Controlled design of Na-P1 zeolite/ porous carbon composites from coal gasification fine slag for high-performance adsorbent.

Low-cost and concentrated industrial wastes have been recognized as a sustainable resource for preparation of new functional materials. Here, a new method was designed for the synthesis of porous composites containing high-purity Na-P1 zeolite and porous carbon from waste coal gasification fine slag (CGFS), which was treated first by acid leaching to controllably remove metal impurities and adjust Si/Al ratio, followed by NaOH fusion and hydrothermal treatment. By leaching with 1.0 mol/L HCl solution, the Si/Al ratio of the raw CGFS increased to 5.7, and the obtained CZ-1.0 consisted of high-purity Na-P1 zeolite with a typical cone-shaped flower cluster shape. The residue carbon in CGFS can be further activated to form porous carbon and graphite carbon layers interposed in the zeolite structure. The specific surface area and pore volume of CZ-1.0 reached 153.91 m2/g and 0.18 cm3/g, respectively. CZ-1.0 exhibited remarkable adsorption performance for methylene blue (MB) with the adsorption capacity reaching 137.5 mg/g for 100 mg/L MB solution. The adsorption process is mainly controlled by the chemisorption mechanism, and the adsorption of MB by CZ-1.0 may include ion exchange, hydrogen bond interaction, π-π bond interaction and van der Waals force. NaCl solution was successfully used as the desorption agent to regenerate the composite material, and the removal rate remained above 92% after five cycles. This work provides an effective strategy to synthesize a practically applicable adsorbent from the waste coal gasification fine slag for the purification of MB wastewater.

Aromatics production from relay catalytic pyrolysis of cow manure using Ru/C and ZSM-5 dual catalysts synthesized from coal gasification fine slag.

Resource utilization of solid waste can aid in gradual substitution of fossil fuels while achieving waste recycling. In this study, residual carbon and ash slag from the coal gasification fine slag were separated by froth flotation, and then was used to prepare Ru/C and ZSM-5 dual catalysts with carbon-rich and ash-rich components as raw materials, respectively. The performance of two catalysts for catalytic upgrading of volatiles from pyrolysis of cow manure (CM) to produce light aromatic hydrocarbons was systematically investigated. The direct pyrolysis products of CM mainly included alcohols, ketones, ethers, and other oxygen-containing compounds. When ZSM-5 was used as the catalyst, the yield of monocyclic aromatic hydrocarbons (MAHs) increased significantly due to the better catalytic cracking and aromatization abilities of ZSM-5 catalyst. However, the yield of phenols in the pyrolysis products improved when Ru/C was used as the catalyst due to the cleavage effect of Ru/C on the C-O bond. When Ru/C and ZSM-5 were used as dual catalysts in relay catalytic pyrolysis of volatiles, the increase in MAHs yield in the pyrolysis product was higher than the total increase obtained under Ru/C and ZSM-5 single catalysis. The possible pathways for the generation of MAHs from CM under Ru/C and ZSM-5 relay catalytic pyrolysis were revealed by the pyrolysis experiment performed on model compounds.

Correlation between Flow Temperature and Average Molar Ionic Potential of Ash during Gasification of Coal and Phosphorus-Rich Biomass.

The co-gasification of biomass and coal is helpful for achieving the clean and efficient utilization of phosphorus-rich biomass. A large number of alkali and alkaline earth metals (AAEMs) present in the ash system of coal (or biomass) cause varying degrees of ash, slagging, and corrosion problems in the entrained flow gasifier. Meanwhile, phosphorus is present in the slag in the form of PO43-, which has a strong affinity for AAEMs (especially for Ca2+) to produce minerals dominated by calcium phosphates or alkaline Ca-phosphate, effectively mitigating the aforementioned problems. To investigate the changing behavior of the slag flow temperature (FT) under different CaO/P2O5 ratios, 72 synthetic ashes with varying CaO/P2O5 ratios at different Si/Al contents and compositions were prepared, and their ash fusion temperatures were tested. The effects of different CaO/P2O5 ratios on the FT were analyzed using FactSage thermodynamic simulation. A model for predicting slag FT at different CaO/P2O5 ratios was constructed on the basis of the average molar ionic potential (Ia) method and used to predict data reported from 19 mixed ashes in the literature. The results showed that Ia and FT gradually increased with a decreasing CaO/P2O5 ratio, and the main mineral types shifted from anorthite → mullite → berlinite, which reasonably explained the decrease in ash fusion temperatures in the mixed ash. The established model showed good adaptability to the prediction of 19 actual coal ash FTs in the literature; the deviation of the prediction was in the range of 40 °C. The model proposed between FT and Ia based on the different CaO/P2O5 ratios can be used to predict the low-rank coal and phosphorus-rich biomass and their mixed ashes.

