This work presents an innovative approach to developing a low-carbon and hazard-free cementitious material (EGC) by activating ground granulated blast-furnace slag (GGBS) with electrolytic manganese ...residue (EMR), which has an excellent heavy metal solidified capacity. Herein, the multi-step leaching was creatively conducted to investigate the solidified morphology of heavy metals in hazardous EMR. CO2 emission per unit strength factor was calculated to quantitatively analyze the low-carbon degree. The results show that the added hazardous EMR rich in sulfate and the dilution effect caused by the decrease in GGBS lessen the final setting time and fluidity. Low-temperature calcination (200 °C) alters the dissolution rate of ettringite and AFm-like phases by changing the sulfate crystal. Excessive acidic EMR consumes more calcium hydroxide and lowers the pH of the EGC system, resulting in weakened GGBS activity. The formation of jouravskite, thaumasite, and henritermierite are AFm-like hydrated lamellated structures, which provides evidence for the immobilization of Mn2+ in EMR. Vast Mn2+ are embedded in the main interlayer of Ca2Al(OH)6+ by substituting Al to form AFm-like phase. The lowest 60d unit compressive strength carbon emission of the EGC system containing 20 % calcinated EMR is 0.78 kg∙MPa−1∙m−3, meaning the substitution barrier is better addressed by adding calcined EMR. This work provides an innovative solution for high value-added and hazard-free utilization for EMR and carbon reduction in the cement industry.
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•The manufactured binder realizes hazard-free and high value-added use of EMR.•Low-temperature calcination improves EMR activity by changing sulfate solubility.•AFm-like products formation can be used as evidence for Mn2+ immobilization.•The substitution barrier is better addressed by adding the calcined EMR.
The reclamation and reuse of electrolytic manganese residue (EMR) as a bulk hazard solid waste are limited by its residual ammonia nitrogen (NH4+-N) and manganese (Mn2+). This work adopts a ...co-processing strategy comprising air-jet milling (AJM) and horizontal-shaking leaching (HSL) for refining and leaching disposal of NH4+-N and Mn2+ in EMR. Results indicate that the co-use of AJM and HSL could significantly enhance the leaching of NH4+-N and Mn2+ in EMR. Under optimal milling conditions (50 Hz frequency, 10 min milling time, 12 h oscillation time, 400 rpm rate, 30 ℃ temperature, and solid-to-liquid ratio of 1:30), NH4+-N and Mn2+ leaching efficiencies were optimized to 96.73% and 97.35%, respectively, while the fineness of EMR was refined to 1.78 µm. The leaching efficiencies of NH4+-N and Mn2+ were 58.83% and 46.96% higher than those attained without AJM processing. The AJM used strong airflow to give necessary kinetic energy to EMR particles, which then collided and sifted to become refined particles. The AJM disposal converted kinetic energy into heat energy upon particle collisions, causing EMR phase transformation, and particularly hydrated sulfate dehydration. The work provides a fire-new and high-efficiency method for significantly and simply leaching NH4+-N and Mn2+ from EMR.
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•Air-jet milling and horizontal-shaking leaching enhance NH4+-N and Mn2+ recovery.•The maximum recovery efficiencies of 97.35% for Mn2+ and 96.73% for NH4+-N.•Air-jet milling gives kinetic energy for particles to be refined after a collision.•Air-jet milling results in phase transformation and hydrated sulfate dehydration.
One-part geopolymeric binders which are considered as cleaner non-Portland cementitious materials are prepared by first mixing the aluminosilicate materials with the solid alkaline activators before ...adding water, which makes the mixing method of the geopolymer being the same as Portland cement. In this paper, sinking spherical beads (SSB) is introduced into the raw materials containing fly ash (CFA) and ground granulated blast furnace slag (GGBS) to synthesize a ternary one-part geopolymer. A systematic investigation of the effect of SSB on the geopolymer pastes and mortars is performed through measuring the fluidity, final setting time, compressive strength and flexural strength. It is found that SSB can significantly improve the fluidity and mechanical properties of geopolymer due to its high reactive effect and remarkable morphological effect. The action mechanism of SSB for improving the performance of the geopolymer was also dissected. It is interesting to note that SSB has little influence on the initial heat flow and increases the cumulative heat relating to the strength development. The changes in the formation of C-A-SH and N-A-SH gels after the introduction of SSB are well captured by the XRD and EDX analysis. It clearly appears that the N-A-SH gel with the optimal Na/Si ratio of 0.5 can be generated by optimizing the rational proportion of raw materials and alkaline activators. This study not only demonstrates the superiority of SSB in synthesizing a ternary one-part geopolymer, but also develops a method to design the novel non-Portland cement only by using industrial wastes.
