High-pressure impregnation and thermal stabilization of pine bark for reuse-oriented textile effluent polishing

Dyes are widely used in the textile industry, and untreated dye-containing effluents pose major environmental risks. This study investigates pine bark (Pinus pinaster), a timber by-product, as a low-cost biosorbent for dye removal. Powdered and granular bark was impregnated with 10% (w/w) iron using Incipient Wetness Impregnation with sonication or High-Pressure Impregnation (HPI) at 75–300 MPa, followed by thermal treatment at 400 °C under nitrogen and hydrogen. Adsorption tests with a synthetic dye mixture (80 mg/L) showed that HPI at 150 MPa provided the best performance, achieving over 90% color removal with no iron leaching. Thermal treatment enhanced iron fixation and adsorption, producing the most effective material (G1FeTT). With real textile effluent, G1FeTT (5.0 g/L) achieved 83.5% dye removal with equilibrium at 16 h (2.12 mg/g). The Elovich model best described the kinetics. Treated effluent reuse in dyeing baths was feasible, enabling 25–75% freshwater substitution while maintaining acceptable color metrics.