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To address the environmental pollution and resource wastage caused by the massive stockpiling of coal gasification slag (CGS), in this study, chlorine salt (CaCl 2 , CC) was adopted to stimulate the potential volcanic ash activity of CGS and to prepare a new modified CGS-based cementitious backfill material (MC-CPB). The optimum CC admixture was determined by comparing the compressive strength, and the effect of different admixtures on the strength of the MC-CPB was investigated. The effects of the CC content on the hydration properties and the composition and the micro-morphology of the hydration products of the MC-CPB were analyzed using hydration heat, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetry (TG) analyses. It was found that the addition of CC promoted the early and mid-strength of the MC-CPB, but an excessive amount of CC (>1%) inhibited the development of the strength in the later stages. A concentration of 1% CC had the best effect on the strength of the MC-CPB in the entire age range, increasing the compressive strength from 3 to 90 days by 65.8%, 56.1%, 80.6%, 30.9%, and 31% compared to the control group. The CC accelerated the hydration reaction process of the MC-CPB by shortening the durations of the induction and acceleration periods, and it enhanced the hydration reaction intensity of the MC-CPB by increasing the second release heat peak and forming a third release heat peak. The MC-CPB sample containing CC generated a new hydration product, Friedel's salt, which increased the compactness of the matrix and thus improved the compressive strength of the sample. However, excessive addition of CC reduced the amount of Ettringite (AFt) generated in the later stage, leading to a decrease in the strength of the high CC content samples in the later stage. The results of this study promote the large-scale and resourceful use of CGS in mine backfill and provide a theoretical basis for the field proportioning design and industrial application of MC-CPB for backfill. [Display omitted] [ABSTRACT FROM AUTHOR]

The hydrating active mineral in the modified magnesium slag-based (MMS-based) backfilling material is mainly β-phase dicalcium silicate characterized with slow speed of hydration and low early strength. This disadvantage restricts the application of modified magnesium slag (MMS) as cementitious material in backfilling mining to some extent. In this work, the strengthening mechanism of granulated blast-furnace slag (GBFS) on the uniaxial compressive strength (UCS) of MMS-based cemented backfilling material has been investigated systematically. The hydration heat tests reveal that the duration of induction and acceleration periods are gradually shortened and the appearance time of the second exothermic peaks are obviously advanced as the proportion of GBFS increases. The total normalized hydration heat releases of MMS-based pastes containing 0, 1%, 2%, 3% and 4% (solid-mass proportion) GBFS at 120 h are 15.76, 16.02, 18.40, 22.31, and 25.54 J/g, respectively. Compared with the blank control group, the hydration heat release of MMS-based paste at 120 h increased by 62% with addition of 4% (solid-mass proportion) GBFS. In addition, the TG-DTG tests shown that the final mass-losses of MMS-based cemented backfilling materials tend to increase with the increase of the amount of GBFS. The 3- and 7-days UCSs of MMS-based backfilling mortars tend to increase dramatically with the increase of proportion of GBFS. A small amount of GBFS (1 wt%) can significantly improve the 28- and 56-days UCSs of the MMS-based mortars. Compared with the blank control group, the UCSs of MMS-based mortars cured 3, 7, 28, and 56 days increased by 74.2%, 94.6%, 38.0%, and 24.1% respectively with addition of 5% (solid-mass proportion) GBFS. The SEM, XRD, FTIR, and TG-DTG tests show that the MMS-based mortars containing GBFS generated more hydration products, yielded more compact microstructures, and consumed CH more quickly compared with that of blank control group. Compared with fly ash (FA), GBFS dissolves faster in alkaline media (leaching reactive Al and Si early), and releases much more hydration heat and Ca2+ ions during the process of pozzolanic reaction. The above three factors strengthen the UCS of MMS-based mortar. The results of this study can provide theoretical guidance for the raw material ratio design and field application of MMS-based cemented backfilling paste. [ABSTRACT FROM AUTHOR]

