Gasification Slag Research Articles

Evaluation of the applicability of gasification coarse slag as a fine aggregate in controlled low-strength material: preparation, performance, and environmental effect.

Gasification slag (GS) is rich in SiO2, Al2O3, and Fe2O3, and has excellent particle size gradation, which has the potential to be employed as an aggregate in the field of controlled low-strength material (CLSM). Nevertheless, the large-scale application of GS as the fine aggregate for the preparation of CLSM has been scarcely investigated. In the present work, the applicability of replacing part of coal gangue (CG) with gasification coarse slag (GCS) as fine aggregate for the preparation of CLSM was investigated. The results revealed that using GCS as a fine aggregate improved the flowability of CLSM, and increasing the GCS content from 0 to 50 wt% improved the flowability from 250.0 to 280.0 mm. The 28-day compressive strength of all CLSM conformed to the requirements of ACI Committee 229. Compared to the Blank group, the 7- and 28-day compressive strength of the CLSM increased by 23.07% and 26.80%, respectively, at a GCS content of 50 wt%. The increase in compressive strength was mainly due to the pore-filling and hydration-promoting effect of the GCS, which made the structure denser. The dense structure reduced the expansion rate, absorption, and porosity rate of CLSM and increased the wet density. The optimal process parameter was the addition of 10 wt% of GCS. The results of heavy metal ion leaching showed that the optimal sample GS10 leached all heavy metal ions in much less than the limit values of GB 8978-1996 and GB 5085.3-2007. The results will provide new ideas and technical approaches for the large-scale application of GCS as the fine aggregate in CLSM.

Influence of liquid-to-solid ratios on properties and microstructure of coal gasification slag-based one-part geopolymer

Limited studies have been conducted on the synthesis of one-part geopolymer involving coal gasification slag by alkali fusion and component additive method (AFCAM). The ratio of liquid-to-solid (L/S) is the key aspect that has a major impact on the one-part geopolymer's compressive strength (UCS). Our research aims to determine how different L/S ratios affect the microstructure and characteristics of one-part geopolymers. MIP analysis and hydration heat test were conducted to analyze the influence caused by different L/S ratios. The results showed that as the L/S ratio increased, the UCS of geopolymers decreased, and the setting time of fresh slurry increased steadily. Additionally, geopolymer with 0.25 as an L/S ratio (G-L/S-0.25) achieved a higher UCS at 48.31 MPa, whereas the total setting time was more than 23 h. The low L/S ratio produced more gel pores and less total porosity in the geopolymer matrix, which improved the UCS. Moreover, lower porosity suggested that the geopolymer sample had higher compactness and a better internal structure. It is found that the dissolution of the fusion product released heat in the first hour, and no coal gasification slag dissolution heat was detected after one hour. This suggested coal gasification slag showed low reactivity as the additive and was embedded in the geopolymer matrix after 28-day curing. The tested results showed that G-L/S-0.25 had a greater reaction degree. This study illustrated the effects of the L/S ratio on one-part geopolymer and provided a new thought to enhance the UCS of coal gasification slag-based geopolymer.

A Hydrothermal Synthesis Process of ZSM-5 Zeolite for VOCs Adsorption Using Desilication Solution

