Effects of pH, organic acids, and inorganic ions on lead desorption from soils

The desorption characteristics of lead in two variable charge soils (one developed from Arenaceous rock (RAR) and the other derived from Quaternary red earths (REQ)) were studied, and the effects of pH value, organic acid, and competitive ions were examined. Desorption of Pb2+ decreased from nearly 100.0 to 20.0% within pH 1.0–4.0 in both soils, and then the decrease diminished at pH > 4.0. Organic ligands at relatively low concentrations (≤10−3 mol L−1) slightly inhibited Pb2+ desorption, but enhanced Pb2+ desorption at higher concentrations. In this study, citric acid or acetic acid at higher concentrations (>10−3 mol L−1) had the greatest improvement of Pb2+ desorption, followed by malic acid; and the smallest was oxalic acid. Desorption of the adsorbed Pb2+ increased greatly with increasing concentrations of added Cu2+ or Zn2+. Applied Cu2+ increased Pb2+ desorption more than Zn2+ at the same loading.