The significant production of bulk solid waste from metallurgy or coal and industrial high-salt wastewater (SW), coupled with limited disposal capacity, high disposal expenses, and uncertain environmental impact, poses technical challenges that impede the green advancement of the metallurgical or coal sector. Based on the aforementioned industry challenges, this study suggests creating an all-solid waste mine backfill material known as magnesium-coal slag (MCBM). The technical requirements of coal mine backfill are assessed through relevant experimentation and microscopic analysis techniques, including fluidity, uniaxial compressive strength, microstructure, and toxicity leaching tests. Additionally, the synergistic reaction mechanism of MCBM is expounded upon. The results show that: (1) The rheological curve of the freshly prepared MCBM slurry is in strong agreement with the Herschel-Bulkley (H-B) model, and the viscosity meets the necessary pumping specifications for coal mine backfilling. It was observed that the fresh MCBM slurry's slump ranges from 134 mm to 146 mm, whereas the yield stress falls between 25 Pa and 37 Pa. (2) The mass concentration and SW content exert a significant influence on the uniaxial compressive strength (UCS) of MCBM specimens, primarily governed by the degree of hydration reaction and pore structure characteristics. (3) The leaching of toxic heavy metal elements such as Ni, Pd, and As in bulk metallurgical or coal-based solid waste greatly surpasses the standard levels. Nevertheless, by mixing such waste within the coal mine backfill materials, the resulting hydration products can achieve stable consolidation of these heavy metal elements through chemical bonding and physical adsorption and storage. Magnesium-coal slag backfilling technology for solid waste is aligned with the primary research objective of supporting green and safe mining, as well as facilitating the clean and efficient usage of coal resources. It represents a popular research topic, aimed at promoting high-quality coal resource development and green, low-carbon growth. [Display omitted] • Metallurgical solid waste, coal-based solid waste, and industrial wastewater with high salinity were co-processed in this study. • The rheological properties of fresh MCBM slurry exhibit excellent agreement with the Herschel-Bulkley (H-B) model. • SW promotes the hydration reaction in MCBM samples, contributing to the strength development. • The hydration reaction of backfill materials derived from solid waste synergistically contributes to the consolidation of heavy metal elements. [ABSTRACT FROM AUTHOR]

Coal mining subsidence and bulk solid waste storage are the bottleneck problems for achieving green and low-carbon development in northern Shaanxi. Aiming at the demand of filling mining in coal mines in northern Shaanxi, a modified magnesium slag-based low-carbon paste backfill materials (MMS-PBM) was proposed, which realized the safe disposal and resource utilization of solid waste. In-depth understanding of the influence of temperature effect (initial temperature: 5 ∼ 50 °C and curing temperature: 20 ∼ 50 °C) on the performance of MMS-PBM is helpful to optimize the mix ratio and filling period of filling materials. Based on this, relevant tests and tests (including setting time test, Mini-slump test, rheological test, uniaxial compressive strength test, microscopic test and leaching toxicity test) were carried out to explore the influence mechanism of temperature effect on the performance of MMS-PBM. results showed: (1) The rheological curve of fresh MMS-PBM slurry is highly consistent with the Herschel-Bulkley (H-B) model, and the fluidity meets the pumping requirements of coal mine filling. With the increase of initial temperature, the yield stress and apparent viscosity of fresh slurry increased, while slump, expansion and thixotropy decreased. (2) The increase of initial temperature inhibits the development of early mechanical properties of MMS-PBM, which is mainly affected by the metastable film hypothesis. (3) The curing temperature is conducive to the development of mechanical properties of MMS-PBM, and meet the requirements of mechanical properties of coal mine. With the increase of curing temperature, the main growth range of mechanical properties gradually changes from 7–28 d to 3–7 d, which is consistent with the change of microstructure. (4) The leaching concentration of heavy metals in MMS-PBM meets the requirements of national standards, but the increase of curing temperature has an inhibitory effect on the solidification of heavy metals. The above results show that MMS-PBM is a safe, green and low-carbon all-solid waste filling material, which is beneficial to the coordinated development of coal resource mining and environmental protection. • Initial and curing temperatures have a significant effect on the properties of MMS-PBM in the slurry and curing stages. • Rheological properties of fresh MMS-PBM slurry are in good agreement with Herschel-Bulkley (H-B) model. • Higher curing temperature inhibits the stabilization/solidification of heavy metals (Ni, Pb, As and Ba) in MMS-PBM. [ABSTRACT FROM AUTHOR]

