Slag-based stabilization/solidification of hazardous arsenic-bearing tailings as cemented paste backfill: Strength and arsenic immobilization assessment

The widespread occurrence of toxic arsenic in sulfidic and non-ferrous waste tailings hinders its disposal as cement paste backfill (CPB). Alkali activated slag (AAS) has recently begun to be practiced as an alternative to normal Portland cement (OPC). Nevertheless, technical information on arsenic immobilization and mechanical characteristics of arsenic-rich AAS-CPB is rather few. The impacts of activator nature, cure temperature and arsenic content on strength and arsenic immobilization of AAS-CPB explored. Despite AAS-CPB having greater strength, OPC-CPB consistently has a stronger (1.7–21.1% higher) ability to immobilize arsenic. The optimum silica modulus for maximal strength and arsenic immobilization capability depends on curing time. Strength at3 days is enhanced by higher activator doses, whereas strength at later ages (≥ 28 days) is decreased. At all curing ages, the lowest arsenic immobilization capacity is produced by medium activator concentration (0.35). Irrespective of cement type, strength increases as curing temperature rose, however OPC-CPB's strength is more responsive to temperature changes than AAS-CPB's. At room temperature (20°C), OPC-CPB has a higher (6.0–21.1% greater) arsenic immobilization efficiency (AIE) than AAS-CPB, but the opposite is true at lower (5°C) and higher (35°C) temperatures (i.e., 5.4–12.0% and 4.4–12.0% lower at 5 and 35°C respectively). Early on, the influence of arsenic content on strength is not immediately apparent, but it tends to become more obvious with longer curing times. As a role of cement type and elapsed time, high arsenic contents cause a rise or a decrease in AIE. Notably, there is no apparent connection between UCS and AIE. Electrical conductivity and moisture content can be steadily employed to portray the hydration progression of both arsenic-free and arsenic-containing CPB.