Effects of different straws on heavy metal release and bioavailability in coal gangue

The purpose of this study was to investigate the effects of the addition of rice straw (RIS), corn straw (CS), pepper straw (PS), and rape straw (RAS) on the release and speciation of heavy metals in coal gangue. Results showed that the addition of rape straw and corn straw significantly increased the pH value of the leachate. Straw addition increased the iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), and cadmium (Cd) concentrations in leachate but inhibited the release of lead (Pb) from coal gangue, with RIS having a particularly significant inhibitory effect. Straw addition promoted the transformation of heavy metals from a reducible to an oxidizable state in coal gangue, with significant differences in the impact on exchangeable heavy metals. Rape straw reduced the exchangeable Fe and Mn concentrations, whereas RIS decreased the exchangeable Zn concentration. The results of the RAC risk assessment indicated that by the end of the trials, RAS significantly reduced the ecological risks of Fe, Mn, Cu, Pb, and Cd. In summary, when using straw to remediate and improve coal gangue, dynamic changes in the activity of heavy metals need to be considered, and the use of RAS should be prioritized to avoid potential secondary environmental pollution.