HEAVY-METAL RELEASE FROM A SERPENTINE SOIL USING A PH-STAT TECHNIQUE

Serpentine soils show high contents of Cr and Ni. Acidification may co nvert the metals bound in silicate structures into bioavailable forms. The effects of mineral acids on a serpentine-derived Typic Hapludoll were examined in column studies. Cadmium and Pb were also examined. On e end of the soil-packed column was placed in 1 mM HCl solution and co nstant pH was maintained by pumping the acid through a H-saturated cat ion-exchange resin. The experiment was conducted for 100 d, after whic h the soil column was vertically sectioned. Chemical and mineralogical analyses showed steep vertical gradients in the sectioned columns. Ba se saturation decreased by about 60% at the contact of the column with the acid; exchangeable Fe, Cr, Pb, and Al increased while Ni decrease d. Cadmium exhibited a differential behavior in that it increased in c oncentration in the middle of the column. Extracts using ethylenediami netetraacetic acid (EDTA) gave similar results. X-ray diffraction indi cated chlorite dissolution by acid loading. The resin-based pH-stat te chnique is a useful method in simulating soil weathering.