an 8 wt.% dosage, the 28-day compressive strength reached 58.76 MPa, a 1.3-fold increase compared to cement mortar (45.21 MPa). The content of reactive SiO2, Al2O3, Ca(OH)2, and CaSO4·2H2O promoted secondary hydration of cement and generated significant ettringite (AFt) and calcium silicate hydrate (C-S-H) gels, forming a dense microstructure. Pollutants in the modified EMR-cement mortar were reduced through precipitation, substitution, and encapsulation, meeting leaching toxicity standards. This study highlights the feasibility and environmental benefits of employing modified EMR as a cement retarder, demonstrating its potential in sustainable building materials.

1. Introduction

With the accelerated pace of global industrialization, the accumulation and disposal of large quantities of industrial solid waste pose significant challenges to the environment and resource utilization. Electrolytic manganese residue (EMR), as one of many industrial solid wastes, generates approximately 9–12 tons of EMR for every ton of electrolytic manganese metal produced [1]. Currently, China emits about 10 million tons of EMR annually, with cumulative stockpiles exceeding 150 million tons [2]. Due to the high content of soluble heavy metals, ammonia nitrogen, sulfates, and other harmful impurities, the stockpiling of EMR not only occupies vast areas of land but also leads to severe soil and groundwater pollution, along with potential safety risks at storage sites [3,4]. Furthermore, the small particle size, high water content, and poor mechanical properties of EMR present numerous technical challenges during resource utilization [5]. Therefore, exploring resource utilization pathways for EMR, particularly its efficient transformation in the field of construction materials, is of significant importance.
In recent years, the reuse of sulfate-rich industrial solid waste as a cement retarder has attracted increasing attention in construction material research [6,7,8,9]. Cement retarders are crucial for adjusting cement setting times and improving workability. However, traditional gypsum-based retarders consume natural mineral resources and produce significant CO2 emissions during calcination. As a result, using sulfate-containing solid waste to partially or completely replace gypsum can reduce resource pressure and promote sustainable cement production. For instance, Akın Altun et al. (2004) investigated weathered phosphogypsum (PG) as a cement retarder and demonstrated that 3% PG improved 28-day strength and resulted in a denser microstructure compared to natural gypsum (NG) [10]. Li et al. (2022) further modified PG with circulating fluidized bed fly ash and carbide slag (CS), finding that 6% CS and 4% fly ash enhanced setting regulation and early strength, while effectively immobilizing phosphorus and fluorine [7]. Similarly, Su et al. (2016) reported that desulfurization ash and gypsum promoted ettringite (AFt) formation through reaction with C3A and C4AF, resulting in a notable retarding effect [11].
According to recent findings, dihydrate gypsum accounts for about 30% of total minerals in EMR and contributes 60–70% of its sulfate content [12,13,14]. Thus, EMR has compositional characteristics comparable to PG and desulfurized gypsum, suggesting its potential as a cement retarder. Nevertheless, most studies on EMR incorporation into cement have yielded unsatisfactory results. For example, Xu et al. (2012), Zhong et al. (2024), and Wang et al. (2023) reported that raw EMR led to prolonged setting times, reduced mechanical strength, and elevated leaching toxicity [15,16,17]. These issues stem from multiple causes: (1) Mn2+ in EMR reacts with Ca(OH)2 to form Mn(OH)2 precipitates that coat cement particles and inhibit hydration [18,19]; (2) NH4⁺-N reacts with C3A to generate unstable intermediates, causing pH fluctuations and suppressing hydration [6,20]; (3) impurities and mixed phases interfere with the normal hydration reactions of cement [21].
The retardation mechanism of EMR lies in its sulfate-induced inhibition of C3A and C4AF hydration, which promotes the formation of AFt and monosulfate (AFm), thereby extending the setting time [22]. To improve the performance of EMR in cementitious systems, researchers have explored several pretreatment methods such as high-temperature calcination, chemical treatment, washing, and electrolytic purification [23,24,25,26,27]. Although these methods reduce pollutant content and improve material stability, they also present limitations: calcination is energy-intensive, washing generates secondary wastewater, and chemical modification may introduce undesirable components that affect cement performance [6].
Recently, the synergistic modification of EMR using reactive solid waste has been proposed as a promising alternative. Granulated blast furnace slag (GBFS) and CS are widely available industrial by-products with high chemical activity [28,29]. CS, rich in calcium hydroxide (Ca(OH)2), can neutralize acidic components, immobilize heavy metals, and remove ammonium ions [30]. GBFS, containing reactive SiO2, Al2O3, and CaO, can promote pozzolanic reactions with EMR to form C-S-H and AFt, further enhancing microstructure and reducing pollutant mobility [31]. The combined use of GBFS and CS not only improves the crystallinity and cement compatibility of EMR but also stabilizes its harmful constituents—offering a green and cost-effective “waste-to-waste” solution that aligns with the goals of the circular economy and carbon reduction [32].
As discussed above, although EMR shows promise as a cement retarder, it still faces major challenges in pollutant control, performance optimization, and practical application. To address these issues, this study proposes a synergistic modification strategy using GBFS and CS to enhance the crystallinity, environmental safety, and compatibility of EMR in cementitious systems. Unlike previous studies that directly incorporated raw EMR, this work emphasizes the effects of both the GBFS/CS mass ratio and the dosage of modified EMR on cement performance.
Specifically, this study systematically evaluates the effects of modified EMR on the workability, setting time, and compressive strength of cement mortar, as well as on hydration behavior, microstructure development, pollutant immobilization, and carbon emissions. The investigation employs a multi-scale characterization approach, including X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), thermogravimetric analysis (TG), Fourier-transform infrared spectroscopy (FTIR), inductively coupled plasma spectrometry (ICP), and isothermal calorimetry (TAM-air), to explore the hydration mechanism and stabilization behavior in detail. By integrating performance evaluation with environmental and economic analysis, this research aims to develop a green, low-carbon, and cost-effective cement retarder, while providing a practical solution for the large-scale utilization of EMR in sustainable construction materials.

2. Materials and Methods

2.1. Used Materials

Electrolytic manganese residue (EMR) was sourced from an electrolytic manganese production enterprise in Chongqing, China. It appears black, with a moisture content of 26.43%, a pH of 5.62, a density of 2.69 g/cm3, and a specific surface area of 462 m2/kg. The primary mineral phases of EMR are quartz, gypsum, and pyrite, with high proportions of SiO2, SO3, and CaO, among which SO3 accounts for 27.32%. SEM observations reveal a loose microstructure and some columnar gypsum.
CEM I 42.5 N standard cement, purchased from Chongqing Hongshi Cement Factory in China, was utilized. It has a pH of 13.3, a specific surface area of 360 m2/kg, and a density of 3.15 g/cm3. The pH value was determined by dispersing 10 g of cement in 100 mL of deionized water (solid-to-liquid ratio 1:10), stirring for 10 min at room temperature (25 ± 1 °C), and measuring the pH of the supernatant using a calibrated digital pH meter (pHS-25, China). Calibration was performed with standard buffer solutions of pH 4.00, 7.00, and 10.00. The cement clinker is gray in color, with C2S, C3A, C4AF, and C3S as its primary mineral phases and a high proportion of SiO2 and CaO. SEM imaging indicates the presence of a significant amount of amorphous material in its microstructure.
S95-grade granulated blast furnace slag (GBFS) was purchased from Henan Borun New Materials Co., Ltd. in Nanyang, China. It is grayish-white with prominent jagged peaks. It has a pH of 10.20, a density of 2.90 g/cm3, and a specific surface area of 500 m2/kg. The main crystalline phases in GBFS are gehlenite and akermanite. SiO2, Al2O3, and CaO are the major chemical components, with CaO accounting for 50.82%. SEM observations reveal amorphous polyhedral structures in the GBFS.
Carbide slag (CS) was obtained from Chongqing Wanzhou Ganning Acetylene Plant in Chongqing, China. It appears gray–white with well-formed crystals, a pH of 13, a density of 0.85 g/cm3, and a specific surface area of 650 m2/kg. The main crystalline phase of CS is Ca(OH)2, with CaO making up 87.33%. SEM analysis shows a considerable presence of amorphous materials in CS.
The sand used in this study was produced according to the GB/T 17671-2021 standard for fine aggregates by Xiamen ISO Standard Sand Co., Ltd. in Xiamen, China. The sand exhibited a well-graded particle size distribution with the following cumulative passing percentages: 0% for 2.0 mm, 7 ± 5% for 1.6 mm, 33 ± 5% for 1.0 mm, 67 ± 5% for 0.5 mm, 87 ± 5% for 0.16 mm, and 99 ± 1% for 0.08 mm [33]. The particle size distribution of the sand meets the requirements of the GB/T 17671-2021 standard, ensuring consistency and suitability for cement mortar preparation.
Details of the morphology, mineral phases, and chemical compounds of the raw materials can be found in Figure 1 and Table 1.