Enrichment of residual carbon from coal gasification fine slag by spiral separator.

Coal gasification is one of the most promising clean coal technologies. However, gasification process also produces a huge amount of solid waste of high carbon content, named coal gasification fine slag. The coal gasification fine slag is mainly handled by landfilling, which is not only a hazardous pollution, but also wasting the energy from residual carbon. Developing a technology to utilize coal gasification fine slag and recover the residual carbon is becoming essential for an eco-friendly coal chemical industry. In this paper, the enrichment behavior of residual carbon in coal gasification fine slag by a spiral separator is studied. The raw coal gasification fine slag sample and separator products are characterized on particle size distribution, size-depending ash content, reactivity, micromorphology and porous structure. The experimental results show that the spiral separator is efficient to remove ash and enriched carbonaceous components in coal gasification fine slag by separating feed (100%) into concentrate (81.2%), middlings (8.8%), and tailings (10.08%), where the ash content in tailings is up to 90%, accounting for 18.5% of total ash in feeding. The beneficial product "concentrate" has a good distribution of size-depending ash content, that most combustibles are enriched in these particles of diameter >100 µm. After spiral separator, the concentrate products have a more pure and developed porous structure with the surface area increasing from 199.8 m2/g (feeding) to 231.8 m2/g, as well as a better combustion reactivity of lower ignition temperature compared with feedings. Accordingly, an economic and feasible combination process of spiral separator connecting sieve can produce an enriched-carbon product of ∼45% yield and ∼80% carbonaceous content. The Iodine adsorption ability of sieved products increases by 47.6% compared with feed, and reaches up to about half of industry activated carbon. The finally sieved concentrate products have a good market prospect as fuel and adsorbent.

Study on the pyrolysis characteristics and kinetic mechanism of cow manure under different leaching solvents pretreatment.

Cow manure (CM) is a kind of biowaste with potential for heat recovery and energy. The effects of different leaching solvents on the physicochemical structure of CM and the catalysis role of AAEMs on the thermal behavior were studied. TGA experiments showed that the maximum weight loss rate and the peak temperature of hemicellulose and cellulose increased after leaching, while the TG/DTG curve moved to a high temperature direction. The devolatilization index (Di) value of the raw and leaching samples increased with the increase of the heating rate, indicating that the higher heating rate promoted the release of volatile. The treatment with leaching not only removed AAEMs in CM effectively, but also led to a larger specific surface area and pore volume, and reduced the crystallinity of cellulose and crystal size in CM. Na salt and K salt were mainly in water soluble state, while Ca salt and Mg salt were mainly in acid soluble salt. Compared with the change of physical and chemical structure caused by leaching, the removal of AAEMs played a dominant role in the pyrolysis characteristics of the samples. The removal efficiency of AAEMs increased with the strength of acid. Based on Kissinger model, the Eα of Raw-CM, H2O-CM, CH3COOH-CM, HCl-CM, HNO3-CM and H2SO4-CM is 171.30 kJ/mol, 187.58 kJ/mol, 190.86 kJ/mol, 292.10 kJ/mol, 287.79 kJ/mol and 280.69 kJ/mol respectively. Both the raw and leaching samples followed the reaction order mechanism and tended to react according to a higher-order reaction model between n = 1.5 and n = 4. In contrast, CH3COOH is an ideal solvent for leaching pretreatment.

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.

Microwave synthesis of amino-functionalized MCM-41 from coal gasification fine slag for efficient bidirectional adsorption of anionic and cationic dyes.

Coal based solid waste has been recognized as a sustainable raw material for the preparation of high added value materials for wastewater treatment. In this paper, a preparation route was designed for the rapid, efficient, and low-cost preparation of MCM-41 zeolite using coal gasification fine slag as raw material. Functionalization modification of MCM-41 was carried out by grafting amino groups on its surface to improve its application performance. Moreover, the prepared functionalized material is used for bidirectional adsorption of anionic and cationic dyes. The experimental results indicate that MCM-41 zeolite with highly ordered pore structure was rapidly prepared using the advantages of fast heating and strong permeability of microwave synthesis method, with a specific surface area of up to 862.03 m2/g. Amine functionalized MCM-41 exhibits strong adsorption capacity for both cationic and anionic dyes, with maximum adsorption capacities for methylene blue and Congo red being 292.40 mg/g and 354.61 mg/g, respectively. The study of adsorption kinetics and adsorption mechanism indicate that the adsorption process is mainly controlled through chemical adsorption, including electrostatic attraction, hydrogen bonding, and π-π interactions. The results of this study will provide useful references for the use of coal based solid waste to prepare functional materials for the treatment of organic wastewater.

