Copper slag flotation tailings as fine aggregate in cement mortars

Abstract

Copper slag flotation tailings (CSFW) are a secondary residue generated during hydrometallurgical copper recovery from smelting slag. At the Manuel Antonio Matta Plant of Empresa Nacional de Minería (ENAMI), Copiapó, Chile, approximately 65,000 t/month are deposited in tailings impoundments. This study evaluated CSFW as a partial replacement for normalised river sand in cement mortars (1:3 mass ratio) at substitution levels of 0, 5, 10, 15, 20, 25, 50 and 75%, tested at 7, 28 and 90 days. Prismatic specimens (40 × 40 × 160 mm) were evaluated for consistency, hardened density, flexural strength and compressive strength. One-way analysis of variance (ANOVA) and Tukey HSD post-hoc tests (α = 0.05) were applied to compressive strength data. CSFW exhibited predominantly crystalline mineralogy (hedenbergite, magnetite, fayalite, albite), real dry density of 3,76 kg/m³ and water absorption of 1.71%. Fresh mortar consistency decreased progressively with CSFW content, while hardened density increased proportionally. The CSFW 25% mix achieved the highest compressive strength at all ages, 44.17 ± 0.83 MPa at 28 days, 22.9% above control (p < 0.05), and the highest flexural strength (7.89 ± 0.35 MPa at 28 days, +7.6%). The strength enhancement is attributed to physical densification of the cement matrix by the fine, high-density CSFW particles, not to pozzolanic reactivity.