2.2. Preparation of Modified EMR and Modified EMR-Cement Mortar

EMR contains high levels of impurities, heavy metals, and NH3-N [12], which can adversely affect the performance of products if applied directly in construction materials. Therefore, EMR needs to undergo pretreatment and modification. In this study, CS and GBFS were used synergistically to modify EMR, with a focus on analyzing the effect of the CS-to-GBFS ratio. Based on the studies of Li et al. (2022), Zhang et al. (2019), and Zhang et al. (2020) [7,32,34], the proportion of solid waste (CS and GBFS) to EMR was set at 1:1, and the CS-to-GBFS ratios were set at 0:10, 2.5:7.5, 5:5, 7.5:2.5, and 10:0, as detailed in Table 2.
Preparation procedure: First, EMR, CS, water and GBFS samples were weighed according to Table 2 and mixed evenly for 2 min in a cement paste mixer (instrument from Ximing Sheng Testing Instruments Co., Cangzhou, China, model: NJ-160A) at a low speed. Next, water was added to the powder mixture during mixing, followed by 10 min of low-speed mixing, 5 min of high-speed mixing, and 3 additional minutes of low-speed mixing. Subsequently, the mixture was placed in Petri dishes and cured in a chamber at 20 ± 2 °C and 95% humidity for 24 h for toxicity leaching tests and microstructural characterization. Finally, the modified EMR was dried at 40 °C, sealed in plastic bags, and labeled as M-EMR1-5 for future use. Preparation of modified EMR-cement mortar: Following the cement mortar strength testing method GB/T 17671-2021, 40 × 40 × 160 mm modified EMR-cement mortar specimens were prepared [33]. Various types of modified EMR, cement, sand, and water were mixed in the mortar mixer according to specified proportions, compacted, and molded. The molded mortar specimens were cured in a chamber at 20 ± 2 °C and 95% humidity for 24 h, then demolded and further cured for subsequent tests and characterizations.

2.3. Mix Design for Modified EMR-Cement Mortar

In this experiment, EMR was modified using CS and GBFS and utilized as a cement retarder to produce modified EMR-cement mortar, raw EMR-cement mortar, and standard cement mortar. This study primarily focused on the performance characteristics of the modified EMR-cement mortar. Since the SO3 content in EMR is lower than that in natural gypsum, and following the Chinese General Portland Cement Standard GB 175-2020 and related studies [7,35], the dosages of various modified and raw EMR were set at 4 wt.%, 6 wt.%, and 8 wt.% (externally added). The water-to-cement ratio (W/C) was fixed at 0.5, and the cement-to-sand ratio (C/S) was 1/3. Detailed mix proportions are shown in Table 3.

2.4. Leaching Toxicity of Modified EMR-Cement Mortar

To assess the potential environmental risk associated with the release of heavy metals and ammonium nitrogen from the hardened EMR-cement mortar, a standardized leaching simulation was performed, mimicking the acid rain exposure that may occur following improper disposal or surface accumulation of solid waste. The leaching procedure followed the HJ/T 299-2007 protocol for acidic leaching and HJ 535-2009 for ammonia nitrogen detection via Nessler’s reagent spectrophotometry [36,37].
Prior to testing, mortar samples were crushed and sieved through a 9.5 mm mesh, and 10 g of each representative sample was accurately weighed into a 250 mL polyfluoroethylene (PFA) extraction bottle. A mixed acid leaching solution (a combination of sulfuric acid and nitric acid) was added at a liquid-to-solid ratio of 10:1 (mL/g). The bottles were tightly sealed and placed in a constant-temperature horizontal oscillator, set at 30 ± 2 rpm and maintained at 23 ± 2 °C for a continuous 18-hour agitation period to ensure sufficient interaction between the sample and leachant.
After leaching, the supernatant was collected, filtered, and analyzed for toxic species. The concentrations of released pollutants were compared against regulatory limits defined in the Integrated Wastewater Discharge Standard (GB 8978-1996) [38], allowing for evaluation of the environmental safety of the modified EMR when incorporated into cement-based materials.

2.5. Analysis and Characterization Methods

This section summarizes the instruments used for the physicochemical characterization of materials, along with their specific functions, operating conditions, and sample preparation procedures.
(1) Mechanical Strength
The compressive strength of mortar specimens was tested using a YAW-300D cement concrete compressive strength tester (Jinan Zhongchuang Company, Jinan, China) at a constant loading rate of 2.4 kN/s. The average value of three parallel samples is reported.
(2) Microstructure and Elemental Analysis
Crushed mortar specimens were sectioned into thin slices, immersed in anhydrous ethanol for 48 h to terminate hydration, oven-dried at 40 °C, and gold-sputtered to enhance conductivity. Microstructural observation was performed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) (ZEISS Gemini 300, Oberkochen, Germany) operated at an accelerating voltage of 15 kV in secondary electron mode.
(3) Mineral-Phase Composition (XRD)
Mineralogical analysis was conducted using X-ray diffraction (XRD, Empyrean, PANalytical, Almelo, The Netherlands) with Cu Kα radiation (λ = 1.5406 Å) in the Bragg–Brentano geometry. Samples were ground to 200 mesh, pressed into flat pellets, and scanned in the 2θ range of 5–70°, with a step size of 0.02°/s and a scan speed of 2°/min, under 40 kV and 30 mA. Diffraction patterns were analyzed with JADE 6.0 software, and quantitative phase analysis was conducted via Rietveld refinement using X’Pert HighScore Plus, with reference to the ICDD PDF-2 database. To improve accuracy, 20 wt.% ZnO was used as an internal standard. Identified phases are listed in Table 4 [39].
(4) Leaching Toxicity Analysis (ICP-OES, UV-Vis)
The leaching solutions extracted from both hardened cement mortar and cement paste were analyzed to evaluate environmental safety. Heavy metal concentrations in the leachates were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES, Agilent 5800, Santa Clara, CA, USA). The ammonia nitrogen content in the same leachates was determined using a UV-visible spectrophotometer (UV-1780, Shimadzu, Kyoto, Japan) in accordance with relevant standard methods.
(5) pH Measurement
The pH of cement slurry supernatant was measured using a digital pH meter (pHS-25, Shanghai, China). A suspension was prepared by dispersing 10 g of cement in 100 mL of deionized water, stirring for 10 min at 25 ± 1 °C, and the pH of the supernatant was recorded after 5 min of settling. The device was calibrated using standard buffer solutions at pH 4.00, 7.00, and 10.00.
(6) Calorimetry (Hydration Heat)
The early hydration behavior of selected cement paste samples was evaluated using an eight-channel isothermal calorimeter (TAM Air, TA Instruments, New Castle, DE, USA). In each test, 6 g of cementitious sample and 3 g of deionized water (w/c = 0.5) were accurately weighed into sealed ampoules and manually mixed by rapid stirring. The ampoules were then placed in the instrument chamber and connected to external probes. The heat flow density and cumulative heat release over 72 h of hydration at a constant temperature of 20 °C were recorded in real time.
(7) Functional Group Identification (FT-IR)
Functional groups were analyzed using Fourier-transform infrared spectroscopy (FT-IR, Nicolet iS10, Thermo Fisher Scientific, Waltham, MA, USA). The KBr pellet method was applied, with a scan range of 4000–400 cm⁻¹ and a resolution of 4 cm⁻¹. Spectral data were interpreted using OMNIC software version 9.0.
(8) Thermal Analysis (TGA)
The thermal behavior and phase evolution of the hardened cementitious matrix were investigated using thermogravimetric analysis (TGA, NETZSCH STA 449C, Selb, Germany). Finely ground powder samples of cured paste were placed in an alumina crucible and heated from 30 °C to 1000 °C at a rate of 10 °C/min under a continuous flow of nitrogen atmosphere (60 mL/min) to prevent oxidation.

3. Results

3.1. Leaching Toxicity and XPS Analysis of Modified EMR

Previous studies have identified Mn and NH3-N as the primary pollutants in EMR, with other contaminants below regulatory limits [12,31,40]. Therefore, this section focuses on the stabilization effects of different CS and GBFS ratios on Mn and NH3-N in EMR, with the results summarized in Table 5. As shown in Table 5, increasing the proportion of CS and decreasing GBFS reduced the leaching concentrations of Mn and NH3-N while raising the pH. At a CS:GBFS ratio of 10:0 (M-EMR5), the lowest leaching concentrations of Mn and NH3-N were 0.0023 mg/L and 0.0871 mg/L, respectively. This is attributed to the higher CaO content and pH of CS compared to GBFS, which releases more OH−, converting soluble divalent manganese into insoluble trivalent and tetravalent forms (Mn3O4, MnO2) [12,31]. Additionally, NH3-N is more readily transformed into ammonia gas and released. Studies by Zhou et al. (2013) and Du et al. (2015) have also demonstrated that increasing alkaline materials (CaO, CS, MgO) enhances OH− release, thereby reducing the leaching toxicity of EMR [41,42]. Conversely, at a CS:GBFS ratio of 0:10, the highest leaching concentrations of Mn and NH3-N were 27.67 mg/L and 3.6224 mg/L, respectively. The leached Mn exceeds the Chinese wastewater discharge standard of 2 mg/L (GB8978-1996), indicating that GBFS alone is insufficient for effective stabilization of EMR.

