Using chemical experiments and plant uptake to prove the feasibility and stability of coal gasification fine slag as silicon fertilizer

Resource utilization of decarbonized coal gasification slag in soil quality improvement: New insights into microbial community composition and environmental risk assessment

Decarbonized coal gasification slag (DCGS) is a coal-based solid waste generated from raw coal through the processes of gasification and decarbonization. However, the excessive production of DCGS has caused large-scale environmental problems and seriously affected the sustainable development of coal chemical enterprises. It's urgent to explore a high-value utilization approach. Here, a field trial was conducted to evaluate the feasibility of soil amendment using DCGS in a sandy soil. The 16S rRNA gene sequencing, soil quality approach and partial least squares path modeling were used to assess the responses of soil properties and relative forage value (RFV) of Leymus chinensis to DCGS addition in soil-plant-microbe system. Results showed that DCGS addition significantly increased soil pH, soil organic carbon (22.4 %), alkaline phosphatase (ALP) enzyme activity (16.5 %) and α-diversity of bacterial communities (1.37 %). Soil microbial biomass CNP in DCGS1, DCGS2, DCGS3 and DCGS4 treatments were 10.7 %, 21.3 %, 44.8 % and 69.1 % higher than control check (CK) treatment, respectively. Our study emphasized the β-diversity of bacterial communities and topological parameters of microbial co-occurrence networks were significantly altered after DCGS addition. Ultimately, higher soil quality and RFV of Leymus chinensis were obtained in DCGS addition treatments rather than the CK treatment (p < 0.01). Moreover, soil pH and p_Methylomirabilota were identified as the crucial factors affecting soil quality, while soil ALP and p_Entotheonellaeota were key factors affecting RFV of Leymus chinensis according to Mantel test. Our result further evidenced that there were relatively low ecological risk level after DCGS addition (Ecological Risk Index < 150), thus DCGS addition was considered as a potential method in improving soil quality. Taking into account the impact of DCGS addition on soil microbial community, soil quality, and ecological safety, the recommended application rate for sandy soil is 60 t·ha-1 (DCGS3). Our findings elucidate that soil amendment with DCGS not only enhance soil quality and RFV of Leymus chinensis, but also provide potential possibility for safe and environmentally friendly utilization of DCGS. These findings deepened our understanding of sustainable development and efficient management of DCGS.

A pilot scale test on the fluidized melting combustion of coal gasification fine slag

To address the issue of coal gasification fine slag (CGFS) disposal, a novel fluidized melting combustion (FMC) process has been proposed. In this study, the operating feasibility, combustion performance and gas pollutant emission were assessed through 0.4 MW pilot-scale test. The results indicated that both temperature and pressure fluctuation remained within the controllable range throughout entire test period. Under the influence of high cycle rate and incomplete combustion, CGFS efficiently achieved the rapid dehydration, preheating and crushing. Some combustible H2 and CO were generated simultaneously. After the preheating modification, the refractory CGFS transformed into hot gas-solid composite fuel. To achieve the complete carbon removal and ash vitrification, the melting combustion temperature was up to 1501.1 °C. Under the excessively high temperature, liquid slag was discharged smoothly from the tap hole without any observed blockage. Carbon content in slag was only 0.4 wt%. The slag captured rate and decarbonization rate were up to 79.0 % and 93.8 %, respectively. The initial CO emission was as low as 103.0 mg/m3. The initial NO emission reached up to 452.5 mg/m3 under radiation boiler afterburning. Due to the combined influence of multiple factors, the initial SO2 emission soared up to 1789.3 mg/m3. Further research will focus on controlling flue gas pollutant emissions, resource utilization of molten slag, and developing oxy-combustion. The objective is to attain full carbon neutrality in the entire coal chemical industry process.

Emission characteristics of coal gasification fine slag direct combustion and co-firing with coal

