Curing temperature dependency of the release of arsenic from cemented paste backfill made with Portland cement

In this research, the effect of curing temperature on the metalloid (As) leachability of cemented paste backfill (CPB; a mix of tailings, cement and water) is studied. ASTM C 1308 leaching protocol is used to determine the leachability of CPB samples subjected to different curing temperatures (2, 20 and 35 °C). In addition, the effect of curing temperature on the microstructure of CPB is assessed to determine if the temperature dependence of the leaching characteristics of CPB is related to variations in the microstructure of the cement matrix. The microstructural techniques used include, powder x-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy techniques. The results obtained indicate that the curing temperature has a significant effect on the leachability of CPB. It is found that as curing temperature increased from 2 °C to 35 °C the performance of the CPB for arsenic immobilization decreased. The magnitude of this temperature-induced change in As-leachability of CPB depends on the curing temperature range (low (≤20 °C) or elevated (35 °C) temperatures). This curing temperature dependency of the leachability of CPB is attributable to the temperature-induced changes in the pore structure of CPB, formation/development of hydration products and pH in the CPBs during the curing process. The results also indicate that diffusion dominates as the leaching mechanism through the studied temperature range and is independent of curing temperature. However, curing temperature does control the availability for arsenic to leach. The new findings presented in this paper will contribute to design more environmental-friendly cemented paste backfill materials and structures, which is vital for sustainable mining.