3.2. XRD and SEM-EDS Analysis of Modified EMR

To investigate the impact of varying CS and GBFS ratios on the mineral phases of EMR, XRD patterns were obtained for raw EMR, M-EMR1, M-EMR3, and M-EMR5. Figure 2 shows that, compared to waw EMR, the main mineral phases of modified EMR are gypsum (CaSO4·2H2O) and quartz (SiO2). Additionally, FeS2 (pyrite), (NH4)3(SnF)F, and MnSO4·2H2O (szmikite) disappear in modified EMR, mainly due to hydroxyl compounds released by CS and GBFS, which transform pyrite and szmikite into MnFe2O4 (Jacobsite), stabilizing the phases, while NH3-N is released as ammonia gas. The figure also indicates that the gypsum phase shifts leftward after the hydration reaction of EMR with CS and GBFS. Furthermore, as the CS content increases, the diffraction peak intensity and crystallinity of gypsum are significantly enhanced. This observation aligns with He et al. (2022), who reported that the diffraction peaks of gypsum in EMR increase with a rising CS content [30].
Figure 3 illustrates the SEM-EDS analysis of raw and modified EMR. The results demonstrate that modified EMR contains more columnar gypsum crystals, surrounded and coated by irregular fine particles. Based on EDS analysis of Areas 2, 3, and 4, elements such as P, Al, and Mg are detected. Together with XRD findings, these particles are inferred to be precipitates of iron–manganese compounds, hydroxides, or heavy metals. Area 1 exhibits high concentrations of S, O, and Ca, which XRD confirms as gypsum. This observation correlates with earlier analyses, where the alkalinity of CS and GBFS, both containing CaO, releases OH− during mixing with EMR, enabling the precipitation of heavy metal cations and enhancing the crystallinity of gypsum within EMR [40].

3.3. Fluidity and Setting Time of Modified EMR-Cement Mortar

Figure 4 shows the effects of different types and dosages of modified EMR as retarders on the fluidity and setting time of cement mortar. As shown in Figure 4a, the fluidity of cement mortar decreases with increasing dosages of both modified and raw EMR. The highest fluidity was observed for cement mortar containing 4 wt.% modified EMR. This is attributed to the high water absorption, large specific surface area, and impurities in EMR, which intensify its water-absorbing effects as the dosage increases, negatively impacting the fluidity of cement mortar [15]. Wu et al. (2024) also reported that calcined EMR, rich in calcium sulfate, retains strong water absorption properties, reducing the fluidity of cementitious materials as the EMR content increases [43]. The figure further indicates that a higher CS content in modified EMR decreases fluidity, while a higher GBFS content improves it. The optimal modified EMR type is M-EMR1 (CS:GBFS = 0:10). This is because the fine particles of GBFS fill the voids between sand and cement, enhancing compaction and reducing water demand, thereby improving fluidity. Conversely, despite the fine particle size of CS, its high CaO content significantly increases water consumption, impairing fluidity [15]. In summary, the fluidity of mortar with 4 wt.% M-EMR1 (223.45 mm) is favorable but still lower than that of pure cement mortar (232.45 mm). This reduction is mainly due to the high water absorption and large specific surface area of the modified EMR particles. Although GBFS in M-EMR1 improves particle dispersion, the porous and rough surface structure of modified EMR absorbs more water, which reduces the amount of free water available for flow, thereby slightly lowering the fluidity compared to pure cement mortar [14,19]. As depicted in Figure 4b, increasing the dosage of modified EMR in cement mortar prolongs its initial and final setting times. This effect arises from the significant sulfate content in EMR, which delays the setting and hardening processes, with greater dosages yielding more pronounced effects. Similar observations were reported by Xu et al. (2019), who found that the addition of EMR to slag cement increased both its initial and final setting times [14]. Figure 4b further shows that the initial and final setting times are reduced as the CS content in modified EMR increases. The use of M-EMR5 (CS:GBFS = 10:0) accelerates the setting and hardening times of cement mortar, consistent with the findings in the fluidity analysis. The higher CS content in modified EMR enhances alkalinity, which promotes early hydration and strengthens the setting and hardening of cement. In summary, modified EMR exhibits a retarding effect on cement mortar. The setting and hardening time for the cement mortar increased from 98 min (initial setting) and 226 min (final setting) for the R0 mix to 169 min (initial) and 298 min (final) for the C1 mix. However, unmodified EMR, due to its soluble manganese, ammonia nitrogen, and impurities, significantly extended the setting times to 186 min (initial) and 322 min (final) for the C0 mix. In some cases, it even disrupted the normal setting capability of the cement paste [18].
Additionally, as the dosage of modified EMR increased from 4 wt.% to 8 wt.%, a general decrease in fluidity and increase in setting time were observed. This trend can be attributed to the high specific surface area and water absorption capacity of the modified EMR, which increase with dosage and reduce the amount of free water available in the mix. Among the five types of modified EMR, those with a higher GBFS content (e.g., M-EMR1 and M-EMR2) helped maintain better fluidity due to their finer particles and latent hydraulic activity, which enhanced particle packing and water distribution. In contrast, types with a higher CS content (e.g., M-EMR4 and M-EMR5) significantly accelerated the hydration of cementitious phases due to the strong alkalinity of CS, resulting in shorter setting times. The presence of Ca(OH)2 from CS promotes the early formation of ettringite and C-S-H gel, but also leads to higher water consumption, which can negatively impact flowability at higher dosages. These results align with previous studies (e.g., Xu et al., 2012; He et al., 2024) [16,44], confirming that the balance of GBFS and CS content is crucial for optimizing both fluidity and setting control when incorporating EMR-based retarders.

3.4. Compressive Strength of Modified EMR-Cement Mortar

Figure 5 illustrates the impact of different dosages and types of modified EMR as retarders on the compressive strength of cement mortar. In Figure 5a, with a modified EMR dosage of 4 wt.%, M-EMR 2 (CS:GBFS = 2.5:7.5) demonstrates the greatest significant improvement in compressive strength, achieving values of 19.4 MPa, 23.9 MPa, and 53.23 MPa at 3, 7, and 28 days, respectively. Other modified EMR types showed slower improvements, particularly M-EMR5 (CS:GBFS = 10:0), where the high CS content reduced strength due to excessive alkalinity. While alkalinity boosts early strength, it can impede later strength development. This is primarily because the high alkalinity—mainly derived from Ca(OH)2 in CS—raises the pH of the hydration environment, accelerating the early dissolution of cement phases such as C3A and C3S and promoting the rapid formation of AFt and C-S-H, which contribute significantly to early strength. However, excessive Ca(OH)2 accumulation can obstruct further hydration by blocking reaction sites and limiting the availability of reactive silico-aluminate species. In addition, a highly alkaline environment may result in a less compact microstructure over time, ultimately impeding the development of long-term strength. This phenomenon is particularly evident in mortars incorporating high-CS modified EMR, such as M-EMR5 [45]. In Figure 5b, at a dosage of 6 wt.%, M-EMR 1 (CS:GBFS = 0:10) shows the fastest strength increase, with 3-day, 7-day, and 28-day compressive strengths of 21.3 MPa, 27.4 MPa, and 55.6 MPa, respectively. Strength consistently declined as the CS proportion in modified EMR increased. As shown in Figure 5c, when the modified EMR content is 8 wt.%, the compressive strength of cement mortar initially increases and then decreases with a higher CS ratio in the modified EMR. M-EMR2 (CS:GBFS = 2.5:7.5) achieves the best improvement, with compressive strengths of 22.1 MPa at 3 days, 26.2 MPa at 7 days, and 58.76 MPa at 28 days. Compared to standard cement mortar (28-day compressive strength: 45.21 MPa), this represents a 1.3-fold increase, and compared to mortar with raw EMR (mix ratio C0, 28-day strength: 44.4 MPa), a 1.32-fold increase. As shown in Figure 5, raw EMR at dosages of 4–6 wt.% slightly improves cement strength but remains less effective than modified EMR. When raw EMR exceeds 6 wt.%, it hinders the strength of cement mortar. This is attributed to excessive sulfates, pollutants, and impurities in the cement mortar, which enhance retardation effects, reduce the C-S-H gel content and moisture retention, and increase voids, ultimately decreasing strength. Comparing studies by Xu et al. (2019) and Fu et al. (2023), where thermally activated EMR or raw EMR was incorporated into cement mortar, the strength exhibited an initial increase followed by a significant decrease with an increasing EMR dosage. This was due to inadequate modification or inappropriate methods, which prevented excess sulfates in EMR from being consumed, resulting in lower strength as the EMR dosage increased [14,46].
In conclusion, modified EMR of type M-EMR2 (CS:GBFS = 2.5:7.5) at a dosage of 8 wt.% effectively enhances cement mortar strength due to two factors: (1) CS and GBFS modification enriches EMR with sulfates, reactive SiO2, Al2O3, and Ca(OH)2, promoting secondary hydration of C2S, C3A, C4AF, and C3S to generate more C-S-H gel and ettringite crystals; (2) the optimal ratio of EMR, CS, and GBFS enables EMR’s own hydration to form additional C-S-H gel and ettringite. These factors synergistically contribute to an increased cement strength.