Coal gasification is an effective way to use coal cleanly and efficiently, and coal gasification fine slag is a by-product of coal gasification with high carbon content, large specific surface area, developed pore structure and large output during production. At present, combustion has become an effective way to dispose of coal gasification fine slag on a large scale, and the coal gasification fine slag after combustion treatment can be further used for construction raw materials. In this paper, the emission characteristics of gas-phase pollutants and particulate matter under different combustion temperatures (900 °C, 1100 °C, 1300 °C) and combustion atmosphere (5%, 10%, 21% O2 concentration) are studied with the drop tube furnace experimental system. By co-firing different proportions of coal gasification fine slag (10%, 20%, 30%) and raw coal, the pollutants formation law under co-firing conditions is studied. Scanning electron microscopy-energy spectroscopy (SEM-EDS) is used to characterize the apparent morphology and elemental composition of particulate samples. The measurement results of gas-phase pollutants show that the increase of furnace temperature and O2 concentration can effectively promote combustion and improve burnout characteristics, but the emission of gas-phase pollutants increases. A certain proportion (10%-30%) of coal gasification fine slag is added to the raw coal, which reduces the total emission of gas-phase pollutants (NOx and SOx). Studies on the characteristics of particulate matter formation show that co-firing with coal gasification fine slag in raw coal can effectively reduce submicron particle emission, and the lower fine particle emission is also detected at lower furnace temperature and oxygen concentration. The element analysis of particulate matter formation shows that the Fe, Si and S elements content of submicron particle generated by YL (the coal gasification fine slag generated by water slurry furnace in of Shaanxi Extended China Coal Yulin Energy Chemical Co., Ltd) sample increases significantly with the increase of furnace temperature and O2 concentration, which is the main influencing factor for the increase of submicron particle. With the increase of the mixing ratio of YL sample, the content of major elements such as Fe, K and Mg of submicron particle decreases significantly, which is an important reason why the amount of the submicron particle decreases.

Study of the synthesis, adsorption property, and photocatalytic activity of TiO2/coal gasification fine slag mesoporous silica glass microsphere composite

In this study, TiO₂/MSGM composite material with adsorption-photocatalytic properties was prepared by extracting mesoporous silica glass microsphere (MSGM) from coal gasification fine slag (CGFS) as a novel TiO₂ carrier. The results of characterization and properties of the composite showed that MSGM could improve the adsorption capacity and photocatalytic activity of the composite by improving the pore structure of the composite, hindering the growth of TiO₂ particles, increasing the phase transition temperature of TiO₂, enhancing the dispersion of TiO₂ particles. The sample 1:3-TiO₂/MSGM-2-500 prepared under the optimized conditions possesses satisfactory morphology characteristics, high adsorption capacity, and photocatalytic activity to rhodamine B (RhB). The synergistic effects of adsorption and photocatalytic significantly increase the total removal rate of RhB. This study not only provides a new direction for high-value-added resource utilization of CGFS but also gives a new kind of low-cost carrier material with adsorption property for TiO₂ loading to remove organic dye pollutants.

Effect of Alkali and Sulfate on the Hydration Characteristic of Cement-Based Materials Containing Coal Gasification Slag

Coal gasification slag is an inevitable by-product of the coal gasification process. This paper explored the feasibility of using activators (calcium hydroxide, sodium hydroxide, calcium sulfate, sodium sulfate) to promote the pozzolanic activity of milled coal gasification coarse slags (MCS), and analyzed the effect of alkali and sulfate activators on the hydration characteristic of cement-based materials containing MCS. Coal gasification slags with ignition lossses more than 15% were removed and the remaining slags were considered as cementitious material after milling. Scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and hydration heat tests were employed to analyze the hydration mechanism of the samples. Besides, the compressive strength values of cement mortars with MCS and activators were evaluated. The results showed that calcium hydroxide was conductive to the formation of hydration products and its crystallization could contribute to the strength improvement of the sample. Calcium sulfate mainly participated in the hydration process of cement to form ettringite (AFt) phases. Sodium hydroxide could accelerate the dissolution of active mineral phases of MCS, resulting in the pozzolanic activity being enhanced. Moreover, sodium sulfate could not only increase the formation of AFt phases, but also improved the alkalinity in sample to facilitate the production of gels. Among them, a better promotion effect could be obtained from the combined application of calcium hydroxide and sodium sulfate. In addition, the compressive strength values of cement mortars containing MCS tended to increase when activators were used. The sample activated by calcium hydroxide and sodium sulfate exhibited the highest strength, increasing by 18.55% at 28 days compared with the sample without an activator.

Using One-Step Acid Leaching for the Recovering of Coal Gasification Fine Slag as Functional Adsorbents: Preparation and Performance

Coal gasification fine slag (FS), a kind of by-product of coal chemical industry, was recovered for the preparation of functional adsorbents by acid leaching process, which was orthogonally optimized by HCl, HNO₃, HF, HAc, and H₂SO₄. Methylene blue (MB) was used to evaluate the performance of functional adsorbents. The results demonstrated that 57.6% of the leaching efficiency (R_LE) and 162.94 mg/g of adsorption capacity (C_AC) of MB were achieved under the optimal conditions of HNO₃ of 2.0 mol/L, acid leaching time of 2.0 h, and acid leaching temperature of 293K. The detections on X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and BET surface area (SBET) indicated that the synthesized functional adsorbents were characterized by mesoporous materials. The good fitting of adsorption process using pseudo-second-order and Langmuir models demonstrated that the chemisorption contributed to MB removal. The results of thermodynamics further revealed that the adsorption process of MB occurred spontaneously due to the exothermic properties. The work is expected to develop a novel and cost-effective strategy for the safe disposal of FS, and potentially offer an alternative pathway to increase the additional value for the coal chemical industry.

