Release and speciation transformation patterns of mercury in soil from an abandoned gold mine in Fujian Province under simulated acid rain conditions

To investigate the effect of simulated acid rain on the release process and speciation of heavy metal mercury(Hg) in contaminated soil,this study used mercury-contaminated soil from an abandoned gold mine in Fujian Province as the research object.Static release experiments and the modified Tessier sequential extraction method were employed to study the release of soil mercury and its transformation among different fractions under simulated acid rain conditions.The results showed that the release of mercury from the soil consisted of two stages:a rapid release stage and a slow release stage.The release kinetics of soil mercury could be well described by multiple kinetic equations,among which the Elovich equation provided the best fit,indicating that the release process approximates a heterogeneous diffusion process.During the release process,with increasing time,the concentration of exchangeable mercury gradually increased,while the concentration of Fe-Mn oxide-bound mercury showed a significant decreasing trend.The concentration of carbonate-bound mercury exhibited a certain degree of fluctuation,and the concentrations of organic-bound mercury and residual mercury decreased slowly,though only to a small extent.The high-risk window period for mercury release and the differences in environmental stability among various mercury speciation were clarified.The research results provide a scientific basis for ecological risk early warning,pollution control,and remediation of legacy mercury-contaminated sites in gold mines in southern China,where acid rain is frequent.