3.5. XRD Analysis of Modified EMR-Cement Paste

To further elucidate how different types of modified EMR affect cement hydration products, XRD patterns and quantitative phase analyses for mixes C1–C5 were performed. Figure 6 shows that the primary hydration products in modified EMR-cement paste include Portlandite (Ca(OH)2), calcite (CaCO3), and ettringite (Ca6A12(SO4)3(OH)12·26H2O), alongside unhydrated phases such as quartz (SiO2), gypsum (CaSO4·2H2O), C2S, C3A, C4AF, and C3S. Because C-S-H is amorphous, it lacks characteristic peaks in the XRD patterns and requires Rietveld analysis for quantification. In Figure 6a, M-EMR2 (CS:GBFS = 2.5:7.5) achieves the best interaction with cement, producing the highest intensity of ettringite diffraction peaks (mix C2). Figure 6b confirms through quantitative analysis that mix C2 not only exhibits a higher proportion of ettringite but also a greater share of amorphous phases (68.52%). This is due to M-EMR2’s CS:GBFS ratio of 2.5:7.5, which supplies abundant CaSO4·2H2O along with reactive Ca(OH)2, Al2O3, and SiO2. When mixed with cement, the CaSO4·2H2O in M-EMR2 reacts with C3A and C4AF to form significant amounts of AFt and interacts with Ca(OH)2 from CS and Al2O3, and SiO2 from GBFS, to form additional AFt and amorphous C-S-H [14,45]. In conclusion, the CS:GBFS ratio in modified EMR has a significant impact on the phase composition of cement paste. Increasing the CS proportion and reducing GBFS in modified EMR raises the proportion of Portlandite while reducing the proportions of ettringite and amorphous phases. This may result from the diminished supply of reactive silico-aluminate tetrahedra from GBFS, which limits secondary hydration and the formation of ettringite and amorphous phases. Additionally, a higher CS proportion increases the Portlandite content, potentially hindering later-stage hydration [44]. Zhang et al. (2019) similarly demonstrated that incorporating CS, GBFS, and RM with EMR is essential for enhancing hydration to generate more ettringite and C-S-H gel [47].
To further clarify the influence of varying dosages of modified EMR on cement hydration products, XRD patterns and quantitative phase analysis diagrams for mixes A2, B2, and C2 were generated. From Figure 7a and Figure 8b, it is evident that increasing the dosage of modified EMR results in a gradual increase in the intensity and proportion of ettringite and Portlandite diffraction peaks in the cement paste, alongside an increase in the proportion of amorphous phases. This phenomenon occurs because insufficient modified EMR supplies inadequate sulfates, yielding minimal ettringite and amorphous phases from cement clinker, GBFS, and CS. Ample sulfate availability enhances the stability of ettringite, preventing its transformation into AFm or thaumasite. Moreover, the disappearance of gypsum diffraction peaks in the XRD patterns, as shown in Figure 7, confirms that the gypsum in the modified EMR has been almost completely transformed into ettringite.
To compare the phase changes in cement paste, raw EMR-cement paste, and modified EMR-cement paste, XRD patterns and quantitative phase analysis diagrams for mixes R0, C0, and C2 were generated. Figure 8a and Figure 9b show that the incorporation of raw and modified EMR increases the content and diffraction peaks of ettringite in the cement paste while decreasing the intensity and proportion of Portlandite diffraction peaks. Direct incorporation of raw EMR hinders the formation of amorphous phases in cement paste, whereas modified EMR promotes the secondary hydration of C2S, C3A, C4AF, and C3S in cement, resulting in higher amorphous phases and ettringite contents in modified EMR-cement paste. This is because the incorporation of raw EMR into cement mortar results in an excess of sulfates that cannot be fully consumed, slowing the setting and hardening of cement and inhibiting amorphous-phase formation. Moreover, manganese, ammonia nitrogen, and impurities in raw EMR adversely affect cement hydration. In contrast, modified EMR, enriched with CS and GBFS, facilitates secondary hydration and consumes excess sulfates, generating more AFt and amorphous phases. Li et al. (2022) similarly found that compared to modified phosphogypsum, unmodified phosphogypsum containing fluorides and phosphates hinders cement hydration [7].

3.6. FTIR Analysis of Modified EMR-Cement Paste

Figure 9 illustrates the FTIR spectra of cement paste with various types and dosages of modified EMR (mixes A2, B2, C1–C5) compared to the control group cement paste (mix R0). The FTIR spectra reveal similar absorption peaks for modified EMR-cement paste and cement paste, indicating no significant changes in the types of hydration products. In Figure 9a, the absorption peaks at 3381–3399 cm−1 and 1650–1658 cm−1 correspond to the stretching vibrations of -O-H bonds in crystallized or bound water in Ca(OH)2 [48]. The peaks at 1412–1419 cm−1 are attributed to the asymmetric stretching vibrations of C-O bonds in CaCO3, which form from the reaction of Ca(OH)2 with air [44]. Peaks around 1104–1108 cm−1 represent the asymmetric stretching vibrations of S-O bonds in SO42−, associated with the formation of ettringite from CaSO4·2H2O. The lowest SO42− peak intensity in mix C2 indicates significant sulfate consumption and vigorous ettringite formation [49]. At 945–954 cm−1, the Si-O-T (T = Al or Si) asymmetric stretching vibrations are observed, corresponding to Al-O vibrations in six coordinated (A1O6)⁻⁹ structures [50]. Peaks at 446–454 cm−1, caused by T-O (Si-O or Al-O) bending vibrations, are characteristic of C-S-H gel. The higher T-O peak intensity in sample C2 suggests better interaction between modified M-EMR2 and cement, resulting in more C-S-H gel formation [46]. Figure 9b compares FTIR spectra for cement paste with varying dosages of modified EMR, showing that the T-O peak intensity of C-S-H gel in sample C2 remains higher than in A2 and B2. This confirms that 8 wt.% M-EMR2 promotes more C-S-H gel formation, consistent with the XRD results. Figure 9c compares FTIR spectra of cement paste, raw EMR-cement paste, and modified EMR-cement paste. The lowest SO42− peak intensity and highest T-O peak intensity in modified EMR-cement paste (C2 mix) indicate that modified EMR enhances hydration, generating more ettringite and C-S-H gel. This further explains why modified EMR-cement paste has a higher compressive strength than raw EMR-cement mortar.

3.7. Hydration Heat of Analysis of Modified EMR-Cement Paste

To investigate the impact of different types of modified EMR on cement hydration heat, the heat release rate, and cumulative heat release, curves for mixes C1–C5 over 168 h were plotted. According to the hydration heat characteristics and Figure 10a, the modified EMR-cement paste exhibits a first heat release peak during the initial stage (0–2 h), caused by the dissolution heat of C3A [51]. For cement paste with M-EMR1 (CS:GBFS = 0:10), the first peak appears earlier and is higher due to the higher GBFS content in M-EMR1, which accelerates C3A dissolution. In other modified EMR samples (mixes C2–C5), the higher CS content promotes ettringite formation, delaying the first peak and lowering its intensity. As hydration continues, the modified EMR-cement paste enters the second stage (2–40 h) and exhibits a second heat release peak (around 12 h), attributed to the formation of C-S-H gel and ettringite [52]. During this stage, sample C2 shows the highest peak, while other samples decline as the CS content increases and GBFS content decreases in the modified EMR. The appropriate ratio of M-EMR2 (CS:GBFS = 2.5:7.5) in C2 provides sufficient sulfates and active SiO2, Al2O3, and CaO, promoting secondary hydration to form more C-S-H gel and ettringite [46]. In the third stage (40–168 h), the reaction rate of modified EMR-cement paste decreases and stabilizes, leading to densification of the cement paste. Figure 10b shows that the cumulative heat release of M-EMR2 cement paste (mix C2) is the highest at 211.29 J·g−1, further confirming that M-EMR2 cement paste exhibits more vigorous reactions, more complete hydration, and higher strength.
Figure 11 shows the hydration heat of cement paste with different dosages of modified EMR (mixes A2, B2, and C2). As shown in Figure 11a, increasing the dosage of modified EMR delays the first heat release peak of the cement paste and decreases its intensity, indicating that a higher sulfate content in modified EMR-cement paste slows the heat release rate of C3A. As hydration continues, higher dosages of modified EMR release more SO42−, OH−, Al3+, Ca2+, and Si4+, which not only promote cement hydration but also form C-S-H gel and ettringite. Therefore, at the second heat release peak, the reaction in cement paste with 8 wt.% M-EMR2 is more intense, and the peak value is higher. Figure 11b shows that, compared to 4 wt.% and 6 wt.% M-EMR2 cement paste, the 8 wt.% M-EMR2 cement paste (mix C2) exhibits the highest cumulative heat release over 168 h, reaching 211.29 J·g−1.
Figure 12 illustrates the hydration heat of cement paste, modified EMR-cement paste, and raw EMR-cement paste (mixes R0, C2, and C0). As shown in Figure 12a, the cement paste exhibits higher and earlier heat release peaks in both the first stage (Peak 1) and the second stage (Peak 2). In contrast, the heat release peaks of cement pastes incorporating raw EMR and modified EMR shift to later times and show reduced intensities, though the modified EMR-cement paste performs better. This can be attributed to (1) impurities and sulfates in both raw and modified EMR, which delay the heat release from C3A in the first peak; (2) the presence of more heavy metals and ammonia nitrogen in raw EMR compared to modified EMR, along with the lack of CS and GBFS, which results in a more pronounced delay of the second peak. Conversely, gypsum, calcium hydroxide, and reactive silica and alumina in modified EMR promote secondary hydration of cement, though the gypsum and ettringite formed reduce the hydration heat to some extent. Similar findings were reported by Li et al. (2022), who found that raw phosphogypsum hindered cement hydration due to phosphates and fluorides, whereas modified phosphogypsum improved hydration as a retarder using carbide slag and circulating fluidized bed (CFB) fly ash [7]. Figure 12b shows that the cumulative heat release at 168 h is highest for cement paste (232.42 J·g⁻¹), followed by modified EMR-cement paste (211.29 J·g⁻¹) and raw EMR-cement paste (205.35 J·g⁻¹). This aligns with the findings of Wang et al. (2022), who used a calcination method to modify EMR and incorporated it into cement, observing that modified EMR reduced both the heat release rate and cumulative heat release of cement [25].

