矿业科学学报

Study on activity characteristics of modified coal gasification coarse slag and its hydration hardening properties of blended cement paste

Wang Dongmin, Fang Kuizhen, Zhang Ming

2022, 7(5): 513-521. doi: 10.19606/j.cnki.jmst.2022.05.001

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Abstract:
The large-scale application of coal gasification technology produces a large amount of coal gasification slag that is difficult to handle. As a kind of coal gasification ash rich in aluminosilicate minerals, coal gasification coarse slag has the characteristics of pozzolanic activity and low carbon content, and can be used as supplementary cementitious material. In order to explore the activity characteristics of coal gasification coarse slag under different modification effects and its influence mechanism on the hydration and hardening performance of cement, this paper analyzed the hydration exotherm, compressive strength, composition and structure of hydration products of the blended cement paste mixed with modified gasification slag, which were compared from macroscopic and microscopic perspectives. The results show that the addition and modification of diethanol monoisopropanolamine (DEIPA) can significantly improve the grinding efficiency and potential hydration activity of gasification coarse slag, effectively reduce the extension of hydration induction period and reduce the retarding effect of gasification coarse slag on cement hydration. The addition order of DEIPA has little effect on the hydration hardening properties of blended cement. The coal gasification coarse slag modified by chemical and physical coordination can be used as the admixture of Portland cement and concrete, and the mechanical properties of blended cement can be improved under the appropriate dosage (10 %).

Investigating the performance of dry chemically modified steel slag powder and pastes by formic acid

Huo Binbin, Zhang Yamei, Wang Dongmin, Li Baoliang

2022, 7(5): 522-528. doi: 10.19606/j.cnki.jmst.2022.05.002

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Abstract:
Understanding the composition and reactivity of formic acid modified steel slag powder (SS) from micro scale is critical to extending the utilization of steel slag. In this study, four representative sources of SS were selected, which were dry chemically modified by formic acid (FA) with a mass fraction of 4 % on the basis of SS. The backscatter electron microscope, hydration calorimeter, X-ray diffractometer and fourier transform infrared spectrometer were applied to characterize the SS and SS pastes before and after modification. Results show that the 3 d and 7 d compressive strength of the different sources of SS pastes are low, and the 72 h cumulative hydration heat varies between 10~40 J/g due to their different mineral compositions. However, after FC modification, the 3 d compressive strength increases by more than 200 %, and the 72 h cumulative hydration heat rises to above 50 J/g with an increase above 80 %.it is found that the Ca(OH)₂ in SS can react with FA to produce calcium formate, while the calcium silicates in SS are not significantly affected.

A review on the research progress of tailings activation methods

Yi Longsheng, Xia Jin, Mi Hongcheng, Zhang Binghang

2022, 7(5): 529-537. doi: 10.19606/j.cnki.jmst.2022.05.003

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Abstract:
This paper briefly introduced the current situation of tailings stockpiling and the associated resource utilization methods of tailings in China. In terms of the low activity of utilizing tailings as building materials, we summarized the research progress made in several activation methods of tailings, including mechanical activation, thermal activation and chemical activation, and the corresponding mechanisms as well as their merits and demerits. We concluded that only integrating multi-methods could achieve the optimal activation. Despite cost-effectiveness, chemical activation still cannot completely substitute other activation methods. If being addressed thoroughly, it would better serve the resource utilization of tailings and remarkably remove the potential environmental issues.

Mechanical anisotropy and interlayer bonding strength of 3D printing geopolymer

Guo Xiaolu, Li Shuhao

2022, 7(5): 538-543. doi: 10.19606/j.cnki.jmst.2022.05.004

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Abstract:
3D printing geopolymer is a new type of building way and material with both of resource utilization and intelligent building. The mechanical properties in all directions and the bonding strength between layers of components are important factors affecting the constructability and durability of buildings.3D printing geopolymer mortar was prepared with fly ash and quartz sand as main raw materials, anhydrous sodium silicate as alkali activator, slag powder as auxiliary cementitious material, magnesium aluminum silicate as special additive. The 3D printing component of fly ash-based geopolymer was prepared under the condition of the optimum dosage and proportion. The interlayer bonding strength and tensile strength were studied, and the mechanical anisotropy properties were characterized by mechanical properties and ultrasonic pulse velocity.