In order to promote the resource utilization of bulk solid waste, it is an effective way to improve the comprehensive utilization level of solid waste and alleviate the environmental pressure caused by storage by using all solid waste as raw material for backfill cementing. In this paper, a magnesium coal based backfill material (MCB) with modified magnesium slag (MMS) and fly ash (FA) as cementing agents, coal gasification coarse slag (CGCS) and coal gangue (CG) as aggregates was proposed. First, the mechanical properties of MCB were studied and then the hydration effect was verified microscopically. Then, the leaching characteristics of raw materials CGCS, CG, and backfill material MCB were characterized. Furthermore, the mechanism of heavy metal leaching and solidifying of MCB was revealed by studying As and Pb. The results show that: (1) The addition of a suitable amount of CGCS with potential pozzolanic activity produces more MCB hydration products such as C-S-H and AFt with a high CG-CGCS ratio. The compressive strength reaches the maximum value of 10.21 MPa when the curing time is 28 days and the CG-CGCS ratio is 3:1. (2) The leaching levels of the target elements (As, Pb, Cr, Mn, Zn, Cu, Cd, Hg, Ag) of CG meet the limits of the class III groundwater quality standard (III-GQSL) in GB/T 14848–2017. The concentration of Pb in CGCS is 12 μg/L, which exceeds the III-GQSL limit of 10 μg/L. The overall leaching risk is CGCS>CG. (3) MCB has a good stabilization/solidification effect on the heavy metal elements Cd, As, and Pb in raw materials. The heavy metal leaching results of MCB with a low CG-CGCS ratio meet the limit of III-GQSL, and the environmental leaching risk is low. (4) In addition to physical encapsulation, the main curing mechanisms of MCB include chemical bonding, alkaline environment, and adsorption. MCB can be used as a potential consolidation agent for the solidification of heavy metal elements. While having good mechanical properties, it can also treat solid waste and effectively stabilize/solidify toxic elements in materials and has the potential for safe application in backfill. [ABSTRACT FROM AUTHOR]

The high-temperature, deep-well environment can affect the mechanical properties and long-term stability of modified magnesium slag cemented coal-based solid waste backfill material (MMS-CBM). The purpose of this study was to investigate the effects of fly ash addition (0 %, 10 %, 20 %, 30 % and 40 %) and curing temperature (20 °C, 30 °C and 40 °C) on the mechanical properties, pore characteristics and microstructure of MMS-CBM. Based on this, relevant laboratory tests (uniaxial compressive strength test, pore structure test and microstructure test) were conducted to characterize the influence mechanism of fly ash addition and curing temperature on the performance of MMS-CBM. The results show that the physical properties (uniaxial compressive strength, pore characteristics and microstructure) of MMS-CBM are significantly affected by fly ash addition and curing temperature. With the increase of fly ash addition, the number of active particles and hydration products involved in the hydration reaction gradually increased, and the physical properties of MMS-CBM were gradually optimized. With the increase of curing temperature, the hydration reaction rate and hydration reaction degree of MMS-CBM gradually deepened, which accelerated the volcanic ash reaction of fly ash particles, which had a promoting effect on the early intensity of MMS-CBM. However, the subsequent strength of MMS-CBM will be affected by thermal damage, resulting in deterioration of physical properties and seriously affecting the long-term stability of MMS-CBM. In addition, the porosity and fractal dimension of MMS-CBM are linearly related to the uniaxial compressive strength, indicating that the pore characteristics can reflect the mechanical properties of MMS-CBM. This study provides a theoretical reference value for the application of MMS-CBM in high-temperature deep wells. [ABSTRACT FROM AUTHOR]

