Thermally induced changes in metalloid leachability of cemented paste backfill that contains blast furnace slag

In this research, the effect of curing temperature on the Arsenic (As(III)) leachability of cemented paste backfill (CPB) that contains blast furnace slag (OPC/Slag-CPB) are studied. ASTM C 1308 leaching protocol is adopted to assess the leachability of OPC/Slag-CPB specimens cured at various temperatures (2 degrees C, 20 degrees C and 35 degrees C). Furthermore, various microstructural techniques are used to relate the temperature-induced changes in the microstructural properties of the OPC/Slag-CPBs to their leaching characteristics. The results show that leaching of arsenic from OPC/Slag-CPB is temperature dependent. Higher curing temperature leads to a decrease in the amount of arsenic released from the OPC/Slag-CPB. The As leachability-decreasing factors are: (i) faster cement hydration rate and pozzolanic reaction with higher curing temperatures, which increase the volume of As immobilizing phases (C-S-H, CH, ettringite) in the OPC/Slag-CPB; (ii) lower volume of connective pores (smaller connective pore surface area) with higher curing temperatures, which decreases the area of reaction sites, thereby reducing the mobility of arsenic. Leaching of As from OPC/Slag-CPBs is dominated by diffusion, irrespective of the curing temperature. Results also reveal that CPBs with ordinary Portland cement (OPC) leach significantly less than CPBs with OPC and Slag (50/50) for all curing temperatures. However, curing temperature has the opposite effect on the OPC/Slag-CPBs compared to OPC-CPBs. OPC is suggested as a binder in situations where the principal design parameter is immobilizing As(III) in CPB subjected to various thermal curing conditions. The results indicate that curing temperature is a critical variable to consider when assessing the ability of CPB structures to release arsenic into the underground environment.