Preparation of admixture by lightly calcinated electronic fluorine-containing sludge mixed with coal gangue and its effect on cement properties

Xu Dongyang, He Tingshu, Da Yongqi

2022, 7(5): 544-553. doi: 10.19606/j.cnki.jmst.2022.05.005

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Abstract:
In view of the problems posed by low pozzolanic activity and large water requirement of normal consistency in the direct light calcinating of electronic fluorine-containing sludge as cement admixture, this paper uses coal gangue as a supplementary silicon and aluminum source of electronic fluorine-containing sludge to mix electronic fluorine-containing sludge and coal gangue and then to prepare cement admixture by light calcinating. This paper studied the effect of cement admixture prepared by light calcinating electronic fluorine-containing mixed with sludge coal gangue on cement properties through strength activity index, mechanical properties of cement, water requirement of normal consistency, setting time, particle size, X-ray diffraction and scanning electron microscopy. The results show that compared with direct light calcinating of electronic fluorine-containing sludge to prepare cement admixture, light calcinating of electronic fluorine-containing sludge mixed with coal gangue can improve the particle gradation of cement and reduce the water requirement of normal consistency of cement. It can significantly improve the activity of cement admixture and the strength of ordinary portland cement. Significantly extending the initial setting time and shorten the final setting time of cement.

Influence of physicochemical properties and shape characteristics of coal gangue coarse aggregate on concrete strength

Wang Yan, Zuo Zhen, Wen Bo, Gao Guanyi

2022, 7(5): 554-564. doi: 10.19606/j.cnki.jmst.2022.05.006

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Abstract:
Natural aggregate is increasingly scarce, and the reuse of solid waste is highly valued. Application of coal gangue aggregate has been drawing broad attention. However, the performance of coal gangue varies greatly in different regions, and physicochemical properties and shape characteristics of coal gangue coarse aggregate significantly affect the performance of concrete. This paper aims at the coal gangue in different mining areas of Shaanxi Province, The crushing index, water absorption, soundness, apparent density and clay content are taken as the macro indexes of coal gangue coarse aggregate, the mineral composition, chemical composition, microstructure and internal pore structure are taken as the microscopic indexes of coal gangue coarse aggregate, and analyses the association between them. In view of the shape difference between coal gangue and nature gravel, the sphericity, angular number(AN) and aggregate particle shape and texture(IAPST) are proposed as shape statistical indexes of coal gangue coarse aggregate, in order to quantify its shape characteristics. Moreover, The influence of macro indexes and shape statistical indexes of coal gangue on workability and strength of concrete are analyzed. The results show that coal gangue with high content of quartz, kaolinite and illite, dense microstructure and small porosity has low water absorption and crushing index. Compared with natural gravel, the coal gangue coarse aggregate has lower sphericity and more irregular shapes. Most coal gangues have high AN and IAPST, showing more sharp edges and rougher surface. Coal gangue with low water absorption and low crushing index is used as coarse aggregate, and the prepared concrete has good workability and high strength, which can meet the C30 strength grade. Shape statistical indexes of coal gangue coarse aggregate affects the strength of concrete when the crushing indexes of coal gangue coarse aggregate is roughly the same. The higher the sphericity, the smaller angular number and texture index, resulting in the lower concrete strength, which is due to the poor interfacial bonding between coal gangue coarse aggregate and cement.

The optimization of pervious concrete ratios with spontaneous combustion gangue aggregates based on the RSM-BBD method

Liu Yan, Zhou Mei, Zhang Kai, Wu Long, Peng Lei

2022, 7(5): 565-576. doi: 10.19606/j.cnki.jmst.2022.05.007

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Abstract:
In order to optimize the ratio of pervious concrete with spontaneous combustion coal gangue aggregate, 17 groups of experiments were designed by the BBD response surface method to study the effects of aggregate-cement ratio, water-cement ratio, and reinforcing agent on the compressive strength, permeability coefficient, and porosity of pervious concrete. The response surface model was constructed to reveal the correlation between various factors and response values and obtain the optimal ratio of comprehensive performance. The results show that each factor and each response value are quadratic polynomial models, and the regression coefficient R² of each model is greater than 0.9, indicating that the model is reasonable and fitting. The influence of water-cement ratio and aggregate-cement ratio on each response value and reinforcing agent on compressive strength is very significant. The influence of the interaction of aggregate-cement ratio and water-cement ratio on compressive strength and the interaction of water-cement ratio and reinforcing agent on porosity is significant. When the ratio of aggregate-cement ratio is 3.2, the ratio of water-cement ratio is 0.22, and the dosage of the reinforcing agent is 4.5 %, the 28 d compressive strength of pervious concrete reaches 28.7 MPa, the permeability coefficient is 3.21 mm/s, and the porosity is 19.7 %, which meets the engineering requirements of C20 pervious concrete.

