Evolutionary law and regulatory technology of roof migration on gob-side entry retaining.

In order to study the evolutionary law of roof migration on Gob-Side Entry Retaining, this paper takes the gob-side entry retaining in the comprehensive mining face of the Ningtiaota coal mine as the engineering background, and analyzes the evolutionary law of the overlying rock layer on the roof at different locations during the roadway stay and the stress distribution around the roadway through numerical simulation software, which shows that there is a concentration of stress inside the Flexible formwork concrete wall, and therefore the maximum settlement of the roof on the side of Flexible formwork concrete wall is 35.35 mm, due to the existence of "arch-shaped" decompression area from the working face. Therefore, the maximum settlement of the roof slab on the side of flexible formwork concrete wall was 35.35 mm. Due to the existence of "arch-shaped" decompression area on the roof and floor of roadway, the settlement of the roof slab on both sides of the roadway gradually increased when it was from - 20 to 10 m away from the working face, and the central position had the following pattern of firstly decreasing and then gradually increasing, and then exceeding the top of the roadway. After decreasing and then gradually increasing, after 10 m ahead of the working face, the two sides of the roadway roof subsidence law and the central part of the roadway to maintain the same; the use of cutting the top of the flexible mold concrete wall support technology as a means of controlling the top of the roof along the empty roadway subsidence, the analysis shows that the roof after roof cutting of the amount of subsidence have been reduced, the maximum difference in the rate of change of the displacement is 0.011%, and the maximum difference in the amount of subsidence of 4.98 mm; through the field monitoring data analysis of the pressure of mining The peak value of the influence curve of the working face is located at 19 m of the working face, 9 m of the lagging working face and 19 m of the roadway outside the working face are less affected by the additional mining stress field, comparing the fracture brokenness of the roadway roof before and after the roof cutting, the fracture area in the uncut section is much larger than that in the section of the roof cutting.

Characteristics of surrounding rock damage and control technology of a facing-mining excavating roadway in north Shaanxi mining area.

In a coal mine in the northern region of Shaanxi Province, China, a facing-mining excavating roadway exists, which is intended to be retained for subsequent working face safety services. This paper investigates the deformation and damage characteristics of the surrounding rock in different stages using FLAC 3D numerical simulation, taking the facing-mining excavating roadway of this coal mine as the research context. At 20 m ahead of the working face, a discontinuous plastic zone appears in the surrounding rock of the roadway, a phenomenon attributed to the varying hardness of the lithologyand termed 'plastic zone jumping.' The numerical simulation results have been were verified using drill hole peeping. Real-time monitoring of the roadway's stability is conducted on-site, showing that the roadway is significantly affected by mining at the 50 m point ahead of the working face. Based on the numerical simulation and on-site monitoring results, the support strength was increased at 50 m from the working face along the roadway, and a new support scheme was adopted. In the lagging section of the roadway, where mining pressure is strongly evident, differentiated reinforcement using anchor rods, anchor ropes, and W steel belts has been employed, resulting in a satisfactory on-site effect.

A core-shell structured magnetic covalent organic framework (type Fe3O4@COF) as a sorbent for solid-phase extraction of endocrine-disrupting phenols prior to their quantitation by HPLC.

A magnetic covalent organic framework (Fe3O4@COF) with core-shell structure was fabricated at room temperature and used as an adsorbent for magnetic solid-phase extraction of polar endocrine-disrupting phenols (4-n-nonylphenol, 4-n-octylphenol, bisphenol A and bisphenol AF). The sorbent was characterized by transmission electron microscopy, FTIR, powder X-ray diffraction and other techniques. The main parameters governing the extraction efficiency were optimized. The phenols were quantified by HPLC with fluorometric detection. The method has attractive features such as low limits of detection (0.08-0.21 ng.mL-1), wide linear ranges (0.5-1000 ng.mL-1), and good repeatability (intra-day: 0.39%-4.99%; inter-day: 1.57%-5.21%). Satisfactory results were obtained when the developed method was applied to determine the four target pollutants in real world drink samples with spiked recoveries over the range of 81.3~118.0%. This indicates that the method is a powerful tool for the enrichment and determination of endocrine-disrupting phenols in drink samples. Graphical abstract A magnetite based covalent organic framework (Fe3O4@COFs) was synthesized with TPAB, TPA and Fe3O4. It was used for magnetic solid-phase extraction of endocrine-disrupting phenols from plastic-packaged tea drink samples coupled with liquid chromatography (LC) for determination.

A Zr(IV)-based porphyrinic metal-organic framework as a solid-phase sorbent for extraction of sulfonamides prior to their quantitation by LC-MS.

A porphyrinic metal-organic framework (PCN-224) was fabricated and used as an adsorbent for solid-phase extraction of ultratrace levels of polar sulfonamide antibiotics from food and drinking waters. The PCN-224 was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and powder X-ray diffraction analyses. Parameters affecting the extraction efficiency were optimized. The sulfonamides were quantified by liquid chromatography-tandem mass spectrometry. Figures of merit include (a) low limits of detection (0.07-0.47 ng·L-1), (b) wide linear ranges (0.5-2000 ng·L-1), and (c) good repeatabilities (2.8%-6.7%) and reproducibilities (1.7%-5.1%). The method was successfully applied to the determination of sulfonamides in food and drinking water samples. Graphical abstract A Zr(IV)-based porphyrinic metal-organic framework (PCN-224) was synthesized from a Zr6 cluster and the H2TCPP ligand. It was used for solid-phase extraction of sulfonamides from food and drinking water samples coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) for determination.

Preconcentration and Determination of Perfluoroalkyl Substances (PFASs) in Water Samples by Bamboo Charcoal-Based Solid-Phase Extraction Prior to Liquid Chromatography-Tandem Mass Spectrometry.

In this work, bamboo charcoal was used as solid-phase extraction adsorbent for the enrichment of six perfluoroalkyl acids (PFAAs) in environmental water samples before liquid chromatography-tandem mass spectrometry analysis. The specific porous structure, high specific surface area, high porosity, and stability of bamboo charcoal were characterized. Several experimental parameters which considerably affect extraction efficiency were investigated and optimized in detail. The experimental data exhibited low limits of detection (LODs) (0.01-1.15 ng/L), wide linear range (2-3 orders of magnitude and R ≥ 0.993) within the concentration range of 0.1-1000 ng/L, and good repeatability (2.7-5.0%, n = 5 intraday and 4.8-8.3%, n = 5 interday) and reproducibility (5.3-8.0%, n = 3). Bamboo charcoal was successfully used for the enrichment and determination of PFAAs in real environmental water samples. The bamboo charcoal-based solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry analysis possessed great potential in the determination of trace PFAA levels in environmental water samples.