The sinking spherical beads can improve the fluidity and compressive strength of one-part geopolymer to some extent due to the high reactive effect and remarkable morphological effect and has little influence on the final setting time. This study gives a perspective on the synthesis of one-part geopolymeric products with the generation of the desired C-A-SH and N-A-SH gels by designing the rational proportion of starting materials and alkaline activators. Display omitted
•In this study, active sinking spherical beads is firstly introduced into one-part geopolymer.•The mechanisms of the sinking spherical beads in geopolymer have been studied by multiple methods.•The optimal gelatinous phases can be designed by the rational contents of precursor materials and activators.
Electrolytic manganese residue (EMR) stockpiles contain significant amounts of Mn2+ and NH4+-N which pose a risk of environmental pollution. For EMR safe disposal, an innovative approach is proposed ...that involves direct sodium silicate-sodium hydroxide (Na2SiO3–NaOH) collaborative technology. This approach utilises Na2SiO3 and NaOH as the solidifying agent and activator, respectively, to treat EMR without hazardous effects. The study also provides insights into the kinetics of Mn2+ leaching under the effect of Na2SiO3–NaOH. Leaching efficiency was determined by varying parameters such as stirring rate, reaction temperature, pH of the initial solution, Na2SiO3 concentration, and reaction time to investigate the efficacy of this method. The study indicates that the co-treatment technology of Na2SiO3–NaOH can achieve maximum solidification efficiencies of 99.7% and 98.2% for Mn2+ and NH4+-N, respectively. The process can successfully solidify Mn2+ by synthesising Mn(OH)2 and MnSiO3 in an alkaline environment under optimal conditions including stirring rate of 450 rpm, initial solution pH of 8, test temperature of 40 °C, test time of 420 min, and Na2SiO3 content of 5%. The findings of this study have confirmed that surface chemistry plays a vital role in regulating the test rate and the proposed equation accurately describes Mn2+ leaching kinetics. Overall, the co-treatment technology involving Na2SiO3–NaOH is a viable solution for EMR resource utilisation without compromising environmental safety. This method has the potential to be implemented for other waste streams with comparable compositions, ultimately promoting the sustainable management of waste.
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•A direct Na2SiO3–NaOH collaborative treatment technology for Mn residue.•Synergistic impact greatly enhances the Mn2+ leaching efficiency.•Treatment procedure is well described by Mn2+ kinetic equation.•The maximum solidification efficiency of NH4+-N and Mn2+ are 98.2% and 99.7%.•The ideal strength of Mn residue-based paste has the potential as binder material.
•The effects of nanoparticles on cement hydration at elevated temperatures were investigated by isothermal calorimeter.•The nucleation and growth process of hydrates in nanoparticles modified cement ...were analyzed by a kinetics model.•The mechanism of nanoparticles on the hydration kinetics of cement was discussed.
The nanometer materials and technology are becoming new ways for cementitious composite innovation due to the significant improvement of microstructure and mechanical performance of cement-based materials. In this study, the isothermal calorimetry was employed to measure the heat release rate and total heat release of multi-scale cement system incorporated with different nanoparticles at elevated temperatures. The nucleation and growth processes of hydration products were simulated through a kinetics model. It is discovered that the effects of nanoparticles on cement hydration depend on itself chemical reactivity and physical properties as well as ambient temperature. Both nano-SiO2 and nano-C-S-H can obviously shorten the induction period of cement hydration and have acceleration effects obviously. Addition of 1% nano-CaCO3 seems to have no obvious effect on cement hydration process at elevated temperatures. The acceleration effects of nano-particles mainly refer to the improvement of the nucleation rate of hydrates. Generally, the effect of nanoparticles on nucleation process is more significant than that on growth process. Nano-SiO2 and nano-CaCO3 have slight influence on the growth rate, but the nano-C-S-H can increase the growth rates to some extent at different temperatures.
The earth-based construction with unique advantages of wide source of raw material, low energy consumption and carbon emission has attracted growing attention recently. This study employs a ...cement-based high-efficiency stabilizer and fly ash to improve the mechanical properties of earth-based construction. And the influences of fly ash on compressive strength and key variables for strength development are studied by measuring the mechanical and physical properties. Total stabilizer content (CT) which changes slightly with curing time and the calculation method of CT values are put forward based on the pozzolanic and dispersing effects of fly ash in stabilized earth. An integrated parameter taking into account multiple variables, such as stabilizer and fly ash contents, curing time and physical indexes, is defined as the ratio of void ratio to total stabilizer content (et/CT), and the relationship of compressive strength to et/CT is analyzed by exponential and power functions. The after-curing physical indexes are dependent upon the initial ones, total stabilizer content and curing age. Subsequently, the calculation formulae for physical indexes are proposed through the multiple linear regression and power regression. Finally, the strength-calculation model with a deviation between calculated values and measured results of lower than 10% is developed to guide the design of earth-based construction admixed with the high-efficiency stabilizer and fly ash. Embodied environmental impact evaluation indicates that the combination use of stabilizer and fly ash is a novel low-CO2 emission method for preparing cleaner earth-based construction.