Study on hydration mechanism of calcium silicon slag composite geopolymer

Yang Zhijie, Zhang De, Kang Dong, Mi Shizhong, Yan Changwang, Zhang Ju

2022, 7(5): 577-584. doi: 10.19606/j.cnki.jmst.2022.05.008

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Abstract:
In order to realize the synergistic utilization of calcium silicon slag, fly ash and blast-furnace slag, this paper researched on hydration mechanism of calcium silicon slag composite geopolymer through preparation experiments of the calcium silicon slag composite geopolymer under different ratio of fly ash / blast-furnace slag.The results show that the calcium silicate slag base geopolymer is a binary composite cementitious material mainly composed of C—S—H and C(N)—A—S—H, which is formed by the hydration of β-calcium silicate itself and alkali-activated hydration.Compared with crystalline minerals, glass minerals are more prone to reaction with Ca(OH)₂ and sodium silicate, resulting in a large amount of unreacted mullite remaining in the hydrates of 7 d when the fly ash / blast-furnace slag ratio is more than 0.5, but the mullite will continue to hydrate with the extension of curing time, and worm-like tetranatrolite and strip-like beidellite will be formed at 28 d.At the same time, when fly ash / blast-furnace slag ratio is 1.0, micromorphology of calcium silicate slag composite geopolymer is the most evenly distributed and dense, and its 28 d compressive strength reaches maximum 37.9 MPa.So, it indicates that the best synergistic effect among calcium silicon slag, fly ash and blast-furnace slag can be released under this condition.

Research progress on recycling technologies of lithium-ion batteries from electric vehicles

Zhu Xueshuai, Hao Tingxiu, Huang Xue, Zhao Cuiyan, Li Tiexin, Li Yunmei, Zhang Guoqing, Feng Ping

2022, 7(5): 585-594. doi: 10.19606/j.cnki.jmst.2022.05.009

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Abstract:
The rapid development of the electric vehicle industry has led to a surge in demand for power lithium-ion batteries, making natural cobalt, lithium, and nickel scarce mineral resources. To promote the sustainable development of the electric vehicle industry and solve the problems of environmental pollution as well as resource scarcity caused by lithium-ion batteries, it is extremely imperative to realize the green recycling of end-of-life electric vehicle lithium-ion batteries. This article systematically reviewed and evaluated the recycling process of lithium-ion batteries from electric vehicles, which focuses on discharging, dismantling, stripping, separation, metallurgy and other operations. The influence of different operation methods on stripping, sorting, metallurgy and other effects is analyzed from the perspectives of technology research and development and industrial application, and the research progress and main problems of each operation link are discussed. The future development of recycling lithium-ion batteries is prospected, which lay the foundation for the green and efficient recycling of spent lithium-ion batteries.

Research on thermal stability of coal gasification coarse slag based geopolymer

Lü Zhengye, Zhang Tong, Liu Ze, Wang Qunying, Wang Dongmin

2022, 7(5): 595-603. doi: 10.19606/j.cnki.jmst.2022.05.010

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Abstract:
Coal gasification crude slag can be used as a precursor to prepare geopolymer, and its high temperature resistance needs to be further explored. In this paper, geopolymers prepared by mixing 10% of TiO₂, 30% of fly ash and 30% of slag in coal gasification crude slag were treated at high temperature, and the thermal stability of four 28d geopolymers at different temperatures was explored. The results show that at 100 ℃, the compressive strength of the sample is not much different from that at room temperature. At 200 ℃, 400 ℃ and 800 ℃, the compressive strengths of the four samples all decreased to different degrees. The strength attenuation is most obvious in the samples doped with mineral powder, and the strength attenuation of the samples doped with TiO₂ is smaller at high temperature. With the increase of temperature, the geopolymers cracked: at 100 ℃ and 200 ℃, only the coal gasification coarse slag geopolymers cracked; at 400 ℃, the geopolymers only mixed with TiO₂ did not crack; at 800 ℃, all geopolymers cracked. Geopolymers doped with TiO₂ have better high temperature resistance due to the anatase content.

Preparation of NaA zeolite with fly ash and its adsorption properties for lead ions

Li Kun, Li Chunquan, Sun Zhiming

2022, 7(5): 604-614. doi: 10.19606/j.cnki.jmst.2022.05.011

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Abstract:
This study synthesized NaA zeolite by alkali melting-hydrothermal method based on fly ash as raw material. The effects of hydrothermal temperature, hydrothermal time, alkali concentration and alkali/FA mass ratio on the preparation of zeolites were investigated by single factor experiments, and the performance of the prepared zeolites was evaluated by water adsorption capacity and Cation Exchange Capacity (CEC) value.Results show that it is beneficial to the synthesis of NaA zeolite under hydrothermal temperature of 100 ℃, hydrothermal time of 5 h, NaOH concentration of 2.73 mol/L, and alkali/FA mass ratio of 2.8, in which the highest CEC value can reach 374.63 mg/g. The adsorption of Pb(Ⅱ) in liquid phase was studied by using the synthetic NaA zeolite. The adsorption capacity was up to 471.51 mg/g with 1 g/L dosage of zeolite, at pH 6.2 and 25 ℃ of adsorption temperature and the adsorption time was 60 min.The adsorption data of Pb(Ⅱ) by NaA zeolite was fitted better with Langmuir model, and the saturated adsorption capacity of Pb(Ⅱ) could reach to 580.18 mg/g.