The backfill with angles will be formed when using the backfill mining technique due to the flow and settlement of the slurry. The structure of a layered surface is loose, making it necessary to analyze its influence on the mechanical properties of backfill from macro, fine, and micro-scales. Standard specimens with four types of layered surfaces and four types of layered surface angles were prepared and tested by uniaxial compression and scanning electron microscopy. Based on the brittleness index, tensor crack hot spot, scalar stress cross, etc., the failure mechanism was investigated from the perspectives of strength, deformation, crack number, fabric anisotropy, cracking mode and microscopic morphology. The results showed that the strength and brittleness index decrease with the increases of layer parameters, and the influence of the layer angle is larger than that of the number of layers. The strain at each stage of the stress-strain curve varies regularly with the layer parameters. The simulation results are in good agreement with the experimental results. The cracks first appear at the layered surface, and then extend to all sides. The layer parameters are positively correlated with the number of total cracks, shear cracks, crack evolution rate, and the number of blocks, while the force between particles is weakened, and the direction of contact force chain and the total coordination number exhibit significant fabric anisotropy. The results indicated that shear cracks are more developed at the layered surface, and the bearing capacity of matrix between the layered surfaces is weak. The results can provide a theoretical basis for the design of the filling and mining processes in such mines. • Strength, deformation anisotropy and brittleness index. • Crack development law in the loading process. • Final failure pattern and number of blocks. • Anisotropy coefficient of fabric based on stress. • Crack mechanism of angular layered backfilling body. [ABSTRACT FROM AUTHOR]

To study the mechanical properties and failure characteristics of all-solid waste cementitious materials prepared in the intense geothermal environment of deep mines. Uniaxial compression, acoustic emission (AE), SEM and other tests were adopted to characterize the energy and deformation failure of backfill materials from different temperatures (20 °C, 30 °C, 40 °C). The results show that the temperature has a promoting effect on the development of modified magnesium slag-fly ash cemented paste backfill (MFPB) strength. The elastic strain energy and the dissipated energy corresponding to the peak stress increase as the curing temperature increases. The high frequency phase of the energy scatter plot is accompanied by a rapid increase in the cumulative ringing count and cumulative energy. Tensile cracks increase with the increase of curing temperature. The temperature effectively promotes the hydration process of MFPB. The decrease of strength in the later stage of curing temperature 40 °C is due to the harmful thermal stress within the backfill. The results provide theoretical guidance for the practical application of MFPB. • Influence of different curing temperatures on strength and deformation. • The law of energy dissipation during loading. • The law of evolution of acoustic emission parameters. • rack evolution law based on RA-AF value. [ABSTRACT FROM AUTHOR]

• Salt modification is the best excitation idea for the hydration activity of CGS. • The salt modification of CGS had a significant effect on the early hydration process of MCGS-CPB. • The effect of salt modification of CGS on the hydration mechanism of MCGS-CPB was clarified. To realize the green mining and clean utilization of coal resources, environmental issues such as coal mine subsidence and coal gasification slag (CGS) solid waste storage require urgent resolution. High residual carbon and low activity serve as bottlenecks for CGS to achieve safe, efficient and resourceful consumption. Therefore, in this study, we proposed the concept of graded utilization of CGS and conducted a study on physical–chemical coupling to stimulate the hydration activity of CGS. We prepared a modified coal gasification slag-based cement paste backfill material (MCGS-CPB) to meet the technical requirements of coal mine backfilling. Through various experimental tests and microscopic characterization methods (uniaxial compressive strength, hydration heat and microscopic tests, etc.), we elucidated the modification mechanism of CGS, and the synergistic reaction law of MCGS-CPB was clarified. The following results were obtained. (1) The best excitation approach for CGS hydration activity was salt modification, and the early strength of MCGS-CPB prepared with CGS excited by sodium sulfate (SS) developed rapidly, while the later strengths showed expansion and deterioration. The strength development of MCGS-CPB prepared by CGS activated with calcium chloride (CC) was relatively stable, and the excitation effect was ideal. (2) The salt modification of CGS had a significant effect on the early hydration process of MCGS-CPB. The durations of the initial dissolution, acceleration, deceleration and slow reaction stages were prolonged, and the duration of the induction stage was shortened, while the hydration heat release rate increased. (3) The salt modification of CGS had a significant effect on the microstructure of MCGS-CPB, primarily due to the difference in excitation effect of salt modification on CGS on pozzolanic activity. This study provided theoretical guidance for the safe, efficient and resourceful utilization of CGS. [ABSTRACT FROM AUTHOR]

