ACIDIFICATION AND SOLUBILIZATION OF HEAVY-METALS FROM SINGLE AND DUAL-COMPONENT MODEL SOLIDS

The solubilisation of Ni, Cd and Pb from 3 model components of soils a nd sediments is investigated as a function of pH. In presence of incre asing acidity, Ni, Cd and Pb are strongly solubilised from kaolinite a nd amorphous ferric hydroxide. Metal solubility tends to decrease, on the other hand, when humic acid is present. The quantity of metal solu bilised from the dual-component, amorphous ferric hydroxide-humic acid system is smallest in the pH range 3.5 to 5.5. In the system kaolinit e-humic acid, the solubility is highest at neutral pH. In these solid mixtures, metal solubility is always minimal (close to nil) in the pH range between the pH(zpt) of the humic acid and the pH(zpt) of the min eral solid. The solubilisation of heavy metals from soils and sediment s is highly pH-dependent but does not always increase with decreasing pH. The solubility of Cd, Ni and Pb depends not only on pH but also on interactions between soil components. Copyright (C) 1996 Elsevier Sci ence Ltd