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Brazilian Archives of Biology and Technology
On-line version ISSN 1678-4324
SOARES, Marcio Roberto; CASAGRANDE, José Carlos and MOUTA, Ernesto Rinaldi. Nickel adsorption by variable charge soils: effect of pH and ionic strength. Braz. arch. biol. technol. [online]. 2011, vol.54, n.1, pp.207-220. ISSN 1678-4324. http://dx.doi.org/10.1590/S1516-89132011000100025.
The effects of pH and ionic strength (I) on Ni adsorption in variable charge soils were evaluated by laboratory batch experiments. Experimental results fitted the Langmuir model. Maximum adsorption (Adsmax) ranged from 260-2818 mg kg-1 (topsoil) to 532-1541 mg kg-1 (subsoil). Nickel affinity (KL) was higher in the subsoil samples (0.022-0.236 L kg-1) than in topsoil (0.003-0.049 L kg-1). Adsorption envelopes showed sharp increase in Ni adsorption (20-90%) in the 4.0-6.0 pH range. Nickel adsorption was affected by I and specific adsorption predominated in the 3.0-5.0 pH range, while above pH 5.0, it was adsorbed by electrostatic mechanisms. Negative values of free energy variation (ΔG) and the separation factor KR<1 indicated that Ni adsorption reaction was favorable and occurred spontaneously, especially when pH increase. Chemical and mineralogical soil attributes should be considered as criteria for selecting the areas for disposal of residues containing Ni to minimize the impact on the environment.
Keywords : adsorption isotherms; free energy; adsorption envelopes; adsorption edges; ionic strength.