Investigation on Pb2+ adsorption characteristics by AAEMs-rich biochar in aqueous solution: Performance and mechanism.

Biochar derived from soybean straw with AAEMs (alkali and alkaline earth metals) enrichment could efficiently remove heavy metals from contaminated water. In this study, the influences of pyrolysis temperature on the physicochemical property and adsorption performance of soybean straw biochar were investigated. The contributions of different adsorption mechanisms were analyzed quantitatively. The results show that the soybean straw biochar exhibits excellent Pb2+ adsorption performance (157.2-227.2 mg g-1), with an order of BC800 > BC400 > BC600 > BC700 > BC500. The mechanisms of metal ion exchange (37.49%-72.58%) and precipitation with minerals (22.38%-58.03%) mainly control the Pb2+ adsorption, whereas complexation with organic functional groups (OFGs) and cation-Cπ interaction make the less contribution. The order of cation exchange capacity (CEC) is BC400 > BC800 > BC700 > BC600 > BC500, showing a high correlation (0.965) with the contribution of metal ion exchange with AAEMs. Moreover, Ca exhibits the strongest exchange capacity. The contribution of precipitation is consistent with the variation of soluble CO32- content in biochar. These results suggest that soybean straw biochar rich in AAEMs is a prospective adsorbent for Pb2+ elimination.

Experimental and Numerical Investigation of Dustfall Effect on Remote Sensing Retrieval Accuracy of Chlorophyll Content.

Chlorophyll is the dominant pigment in the photosynthetic light-harvesting complexes that is related to the physiological function of leaves and is responsible for light absorption and energy transfer. Dust pollution has become an environmental problem in many areas in China, indicating that accurately estimating chlorophyll content of vegetation using remote sensing for assessing the vegetation growth status in dusty areas is vital. However, dust deposited on the leaf may affect the chlorophyll content retrieval accuracy. Thus, quantitatively studying the dustfall effect is essential. Using selected vegetation indices (VIs), the medium resolution imaging spectrometer terrestrial chlorophyll index (MTCI), and the double difference index (DD), we studied the retrieval accuracy of chlorophyll content at the leaf scale under dusty environments based on a laboratory experiment and spectra simulation. First, the retrieval accuracy under different dustfall amounts was studied based on a laboratory experiment. Then, the relationship between dustfall amount and fractional dustfall cover (FDC) was experimentally analyzed for spectra simulation of dusty leaves. Based on spectral data simulated using a PROSPECT-based mixture model, the sensitivity of VIs to dust under different chlorophyll contents was analyzed comprehensively, and the MTCI was modified to reduce its sensitivity to dust. The results showed that (1) according to experimental investigation, the DD model provides low retrieval accuracy, the MTCI model is highly accurate when the dustfall amount is less than 80 g/m2, and the retrieval accuracy decreases significantly when the dustfall amount is more than 80 g/m2; (2) a logarithmic relationship exists between FDC and dustfall amount, and the PROSPECT-based mixture model can simulate the leaf spectra under different dustfall amounts and different chlorophyll contents with a root mean square error of 0.015; and (3) according to numerical investigation, MTCI's sensitivity to dust in the chlorophyll content range of 25 to 60 µg/cm2 is lower than in other chlorophyll content ranges; DD's sensitivity to dust was generally high throughout the whole chlorophyll content range. These findings may contribute to quantitatively understanding the dustfall effect on the retrieval of chlorophyll content and would help to accurately retrieve chlorophyll content in dusty areas using remote sensing.

Remote Sensing Assessment of Safety Risk of Iron Tailings Pond Based on Runoff Coefficient.

Iron tailings ponds are engineered dam and dyke systems used to capture iron tailings. They are high-risk hazards with high potential energy. If the tailings dam broke, it would pose a serious threat to the surrounding ecological environment, residents' lives, and property. Rainfall is one of the most important influencing factors causing the tailings dam break. This paper took Chengde Area, a typical iron-producing area, as the study area, and proposed a remote sensing method to evaluate the safety risk of tailings ponds under rainfall condition by using runoff coefficient and catchment area. Firstly, the vegetation coverage in the study area was estimated using the pixel dichotomy model, and the vegetation type was classified by the support vector machine (SVM) method from Landsat 8 OLI image. Based on DEM, the slope of the study area was extracted, and the catchment area of the tailings pond was plotted. Then, taking slope, vegetation coverage, and vegetation type as three influencing factors, the runoff coefficient was constructed by weight assignment of each factor using analytic hierarchy process (AHP) model in both quantitative and qualitative way. Finally, the safety risk of tailings ponds was assessed according to average runoff coefficient and catchment area in the study area. The results showed that there were 124 low-risk tailings ponds, 16 moderate-risk tailings ponds, and 4 high-risk tailings ponds in the study area. This method could be useful for selecting targeted tailings ponds for focused safety monitoring. Necessary monitoring measurements should be carried out for the high-risk and moderate-risk tailings ponds in rainy season.

