3D-Printed phosphoric acid-activated metakaolin-based geopolymers for acid mine drainage remediation

This study investigates a 3D-printed phosphoric acid-based geopolymer (PAGP) for remediation of real acid mine drainage (AMD). Lattice structures were fabricated by direct ink writing (DIW) from metakaolin and phosphoric acid. Laponite was added as a rheological agent to ensure shape retention, and a non-ionic triblock copolymer (poloxamer-type surfactant) was used to improve printability and promote macropore formation. Among the formulations, 0.7 wt% triblock copolymer provided the best rheological balance, combining high viscosity at rest with fast thixotropic recovery. The printed PAGP exhibited high total porosity (∼45 vol%) and compressive strength of 13.72 ± 0.33 MPa. However, the BET specific surface area remained low (4.89 m 2 g −1 ), consistent with negligible micro/mesoporosity despite the macroporous architecture. Remediation was assessed in batch and recirculating fixed-bed tests using raw and pre-neutralized AMD. Rather than a monotonic adsorption-controlled decrease in metals, concentration profiles were dominated by solid–liquid re-equilibration, including sorbent-induced acidification and magnesium release attributed to laponite instability under highly acidic, multicomponent conditions. Overall, the results show that DIW can produce robust, highly porous PAGP architectures, but additive stability and solution conditioning effects must be controlled for practical mining-water treatment applications. • Laponite ensures rheological stability for 3D printing phosphoric acid geopolymers. • Pluronic F-127 acts as a macropore-creating agent, optimizing also ink printability. • 3D-printed lattices possessed 45 vol% total porosity and 13.72 ± 0.33 MPa compressive strength. • Laponite instability in acidic AMD leads to undesirable magnesium leaching. • Low surface area and sorbent acidification limit metal removal from real AMD.