This paper is the result of mineral exploration engineering.

Objective To investigate soil quality degradation and heavy metal pollution triggered by coal mining, this study selected the coal mining aggregation areas of Yijinhuoluo Banner as the research site.

Methods Surface and profile soil samples were collected to analyze variations in soil physicochemical properties under different land use types and mining conditions. The geochemical fractions of heavy metals were determined using the modified BCR sequential extraction method. Multivariate statistical analysis and structural equation modeling were employed to further explore the environmental drivers influencing heavy metal accumulation patterns and their bioavailability.

Results The findings indicate that: the soils in the study area were generally alkaline and sandy, with significant pollution from Cd, Pb, and Hg. The total heavy metal concentrations across different land-use types followed the order: forestland > farmland > bare land > grassland > building land. Coal mining subsidence reduced surface soil water content (WC), total nitrogen (TN), and soil organic matter (SOM) content. Cd was predominantly present in the acid-soluble fraction (43%), indicating high bioavailability, whereas Pb and Cr were primarily in the residual fraction (>50%), suggesting lower ecological risk. In farmland soils, the proportions of acid-soluble (F1) Cd and As and reducible (F3) Hg were significantly elevated. The F1 fraction showed a highly significant positive correlation with WC and SOM of soil, while the F3 fraction was significantly negatively correlated with pH, electrical conductivity (EC), and total phosphorus (TP). Precipitation, air temperature, elevation, and soil physicochemical properties were key factors influencing the content and bioavailability of heavy metals. Among these, soil physicochemical properties dominate source-sink dynamics through adsorption-desorption processes, whereas meteorological factors indirectly regulated migration and morphological transformations via physical transport, chemical conversion, and topographic effects.

Conclusions Mining subsidence intensifies water-gas interactions in the unsaturated zone, potentially causing neutralization shifts in weakly alkaline soil backgrounds. This process may lead to soil moisture loss, fertility decline, and heavy metal contamination with speciation transformation, thereby posing threats to human health and the ecological environment.