Soil Column Breakthrough: pH-Retarded Heavy Metal Transport

The 3D particle view of heavy-metal sorption shows why pH controls how much lead, cadmium or zinc stays bound to soil colloids — this 2D companion shows what that chemistry does over depth and time to a real soil profile. A finite-difference solver advances a retarded advection–dispersion equation down a one-dimensional soil column: a contamination pulse infiltrates from the surface, and the same pH-dependent partition coefficient K_d that governs the particle exchange here sets a single retardation factor R that slows the whole plume's descent toward the water table. Tune pH, cation-exchange capacity and infiltration rate to watch the front's speed change in real time, and read the live K_d(pH) isotherm and breakthrough curve — the two plots a real contaminated-site investigation would actually produce.