3.8. TG-DTG Analysis of Modified EMR-Cement Paste

To further investigate the effect of raw EMR and modified EMR as retarders on cement hydration, TG-DTG curves for raw EMR-cement, modified EMR-cement, and cement paste (mixes C0, C2, R0) were plotted. Based on FTIR, XRD, and the literature [53], cementitious materials were divided into three stages: the first stage (50–350 °C) corresponds to the dehydration decomposition of chemically bound water in C-S-H, AFt, and AFm phases; the second stage (350–500 °C) involves the decomposition of Ca(OH)2; and the third stage (500–700 °C) involves the decomposition of CaCO3 [44]. Figure 13 shows that the mass losses in the first stage for raw EMR-cement paste, modified EMR-cement paste, and cement paste are 9.73%, 15.68%, and 13.26%, respectively. This indicates that the addition of modified EMR promotes cement hydration, producing more C-S-H, AFt, and AFm, while raw EMR hinders cement hydration, consistent with XRD, FTIR, and hydration heat analysis results. In the second stage, cement paste exhibits a smaller mass loss (4.17%) compared to raw EMR-cement (4.24%) and modified EMR-cement paste (4.20%). This is due to the gypsum content in both raw and modified EMR, which forms ettringite and consumes Ca(OH)2, resulting in greater mass loss in the second stage. In the third stage, the mass loss for modified EMR-cement paste is 4.22%, higher than that of cement paste (3.62%), indicating that raw EMR-cement paste contains more carbonates and is more prone to carbonation.

3.9. SEM-EDS Analysis of Modified EMR-Cement Paste

To further investigate the effect of raw and modified EMR as retarders on the microstructure of cement, SEM-EDS images were prepared for raw EMR-cement paste, modified EMR-cement paste, and cement paste (mixes C0, C2, and R0). As shown in Figure 14a, raw EMR-cement paste contains abundant needle-like ettringite and a small amount of foil-like C-S-H. This may be attributed to the sulfates in raw EMR promoting ettringite growth, while pollutants and impurities hinder the growth of C-S-H. Figure 14b shows that in modified EMR-cement paste, the needle-like ettringite and foil-like C-S-H grow interlaced, forming a dense structure. In Figure 14c, cement paste also contains abundant ettringite, C-S-H, and flaky Ca(OH)2. In EDS-Area 1, raw EMR-cement paste shows higher contents of O, Ca, Al, and S, suggesting the presence of ettringite crystals, as inferred from XRD. In EDS-Area 2, modified EMR-cement paste has higher O, Ca, Al, and Si contents, indicating the presence of C-S-H gel. In EDS-Area 3, cement paste primarily shows O and Ca, which likely correspond to Ca(OH)2 based on the XRD results. In conclusion, consistent with XRD, FTIR, and hydration heat analyses, modified EMR as a retarder promotes the secondary hydration of cement, leading to the formation of more ettringite and C-S-H gel in cement paste.

3.10. Leaching Toxicity and Solidification Mechanism of Modified EMR-Cement Mortar

Using cement mortar containing 8 wt.% modified EMR as a representative, the leaching toxicity of different types of modified EMR-cement mortar (mixes C1–C5) was studied, as shown in Table 6. From Table 6, it is evident that adding various types of modified EMR to cement reduces leaching toxicity without increasing the pollutant content. Furthermore, all modified EMR-cement mortars meet the requirements of GB8978-1996 (Integrated Wastewater Discharge Standard). Notably, in mortars containing modified electrolytic manganese residues R-EMR4 and R-EMR5, Mn and NH₃-N are below the detection limit (0.0001 mL) and lower than the standards for Mn (2 mg/L) and NH₃-N (15 mg/L). The pollutant solidification mechanism of modified EMR-cement mortar is analyzed as follows:
(1) CS, GBFS, and cement in modified EMR release OH⁻, which converts heavy metal ions in EMR into hydroxide precipitates. Additionally, NH₃-N in EMR reacts to form ammonia gas, as shown in reactions (1)–(2) [31].
(2) The hydration of modified EMR-cement mortar generates abundant AFt, C-S-H, and AFm, enabling heavy metal ions in EMR (Mn2+) to replace metal ions or ion groups in these hydration products, thereby encapsulating the heavy metals within the structure of the hydration products [40,54].
(3) Furthermore, the hydration products of modified EMR-cement mortar (e.g., CaCO₃, AFt, AFm, C-S-H, Ca(OH)2) interweave to form a dense network structure that seals and encapsulates pollutants within EMR [40].
M2+ + 2OH− → M(OH)2 ↓ M = (Mn, Cd, Ba, Pb, Ni)
NH4+-N + OH− → NH3 ↑+ H2O

3.11. Carbon Emissions and Cost Analysis of Modified EMR-Cement Mortar

As modified EMR demonstrates an excellent performance in workability, mechanical properties, microstructure, and hydration as a cement retarder, it is necessary to calculate its CO2 emissions and cost, comparing it with natural gypsum to highlight the advantages of modified EMR in reducing carbon emissions and costs. Based on the modified EMR mix proportions in Table 2, the raw material and modified EMR carbon emissions and costs were calculated, as shown in Figure 15. Raw material data were sourced from the literature [55,56,57,58] and are summarized in Table 7. From Figure 15, it can be seen that the CO2 emissions of modified EMR range from 25.67 to 31.00 kg CO2/t, which are 4.52–5.46 times lower than that of natural gypsum (140.2 kg CO2/t). This significant reduction is attributed to the drying and grinding processes of CS and EMR, with a large portion of carbon emissions linked to the use of GBFS. However, higher emissions reported in some studies may result from the increased use of cement, chemical agents, and industrial activators, which contribute to a higher carbon footprint [59,60]. Cost calculations reveal that modified EMR costs range from 28.06 to 108.07 RMB/t, compared to 400 RMB/t for commercial natural gypsum, representing a cost reduction of 3.7–14.26 times. The variability in cost reduction is mainly due to the higher cost of GBFS and fluctuations in its dosage.
In summary, compared to natural gypsum, modified EMR avoids mining, crushing, and calcination steps, requiring only drying, grinding, and mixing. This significantly reduces both carbon emissions and costs. From this perspective, EMR can be regarded as an environmentally beneficial and sustainable material.
It should be noted that the unit prices adopted in this cost analysis are based on market data from the study region, which is also where the raw materials were sourced and tested. This approach ensures internal consistency between material procurement, experimental conditions, and economic evaluation. While we acknowledge that material costs may vary across regions, the current analysis focuses on a localized comparison between modified EMR and natural gypsum. Incorporating regionally diverse prices, though valuable in broader economic studies, is beyond the scope of this work.

4. Conclusions

This study explored the feasibility of utilizing electrolytic manganese residue (EMR) as a cement retarder through synergistic modification with granulated blast furnace slag (GBFS) and carbide slag (CS). A comprehensive evaluation was conducted on workability, mechanical strength, hydration mechanisms, pollutant leaching, and environmental impact. The main findings are summarized as follows:
(1) The synergistic addition of GBFS and CS significantly improved the physicochemical properties of EMR. When the GBFS:CS ratio was 0:10, the concentrations of Mn and NH3-N in EMR were reduced from 1220 mg/L and 149 mg/L to 0.0023 mg/L and 0.0871 mg/L, respectively, due to redox and alkaline volatilization effects. Meanwhile, the crystallinity of gypsum in EMR was notably enhanced, as evidenced by stronger XRD diffraction peaks.
(2) Modified EMR effectively acted as a cement retarder. At an 8 wt.% dosage, the initial and final setting times increased from 98 min and 226 min (control) to 169 min and 298 min (M-EMR5), respectively. In contrast, unmodified EMR caused excessive setting delays due to residual soluble impurities. Strength tests showed that mortar containing 8 wt.% M-EMR2 (CS:GBFS = 2.5:7.5) achieved a 28-day compressive strength of 58.76 MPa, representing a 30% increase compared to the control group (45.21 MPa).
(3) The hydration performance of cement was significantly influenced by the CS:GBFS ratio in the modified EMR. A ratio of 2.5:7.5 provided an optimal balance of active SiO2, Al2O3, Ca(OH)2, and CaSO4·2H2O, promoting the formation of hydration products such as AFt and C-S-H. This led to a denser microstructure and slower heat evolution. The cumulative hydration heat at 168 h decreased from 232.42 J·g⁻¹ to 211.29 J·g⁻¹, indicating the effectiveness of modified EMR in regulating hydration kinetics.
(4) Modified EMR significantly reduced the environmental risks associated with EMR reuse. Heavy metals and NH3-N were effectively immobilized through precipitation, ion exchange, and encapsulation mechanisms involving hydration products. The resulting mortars met Chinese leaching standards. Compared to natural gypsum, the use of modified EMR reduced CO2 emissions by 4.52–5.46 times and overall material costs by 3.7–14.26 times.
(5) The synergistic modification of EMR using CS and GBFS offers a sustainable, low-carbon alternative to conventional cement retarders, with clear advantages in environmental safety, mechanical performance, and economic feasibility.
Future research should focus on long-term durability, compatibility with blended cements, field application trials, and the development of scalable pretreatment processes, to further support the industrial application of modified EMR in eco-friendly building materials.

