Groundwater environmental assessment of cemented backfill prepared from decyanidated tailings: evidence from 30-day static immersion tests

Decyanidated tailings are increasingly used as aggregates for underground cemented backfill, but their potential effects on groundwater quality remain uncertain. In this study, cemented backfill samples prepared from decyanidated tailings from Suichang Gold Mine were subjected to 30-day static immersion tests in groundwater. A groundwater blank and an uncemented decyanidated tailings control were included to identify the baseline contribution of the immersion medium and evaluate the effect of cementation. Selected indicators, including pH, CN⁻, F⁻, Hg, and metal elements, were analyzed and classified according to GB/T 14848–2017, and a fuzzy comprehensive evaluation was used to characterize the integrated water-quality membership of the cemented backfill leachates. The groundwater blank showed near-neutral pH and relatively low background concentrations. The uncemented tailings control was classified as Category IV, mainly controlled by Pb, Cr, and Be. Compared with this control, the cemented backfill leachates showed reduced leaching of selected metals and CN⁻, indicating that cementation reduced the release of some components under the tested conditions. However, cementation also increased leachate alkalinity. The high-strength backfill leachate was classified as Category V, mainly controlled by pH, while the low-strength leachate was classified as Category IV, mainly controlled by pH and Pb. Therefore, the groundwater impact of decyanidated tailings backfill cannot be considered negligible under 30-day static immersion conditions, and longer-term flow-through tests and field monitoring are required.