Ageing of Pb in Farmland Soil near an Ionic Rare Earth Mine

The total concentration of heavy metals can effectively reflect the enrichment of heavy metal contaminants in a soil environment; however, their bioavailability and environmental toxicity are more influenced by the distribution of their elemental forms. In this study, the farmland soil around an ionic rare earth mining area in the Jiangxi province was used as the research object. Indoor culture was used as the experimental method to explore the transformation and ageing process of exogenous Pb species in the short term after entering the soil environment, and a variety of kinetic models were used. The aim of this study was to provide a basis for environmental behaviour and pollution risk assessment of Pb-contaminated soil. The results showed that in the short term (60 d), the ageing of heavy metals was mainly reflected by a conversion from the mild acid-soluble fraction to reducible fraction. At the initial experimental stage (10 d), the mild acid-soluble fraction was rapidly converted into the reducible fraction, and the conversion rate then gradually reduced, and finally tended to equilibrium. The Elovich equation showed the best fit for the ageing of heavy metals in the soil environment in the short term, which indicates that the ageing is a heterogeneous dispersion process.