02041naa a2200265 a 450000100080000000500110000800800410001910000220006024500470008226000090012950000820013852012460022065000190146665000070148565300240149265300240151665300200154065300270156065300190158765300270160665300180163370000180165170000170166977300890168611232402018-06-28       2008    bl uuuu     u00u1 u    #d1 aCASAGRANDE, J. C.  aZinc adsorption in highly weathered soils.  c2008  aTítulo em português: Adsorção de zinco em solos altamente intemperizados.  aThe objective of this work was to assess the effects of pH and ionic strength upon zinc adsorption, in three highly weathered variable charge soils. Adsorption isotherms were elaborated from batch adsorption experiments, with increasing Zn concentrations (0?80 mg L-1), and adsorption envelopes were constructed through soil samples reactions with 0.01, 0.1 and 1 mol L-1 Ca(NO3)2 solutions containing 5 mg L-1 of Zn, with an increasing pH value from 3 to 8. Driving force of reaction was quantified by Gibbs free energy and separation factor. Isotherms were C-, H- and L-type and experimental results were fitted to nonlinear Langmuir model. Maximum adsorption ranged from 59?810 mg kg-1, and Zn affinity was greater in subsoil (0.13?0.81 L kg-1) than in the topsoil samples (0.01?0.34 L kg-1). Zinc adsorption was favorable and spontaneous, and showed sharply increase (20?90%) in the 4?6 pH range. No effect of ionic strength was observed at pH values below 5, because specific adsorption mechanisms predominated in the 3?5 pH range. Above pH 5, and in subsoil samples, Zn was adsorbed by electrostatic mechanisms, since ionic strength effect was observed. Despite depth and ionic strength effects, Zn adsorption depends mainly on the pH.  aionic strength  aPh  aadsorption envelope  aadsorption isotherm  aelemento-traço  aenvelope de adsorção  aforça iônica  aisoterma de adsorção  atrace element1 aSOARES, M. R.1 aMOUTA, E. R.  tPesquisa Agropecuária Brasileira, Brasília, DFgv. 43, n. 1, p. 131-139, jan. 2008