Carbon coated In2O3 hollow tubes embedded with ultra-low content ZnO quantum dots as catalysts for CO2 hydrogenation to methanol.

CO2 hydrogenation coupled with renewable energy to produce methanol is of great interest. Carbon coated In2O3 hollow tube catalysts embedded with ultra-low content ZnO quantum dots (QDs) were synthesized for CO2 hydrogenation to methanol. ZnO-In2O3-II catalyst had the highest CO2 and H2 adsorption capacity, which demonstrated the highest methanol formation rate. When CO2 conversion was 8.9%, methanol selectivity still exceeded 86% at 3.0 MPa and 320 °C, and STY of methanol reached 0.98 gMeOHh-1gcat-1 at 350 °C. The ZnO/In2O3 QDs heterojunctions were formed at the interface between ZnO and In2O3(222). The ZnO/In2O3 heterojunctions, as a key structure to promote the CO2 hydrogenation to methanol, not only enhanced the interaction between ZnO and In2O3 as well as CO2 adsorption capacity, but also accelerated the electron transfer from In3+ to Zn2+. ZnO QDs boosted the dissociation and activation of H2. The carbon layer coated on In2O3 surface played a role of hydrogen spillover medium, and the dissociated H atoms were transferred to the CO2 adsorption sites on the In2O3 surface through the carbon layer, promoting the reaction of H atoms with CO2 more effectively. In addition, the conductivity of carbon enhanced the electron transfer from In3+ to Zn2+. The combination of the ZnO/In2O3 QDs heterojunctions and carbon layer greatly improved the methanol generation activity.

Low-cost Y-type zeolite/carbon porous composite from coal gasification fine slag and its application in the phenol removal from wastewater: fabrication, characterization, equilibrium, and kinetic studies.

As an industrial solid waste, coal gasification fine slag (CGFS), which consists of many elements, such as silicon, aluminum, and carbon, could be used as an important resource. Therefore, this solid waste was used as a raw material to prepare high-value-added adsorption material for the treatment of industrial wastewater in this study. A hydrothermal synthesis method was applied to convert CGFS into a Y-type zeolite/carbon porous composite. The effects of time and temperature on the synthesis were studied. XRD, SEM, and other techniques were used to analyze the material and its physicochemical properties. Additionally, the adsorption performance of the material for phenol was studied. The results showed that the composite has better adsorption capacity for phenol than CGFS. The Freundlich model and pseudo-second-order kinetics well fitted the adsorption behavior of the composite, which demonstrated that the adsorption of phenol was dominated by chemical adsorption.

Zonation of Landslide Susceptibility in Ruijin, Jiangxi, China.

Landslides are one of the major geohazards threatening human society. The objective of this study was to conduct a landslide hazard susceptibility assessment for Ruijin, Jiangxi, China, and to provide technical support to the local government for implementing disaster reduction and prevention measures. Machine learning approaches, e.g., random forests (RFs) and support vector machines (SVMs) were employed and multiple geo-environmental factors such as land cover, NDVI, landform, rainfall, lithology, and proximity to faults, roads, and rivers, etc., were utilized to achieve our purposes. For categorical factors, three processing approaches were proposed: simple numerical labeling (SNL), weight assignment (WA)-based and frequency ratio (FR)-based. Then 19 geo-environmental factors were respectively converted into raster to constitute three 19-band datasets, i.e., DS1, DS2, and DS3 from three different processes. Then, 155 observed landslides that occurred in the past decades were vectorized, among which 70% were randomly selected to compose a training set (TS1) and the remaining 30% to form a validation set (VS1). A number of non-landslide (no-risk) samples distributed in the whole study area were identified in low slope (<1-3°) zones such as urban areas and croplands, and also added to the TS1 and VS1 in the same ratio. For comparison, we used the FR approach to identify the no-risk samples in both flat and non-flat areas, and merged them into the field-observed landslides to constitute another pair of training and validation sets (TS2 and VS2) using the same ratio of 7:3. The RF algorithm was applied to model the probability of the landslide occurrence using DS1, DS2, and DS3 as predictive variables and TS1 and TS2 for training to obtain the SNL-based, WA-based, and FR-based RF models, respectively. Verified against VS1 and VS2, the three models have similar overall accuracy (OA) and Kappa coefficient (KC), which are 89.61%, 91.47%, and 94.54%, and 0.7926, 0.8299, and 0.8908, respectively. All of them are much better than the three models obtained by SVM algorithm with OA of 81.79%, 82.86%, and 83%, and KC of 0.6337, 0.655, and 0.660. New case verification with the recent 26 landslide events of 2017-2020 revealed that the landslide susceptibility map from WA-based RF modeling was able to properly identify the high and very high susceptibility zones where 23 new landslides had occurred, and performed better than the SNL-based and FR-based RF modeling, though the latter has a slightly higher OA and KC. Hence, we concluded that all three RF models achieve reasonable risk prediction, but WA-based and FR-based RF modeling deserves a recommendation for application elsewhere. The results of this study may serve as reference for the local authorities in prevention and early warning of landslide hazards.