Possibilities of Using Organic Waste after Biological and Physical Processing—An Overview

With a rapidly increasing amount of waste, waste management is an extremely important issue. Utilising processes such as combustion and biological processing significantly decreases the accumulation and volume of waste. Despite this, huge volumes of resulting waste that still need to be managed remain. This paper identifies various methods of processing organic waste, discussing both thermal and biological techniques for waste management. Additionally, this paper demonstrates that the end products remaining after processing waste are oftentimes functional for agricultural use. These materials are excellent byproducts used to produce various organic, mineral and organomineral fertilisers. For instance, it appears that the production of fertilisers is the most promising method of utilising fly ash that results from the combustion of waste. In order to minimise the environmental risk of polluting soil with heavy metals, waste, as well as ashes resulting from combustion, must meet the criteria for the limit of contaminants.

Combustibility analysis of high-carbon fine slags from an entrained flow gasifier

The fine slag produced from the entrained flow gasifier in coal chemical industry contains a high amount of unburned carbon content, which can reach more than 40%. The coal gasification fine slag is dissipated just by land filling which occupies a lot of land. Consequently, it causes the pollution of soil, water and wastes the combustible carbon in coal gasification fine slag. It is crucial to develop an environmental friendly and economical scheme for the utilization of coal gasification fine slag. To achieve this aim, it is significant to investigate the combustibility of coal gasification fine slag and then propose a comprehensive utilization technology. In this study, the physical and chemical properties of the raw bituminous coal and the produced coal gasification fine slag, including proximate and ultimate analysis, particle size distribution, ash composition, morphology, and specific area were investigated. The combustion and co-combustion characteristics of coal gasification fine slag were analyzed by a thermo-gravimetric analyzer. A drop tube furnace and a fluidized bed reactor were employed to test the combustibility of coal gasification fine slag in a pulverized furnace and a fluidized bed furnace, respectively. Results show that the carbon content in dried coal gasification fine slag is >40% with a heating value > 16 MJ kg^-1. Further, thermo-gravimetric analyzer test showed that the combustion property of coal gasification fine slag is worse than that of anthracite and close to that of high ash coal, and there is a non-negligible synergistic effect for raw bituminous coal and coal gasification fine slag co-firing. The combustibility test in drop tube furnace and fluidized bed reactor showed that coal gasification fine slag can be well burned in a pulverized furnace requiring combustion temperature >900 °C and oxygen concentration >10 vol%. However, the fluidized bed furnace was not appropriate for high efficiency coal gasification fine slag burning, because the unburned carbon content of fly ash after coal gasification fine slag combustion is still >14%, even at 900 °C, 21% oxygen concentration and a low fluidization number. It is suggested that coal gasification fine slag will be better to burned it in a pulverized furnace rather than fluidized furnace.

Carbon-silica mesoporous composite in situ prepared from coal gasification fine slag by acid leaching method and its application in nitrate removing

Coal gasification fine slag (CGFS) was produced in the coal gasification process which was classified as an industrial solid waste. It was featured with naturally formed amorphous structures and an abundance of silicon, carbon and metal oxides. In this study, on the basis of the composition and structure characteristics of CGFS, a simple hydrochloric acid (HCl) leaching technology was applied to in situ prepare carbon-silica mesoporous composites (CSMCs) from CGFS by fully considering the value of the residual carbon. Special focus was put on the novel mechanism of pore formation in amorphous silica glass microspheres (SGM) during acid leaching. Experimental evidences showed that the metal oxides were uniformly distributed in SGM thus the dissolution of the metal oxides were starting from the surface of SGM, then gradually extending to the interior, and finally leading to form "tree branch" mesoporous channels. In addition, a response surface method was used to predict the optimal reaction conditions and the optimal sample (named as CGFS-O) was successfully prepared. CGFS-O possessed a prominent specific surface area (SSA) (337.51 m²/g) as well as an excellent pore volume (0.341 cm³/g). CGFS-O also exhibited a desirable capacity for NO₃^- removing and the adsorption process was studied detailed by changing different adsorption conditions. Adsorption results proved that CSMCs have the potential to purify wastewater in an economically and environmentally way. Therefore, combined with a proof-of-concept adsorption performance experiment, our study has not only provided a cost-effective strategy to industrially prepare CSMCs, reutilizing CGFS in an environmentally friendly way, but also contributed to the future applications of CSMCs with valuable insights into the pore formation mechanism in SGM during acid leaching process.