TEA-modified anthill clay for tannery wastewater treatment: COD and BOD adsorption

Existing wastewater treatment methods often struggle to achieve slow, ineffective removal of complex organics, such as biochemical oxygen demand (BOD) and chemical oxygen demand (COD), particularly in challenging industrial applications, such as tannery wastewater treatment. Triethanolamine (TEA)-functionalized anthill clay was prepared as an effective adsorbent for the removal of BOD and COD from tannery wastewater. Raw anthill clay was purified by sedimentation, then subjected to acid activation and TEA functionalization. X-ray diffraction (XRD) analysis confirmed the retention of the aluminosilicate structure, while Fourier transform infrared (FTIR) spectra confirmed the incorporation of the amine functions through the formation of C-N and N-H bonds. Scanning electron microscope (SEM) images showed increased surface roughness, and Brunauer-Emmett-Teller (BET) surface area analysis indicated a high surface area (SBET = 138.34 m²/g) with retention of mesoporous characteristics. Thermogravimetric Analysis (TGA) revealed enhanced thermal stability of the modified clay. Batch studies demonstrated rapid uptake, reaching equilibrium within 60 min, with removal efficiencies of 95.82% for BOD and 96.98% for COD at the optimal dosage. There was an increase in removal capacity with rising temperature, indicating an endothermic nature. Sorption saturation capacities using the Langmuir model resulted in 125.07 mg/g (BOD) with 131.29 mg/g (COD), while the pseudo-second-order kinetics model (R²> 0.999) suggested the occurrence of chemisorption. Thermodynamic studies unveiled spontaneity with the enhancement of entropy. TEA-functionalized clay maintained > 50% removal capacity after six consecutive regeneration cycles, establishing its potency in the regeneration process.