ZSM-5 zeolite is a kind of high-value-added porous aluminosilicate zeolite. The use of the coal gasification slag utilization process by-product desilication liquid as a silicon raw material to replace the current raw materials such as water glass will help reduce production costs and achieve high-value utilization of solid waste. ZSM-5 zeolites for volatile organic compounds (VOCs) adsorption were prepared by a one-step hydrothermal method using the desilication solution prepared from coal gasification slag as the main silicon source and sodium source. The effects of crystallization reaction time, the crystallization temperature, the Na2O/SiO2 molar ratio, and the SiO2/Al2O3 molar ratio on the relative crystallinity and the specific surface area of the ZSM-5 zeolite were investigated and optimized. The optical reaction conditions were as follows: a crystallization time of 12 h, a crystallization temperature of 170 °C, a Na2O/SiO2 molar ratio of 0.2, and a SiO2/Al2O3 molar ratio of 200. The optimal ZSM-5 zeolite synthesized is hexagonal, with regular grains, a relative crystallinity of 101.48%, a specific surface area of 337.48 m2·g−1, and a pore volume of 0.190 cm3·g−1. And the optimal ZSM-5 zeolite was composed of SiO2 content of 97.52 wt%, Al2O3 content of 1.58 wt%, Na2O content of 0.33 wt%, and SiO2/Al2O3 molar ratio of 104.93. Na2O/SiO2 molar ratio is 0.0033. The results of static adsorption experiments show that the static adsorption capacities of ZSM-5 zeolite for p-xylene, benzene, toluene, and butyl acetate were 118.85, 69.98, 68.74, and 95.85 mg·g−1, respectively, which can effectively adsorb VOCs. The synthetic process of the ZSM-5 zeolite is a simple preparation process and short in synthesis time. The results of this study not only help to realize the high-value utilization of silicon components in solid waste, but also provide an economical and effective way to synthesize VOCs adsorption materials.

Study on the excitation effect and mechanism of coal gasification slag based on solid waste

Coal gasification slag (CGS) has pozzolanic activity, and it could be used as a supplementary cementitious material after be activated by some solid waste, which will promote resource utilization of solid waste. In this paper, coal calcium carbide slag and desulfurization gypsum were chosen to activate CGS, the excitation effects were evaluated in different ways and compared with those of salt activators. The microscopic were measured by thermal gravimetry (TG), scanning electron microscopy (SEM) and X-ray diffractometer (XRD) to analyze the excitation mechanism of CGS. The results show that the excitation effects of calcium carbide slag and desulfurization gypsum on CGS are superior to those of salt activators; Through microscopic analysis, the activator promotes the dissolution of glassy state in CGS, accelerates the disaggregation of network structures such as silicon and oxygen, enhancing the activity of CGS. The results of this study can provide references for the excitation of CGS.

Present situation of comprehensive utilization of coal-based solid waste

At present, the annual discharge of coal-based solid waste in China has exceeded 800 million tons, but the mainstream treatment methods are still simple treatment methods such as goaf backfilling and openpit stacking. The massive stacking of coal-based solid waste is not only a serious waste of resources itself, but also brings a series of problems such as environmental pollution. Under the “Carbon Peak” and “Carbon Neutrality” strategy in China, in order to achieve green and rapid development of the coal industry, it is necessary to solve the problem of coal-based solid waste treatment and achieve green and comprehensive utilization of coal-based solid waste. Taking coal gangue, gasification slag and fly ash as representative coal-based solid waste, the present situation of coal-based solid waste production in China and the basic properties of coal-based solid waste are introduced. The utilization status and application characteristics of coal-based solid waste in cement concrete, roadbed materials, soil improvement and so on are focused on, and the resource utilization potential of coal-based solid waste is analyzed and summarized. Then the application prospect of coal-based solid waste in high-value utilization in the future is analyzed and prospected.

Rheology, mechanical properties, and hydration of synergistically activated coal gasification slag with three typical solid wastes

The utilization of multiple solid-waste-activated slags to prepare clinker-free binders has garnered considerable interest due to their environmental friendliness and low cost. In this study, a novel binder was developed by incorporating multiple solid wastes, namely red mud (RM), carbide slag (CS), phosphogypsum (PG), and coal gasification slag (CGS). RM, CS, and PG were used as activators to synergistically activate two kinds of ultra-fine CGS precursors with median particle sizes of 5.2 μm and 6.1 μm, respectively. The effects of parameters including precursor fineness and activator dosage were systematically investigated. The hydration products were then characterized to elucidate the activation mechanism. The results showed that the rheology of the pastes fitted well with Herschel-Bulkley model, exhibiting shear thinning behavior regardless of the proportion of the activators. The low CGS fineness and high PG dosage reduced viscosity, yield stress, and shear stress of the pastes. Fine CGS particles were found to shorten the hydration dormancy period and accelerate the appearance of the second exothermic peak, thus promoting strength development. CGS with small particles facilitated the formation of ettringite but restricted hydrotalcite generation. This study reported a binder utilizing full solid wastes and confirmed its feasibility as a sustainable alternative in construction applications.

