Effect of sulfate erosion on strength and leaching characteristic of stabilized heavy metal contaminated red clay

Solidification/stabilization (S/S) technology has been widely used for remediation of the heavy metal contaminated soils. The heavy metal ions will be leached from the stabilized contaminated soil under sulfate erosion conditions, which gives rise to secondary contamination to the areas around the mine sites. The commonly used Portland cement, fly ash and quicklime were taken as binder raw materials with various mix proportions. And then, the sulphuric acid and nitric acid method was used to investigate the leaching characteristic of stabilized heavy metal contaminated soils. The effects of binder types and binder contents, sulfate concentrations (1.5, 3.0 and 6.0 g/L) and erosion time (0, 7, 14 and 28 d) on leached concentrations of heavy metal ions from contaminated soils were studied. Moreover, a parameter named immobilization percentage (IP) was introduced to evaluate the influence of erosion time and sulfate concentration on immobilization effectiveness for heavy metal ions. The results showed that, the leached heavy metal concentrations increased with sulfate concentration and erosion time. Comparatively speaking, the composite binders that had calcium oxide in it exhibited the worst solidification effectiveness and the lowest immobilization percentage, with the largest leached heavy metal concentration.