Reuse-oriented treatment of textile effluents requires polishing processes that remove residual colour without introducing secondary contamination or compromising downstream dyeing quality. In this study, pine bark, a forestry by-product, was converted into iron-functionalized materials for the polishing of textile wastewater and subsequent process-water reuse. Two impregnation routes, incipient wetness impregnation and high-pressure impregnation, were compared for loading 10 wt% Fe onto pine bark, followed by thermal stabilization under N₂/H₂ atmosphere to improve iron retention.Synthetic dye mixtures were first used as controlled screening systems, while real textile effluent was used to assess treatment performance under industrially relevant matrix conditions. High-pressure impregnation improved iron retention compared with incipient wetness impregnation; however, tests with real effluent showed that non-stabilized materials could release iron and operate partly through coagulation-assisted colour removal. Thermal treatment suppressed detectable iron release and identified the material prepared from granular pine bark by high-pressure impregnation at 150 MPa for 5 min as the best compromise between colour removal, iron stability, and treated-water quality.At an adsorbent dosage of 5.0 g/L, the optimized material achieved 83.5% colour removal from real textile wastewater after 24 h, with final colour below the reuse threshold defined for dyeing applications. Kinetic data were best described by the Elovich model, consistent with heterogeneous adsorption behaviour in a complex effluent matrix. Reuse trials showed that the treated effluent could replace up to 75% and 25% of freshwater in light-colour and dark-colour dyeing while maintaining acceptable colour quality and suggesting that forestry residues may serve as materials for wastewater polishing under the tested conditions. Adsorbent lifetime and fixed-bed operation were not established.
Calcium-based precipitation is widely used for treating concentrated fluoride wastewater, but rapid homogeneous nucleation often generates fine CaF2particles that are difficult to recover. In this study, a silica-supported Fe3O4-NH2/UiO-66 composite was developed as a magnetically recoverable crystallization seed for directing CaF2 formation. At an initial fluoride concentration of 2000 mg/L, a Ca:F molar ratio of 0.8:1, 0.5 g seed dosage, pH 7-8, and 25 degrees C reduced residual fluoride to 2.56 mg/L, corresponding to 99.87% removal. Ca2+-free tests yielded equilibrium fluoride uptakes of 570 and 755 mg/g for UiO-66 and the composite, respectively, indicating that adsorption contributed to interfacial enrichment but was insufficient to account for the high fluoride conversion after Ca2+ addition. Thermodynamic analysis showed that the initial saturation index increased from 3.1 to 7.5 and relative supersaturation from 28.9 to 288 as the initial fluoride concentration increased from 250 to 2000 mg/L. The crystallization rate followed a supersaturation-dependent power law with a kinetic exponent of 2.146 (R2 = 0.993). After 8 cycles, fluoride-removal and magnetic-recovery efficiencies remained at 80.09% and 80.50%, respectively. In actual industrial wastewater, 98.82% fluoride removal was achieved after pH adjustment to 7. These results demonstrate the potential of Fe3O4-NH2/UiO-66/SiO2 as a reusable crystallization seed for fluoride recovery.