Study on the fluidity and mechanical properties of multi-source coal-based solid waste (MCSW) filling material

The backfilling mining technology for multi-source coal-based solid waste (MCSW) aligns with the key challenges and emerging paradigms in the coal industry, aiming at intelligent and cleaner coal mining, high efficiency, and low carbon utilization. This research area has gained considerable attention and significance for promoting high-quality coal mining, low environmental impact, and sustainable development. In this study, a response surface experiment was designed with desulfurization gypsum (DG), gasification slag (GS), and furnace bottom slag (FBS) as factors to analyze the performance of backfill materials with varying compositions. Parameters such as bleeding rate, compactness, viscosity, setting time, and age strength were tested. An optimal composition of backfill materials was obtained, with a MCSW content exceeding 90 %, 28-day strength exceeding 2 MPa, initial setting time between 240 and 480 min, and final setting time ranging from 300 to 600 min. The investigation of the optimal materials involved characterizing the pore structure, microstructure, composition, and silica gel structure through techniques such as X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Additionally, the study explored micro-interface structures and enhancement mechanisms. After 28 days of curing, the backfill with a composition of DG 0.3, FBS 0.2, GS 0.1 exhibited a compressive strength of 5.18 MPa, with an initial setting time as short as 140 min. This can be attributed to the precipitation of silica gel on the grain surface, which mitigated the segregation effect. The silica gel promoted inter-particle bonding and rapid viscosity, preventing particle settling. This method not only ensures the safe disposal of coal-based solid waste but also contributes to the coordinated development of coal resource exploitation, environmental protection, and reduced carbon footprint.

Mechanical activation of coal gasification slag for one-part geopolymer synthesis by alkali fusion and component additive method

Coal gasification slag is an industrial by-product obtained after valuable gas production from coal gasification. There is little research concentrating on geopolymer synthesis using coal gasification slag. In this study, the suitability of mechanical activation for coal gasification slag-based one-part geopolymer synthesis has been investigated by alkali fusion and component additive method. The results showed that coal gasification slag ground at 20 min (S-20) presented the finest particle size, and the corresponding geopolymer (G-20) had the highest compressive strength. The reaction degree test proved that mechanical activation improved the reaction degree of geopolymers. However, different mechanical activation times had little influence on the reaction degree of geopolymers. It can be concluded that the particle size of the coal gasification slag was the primary reason for the compressive strength in geopolymers, and finer coal gasification slag led to higher compressive strength. Fine coal gasification slag additive particles could fill the pores of the geopolymer or be connected by the newly formed hydration products. This helped to form a dense, uniform, and compact matrix and increased the compressive strength of the geopolymers. As the mechanical activation time went up, the coal gasification slag particles got bigger, and the coal gasification slag additive's filling effect got weaker, which decreased the compressive strength of geopolymers. Furthermore, this study gave a new explanation of the role of the coal gasification slag additive in one-part geopolymer, which improved the feasibility of the other materials for one-part geopolymer synthesis by the alkali fusion and component additive method.

Modified Gasification-Slag-Driven Persulfate Activation for Highly Efficient Degradation of Acetaminophen: N/O Active Site Regulation and Nonradical Oxidation

With the development of coal chemical technology, a large amount of gasification slag and wastewater are produced through coal gasification. Efficient gasification slag utilization and wastewater treatment have attracted much attention. In this study, gasification slag was modified and used as a low-cost and efficient catalyst to activate persulfate for acetaminophen degradation. Via the analysis of high-resolution X-ray photoelectron spectroscopy, the surfaces of nitric acid and calcined modified gasification slag retained a considerable number of carbonyl and graphite N functional groups. These proved to be effective active sites for the activation of persulfate. X-ray diffraction analysis revealed that the gasification slag was composed of carbon and SiO2. The evaluation of catalytic activity and application of density functional theory proved that the interaction between carbonyl and graphitic nitrogen significantly affected the catalyst activity. When the ratio of graphitic nitrogen to carbonyl was 1:3, the adsorption and activation of persulfate were significantly enhanced. The results of the quenching experiments also confirmed that the non-free radical pathway is the main pathway to activate persulfate using the gasification slag. This study provides a new approach to industrial waste utilization in wastewater treatment.

