Alkali-activated copper tailings-based pastes: compressive strength and microstructural characterization

Abstract

Alkali-activated copper tailings based-pastes (AACTP) were synthesized using 90 wt% copper tailings and 10 wt% coal fly ash as the precursors, and water glass with sodium hydroxide as the alkaline activator. The effects of the formation pressure, the liquid/solid mass ratio of water to precursor materials, and the partial substitution of CaO for NaOH as the alkaline activator were investigated. The highest compressive strength of 40.9 MPa was obtained using a formation pressure of 20 MPa, a liquid/solid of 0.15, and a substitution of 20% CaO for NaOH as the alkaline activator. The characterization using a Mercury Intrusion Porosimeter (MIP) indicated that the formation pressure affected the pore structure, as well as the amount of the gel formed. XRD, FTIR, SEM and 29Si NMR showed that a 20% CaO substitution for NaOH promoted the dissolution of raw materials and led to more [AlO4]− being incorporated into the tetrahedron [SiO4] backbone. Additionally, the gel formed in the AACTP was predominantly a N-A-S-H gel. Partial substitution of CaO for NaOH as alkaline activator did not lead to the formation of a C-S-H gel.

Keywords

• Alkaline activation
• Copper tailings
• Formation pressure
• Compressive strength
• Microstructure