Solidification/stabilization and leaching behavior of heavy metals in low-binder cemented tailings backfill

Considering the high consumption and cost of tailings cemented backfill materials and the risk of groundwater pollution due to heavy metal ion leaching from tailings, four groups of cement and tailings in different proportions were used to prepare low-binder cemented backfill materials. These developed specimens were are immersed in varying pH values, and the speciation distribution of heavy metals and microstructural attributes were evaluated. The results indicate that heavy metal content in tailings water was in the order of Zn > Pb > Cu > Ni. The compressive strength of low-binder cemented tailings backfill with a ratio ranging from 1:15-1:30 was the highest in an alkaline environment and was found as 1.68 MPa, 1.47 MPa, 0.95 MPa, and 0.72 MPa, respectively. Soluble heavy metals in tailings can be transformed into other forms over time. The proportion of available heavy metals of Zn was as high as 53.8 %. With the increase in soaking time, the rate of heavy metal leaching gradually slows down. At pH = 4 and after 60 days, Cu and Zn leaching amounts reached 18.016 mg/L and 14.115 mg/L, respectively. SEM and XRD analyses confirmed that hydration products enhance the strength of low-binder cemented tailings backfill and solidify heavy metal ions through various mechanisms such as adsorption, precipitation, and ion exchange.