Experimental Study on the Diffusion Law of Coal-Based Solid Waste Slurry with Grouting Filling in the Gangue Voids of the Caving Zone.

Due to the concealment of the caving zone, it is difficult to detect and grasp the diffusion law of the slurry in the voids of the gangue pile. On the preparation of reasonable grouting filling materials, a large-scale three-dimensional gangue grouting filling test system has been established to detect the slurry pressure and resistivity inside the gangue pile and analyze the flow pattern of the slurry in the voids of the gangue pile. The research results show that the slump and bleeding rate of the filling slurry are significantly reduced with the increase of the fly ash content. The optimal ratio of fly ash, coal gangue, and gasification slag is 7:2:1, with a mass fraction of 72%. In the process of grouting, the internal pressure of the gangue pile can be divided into the initial stable stage, the step growth stage, and the pressure stability stage, and the change curve of the pressure sensor at the lower level is similar. The resistance value of the original broken gangue in the experiment is approximately 1600 Ω. Grouting filling forms a slurry-rock mixture, and its resistance continuously decreases with the stable injection of the slurry (minimum value 150 Ω). It is determined that the slurry near the grouting hole mainly diffuses longitudinally with a good void filling effect. The void channels of slurry diffusion are randomly distributed and have different shapes, which hinder slurry flow and diffusion. Slurry particles accumulate and settle at local small voids. Meanwhile, the surface of the gangue blocks is dry, and the slurry absorbs part of the water during diffusion, resulting in the increase of the slurry concentration and the weakening of the lateral diffusion ability. Secondary or multiple grouting can effectively fill the void of the broken gangue and further improve the filling effect.

Hydration mechanism of calcium chloride modified coal gasification slag-based backfill materials

To address the environmental pollution and resource wastage caused by the massive stockpiling of coal gasification slag (CGS), in this study, chlorine salt (CaCl2, 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.

Coal gasification slag-derived highly reactive silica for high modulus sodium silicate synthesis: Process and mechanism

Coal gasification slag (CGS) was used to synthesize highly reactive silica, which can be rapidly dissolved in dilute alkali solution at ambient temperature. High modulus sodium silicate was further synthesized by alkali dissolution at ambient temperature instead of the conventional high temperature melting method. During the acid activation process, the inert Si-O-M (M = Al, Ca, Fe) bonds are broken, resulting in the formation of Q3 and Q2 coordination structures with active Si-O-H bonds. The active Si-O-H bonds are further spontaneously condensed to generate highly reactive amorphous silica with a low Si-O-Si bond strength. Under the optimum reaction temperature of 25℃ and reaction time of 0.5 h, the leaching efficiency of Al, Ca and Fe are 86.20 %, 97.61 % and 97.83 % respectively, and the solubility of silica can reach 97.85 %. During the alkali dissolution of silica process, with the decrease of NaOH concentration and liquid–solid ratio, the breaking of Si-O-Si bridging oxygen bond and the formation of Si-O-Na non-bridging oxygen bond can be decreased, resulting in the direct dissociation of the Si-O groups into the liquid phase in the form of polysilicate, thus synthesizing high modulus sodium silicate. Under the optimum reaction temperature of 25℃ and reaction time of 0.5 h, the leaching efficiency of silica is 76.35 % and the modulus of sodium silicate can reach 3.28. The findings of this study provide valuable insights for enriching the theoretical basis of alkali solution-based silica dissolution and for improving the energy-intensive status of the silica industry.