Author Contributions

Conceptualization, L.T. and Z.H.; methodology, L.T. and Z.H.; software, L.T.; validation, L.T., J.F. and R.Č.; formal analysis, J.F.; investigation, L.T.; resources, L.T.; data curation, L.T.; writing—original draft preparation, L.T.; writing—review and editing, J.F. and Z.H.; visualization, L.T.; supervision, R.Č. and Z.H.; project administration, Z.H. and R.Č.; funding acquisition, Z.H. and J.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the specific university research of the Czech Technical University in Prague under project SGS24/116/OHK1/3T/11 and the National Natural Science Foundation of China (52478444).

Data Availability Statement

The data that have been used are confidential.

Conflicts of Interest

The authors declare no conflicts of interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

  1. Zeng, T.; Xue, S.; Zhuang, S.; Zhou, X.; Hou, H.; Huang, B.T.; Lan, J. Activated Electrolytic Manganese Residue-Based Environmental Materials for Mine Remediation: Performance and Mechanism. J. Hazard. Mater. 2025, 482, 136560. [Google Scholar] [CrossRef] [PubMed]
  2. Wei, M.; Wang, B.; Chen, M.; Wu, P.; Zhang, X. Remediation of Antimony and Arsenic in Co-Contaminated Soil by Electrolytic Manganese Residue–Biochar Composite: Effects, Mechanisms, and Microbial Response. Environ. Pollut. 2025, 366, 125371. [Google Scholar] [CrossRef]
  3. Li, X.; Li, X.; Ma, X.; Li, C.; Xue, J.; Wang, S. Highly Efficient CO2 Mineralization: Mechanisms and Feasibility of Utilizing Electrolytic Manganese Residue as a Feedstock and Implementing Ammonia Recycling. Sci. Total Environ. 2024, 954, 176711. [Google Scholar] [CrossRef]
  4. Wang, J.; Ma, K.; Shang, S.; Ran, J.; Xia, H.; Luo, Z.; Dong, R. Exploration of the Effects of Electrolytic Manganese Residue on the Environmental, Economic, and Engineering Performance of Magnesium Oxychloride Cement: A Possible Utilization Method of Electrolytic Manganese Residue. Constr. Build. Mater. 2024, 411, 134230. [Google Scholar] [CrossRef]
  5. Lang, L.; Zhu, M.; Pu, S. Recycling engineering sediment waste as sustainable subgrade material using ground granulated blast-furnace slag, electrolytic manganese residue and cement. Environ. Technol. Innov. 2025, 37, 103969. [Google Scholar] [CrossRef]
  6. He, D.; Shu, J.; Wang, R.; Chen, M.; Wang, R.; Gao, Y.; Wang, N. A Critical Review on Approaches for Electrolytic Manganese Residue Treatment and Disposal Technology: Reduction, Pretreatment, and Reuse. J. Hazard. Mater. 2021, 418, 126235. [Google Scholar] [CrossRef] [PubMed]
  7. Li, B.; Li, L.; Chen, X.; Ma, Y.; Zhou, M. Modification of Phosphogypsum Using Circulating Fluidized Bed Fly Ash and Carbide Slag for Use as Cement Retarder. Constr. Build. Mater. 2022, 338, 127630. [Google Scholar] [CrossRef]
  8. Shen, W.; Gan, G.; Dong, R.; Chen, H.; Tan, Y.; Zhou, M. Utilization of Solidified Phosphogypsum as Portland Cement Retarder. J. Mater. Cycles Waste Manag. 2012, 14, 228–233. [Google Scholar] [CrossRef]
  9. Zhang, J.; Wang, X.; Ma, J.; Li, C.; Lu, W.; Rong, T.; Huang, P.; Hu, T. Study on Retarders for Desulfurized Building Gypsum. New Build. Mater. 2017, 44, 143–145. [Google Scholar]
  10. Altun, İ.A.; Sert, Y. Utilization of Weathered Phosphogypsum as Set Retarder in Portland Cement. Cem. Concr. Res. 2004, 34, 677–680. [Google Scholar] [CrossRef]
  11. Su, Q.; Zhou, Y.; Chen, Y.; Wu, M. Hydration behavior of clinker with dry flue gas desulfurization byproduct and desulfurization gypsum. J. Chin. Ceram. Soc. 2016, 44, 663–667. (In Chinese) [Google Scholar]
  12. Tang, L.; He, Z.; Pei, S.; Han, J.; Zou, M.; Qin, M.; Yu, Z. Hydration Characteristics and Pollutant Solidification Mechanism of Full Solid Waste Electrolytic Manganese Residue Super Sulfate Cement. J. Build. Eng. 2024, 84, 108563. [Google Scholar] [CrossRef]
  13. Wang, D.; Wang, Q.; Xue, J. Reuse of Hazardous Electrolytic Manganese Residue: Detailed Leaching Characterization and Novel Application as a Cementitious Material. Resour. Conserv. Recycl. 2020, 154, 104645. [Google Scholar] [CrossRef]
  14. Xu, Y.; Liu, X.; Zhang, Y.; Tang, B.; Mukiza, E. Investigation on Sulfate Activation of Electrolytic Manganese Residue on Early Activity of Blast Furnace Slag in Cement-Based Cementitious Material. Constr. Build. Mater. 2019, 229, 116831. [Google Scholar] [CrossRef]
  15. Wang, J.; Long, G.; Dong, R.; Li, Y. Analysis of Strength, Microstructure and Carbon Emission of Mortar Mixed with Electrolytic Manganese Residue. J. Railw. Sci. Eng. 2023, 20, 1382–1391. (In Chinese) [Google Scholar]
  16. Xu, J.; Long, Y. Experimental Study on Electrolytic Manganese Residue as a Cement Retarder. Fujian Build. Mater. 2012, 9, 12–14. (In Chinese) [Google Scholar]
  17. Zhong, Y.; Zeng, R.; Tao, C. Experimental Study on Using Electrolytic Manganese Slag as a Cement Retarder Instead of Industrial Gypsum. Cem. Eng. 2024, 2, 10–19. (In Chinese) [Google Scholar]
  18. Fu, Y.; Qiao, H.; Feng, Q.; Chen, K.; Li, Y.; Xue, C.; Zhang, Y. Review of New Methods for Resource Utilisation of Electrolytic Manganese Residue and Its Application in Building Materials. Constr. Build. Mater. 2023, 401, 132901. [Google Scholar] [CrossRef]
  19. Li, W.; Jin, H.; Xie, H.; Wang, D. Progress in Comprehensive Utilization of Electrolytic Manganese Residue: A Review. Environ. Sci. Pollut. Res. 2023, 30, 48837–48853. [Google Scholar] [CrossRef]
  20. Shu, J.; Chen, M.; Wu, H.; Li, B.; Wang, B.; Li, B.; Liu, Z. An Innovative Method for Synergistic Stabilization/Solidification of Mn2+, NH4+-N, PO43− and F− in Electrolytic Manganese Residue and Phosphogypsum. J. Hazard. Mater. 2019, 376, 212–222. [Google Scholar] [CrossRef]
  21. Wang, F.; Long, G.; Bai, M.; Wang, J.; Shi, Y.; Zhou, X.; Zhou, J.L. A New Perspective on Belite-Ye’elimite-Ferrite Cement Manufactured from Electrolytic Manganese Residue: Production, Properties, and Environmental Analysis. Cem. Concr. Res. 2023, 163, 107019. [Google Scholar] [CrossRef]
  22. Costa, R.; Cardoso, T.; Degen, M.; Silvestro, L.; Rodríguez, E.; Kirchheim, A.P. Influence of Retarder Admixtures on the Hydration, Rheology, and Compressive Strength of White Portland Cements under Different Temperatures. Cement 2023, 11, 100057. [Google Scholar] [CrossRef]
  23. Shu, J.; Liu, R.; Liu, Z.; Chen, H.; Du, J.; Tao, C. Solidification/Stabilization of Electrolytic Manganese Residue Using Phosphate Resource and Low-Grade MgO/CaO. J. Hazard. Mater. 2016, 317, 267–274. [Google Scholar] [CrossRef] [PubMed]
  24. He, D.; Luo, Z.; Zeng, X.; Chen, Q.; Zhao, Z.; Cao, W.; Chen, M. Electrolytic Manganese Residue Disposal Based on Basic Burning Raw Material: Heavy Metals Solidification/Stabilization and Long-Term Stability. Sci. Total Environ. 2022, 825, 153774. [Google Scholar] [CrossRef]
  25. Wang, F.; Long, G.; Bai, M.; Wang, J.; Zhou, J.L.; Zhou, X. Application of Electrolytic Manganese Residues in Cement Products through Pozzolanic Activity Motivation and Calcination. J. Clean. Prod. 2022, 338, 130629. [Google Scholar] [CrossRef]
  26. Zheng, F.; Zhu, H.; Luo, T.; Wang, H.; Hou, H. Pure Water Leaching Soluble Manganese from Electrolytic Manganese Residue: Leaching Kinetics Model Analysis and Characterization. J. Environ. Chem. Eng. 2020, 8, 103916. [Google Scholar] [CrossRef]
  27. Wu, T.; Ma, B.; An, Y.; Chen, Y.; Wang, C. Improvement of Manganese Electrolytic Process and Secondary Resources Recovery of Manganese: A Review. Process Saf. Environ. Prot. 2024, 186, 895–909. [Google Scholar] [CrossRef]
  28. Zhao, Y.; Zhan, J.; Liu, G.; Zheng, M.; Jin, R.; Yang, L.; Wang, P. Evaluation of Dioxins and Dioxin-Like Compounds from a Cement Plant Using Carbide Slag from Chlor-Alkali Industry as the Major Raw Material. J. Hazard. Mater. 2017, 330, 135–141. [Google Scholar] [CrossRef] [PubMed]
