This study investigates the extrusion-based 3D printing response of hybrid geopolymer-cement mortars formulated with copper mine tailings and silt as alternative raw materials. A Taguchi design was employed to evaluate the effects of extrusion pressure, nozzle diameter-to-layer height (ND/LH) ratio, and print speed under varying Z-Max settings on print quality, dimensional accuracy, and defect formation. Twenty-seven experimental runs using a hollow cylindrical geometry were conducted, with both qualitative and quantitative assessments of surface finish, layer consistency, and dimensional errors. Results showed that a Z-Max setting of 413 mm yielded the highest print success rate, while settings between 412.7 and 412.9 mm led to frequent failures due to over-extrusion, under-extrusion, and poor interlayer adhesion. The ND/LH ratio was identified as the most statistically significant factor, strongly affecting total height (p = 0.000) and outer diameter (p = 0.002), whereas extrusion pressure had minimal influence. Best parameters for height and dimensional accuracy were 2.5 bar pressure, a 4:1 ND/LH ratio, and 20 mm/s print speed. For improved inner and outer diameter control, 2 bar pressure, a 2:1 ND/LH ratio, and 15 mm/s proved more effective. A demonstration block printed using the best-performing settings confirmed the influence of path design on geometric fidelity. Notable defects such as edge curvature, center voids, and inconsistent layering underscore the importance of refined path coding. In summary, the findings support the viability of mine tailings and silt in 3D-printable construction applications and highlight the critical role of process parameter optimization in achieving geometric precision.

Mine waste remains a persistent challenge for the minerals industry, posing significant environmental concerns if not properly managed. The 1996 Marcopper mining disaster in Marinduque, Philippines, left a legacy of mine tailings that continue to threaten local ecosystems and communities. This study investigates the valorization and stabilization of Marcopper river sediments contaminated with mine tailings using a combined geopolymerization and cement hydration approach. Hybrid mortar samples were prepared with 7.5%, 15%, 22.5%, and 30% mine tailings by weight, incorporating potassium hydroxide (KOH) at 1M and 3M concentrations as alkaline activators, along with ordinary Portland cement (OPC). The mechanical properties of the hybrid geopolymer-cement mortars were evaluated through unconfined compressive strength tests, while their crystalline structure, phase composition, surface morphology, and chemical bonding characteristics were also analyzed. Static leaching tests were conducted to assess the mobility of heavy metals within the geopolymer matrix. Compressive strengths ranged from 24.22 MPa to 53.99 MPa, satisfying ASTM C150 requirements. In addition, leaching results confirmed effective heavy metal encapsulation and immobilization, demonstrating the potential of this method for mitigating environmental risks associated with mine tailings.