Biofuel ash (BFA), which is the ash generated by biomass combustion in a biomass power plant, can be prepared as a heavy metal immobilizer and have a good immobilization effect on Cd in the soil environment of southern China, but the long-term effects of BFA on Cd immobilization remained unclear. Therefore, research about BFA aging and its influence on Cd immobilization was conducted in the paper. BFA was naturally aged into BFA-Natural aging (BFA-N) in the soil environment of southern China, and to simulate BFA-N, BFA was also artificially acid aged into BFA-Acid aging (BFA-A). The result indicated that BFA-A could partially simulate BFA-N in physicochemical properties. The Cd adsorption capacity of BFA reduced after natural aging and the decrease was more obvious in BFA-A according to $Q_m$ in Langmuir equation and $q_e$ from the pseudo-second-order kinetic model. The adsorption processes of BFA before and after aging were mainly controlled by chemical action rather than physical transport. The immobilization of Cd included adsorption and precipitation, and adsorption was the dominant factor; the precipitation proportion was only 12.3%, 18.8%, and 1.7% of BFA, BFA-N, and BFA-A, respectively. Compared with BFA, both BFA-N and BFA-A showed Ca loss, and BFA-A was more obvious than BFA-N. Ca content level was consistent with Cd adsorption level among BFA, BFA-N, and BFA-A. It could be inferred that the main immobilization mechanism of Cd by BFA before and after aging was consistent and closely related to Ca. However, the adsorption mechanism of electrostatic interaction, ion exchange, and hydroxyl complexation changed to varying degrees in BFA-N and BFA-A.

The serious shortages and destruction of groundwater resources caused by coal mining, especially group mining, is a major hurdle for the sustainable development of the mining economy, resource management, and preserving the environment that urgently needs to be addressed. Large efforts have been made to protect the groundwater resources affected by coal mining but they have had little effect. The difficulty and uncertainty in investigating the structural changes in roof strata and the relationship between the roof rock fissure formation rate and hydraulic conductivity are the main obstacles hindering the investigation, assessment and management of groundwater resources in roof strata. In this study, we tackled this problem by performing water injection tests in ground surface boreholes and underground boreholes in the roof strata, and pumping tests in wells over the goaf. Clear differences in hydraulic conductivity changes in the collapsed roof strata were observed. These observations provide valuable information on changes in groundwater flow and the distribution of collapsed and fissured zones. The pumping tests also revealed an increase in hydraulic conductivity in the subsidence basin of Quaternary deposits over the goaf. This increased hydraulic conductivity is useful for the assessment of groundwater resources and the prediction of single-well water yields.