  29. Yu, Z.; Wang, B.; Li, T.; Wang, W. Toughness Study of Polyacrylamide-Modified Slag/Fly Ash-Based Alkali-Activated Cementitious Materials. Constr. Build. Mater. 2024, 450, 138622. [Google Scholar] [CrossRef]
  30. He, D.; Shu, J.; Zeng, X.; Wei, Y.; Chen, M.; Tan, D.; Liang, Q. Synergistic Solidification/Stabilization of Electrolytic Manganese Residue and Carbide Slag. Sci. Total Environ. 2022, 810, 152175. [Google Scholar] [CrossRef]
  31. Tang, L.; He, Z.; Chen, K.; Wang, X.; Xiao, Y.; Yu, Z.; Xiao, H. Study of Microscopic Properties and Heavy Metal Solidification Mechanism of Electrolytic Manganese Residue-Based Cementitious Materials. Environ. Sci. Pollut. Res. 2023, 30, 105056–105071. [Google Scholar] [CrossRef]
  32. Zhang, Y.; Liu, X.; Xu, Y.; Tang, B.; Wang, Y. Preparation of Road Base Material by Utilizing Electrolytic Manganese Residue Based on Si–Al Structure: Mechanical Properties and Mn²⁺ Stabilization/Solidification Characterization. J. Hazard. Mater. 2020, 390, 122188. [Google Scholar] [CrossRef] [PubMed]
  33. GB/T 17671-2021; Cement Mortar Strength Test Method (ISO Method). Standard Press of China: Beijing, China, 2021. (In Chinese)
  34. Zhang, Y.; Liu, X.; Xu, Y.; Tang, B.; Wang, Y.; Mukiza, E. Synergic Effects of Electrolytic Manganese Residue–Red Mud–Carbide Slag on the Road Base Strength and Durability Properties. Constr. Build. Mater. 2019, 220, 364–374. [Google Scholar] [CrossRef]
  35. GB 175-2020; Portland Cement. General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China: Beijing, China, 2020. (In Chinese)
  36. HJ/T 299-2007; Sulphuric Acid and Nitric Acid Method for Total Digestion of Solid Waste. Standard Press of China: Beijing, China, 2007. (In Chinese)
  37. HJ 535-2009; Water Quality—Determination of Ammonia Nitrogen—Nessler’s Reagent Spectrophotometry. Standard Press of China: Beijing, China, 2009. (In Chinese)
  38. GB 8978-1996; Integrated Wastewater Discharge Standard. Standard Press of China: Beijing, China, 1996. (In Chinese)
  39. Fu, Y.; Qiao, H.; Feng, Q.; Chen, K.; Li, Y.; Jia, Z.; Xue, C. Impact of Desulphurized Electrolytic Manganese Residue-Assisted Cementitious Materials on Silicate Cement Hydration and Environmental Safety Assessment. J. Build. Eng. 2024, 94, 109906. [Google Scholar] [CrossRef]
  40. Tang, L.; He, Z.; Tang, J.; Yang, R.; Pei, S.; Xia, Y.; Yu, J. Study on the Microscopic Characteristics and Hydration Mechanism of Thermo-Alkali Activated Electrolytic Manganese Residue Geopolymers. Constr. Build. Mater. 2024, 438, 137279. [Google Scholar] [CrossRef]
  41. Zhou, C.; Wang, J.; Wang, N. Treating Electrolytic Manganese Residue with Alkaline Additives for Stabilizing Manganese and Removing Ammonia. Korean J. Chem. Eng. 2013, 30, 2037–2042. [Google Scholar] [CrossRef]
  42. Du, B.; Hou, D.; Duan, N.; Zhou, C.; Wang, J.; Dan, Z. Immobilization of High Concentrations of Soluble Mn(II) from Electrolytic Manganese Solid Waste Using Inorganic Chemicals. Environ. Sci. Pollut. Res. 2015, 22, 7782–7793. [Google Scholar] [CrossRef]
  43. Wu, Z.; Feng, Z.; Pu, S.; Zeng, C.; Zhao, Y.; Chen, C. Mechanical Properties and Environmental Characteristics of the Synergistic Preparation of Cementitious Materials Using Electrolytic Manganese Residue, Steel Slag, and Blast Furnace Slag. Constr. Build. Mater. 2024, 411, 134480. [Google Scholar] [CrossRef]
  44. He, D.; Chen, M.; Liu, H.; Wang, J. Preparation of Activated Electrolytic Manganese Residue–Slag–Cement Ternary Blended Cementitious Material: Hydration Characteristics and Carbon Reduction Potential. Constr. Build. Mater. 2024, 425, 135990. [Google Scholar] [CrossRef]
  45. Zhang, M.; Zunino, F.; Yang, L.; Wang, F.; Scrivener, K. Understanding the Negative Effects of Alkalis on Long-Term Strength of Portland Cement. Cem. Concr. Res. 2023, 174, 107348. [Google Scholar] [CrossRef]
  46. Fu, Y.; Qiao, H.; Feng, Q.; Chen, K.; Li, Y.; Jia, Z. Self-Stabilisation of High-Temperature Calcined Electrolytic Manganese Residue in Mortar. Constr. Build. Mater. 2023, 386, 131460. [Google Scholar] [CrossRef]
  47. Zhang, Y.; Liu, X.; Xu, Y.; Tang, B.; Wang, Y.; Mukiza, E. Preparation and Characterization of Cement Treated Road Base Material Utilizing Electrolytic Manganese Residue. J. Clean. Prod. 2019, 232, 980–992. [Google Scholar] [CrossRef]
  48. Wang, Z.; Shui, Z.; Sun, T.; Li, H.; Chi, H.; Ouyang, G. Effect of MgO and Superfine Slag Modification on the Carbonation Resistance of Phosphogypsum-Based Cementitious Materials: Based on Hydration Enhancement and Phase Evolution Regulation. Constr. Build. Mater. 2024, 415, 134914. [Google Scholar] [CrossRef]
  49. Pratap, B.; Mondal, S.; Rao, B.H. Mechanical and Durability Assessment of Phosphogypsum–Bauxite Residue–Fly Ash-Based Alkali-Activated Concrete. Constr. Build. Mater. 2024, 411, 134670. [Google Scholar] [CrossRef]
  50. Cretescu, I.; Harja, M.; Teodosiu, C.; Isopescu, D.N.; Chok, M.F.; Sluser, B.M.; Salleh, M.A.M. Synthesis and Characterisation of a Binder Cement Replacement Based on Alkali Activation of Fly Ash Waste. Process Saf. Environ. Prot. 2018, 119, 23–35. [Google Scholar] [CrossRef]
  51. Shen, Y.; Qian, J.; Huang, Y.; Yang, D. Synthesis of Belite Sulfoaluminate–Ternesite Cements with Phosphogypsum. Cem. Concr. Compos. 2015, 63, 67–75. [Google Scholar] [CrossRef]
  52. Gao, Y.; Li, Z.; Zhang, J.; Zhang, Q.; Wang, Y. Synergistic Use of Industrial Solid Wastes to Prepare Belite-Rich Sulphoaluminate Cement and Its Feasibility Use in Repairing Materials. Constr. Build. Mater. 2020, 264, 120201. [Google Scholar] [CrossRef]
  53. Sari, M.; Yilmaz, E.; Kasap, T.; Guner, N.U. Strength and Microstructure Evolution in Cemented Mine Backfill with Low and High pH Pyritic Tailings: Effect of Mineral Admixtures. Constr. Build. Mater. 2022, 328, 127109. [Google Scholar] [CrossRef]
  54. Gougar, M.L.D.; Scheetz, B.E.; Roy, D.M. Ettringite and C–S–H Portland Cement Phases for Waste Ion Immobilization: A Review. Waste Manag. 1996, 16, 295–303. [Google Scholar] [CrossRef]
  55. Liang, J.; Liu, R.; Jing, D.; Lu, F.; Zhao, Y.; Xie, Z. Study on the Alkali–Sulfur Co-Activation and Mechanical Properties of Low-Carbon Cementitious Composite Materials Based on Electrolytic Manganese Residue, Carbide Slag, and Granulated Blast-Furnace Slag. Appl. Sci. 2024, 14, 4355. [Google Scholar] [CrossRef]
  56. Tu, C.; Lang, L.; Nie, X.; Yang, Y.; Liu, L.; Ping, W.; Li, J. Utilization of Ground Granulated Blast-Furnace Slag and Electrolytic Manganese Residue as a Low-Carbon Cementitious Material. J. Sustain. Cem.-Based Mater. 2024, 13, 450–461. [Google Scholar] [CrossRef]
  57. Wang, F.; Long, G.; Bai, M.; Shi, Y.; Zhou, J.L. Feasibility of Low-Carbon Electrolytic Manganese Residue-Based Supplementary Cementitious Materials. Sci. Total Environ. 2023, 883, 163672. [Google Scholar] [CrossRef] [PubMed]
  58. Fořt, J.; Černý, R.J. Carbon Footprint Analysis of Calcined Gypsum Production in the Czech Republic. J. Clean. Prod. 2018, 177, 795–802. [Google Scholar] [CrossRef]
  59. Dinh, H.L.; Doh, J.H.; Liu, J.; Lu, L.; Song, H.; Park, D. Comprehensive Assessment of Geopolymer Concrete Mechanical and Environmental Performance with Glass Cullet Fine Aggregates. J. Build. Eng. 2023, 76, 107094. [Google Scholar] [CrossRef]
  60. Fořt, J.; Mildner, M.; Černý, R. Consequences of Omitting Some Important Factors in the Environmental Analyses of Commercial Sodium Silicate/Sodium Hydroxide Use for Alkaline Activation in the Light of Comparison with Cement-Based Composites. Sci. Total Environ. 2024, 928, 172324. [Google Scholar] [CrossRef]
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Figure 1. Appearance, SEM, and XRD of raw materials.
