Nitrate ions constitute one of the major nitrogen resources for plant growth. However, the large amount of nitrate ions released into nearby waterbodies could cause eutrophication problems. This study developed a bio-based adsorbent from biowaste materials and functionalized it with amine groups through the Mannich reaction. The successful modification was confirmed using FTIR, SEM, and elemental analysis. Batch adsorption experiments were conducted under varying conditions, including contact time, pH, and initial nitrate concentration. Results showed that the amine-functionalized bio-adsorbent exhibited an enhanced capacity for nitrate removal, with a maximum adsorption capacity of 65.79 mg g⁻¹. Electrostatic interactions between amine-functionalized bio-adsorbent and nitrate ions were identified as the dominant sorption mechanism. These findings highlight the potential of this bio-based adsorbent as a sustainable and effective solution for nitrate removal from contaminated water sources.

In this study, to address the overlying strata control issue for the isolated working face of a super-thick coal seam confined by surrounding goafs and open-pit boundaries, we focus on mining via upward slicing strip paste filling in a Ningxia coal mine. We adopt strip coal pillar stability theory for safety factor analysis and conduct FLAC3D three-dimensional numerical simulations to quantitatively reveal overlying strata displacement, stress redistribution, plastic zone evolution, and surface subsidence response. Our theoretical calculations show that, when the mining width is 5 m, the safety factors of retained coal pillars with widths of 5, 10, and 15 m are <1, 1.3, and 1.8, respectively. Our numerical results indicate that the overlying strata of the first slice are dominated by continuous bending subsidence, with a maximum vertical displacement of 21.4 cm, increasing to 55.5 cm after four slices without through damage. High stress is mainly controlled by mined-out area boundaries and inter-face coal pillars, with the maximum principal stress of the fourth slice reaching 18.9 MPa. The surface subsidence center stably corresponds to the underlying backfill goaf, with a maximum value of 11.4 cm. Our research demonstrates that slicing strip filling can suppress deformation and stress concentration risks by reconstructing load transfer and realizing synergistic bearing, as reflected by the limited surface subsidence of 11.4 cm, the controlled maximum principal stress of 18.9 MPa, and the improved coal pillar safety factor from <1 to 1.3–1.8 under wider retained pillars, providing a basis for optimizing strip pillar width and mining–filling parameters.