Nickel and copper sorption in acid forest soils

Five acid forest soils of eastern Austria were used to study nickel and cop per sorption at metal concentrations ranging over five orders of magnitude. Distribution coefficients were calculated, and the Langmuir equation was f itted to the experimental isotherm data. Exchange for mono- and divalent cations is considered the primary mechanism of Ni sorption, whereas complexation on organic surfaces may contribute si gnificantly to Cu sorption in the studied soils. Organic matter is consider ed the most effective sorbent in topsoils, while sorption in subsoils may i nvolve primarily Mn-oxide and clay mineral surfaces. The soils studied show ed higher affinity for Cu than for Ni; however, at low metal levels, compet itive complexation of Cu with soluble organic compounds counteracted sorpti on in topsoil horizons. Using the van Bemmelen-Freundlich equation, general sorption density isothe rms were developed for the studied soils. For Ni, similar fits were obtaine d by using specific surface area (SSA) and cation exchange capacity (CEC) a s reference quantities; however, the quality of fit was improved when only the proportion of CEC occupied by mono- and divalent cations (CEC(2+)) was used as a reference. For Cu, the surface area-based approach yielded a bett er fit than the charge-based isotherms. Comparison with independent dataset s from the literature showed good agreement with the proposed general sorpt ion density isotherms, suggesting general applicability for acid soils of v arying origin and composition.