The crystallization kinetics analysis and the new prediction index of melilite-bearing slag under solid fuel gasification condition

Melilite represents a prevalent crystalline phase precipitated from the gasification slag produced by various solid fuels, including coal and biomass. The crystallization of melilite can lead to gasifier blockage, posing significant challenges. This study investigated the crystallization behavior of melilite-bearing slags during slag tapping. To achieve this, FactSage, XRD, SEM-EDS, and DSC were employed to investigate the crystallization thermodynamics and kinetics of 12 synthetic melilite-bearing slag samples. The results revealed that the crystallization temperatures of slags with the mass fraction of SiO2 + Al2O3 is 50 wt% (SiO2 + Al2O3 = 50 wt%) ranged between 1150 and 1100 °C. Slags with the SiO2 + Al2O3 = 60 wt% and mass ratio of SiO2 to Al2O3 > 1.0 (Si/Al > 1.0) showed no crystals precipitate, which is conducive to slag tapping. Thermodynamics plays a crucial role in melilite crystallization, as it involved the uphill diffusion of Ca and Al. To quantify the thermodynamic crystallization ability, a parameter called Thermodynamic Crystallization Ability (TCA) is defined. Increasing Si/Al contributes significantly to reducing TCA. When the TCA is less than 0.33 wt%/K, the melilite-bearing slag will not crystallize. Furthermore, the kinetic analysis results demonstrated that the crystallization activation energy (EC) of melilite-bearing slag ranged from 310.64 to 458.54 kJ/mol. Moreover, the rate-determining step is the surface reaction, which was influenced by cluster structure. The essential short-range ordered structure that composes the melilite crystal is Al-O-Al; however, due to higher Si/Al, the concentration of the Al-O-Al structure in the slag decreases, resulting in higher EC value. These findings provide theoretical guidance for the stable operation of the gasifier.

Pore characteristics of sulfate-activated coal gasification slag cement paste backfill for mining.

With the mass production of coal-based solid waste, coal mine filling can effectively consume it. The coal gasification slag is modified and prepared as coal mine filling material to meet the relevant technical requirements, which can realize the recycling of coal mine → coal chemical industry → coal mine. In this paper, in order to explore the evolution law of the mechanical properties and pore structure characteristics of the modified coal gasification slag-cement cemented paste backfill (MCGS-CPB) prepared by sodium sulfate excitation coal gasification slag, a combined macro-meso-micro testing method is used. MCGS-CPB with different sodium sulfate contents (1~5%) were prepared and tested for uniaxial compressive strength (UCS), mercury intrusion (MIP) and microscopic tests. The results show that sodium sulfate has a significant effect on the UCS and pore structure characteristics of MCGS-CPB. The mechanical properties and pore structure characteristics of MCGS-CPB were best when sodium sulfate was doped at 3%; the mechanical properties and pore structure characteristics of MCGS-CPB were deteriorated when the addition of sodium sulfate is higher than 3%. On the meso-scale, when sodium sulfate was doped with 3%, the more harmful pores of MCGS-CPB gradually changed into harmless, less harmful, and harmful pores, and the macroscopic mechanical properties were gradually improved; when the addition of sodium sulfate is higher than 3%, the harmless, less harmful, and harmful pores of MCGS-CPB gradually changed into more harmful pores, and the macroscopic mechanical properties were deteriorated. On a microscopic scale, sodium sulfate can cause MCGS-CPB to form hydration products with expansion properties. The presence of a reasonable amount of sodium sulfate in the pores of MCGS-CPB is beneficial to the development of mechanical properties. However, excessive presence will lead to the formation of expansion stress, gradual formation of micro-expansion cracks, and deteriorate the macroscopic mechanical properties. Hence, the volcanic ash activity of coal gasification slag excited by external addition of sodium sulfate should not exceed 3%. This study provides a reference value for application ratio of sodium sulfate-stimulated MCGS-CPB used in coal mine filling design.

A Preliminary Study on the Improvement of Gangue/Tailing Cemented Fill by Bentonite: Flow Properties, Mechanical Properties and Permeability.