Experimental Study on Vacuum Distillation Separation Characteristics of Tar Containing Solid Particles: Distributions of Light Components.

The impacts of the composition and properties of tar products on their utilization are of great importance, while the consequences of varying tar separation conditions on distillation fractions remain underexplored. Solid impurities in special tar products (e.g., subsurface in situ pyrolysis-derived tar-like substances) can contribute to the separation as well. In the present study, low-temperature coal tar (LTCT) was used as an analogue to pyrolysis product, mixed with semi-coke and coal dust, representing pyrolytic byproducts and nonpyrolytic substances, respectively. The LTCT mixtures were tested with vacuum distillation at various pressures and temperatures. The results revealed the role of pressure in fraction distribution across temperatures, with higher pressure concentrating fractions at lower temperatures. The impact of solid impurities on distillation primarily stemmed from adsorption. Minimal concentrations of solid impurities carried coal dust/semi-coke into the distillation, but higher levels retained them in the residue. The adsorption of coal dust was quite high at lower temperatures and waned as temperature increased, unlike semi-coke, which had consistent adsorption throughout the distillation. The present study can advance the understanding of vacuum distillation for tar products in the presence of solid impurities, offering a framework for the effective distillation/utilization of coal tar. By probing separation conditions, tar properties, and solid impurity effects, the present research will refine strategies for optimizing coal tar use, crucial for enhancing energy security and sustainable progress in China.

Experimental Study on the Erosion-Corrosion Characteristics of Desulfurization Slurry on Stainless Steel Pipe Materials.

The recovery of low-grade waste heat from power plants greatly benefits energy conservation and emission reduction during electricity generation, while the waste heat utilization directly from desulfurization slurry is a significantly promising method to deeply recover such low-grade energy and has been developed in practical application. However, the pipe materials are subjected to erosion and corrosion challenges due to the high level of solid compositions and the presence of harmful ions, such as Cl-1, which requires further evaluation under the condition of slurry heat exchange. The present study aimed at an experimental study on the erosion-corrosion characteristics of desulfurization slurry on three types of stainless steel, including type 304, 316L, and 2205. Both mass loss and micromorphology features were analyzed with possible mechanisms elucidated. The erosion-corrosion rate is weak at low temperatures, while the increase in the slurry temperature clearly promotes its rate. The influence of the temperature on the corrosion resistance of 304 is much greater than that of 2205. With an increase in duration time, the weight loss rate of stainless steel in the desulfurization slurry declines, and the changing trend of metal mass slightly slows down. The present study offers a better understanding of the erosion-corrosion behaviors of three types of stainless steel under flow and heat transfer conditions of a desulfurization slurry.

Experimental Investigation on Combustion and NO x Formation Characteristics of Low-Ash-Melting-Point Coal in Cyclone Furnace.

Slag tapping cyclone furnace is suitable and promising for the utilization of low-ash-melting-point coals without worrying about the fouling and slagging problems, but its high NO x emission has limited its application. In this study, the temperature profiles, species concentration distributions, and slag tapping behavior of the cyclone barrel were explored on a self-built 100 kW cyclone furnace system. A reasonable slag capture ratio of 0.70 can be achieved for the cyclone barrel even under air-staged conditions. The coincidence of high temperature and high O2 concentration in the annular near-wall area of the cyclone barrel can lead to a large amount of NO x formation, while a NO x reduction area with high CO concentration is formed in the central and lower zones of the cyclone barrel due to strong swirling effect. The NO x emission of cyclone staged combustion is lower than that of laminar drop-tube staged combustion in either air-staged or nonstaged cases, which could be attributed to the swirling effect. The NO x reduction area can be expanded by decreasing the cyclone stoichiometric ratio (SR) or reducing the primary air rate (PAR). Compared with the limit effects on the reduction of NO x emission by overall-SR, NO x formation can be greatly dropped by 56% when the cyclone-SR decreases from 1.1 to 0.7. The swirling intensity in cyclone barrel increases from 1.23 to 12.81 as PAR reduces from 0.4 to 0.2, which results in a reduction of NO x formation at the outlet of the cyclone barrel by half. Besides, the O2 concentration in the annular near-wall region can be remarkably reduced by the decentralized secondary air supply, resulting in a 23% reduction in NO x formation in the cyclone barrel.

