Nickel Adsorption by Variable Charge Soils: Effect of pH and Ionic Strength

Ano: 2011 | Volume: 54 | Número: 1

Autores: Marcio Roberto Soares, José Carlos Casagrande, Ernesto Rinaldi Mouta

Palavras-chave: adsorption isotherms, free energy, adsorption envelopes, adsorption edges, ionic strength

Resumo Inglês:

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 (DG) 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.