Free energy of copper adsorption was studied in surface and subsurface samples from three soils of the State of São Paulo, Brazil [Rhodic Kandiudalf (TE), Anionic "Rhodic" Acrudox (LR) and Anionic "Xanthic" Acrudox (LU)], after addition of 5, 20, 50, 100, 200, 300, 400 and 600 mg L-1 of copper. Copper adsorption was considered spontaneous, since the measured free energy was negative in all concentration. Free energy values decreased with the increase of added copper. TE showed higher free energy liberated than LR and LU, mainly in surface samples. For the same soils, surface horizons showed higher values for free energy liberation than subsurface horizons, probably due to the effect of organic matter, whose affinity for copper is high.
Anionic Acrudox; copper; adsorption; free energy