Backfill mining has significant advantages in safe mining, solid waste utilization and ecological environmental protection, but solid waste materials (tailings, gangue and coal gasification slag, etc.), as derivative residues of the chemical and metallurgical industries, contain a large number of heavy metal elements, which is posing great challenges to the underground environment after backfill. In order to study the feasibility of bentonite for reducing the permeability of gangue/tailing sand cemented backfill body, relevant tests were carried out from the basic performance index, flow performance and mechanical properties of paste backfill materials. The test results show that bentonite has a significant effect on the water secretion rate of cemented fillers, and also promotes the improvement of slump and diffusion diameter of backfill slurry. The enhancement effect of mechanical properties in the early stage is not obvious, mainly concentrated in the middle and late stages of specimen curing. With the increase of bentonite content, the 28-day uniaxial compressive strength increased from 7.1 MPa and 7.9 MPa to 8.7 MPa and 9.0 MPa, respectively. Bentonite is filled between the pores of the cemented backfill with its fine particles and water swelling, which can reduce the porosity and permeability of the gangue and tailings cemented backfill. Therefore, on the premise of satisfying the flow and mechanical properties of paste backfill, bentonite can be used to improve the permeability of cemented backfill and reduce the leaching and migration of heavy metal ions.

Nitrogen doped residual carbon from gasification slag to enhance trifluoroacetate adsorption in groundwater: Experiments and calculations

In this work, a nitrogen doped residual carbon (RCN) from gasification slag was prepared to adsorb trifluoroacetate (TFA) from groundwater. The physicochemical properties of the residual carbon variants were characterized using BET, SEM, XPS and Boehm titration techniques, which determines the porous structure and basic surface property of RCN. For all residual carbon variants, the TFA adsorption kinetics conform the pseudo-second-order model and isotherm data followed the Langmuir model. The RCN exhibited the highest TFA monolayer adsorption capacity of 24.8 mg/g. Thermodynamics study indicated that TFA adsorption onto these adsorbents was spontaneous and the increasing temperature is not conductive to TFA adsorption. During the rapid small scale column tests, the RCN offered 1390 bed volumes (BV) to 3 μg/L breakthrough which was >4 times higher than did the pristine residual carbon (290 BV). Moreover, the DFT calculations obtained the adsorption strength sequence of sulfate > TFA > nitrate onto nitrogen doped carbon, which manifested most unfavorable effect of sulfate on TFA adsorption. This research offers a theoretical and practice reference for the simultaneous gasification slag utilization and perfluorochemicals purification.

Effect of Alkali Fusion Methods on the Preparation of One-Part Geopolymer From Coal Gasification Slag.

This study investigated the one-part geopolymer synthesis by coal gasification slag through a calcination treatment. Two preparation methods, the traditional alkali fusion method (M-I) and the alkali fusion and modification method (M-II), were compared to illustrate the more suitable way for coal gasification slag-based one-part geopolymer (CGS-based geopolymer) synthesis. The reaction products and structure of the geopolymer were tested by XRD, FTIR, TG-DTG, and SEM. The results showed that the compressive strength of geopolymers prepared by M-I was raised as the NaOH amount increased, and the maximum compressive strength of geopolymers was achieved at 8.44 MPa. The low compressive strength suggested that M-I failed to be used for CGS-based geopolymer synthesis. When solid NaOH was selected for one-part geopolymer synthesis by M-II, the geopolymer possessed a compressive strength of 25.52 MPa and exhibited a well-combined and dense matrix. More Si and Al species in F-SH could be released for geopolymerization, and the coal gasification slag additive could be partially dissolved and act as the filler in the geopolymer matrix, which enhanced the geopolymerization degree. The M-II has been proven to be more suitable for preparing CGS-based geopolymers than the M-I.