Investigation of Pyrolysis and Mild Oxidation Characteristics of Tar-Rich Coal via Thermogravimetric Experiments.

Tar-rich coal has the potential to substitute the supply of oil-gas resources, which is abundant in China. The effective conversion of tar-rich coal into oil-gas products can promote coal utilization, reduce resource wastage, alleviate environmental pollution, and benefit carbon neutrality. Nevertheless, less work, if any, has been performed on the pyrolysis and mild oxidation behaviors of tar-rich coal in Northwestern China. The influences of limited oxygen addition and an extremely low heating rate on the micromorphology of the residual semi-coke are yet to be fully understood. Here, an experimental study on the pyrolysis and mild oxidation characteristics of tar-rich coal was conducted by the thermogravimetric analysis method, with further elucidation of the physical-chemical properties of the residual semi-coke. Experimental results show that an increase in the ultimate temperature of pyrolysis leads to a decline in the residue mass, while the mass loss from 500 to 550 °C presents the maximum elevation. Volatile matter is inclined to discharge from a certain direction, and the pores formed in various directions hold different possibilities. The organic components undergo both pyrolysis and slow oxidation with limited oxygen in the heating medium. Compared with an inert atmosphere, the mass loss under conditions of a small amount of O2 is brought forward but prolonged. Compared with a N2 atmosphere, the oxidation reactions of tar-rich coal are weakened in the presence of CO2. A large decrease in the heating rate exerts an unfavorable effect on the production of total volatiles. An extremely low heating rate possibly brings about a change in the mechanism of chemical bond cracking during pyrolysis. More pores can be yielded in tar-rich coal with an increase in the heating rate, and the morphology of the residual semi-coke after pyrolysis is susceptible to the heating rate. The present study offers an improved understanding of the pyrolysis characteristics of tar-rich coal as well as insights into the efficient utilization of tar-rich coal.

Simultaneous removal of SO2 and NOx with OH from the catalytic decomposition of H2O2 over Fe-Mo mixed oxides.

In this paper, the simultaneous removal of SO2 and NOx catalyzed by Fe-Mo mixed oxides at varying Mo/Fe atomic ratios was reported for the first time with the aim of reducing H2O2 consumption and elucidating the roles of Fe and Mo species in the catalytic process. Fe-Mo mixed oxides with varying Mo/Fe atomic ratios were synthesized and the catalytic performances were systematically studied. The catalyst with Mo/Fe atomic ratio of 2.0 exhibited the highest activity, with which removal efficiencies of 89.4 % for NOx and 100 % for SO2 can be attained at extremely low H2O2 dosage. Products analysis revealed that SO2 was mainly removed via wet scrubber, while the adequate oxidation resulting from OH radicals was the prerequisite for NOx removal. The redox pair of Fe2+/Fe3+ played a significant role in decomposing H2O2, while Mo species had double effect on catalytic activity. Higher Mo content resulted in abundant oxygen vacancies and stronger surface acidity, which favored OH formation. However, the excessive Mo content involved severe surface Mo enrichment and remarkably reduced the active sites of Fe species. The H2O2/Fe-Mo catalyst system showed excellent stability and had a promising prospect for simultaneously removing SO2 and NOx in coal-fired flue gas.

Effect of volatile-char interaction on the NO emission from coal combustion.

To clarify the effects of volatile-char interaction on the redistribution of fuel-N to N2 during devolatilization and the reduction of NO through gas-solid reactions during combustion, two types of experiments were performed on a novel reactor. The separate combustion of volatile and char and the combustion of entrained pulverized coal, and the formation of NO was examined between 800 and 1100 degrees C by using four typical Chinese coals with different ranks. The effect of volatile-char interaction on fuel-N conversion to NO during combustion was elucidated through comparing the NO emissions from the two types of combustion experiments. The results show that the volatile-char interaction is more important in the redistribution of fuel-N to N2 during devolatilization than in the reduction of NO over 900 degrees C, and a contrary conclusion is obtained below 850 degrees C for all used coals. A specific parameter has been proposed to characterize the relative importance of the volatile-char interaction in the redistribution of fuel-N to N2 during devolatilization to the interaction in the reduction of NO to N2 during simulataneous combustion of volatile and char. The results are of significance for minimizing the NO formation in industrial combustion processes.