Adsorption mechanism of methylene blue by magnesium salt-modified lignite-based adsorbents.

The rich pore structure and carbon structure of lignite make it a suitable adsorbent for effectively removing methylene blue (MB) from wastewater. This article reports the preparation of lignite-based adsorbents modified by magnesium salts, and the key factors and adsorption mechanism are analyzed to effectively improve the adsorption performance for MB. The results showed that the lignite was modified by magnesium salts, and the Mg2+ in the magnesium salts had a good binding effect on the oxygen-containing functional groups in the lignite. This improved the adsorption performance of the lignite-based adsorbents for MB. The Mg(NO3)2-modified lignite-based adsorbent showed the best adsorption performance and removal rate of MB (99.33%) when prepared with 8 wt % Mg(NO3)2. Characterization analysis showed that a "-COOMg" structure was formed between Mg2+ in the magnesium salts and the carboxylic acid functional group in the lignite, which was postulated to be the absorption site that promoted the adsorption performance for MB. It is speculated that the MB adsorption mechanism of this lignite-based adsorbent is ion exchange.

Effect of Iron Component on the Structural Evolution of Carbon Bonds in Hydrochloric Acid-Demineralized Lignite During Pyrolysis.

The pyrolysis characteristics of hydrochloric acid-demineralized Shengli lignite (SL+) and iron-added lignite (SL+-Fe) were investigated using a fixed-bed reactor. The primary gaseous products (CO2, CO, H2, and CH4) were detected via gas chromatography. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques were used to study the carbon bonding structures of the lignite and char samples. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to better understand the effect of the iron component on the transformation of the carbon bonding structure of lignite. The results showed that CO2 was released first during pyrolysis, followed by CO, H2, and CH4, and this order was unaffected by the addition of the iron component. However, the iron component promoted the generation of CO2, CO (<340 °C), and H2 (<580 °C) at lower temperatures and inhibited the formation of CO and H2 at higher temperatures while also inhibiting the release of CH4 throughout the pyrolysis process. The iron component may form an active complex with C=O and a stable complex with C-O, which can promote the fracture of carboxyl functional groups and inhibit the decomposition of ether bonds, phenolic hydroxyl groups, methoxy groups, and other functional groups, thus promoting the decomposition of aromatic structures. At low temperatures, it promotes the decomposition of aliphatic functional groups and finally the bonding and fracture of functional groups in coal, leading to the change of the carbon skeleton, resulting in the change of gas products. However, it did not significantly affect the evolution of -OH, C=O, C=C, and C-H functional groups. According to the above results, a developing reaction mechanism model of Fe-catalyzed lignite pyrolysis was established. Therefore, it is worth doing this work.

Effect of the Iron Component on Microcrystalline Structure Evolution of Hydrochloric Acid-Demineralized Lignite during the Pyrolysis Process.

Hydrochloric acid-demineralized Shengli lignite (SL+) and iron-added lignite (SL+-Fe) were thermally degraded using a fixed-bed device to better understand the effect of the iron component on the microcrystalline structure transformation properties of lignite during the pyrolysis process. The primary gaseous products (CO2, CO, H2, and CH4) were detected by pyrolysis-gas chromatography. X-ray diffraction and Raman spectra were adopted to analyze the microcrystalline structure of lignite and chars. The results indicated that the iron component had a catalysis effect on the pyrolysis of SL+ below 602.6 °C. The pyrolysis gases released in the order of CO2, CO, H2, and CH4, and the addition of the iron component did not change the sequences. The iron component promoted the generation of CO2, CO, and H2 in the low-temperature stage. During the high-temperature stage, the iron component inhibited the formation of CO and H2. The formation of CH4 was inhibited by the iron component throughout the pyrolysis process. The evolution characteristics of -OH, C=O, C=C, and C-H functional groups were not significantly affected, and the fracture of aliphatic functional groups and C-O functional groups was inhibited by the iron component during the pyrolysis process. The iron component restricted the spatial regular arrangement tendency of aromatic rings and facilitated the decrease in the small-sized aromatic ring but inhibited the formation of large aromatic rings (≥6 rings) and the content decrease in side chains during the pyrolysis process. Notably, the effects of the iron component on the formation of gaseous products were associated with the microstructure evolution of lignite.

Effects of Water-Soluble Sodium Compounds on the Microstructure and Combustion Performance of Shengli Lignite.

Different water-soluble sodium compounds (NaCl, Na2CO3, and NaOH) were used to treat Shengli lignite, and the resulting effects on the microstructure and combustion performance of the coal were investigated. The results showed that Na2CO3 and NaOH had a significant impact on combustion performance of lignite, while NaCl did not. The Na2CO3-treated lignite showed two distinct weight-loss temperature regions, and after NaOH treatment, the main combustion peak of the sample moved to the high temperature. This indicates that both Na2CO3 and NaOH can inhibit the combustion of lignite, with the latter showing a greater effect. The FT-IR/XPS results revealed that Na+ interacted with the oxygen-containing functional groups in lignite to form a "-COONa" structure during the Na2CO3 and NaOH treatments. It is deduced that the inhibitory effect on combustion of lignite may be attributed to the stability of the "-COONa" structure, and the relative amount is directly correlated with the inhibitory effect. The XRD/Raman analysis indicated that the stability of the aromatic structure containing "-COOH" increased with the number of "-COONa" structures formed. Additionally, experiments with carboxyl-containing compounds further demonstrated that the number of oxygen-containing functional groups combined with Na was the main reason for the differences in the combustion performance of treated lignite.