Chemical forms and sorption of copper and zinc in soils of central Chile

Abstract

Soil samples from a field irrigated with untreated industrial and municipal wastewater for several decades and from a field not receiving wastewater (control) were analyzed for total copper (Cu) and zinc (Zn) and for the amount of these elements removed in sequential extractions with MgCl2, NaOAc, NH2OH . HCl, 6H(2)O(2)-HNO3-NH4OAc, and HNO3-HF-HCl. Organically-bound Cu forms predominated in the wastewater-affected soil while in the control soil both residual and organic forms yielded the same proportion of Cu. Distribution of Zn was different in the diverse fractions, and in the polluted soil the reducible and the residual forms predominated while in the control soil the residual form accounted for the highest proportion of recovered Zn. Sequential extraction of Cu from a copper sulfate-treated soil incubated for 32 days at constant temperature resulted in the same proportional distribution of Cu forms in the polluted soil. In the control soil the oxidizable form decreased and the residual one increased noticeably. The two-surface Langmuir adsorption model was used to adjust data and to interpret Cu and Zn adsorption by soils excepting Cu sorption by the polluted soil, where the one-surface model was applied.