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•Up to 5% WTS can be applied without significant effect on concrete performance.•10% of alum-WTS reduces the mechanical strength of bricks by 24.6–45.5%.•10% of iron-WTS increases ...mechanical strength of bricks by 7–97%.•Application of WTS in construction materials increases permeability.•WTS-fly ash geopolymer being 12 times stronger than clay–cement during wetting/drying cycles.
Water treatment sludge (WTS) management is a growing global problem for water treatment plants (WTPs) and governments. Considering the scarcity of raw materials in many parts of the planet and unique properties of WTS, extensive research has been conducted on the application of WTS in the production of construction materials such as roof tiles, bricks, lightweight aggregates, cement, concrete and geopolymers. This paper critically reviews the progress in the application of WTS in construction materials, by synthesizing results from recent studies. Research findings have revealed that incorporation of ≤10% alum-based sludge in ceramic bricks is satisfactory with a small reduction of mechanical performance. Using the iron-based sludge, the bricks presented better mechanical strength than the reference clay-bricks. Concerning WTS application in concrete, 5% replacement of cement or sand by WTS was considered as the ideal value for the application in a variety of structural and non-structural concrete without adverse effect on concrete mechanical performance. Furthermore, this paper discusses sludge-amended concrete in terms of durability, potential leaching of toxic elements and cost, and suggests topics for future research on the sustainable management of WTS.
Degradation in grade of manganese ore aggravates the complexity of electrolytic manganese residue (EMR). Calcination is one of the most practical pretreatment methods to improve EMR activity and ...dispose the hazardous elements. In this paper, the evolution of mineral phase, pozzolanic activity, pore structure and harmful components induced by calcining EMR was investigated. The results show that EMR calcined at 800 °C has the strength activity index (SAI) of 84.79 at 28 d, which is attributed to the decomposition of dihydrate gypsum and the formation of activated calcium, silicon and aluminum oxide. The formation of β-type hemihydrate gypsum increases the pozzolan activity, while the latter is limited by the formation of stable Mn-spinel (Mn3O4) and Mn-hercynite (MnFe2O4). In the EMR-doped mortar matrix, the production of a large amount of ettringite due to the existence of gypsum, as well as common C-S-H, portlandite and AFm, which strongly verify the pozzolanic activity of EMR. Leaching results show that Mn2+ and NH4+-N could not be eliminated completely at low temperature (<600 °C), but could be completely stabilized in the alkaline environment provided by the cement. The Mn2+ and NH4+-N levels in mortar are fully below the regulatory standards when calcinated above 800 °C. All heavy metals are fixed in the cement and calcination process, ensuring the cleaner utilization of EMR in building materials.
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•EMR calcined at 800 °C has the optimum strength activity index of 84.79 at 28-d.•Pozzolan activity of EMR is boosted in β-CaSO4·0.5H2O and weakened in Mn3O4 and MnFe2O4.•Presence of gypsum in EMR retards the cement hydration and forms ettringite.•Mn2+ and NH4+-N below national standards at calcination above 800 °C.
•Higher calcination temperature reduced the dissolved degree of Al in sludge ash.•S600 ash promoted the formation of Al-bearing products but inhibited the C3S hydration significantly.•The reaction of ...S800 ash with cement contributed to more hydration heat and hydration products.
Sewage sludge ash has potential to be used as supplementary cementitious material in the production of building materials. The chemical effect of sewage sludge ash on early-age hydration of cement was investigated in this study. Two types of sludge ash calcined at 600 °C (S600) and 800 °C (S800) were blended with cement for analysis of hydration heat evolution, solid phase assemblage and aqueous composition. The aluminate dissolution of S600 ash promoted the formation of ettringite and consumption of gypsum, resulting in a high initial hydration heat. However, high concentrations of Al and Si caused by continuous dissolution of aluminate and silicate in S600 ash inhibited significantly the C3S dissolution. Interestingly, S800 ash had slight effect on early cement hydration since higher calcination temperature decreased the activity of aluminate. As compared with the reference, cumulative hydration heat of blended paste with 30% S800 ash at 7 days was increased by 18.72% indicating the occurrence of reaction between sludge ash and cement. Further study is recommended to focus on the long-term performance of cement-based materials blended with sludge ash.
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