Co-Gasification of Cow Manure and Bituminous Coal: A Study on Reactivity, Synergistic Effect, and Char Structure Evolution.

As special waste biomass, cow manure (CM) is also the main pollutant in agricultural production. The combination of cow manure and coal is conducive to the sustainable development of energy and the solution to pollution problems. This work aims to investigate the co-gasification reactivity and synergy of cow manure and Meihuajing (MHJ) bituminous coal blends at 800-1100 °C using a thermogravimetric analyzer, and the correlation between char gasification reactivity and its structural characteristics is performed. The results indicate that the sensitivity of gasification reactivity to temperature is gradually weakened with the proportion of CM increasing. The synergistic effect on reactivity was observed in the co-gasification process of CM/MHJ. The addition of CM promoted the synergistic effect obviously at the low carbon conversion level, and the inhibitory effect with the CM addition on the order degree of char carbon structure was enhanced during the co-gasification process according to Raman spectroscopy analysis. The addition of CM promoted the porous structure evolutions, which make the pore size distribution and the specific surface developed remarkable. The changes in carbon and pore structures can be well related to the gasification reactivity. The findings in this study would be helpful in the understanding of the co-gasification synergy mechanism of cow manure and coal blends.

Investigation into the co-pyrolysis behaviors of cow manure and coal blending by TG-MS.

In this study, the co-pyrolysis characteristics of cow manure (CM) and Meihuajing bituminous coal (MHJ) blends were investigated in detail. The mass loss behavior and gas evolution characteristics of the blends were analyzed online by thermogravimetry-mass spectrometry (TG-MS), and kinetic analysis was performed. The results demonstrate that the addition of CM to the MHJ increases the reactivity of blends, indicating that interaction between the CM and MHJ occurred during co-pyrolysis. For conventional gases, the release order of gases during CM and MHJ blend pyrolysis is H2O, CO2, CO, CH4, H2. For sulfur-containing gases, with increasing proportion of CM, the emissions of H2S, COS, and C4H4S increase and that of SO2 decrease, and the release temperature interval shifts to lower directions. The Coats & Redfern model was used, an increase of activation energy with CM addition was observed. The optimum blending ratio based on the lowest activation energy is CM:MHJ = 1:3 and the activation energy is 41.9 kJ/mol.

[Soil stoichiometry of Pinus massoniana forest in red soil erosion area under different management patterns]. / 红壤侵蚀退化马尾松林下不同治理模式土壤化学计量特征.

We investigated the concentrations of carbon (C), nitrogen (N), and phosphorus (P) and C:N:P stoichiometry in soil and litter of Pinus massoniana forest under four different management patterns: inefficient forest transformation, mixture of arbor with shrub and herb, shallow ditch grass planting, and being banned in serious erosion and degradation of red soil in southern China. Our findings could provide scientific basis for soil erosion control and vegetation restoration in this area. The results showed that there were significant differences in soil organic carbon (SOC), TN, TP and litter nutrient content among different management patterns. The nutrient contents in soil and litter under all the four management patterns were significantly higher than that of control, with mixture of arbor with shrub and herb having the highest concentrations. The concentrations of SOC, TN and TP decreased with the increases of soil layer. However, the shallow ditch grass planting mana-gement pattern presented as follows: the concentrations of SOC, TN and TP decreased first and then increased with the increases of soil layer, with the lowest value in 5-20 cm soil layer. There were significant differences in soil C:N, C:P, N:P and litter C:P among different management patterns, and the soil spatial variation was C:N>C:P>N:P. Excepted for mixture of arbor with shrub and herb, C:N was still at a lower level in the other management patterns, and soil C:P and N:P showed higher values overall. Litter C:N, C:P and N:P had opposite change pattern, with inefficient forest transformation and mixture of arbor with shrub and herb being much smaller than the control. Soil C:N and C:P were mainly controlled by SOC content and litter C content, and soil N:P was mainly controlled by soil TP content and litter P content. Soil stoichiometry was affected by soil water content, soil bulk density, pH, and other factors. The relationship between litter and soil nutrients was closely related and showed similar changes.