A performance study of hydrophobically modified coal gangue mortar

Xu Wei, Wang Guoxuan, Liu Bo, Wang Bin, Pang Yukun

2022, 7(5): 615-623. doi: 10.19606/j.cnki.jmst.2022.05.012

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Abstract:
Coal gangue has the characteristics of complex physical and chemical properties, low strength, loose and porous, which limit its extensive use in building materials. In this paper, coal gangue was modified by soaking in hydrophobic solution under uncalcining and non-prewetting conditions. The basic characteristics of coal gangue before and after modification was systematically studied, and hydrophobically modified coal gangue mass substitution rates of 0%, 30%, 50%, 70% and 100% were set. Contact angel, flexural strength, compressive strength, electric flux were used as characteristic parameters to evaluate the influence of modified coal gangue replacement rate on the basic properties of mortar under different substitution rates.Results showed that, by using the binary cooperative complementary method, when the replacement rate of modified coal gangue was lss than 50%, the hydrophobic state of the surface of coal gangue mortar could be achieved. As the replacement rate of modified coal gangue increases, the compressive strength showed a decreasing trend, the maximum decrease was 15.7% compared with none modified coal gangue added. The 28 d compressive strength was 58.5 MPa with 30% replacement rate of modified coal gangue. The electric flux was less than 250 C under different modified coal gangue replacement rate, which indicated excellent resistance to chloride permeability. When the modified coal gangue replacement rate is 30%, the electric flux was the smallest (130 C). The hydrophobic modification method could ensure good mechanical strength and resistance to chloride penetration under the condition of uncalcined and non-prewetted coal gangue, which fully utilizes coal gangue.

Study on the properties of steel slag used as sulfur fixation agent in coal burning

Zhao Jianbing, Yang Qiaowen, Wen Xin, Tian Libin

2022, 7(5): 624-631. doi: 10.19606/j.cnki.jmst.2022.05.013

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Abstract:
In order to research the sulfur fixation performance of steel slag in the coal-fired sulfur fixation process, the effect of single parameters such as calcium-sulfur ratio, air flow rate, furnace temperature, and furnace residence time on the sulfur fixation efficiency was studied. In addition, orthogonal experiments were constructed to assess the effect of each variable on the main and secondary order of sulfur fixation efficiency, and the ideal experiment design was identified. Utilizing XRF, the slagging features of the ash and the sulfur-fixing effect of the steel slag were analyzed.XRD was utilized to characterize the diffraction peaks of steel slag and sulfur fixation slag, which indicated the steel slag's capacity to fixate sulfur. SEM was used to describe the microscopic morphology of sulfur fixing ash, and the surface structure and microscopic morphology of steel slag before and after sulfur fixing were compared to evaluate the validity of other characterisation results. The results suggest that the slag has a good sulfur fixation capacity at 900 ℃, with a sulfur fixation efficiency of 63.17%, and that the sulfur fixation efficiency of the slag may reach 70.08% when 2% Na₂CO₃ is added.

Effects of slag powder/metakaolin on the early performance of natural hydraulic lime

Xu Dong, Zhang Dajiang, Wang Dongming, Qi Guodong, Zhang Shuai

2022, 7(5): 632-642. doi: 10.19606/j.cnki.jmst.2022.05.014

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Abstract:
Natural Hydraulic Lime (NHL) has exceptional application in restoring ancient buildings compared to Portland cement and conventional air-hardening lime, but the characteristic of slow early performance development limits its fields of application. This paper studied the physical and mechanical properties, hydration exothermic properties, phase composition and transformation, and microstructure evolution of slag powder/metakaolin composite NHL during the early hardening process. The influence of slag powder/metakaolin on the hardening process and performance development of NHL are systematically evaluated. Results show that slag powder can improve the fluidity of NHL-based mortar; slag powder/metakaolin generates calcium aluminate hydrate (C₃AH₆), calcium carboaluminate hydrate (C₄AĈH₁₁) and calcium silicate hydrate (C—S—H) through pozzolanic reaction to promote the setting and hardening of NHL-based materials and significantly improve their compressive and flexural strength. This study provides reference for promoting the application of pozzolanic material composite NHL in the restoration of ancient buildings.

2022 Vol. 7, No. 5