IntraPD model: Leaching of heavy metals from naturally contaminated soils

This paper presents a novel method for predicting the migration of heavy metal contaminants in soils that contain heavy metal pollutants deep within the particles, which may cause delayed leaching. The proposed approach, the intraparticle pore-diffusion (IntraPD) model, incorporates both intraparticle diffusion and sorption equilibrium and is utilized to simulate batch leaching tests of heavy metal-contaminated soils using the finite difference method. The IntraPD model can solve the leakage of heavy metals from contaminated soil particles of arbitrary particle size distribution as a one-dimensional, polar-symmetric problem in the spherical coordinate system, assuming the soil particles to be porous perfect spheres. The findings from the simulation demonstrate a notable impact of soil particle size distribution on both the leaching rate and the amount of contaminants. Specifically, the coefficient of uniformity, which indicates the ratio of the maximum to minimum particle size, was identified as a significant factor influencing the leaching rate. When the coefficient of uniformity is less than or equal to 5, it has a combined effect on the leaching rate. However, when the coefficient of uniformity exceeds 5, the maximum particle size becomes the primary determinant of the leaching rate. The proposed model pro-vides a valuable tool for accurately simulating batch leaching tests of naturally contaminated soils with diverse particle size distributions.