Figure 1. Appearance, SEM, and XRD of raw materials.
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Figure 2. XRD patterns of raw EMR, M-EMR1, M-EMR3, and M-EMR5.
Figure 2. XRD patterns of raw EMR, M-EMR1, M-EMR3, and M-EMR5.
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Figure 3. SEM-EDS images of raw EMR, M-EMR1, M-EMR3, and M-EMR5.
Figure 3. SEM-EDS images of raw EMR, M-EMR1, M-EMR3, and M-EMR5.
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Figure 4. Fluidity and setting time of cement mortar with different dosages and types of modified EMR.
Figure 4. Fluidity and setting time of cement mortar with different dosages and types of modified EMR.
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Figure 5. Compressive strength of cement mortar with different dosages and types of modified EMR.
Figure 5. Compressive strength of cement mortar with different dosages and types of modified EMR.
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Figure 6. XRD and quantitative phase analysis of cement with different types of modified EMR.
Figure 6. XRD and quantitative phase analysis of cement with different types of modified EMR.
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Figure 7. XRD and quantitative phase analysis of cement with different dosages of modified EMR.
Figure 7. XRD and quantitative phase analysis of cement with different dosages of modified EMR.
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Figure 8. XRD and quantitative phase analysis of cement paste with raw EMR, modified EMR, and cement paste.
Figure 8. XRD and quantitative phase analysis of cement paste with raw EMR, modified EMR, and cement paste.
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Figure 9. FTIR spectra of different types and dosages of modified EMR cement paste and control group cement paste.
Figure 9. FTIR spectra of different types and dosages of modified EMR cement paste and control group cement paste.
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Figure 10. Hydration heat of cement paste with different types of modified EMR.
Figure 10. Hydration heat of cement paste with different types of modified EMR.
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Figure 11. Hydration heat of cement paste with different dosages of modified EMR.
Figure 11. Hydration heat of cement paste with different dosages of modified EMR.
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Figure 12. Hydration heat of cement paste, modified EMR-cement paste, and raw EMR-cement paste.
Figure 12. Hydration heat of cement paste, modified EMR-cement paste, and raw EMR-cement paste.
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Figure 13. TG-DTG curves of raw EMR-cement paste, modified EMR-cement paste, and cement paste.
Figure 13. TG-DTG curves of raw EMR-cement paste, modified EMR-cement paste, and cement paste.
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Figure 14. SEM-EDS images of raw EMR-cement paste, modified EMR-cement paste, and cement paste.
Figure 14. SEM-EDS images of raw EMR-cement paste, modified EMR-cement paste, and cement paste.
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Figure 15. Economic costs and carbon emissions of modified EMR.
Figure 15. Economic costs and carbon emissions of modified EMR.
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Table 1. Chemical compounds of EMR, CS, GBFS, and cement (wt.%).
Table 1. Chemical compounds of EMR, CS, GBFS, and cement (wt.%).
CompoundSiO2SO3CaOAl2O3Fe2O3MgONa2OK2OMnOP2O5Other
EMR38.5527.329.347.786.582.340.783.013.11—1.2
Cement19.883.4765.665.222.750.49————1.59
GBFS32.491.6235.2819.220.528.760.610.400.19—1.1
CS5.230.9787.330.671.890.860.21———2.84
Table 2. Mix proportions of modified EMR.
Table 2. Mix proportions of modified EMR.
NumberEMR Dosage (g) CS Dosage (g)GBFS Dosage (g)Water (g) (Water Solid Ratio = 0.5)CS:GBFS
M-EMR110001001000:10
M-EMR210025751002.5:7.5
M-EMR310050501005:5
M-EMR410075251007.5:2.5
M-EMR5100100010010:0
Table 3. Mix proportions of modified EMR-cement mortar.
Table 3. Mix proportions of modified EMR-cement mortar.
NumberStandard Cement
Dosage (g) 		Raw EMR
Dosage (g) 		M-EMR1
Dosage (g) 		M-EMR2
Dosage (g) 		M-EMR3
Dosage (g) 		M-EMR4
Dosage (g) 		M-EMR5
Dosage (g)
R0450//////
A045018 (4 wt.%) /////
A1 450/18 (4 wt.%)////
A2450//18 (4 wt.%)000
A3450///18 (4 wt.%)//
A4450////18 (4 wt.%) 0
A5450/////18 (4 wt.%)
B045027 (6 wt.%)/////
B1450/27 (6 wt.%)////
B2450//27 (6 wt.%)///
B3450///27 (6 wt.%)//
B4450////27 (6 wt.%)/
B5450/////27 (6 wt.%)
C045036 (8 wt.%)/////
C1450/36 (8 wt.%)////
C2450//36 (8 wt.%)///
C3450///36 (8 wt.%)//
C4450////36 (8 wt.%)/
C5450/////36 (8 wt.%)
Table 4. Structural information of main mineral phases [39].
Table 4. Structural information of main mineral phases [39].
PhaseSpace GroupLattice ParameterICSD
abcαβγ
AliteR3m33.1087.03618.521–94.137–94,742
BeliteP21/n5.5126.7589.314–94.58–81,096
Tricalcium aluminatePa-315.26–––––1,841
GypsumC2/c6.28415.26.523–127.41–409,581
PortlanditeP-3m3.592–4.906–––202,220
EttringiteP3c11.229–21.478–––155,395
ZinciteP63mc3.2533.2535.20790901209,004,179
Table 5. Leaching toxicity of modified EMR (mg/L).
Table 5. Leaching toxicity of modified EMR (mg/L).
NumberMn (mg/L)NH3-N (mg/L)pH Value
Raw EMR12201495.80
M-EMR127.6723.622410.66
M-EMR20.07362.786111.43
M-EMR30.02511.565412.25
M-EMR40.00840.583112.78
M-EMR50.00230.087113.14
GB8978-1996 standard215/
Table 6. Leaching concentrations of pollutants from cement mortar with different types of modified EMR (mg/L).
Table 6. Leaching concentrations of pollutants from cement mortar with different types of modified EMR (mg/L).
GroupLeaching Concentration (mg/L)
MnNH3-NHgPbCdCrCuZn
Raw EMR12201490.00120.01320.07320.02520.46401.700
C10.05450.08620.00050.00140.0088N.D.0.15420.0932
C20.00580.0056N.D.0.00020.0043N.D.0.02600.0256
C30.00120.00130.00030.00180.0019N.D.0.00520.0075
C4N.D.N.D.0.00020.00110.0008N.D.0.00210.0053
C5N.D.N.D.0.0004N.D.0.0002N.D.0.00340.0021
GB8978-19962150.0510.10.50.52
N.D. Values below the detection limit of the instrument.
Table 7. Economic costs and carbon emissions of raw materials.
Table 7. Economic costs and carbon emissions of raw materials.
MaterialCO2 Emission (kg CO2/t)Cost (RMB/t)
EMR [55,56]720
GBFS [55,56]83300
CS [55,57]6760
Water [57]34.2
Natural gypsum [58]140.2400
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Tang, L.; Fořt, J.; Černý, R.; He, Z. Sustainable Utilization of Modified Electrolytic Manganese Residue as a Cement Retarder: Workability, Mechanical Properties, Hydration Mechanisms, Leaching Toxicity, and Environmental Benefits. Buildings 2025, 15, 1586. https://doi.org/10.3390/buildings15101586

AMA Style

Tang L, Fořt J, Černý R, He Z. Sustainable Utilization of Modified Electrolytic Manganese Residue as a Cement Retarder: Workability, Mechanical Properties, Hydration Mechanisms, Leaching Toxicity, and Environmental Benefits. Buildings. 2025; 15(10):1586. https://doi.org/10.3390/buildings15101586

Chicago/Turabian Style

Tang, Liang, Jan Fořt, Robert Černý, and Zhaoyi He. 2025. "Sustainable Utilization of Modified Electrolytic Manganese Residue as a Cement Retarder: Workability, Mechanical Properties, Hydration Mechanisms, Leaching Toxicity, and Environmental Benefits" Buildings 15, no. 10: 1586. https://doi.org/10.3390/buildings15101586

APA Style

Tang, L., Fořt, J., Černý, R., & He, Z. (2025). Sustainable Utilization of Modified Electrolytic Manganese Residue as a Cement Retarder: Workability, Mechanical Properties, Hydration Mechanisms, Leaching Toxicity, and Environmental Benefits. Buildings, 15(10), 1586. https://doi.org/10.3390/buildings15101586

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