Paste backfill of high-sulphide mill tailings using alkali-activated blast furnace slag: Effect of activator nature, concentration and slag properties

• Published in: Minerals engineering 2015-11, Vol.83, p.117-127
• Main Authors: Cihangir, Ferdi, Ercikdi, Bayram, Kesimal, Ayhan, Deveci, Haci, Erdemir, Fatih
• Format: Article
• Language: English
• Subjects: A. Alkali-activated slag; B. Activator nature; C. Activator concentration; D. Slag composition; E. Paste backfill; F. Pozzolanic activity
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/j.mineng.2015.08.022

•Activator nature and concentration, and slag type affect the mechanical performance of CPB.•High concentrations resulted in loose structure in sodium hydroxide (SH) samples.•Drying shrinkage cracks occurred at high SH concentrations in neutral slag (NS) samples.•A reduction in total porosity up to 20% can be obtained based on AAS design for CPB.•Amorphousness and chemical composition of the slag control the alkali-activation and hardening process. The effect of activator type, concentration and slag composition on the strength and stability properties of paste backfill (CPB) of high-sulphide tailings using alkali-activated slag (AAS) as binder (7wt.%) were investigated in this study. Acidic and neutral (AS–NS) slags were activated with liquid sodium silicate (LSS) and sodium hydroxide (SH) at 6–10wt.% concentrations. Ordinary Portland cement (OPC) results were used for comparison. The strength development was found to remarkably improve with increasing the concentration from 6 to 8wt.%. Further increase in concentration did not enhance the strength. SH was determined to produce higher early-age strength whilst LSS produced higher long-term strengths as an indication of slag selectivity for activators. More extensive gypsum formation was observed at lower concentrations in SEM/EDS studies. An increase in Na2O concentration raised the activator consumption. High concentrations also led to poorly crystallized C–S–H gel, loose structure and drying shrinkage cracks especially in NS–SH samples. A reduction in total porosity up to 20% was obtained in AAS samples compared to OPC. Amorphous structure, chemical modulus ratio and/or basicity index (BI) values were seen to control the pozzolanic reactivity, and therefore, the alkali-activation and hardening process.