SOLID-PHASE SPECIATION AND SURFACE ASSOCIATION OF METALS IN SERPENTINITIC SOILS

Serpentinitic soils are of great ecological and environmental interest , yet pedologic studies of such soils are relatively rare, particularl y concerning heavy metal solid-phase speciation. This study examined t he surface association and solid-phase speciation of metals, the miner alogy and the surface chemistry of serpentinitic soils. Surface associ ation and solid-phase speciation were assessed by selective wet chemic al methods. Mineralogy was determined by X-ray diffraction and surface chemistry by potentiometric titration. The morphology of clay mineral s was studied by transmission electron microscopy. Surface-associated metals were divided into exchangeable and nonexchangeable fractions. A dsorbed Mg and Ca were predominantly in exchangeable form. More than 1 0% of adsorbed Mn and Ni were present in exchangeable form, but genera lly <1% of adsorbed Al and Fe were exchangeable. Serpentine and Fe oxi des were the major soil mineral components, along with lesser amounts of quartz, whereas gibbsite and smectite were not detected. Iron oxide s contained more than 10 mole-% of non-Fe elements (Al, Cr, Ni, and Si ). The soils also contained Mn oxides that appeared to incorporate Co and Ni.