Fabrication of one-part geopolymer from coal gasification slag via alkali fusion and component additive method: Effect of different alkali-to-slag ratios

This research aims to explore using coal gasification slag (slag) to synthesize one-part geopolymer by alkali fusion and component additive method. The effect of various alkali-to-slag (A/S) ratios on the synthetic one-part geopolymer was studied. The geopolymer reaction products were analyzed using XRD, FTIR, TG-DTG, SEM, and XPS. The dissolution test, reaction degree experiment, and alkalinity of the pore structure were conducted to study the reaction process of the one-part geopolymer. The results demonstrated that the dissolution amount of Si and Al elements in the fusion product was raised with the increase of A/S ratio, and the fusion product with a high A/S ratio possessed high activity. In addition, as the A/S ratio was raised, the compressive strength of geopolymers increased initially before falling off, and geopolymer with an alkali-to-slag ratio of 1.2 (G-1.2) exhibited the highest compressive strength of 26.52 MPa. SEM images showed that geopolymers with a high A/S ratio had a relatively less porous matrix. Furthermore, the reaction degree of geopolymers and dissolution amount of the fusion product was raised as the A/S ratio increased, demonstrating that the fusion product was the primary reactant to provide active Si and Al species for geopolymerization. Moreover, the geopolymer with a low A/S ratio had a low reaction degree, and the slag additive could not be dissolved efficiently. The high A/S ratio of fusion product produced more Q4(mAl) structure in geopolymers, which reflected a relatively complete geopolymerization reaction. Additionally, a high A/S ratio improved the reactivity of the fusion product and led to the consumption of newly formed products in geopolymer, which destroyed the microstructure of geopolymer. An appropriate A/S ratio in the fusion product ensured the integrity of the geopolymer structure. The obtained results provide a new idea for the utilization of slag via alkali fusion and component additive method.

Study on effect of furfural residue addition on fusion characteristics of gasification coal ash

The co-gasification of furfural residue with coal is a feasible way to realize its clean and efficient utilization, but there is a high content of alkaline components in the furfural residue ash. Therefore, the effect of furfural residue addition on the fusion temperature of gasification coal ash was investigated, in which a typical furfural residue and two gasification coals with different ratios of silicon to aluminum (Si/Al) were selected. X-ray diffraction instrument (XRD) was used to measure the mineral evolution of co-gasification ash at different temperatures. The phase change in equilibrium state was calculated by the software FactSage. The results show that with the increase in furfural residue addition ratio, the fusion temperatures of both gasification coal ashes first increase and then decrease, while the increase trend of fusion temperatures for the coal with a high Si/Al ratio is more significant. When the furfural residue is added, the resulting high melting point mineral of gasification slag is changed from anorthite (CaAl2Si2O8) to leucite (KAlSi2O6) that is still present as a solid phase at 1300 °C, resulting in an increase of AFTs. The coal ash with more amount of SiO2 can react with K2O to produce more leucite (KAlSi2O6) with a higher fusion point, thus causing the ash fusion temperatures to rise. However, as the ratio of furfural residue addition continues to increase, the ash fusion temperatures decrease, which is attributed to the formation of kaliophilite (KAlSiO4) with a low fusion point that is generated in the presence of higher content of K2O.

Land Reclamation Using Typical Coal Gasification Slag in Xinjiang: A Full-Cycle Environmental Risk Study

A rising quantity of coal gasification slag (CGS) is produced annually. Land reclamation is a valuable method for efficiently utilizing coal gasification slag on a large scale. The ecological influence of CGS during land reclamation has not been widely investigated. This article covers the entire CGS use cycle for land reclamation, which includes generation, storage, and disposal. The environmental risk of using CGS for land reclamation was assessed by combining four environmental risk assessment methods. The results show no environmental risk for coal gasification coarse slag (CGCS) and coal gasification fine slag (CGFS) at the generation and storage stages. However, a concern remains regarding manganese leaching from CGCS during the storage stage. In the disposal phase, no environmental risk is present when up to 15% of CGCS and CGFS are applied to land reclamation projects. However, the environmental risk of disposing of 100% of CGS in a landfill cannot be disregarded. Conversely, the full-cycle use of CGS for land reclamation carries no environmental risk.