Abstract: Processes involving enzymatic modifications of industrial lignin have received wide attention due to the enormous supply and potential use of this inexpensive raw material. However, these reactions are affected by the enzyme–substrate adsorption process resulting in the formation of unproductive enzyme–lignin complex. In this study we have investigated the kinetic and isotherm of Trametes versicolor laccase (benzendiol: oxygen oxidoreductase, EC 1.10.3.2) adsorption onto alkali lignin. We have also examined the effect of a mediator (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt) on the process. In order to get more insights into the process, laccase was conjugated to colloidal gold nanoparticles and the laccase–gold complex adsorbed to lignin surface was visualized by electron microscopy. The adsorption process was better explained by a Langmuir isotherm model (R 2 = 0.9626) while the kinetics data were better described by a pseudo-second-order model. Moreover, data showed that laccase exhibited higher affinity for lignin in the presence of a mediator. Examination of the lignin–laccase complex obtained after 72 h of treatment suggested that lignin bond cleavages and oxidative couplings had occurred during the treatment, which negatively influenced its surface accessibility. However, the presence of a mediator facilitated laccase adsorption to lignin. The present findings will advance the understanding of enzymatic modification mechanisms, which could provide useful references for developing industrial lignin biotreatment technology. [Copyright &y& Elsevier]

Abstract: The production of oxalate at different initial Pb2+ concentrations during solid-state fermentation of straw with Phanerochaete chrysosporium was investigated. It was found that the maximal peak value of oxalate concentration (22.84mM) was detected at the initial Pb2+ concentration of 200mgkg−1 dry straw, while the minimum (15.89mM) at the concentration of 600mgPb2+ kg−1 dry straw, and at moderate concentration of Pb2+ the capability of oxalic acid secretion was enhanced. In addition, it was also found that more oxalic acid accumulation went together with better Pb2+ passivation effect and higher manganese peroxidase (MnP) activity. The present findings will improve the understandings of the interactions of heavy metals with white-rot fungi and the role of oxalate in lignin degradation system, which could provide useful references for more efficient treatment of Pb-contaminated lignocellulosic waste. [Copyright &y& Elsevier]

[Display omitted] • The hydration exothermic characteristics of MGCAPB by isothermal microcalorimetry. • Hydration kinetic of MGCAPB was analysed by Krstulović-Dabić model. • Mechanical properties of MGCAPB was investigated by UCS and elastic modulus. • Microstructure of MGCAPB was studied by TG-DTG and SEM. A clear understanding of the hydration characteristics of cemented paste backfill (CPB) is helpful to analyze the reasons for the defects of low strength, large deformation and high cost in the early curing period of CPB. This is conducive to realizing the sustainable utilization of solid waste. In this paper, the hydration exothermic characteristics of MGCAPB slurry was tested. Moreover, uniaxial compressive strength(UCS) tests were carried out on the MGCAPB with curing times of 3 and 28 d. In addition, microstructure tests such as TG-DTG and SEM were performed on the MGCAPB with curing time of 3d. The hydration exothermic characteristics of MGCAPB were emphatically studied, the hydration kinetic parameters of MGCAPB were analyzed exclusively by using Krstulović-Dabić model. In addition, the mechanical properties and microscopic characteristics of MGCAPB were studied. The results shows that the hydration kinetic process of MGCAPB slurry can be described by nucleation and crystal growth (NG), phase boundary reaction (I) and diffusion (D). All the formulations of MGCAPB went through the NG-I-D stage. The process of hydration reaction was controlled by NG at the initial hydration stage, and gradually changed to process I and process D with the increase of hydration degree. Compared to the Control group, The α 1 of the MGCAPB activated by the activator was high, indicating that the NG process changed to the I process only when the hydration degree was high, which was related to the effective water-cement ratio of the slurry and nucleation effect. In addition, according to the requirement(3d ≥ 0.5 MPa and 28d ≥ 1.0 MPa) that CPB can provide good roof support in a typical underground mine. In this experiment, the mechanical propertiesof all formulations met the requirements, except for the 3d UCS of the Control group(0.37 MPa) and the C-C1(0.46 MPa). Finally, TG-DTG and SEM were used to analyze the microstructures of MGCAPB with activator type and dosage. The research results can provide a new approach for intensive and comprehensive utilization of solid waste resources. [ABSTRACT FROM AUTHOR]