Multi-walled carbon nanotube-modified hydrothermal carbon: A potent carbon material for efficient remediation of cadmium-contaminated soil in coal gangue piling site

Coal gangue contains numerous metal ions. After rainwater leaching, the metal ions in coal gangue migrate into the surrounding soil, posing significant threats to human health and ecosystems. To remove Cd from contaminated soil surrounding a coal gangue pile area, loofah, oak chips, and corn stalks were used as raw materials to prepare loofah hydrothermal carbon (LH), oak chip hydrothermal carbon (OH), corn stalk hydrothermal carbon (CH). Next, LH, OH, and CH were modified using multiwalled carbon nanotubes (MWCNTs) to obtain loofah–, oak-chip–, and corn-stalk–MWCNTs hydrothermal carbon composites (LMH, OMH, and CMH). The loofah hydrothermal carbon with excellent pore structure, specific surface area and pore capacity was selected, and the loading of MWCNTs was varied to give it better adsorption performance. The N2 adsorption-desorption experiments showed that the specific surface area and pore volume of LMH, OMH and CMH were significantly higher than those of LH, OH and CH, respectively. The specific surface area and pore volume of LMH are 101.948 m2 g−1 and 6.226 cm3 g−1, respectively. By EDS analysis and infrared spectroscopy, it can be seen that LMH has more o-containing functional groups than OMH and CMH. Remediation experiments were carried out on the actual contaminated soil obtained from Chaili Coal Mine. It was found that the mass fractions of Cd in the acid-soluble state in the soil samples that were treated with LH and LMH decreased by 18.54% and 26.3%, respectively, after 20 d. Therefore, LMH significantly affected Cd fixation and promoted Cd pollution remediation in the coal gangue pile area.