Investigation of gold mine tailings as supplementary cementitious material: Performance and carbon footprint

Abstract

This study investigates the potential of using gold mining tailing sludge to produce low-carbon mortar through physical grinding and calcination treatments. Tailing sludge was ground for 20 min to produce tailing powder (WKN), which was then calcined at 750 °C to obtain calcined tailing powder (CWKN). The effects of substituting cement with WKN and CWKN on the workability, strength, and durability of mortar were evaluated. Results show the density of mortar decreases with increase of tailing substitution rate. The CWKN-based mortar requires higher water demand (additional superplasticizer was used to ensure similar flowability) and increase the density of mortar at fresh state compared to the WKN-based mortar. Using WKN significantly reduces the compressive strength of mortar after 28 days (with a 43.9 % drop at 30 % replacement). In contrast, CWKN exhibits pozzolanic activity, with only a 9 % strength reduction at 20 % substitution compared with the reference one (a 34.4 % strength improvement over the case of WKN). CWKN-based mortar has a higher electric flux and carbonation depth, which is due to higher reactivity of CWKN than that of WKN. Life cycle assessment indicates that 30 % WKN reduces CO₂ emissions by 156.7 kg/m³, while 20 % CWKN achieves the best unit strength carbon emission, reducing emissions by 1.05 kg CO₂-eq./m³/MPa compared to pure cement-based mortar. The study highlights that the aluminum content in mortar significantly affects its properties, which is due to the formation of calcium-aluminate-silicate-hydrate gels. This study demonstrates that recycling gold tailings sludge can effectively address industrial waste issues while significantly reducing carbon emissions of mortars.