Thermoexfoliated commercial vermiculites for Ni2+ removal

摘要

The aim of the present study was to investigate the effect of thermal expansion on the removal efficiency of commercial vermiculites towards Ni2+ ion from aqueous solutions. Three effects were studied: 1) Contact time between the adsorbent and Ni2+ dissolved in the retention process; 2) adsorbent mass; 3) concentration of Ni2+ in adsorption. Ni2+ uptake was quantitatively evaluated using the Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich (DKR) models. In addition, the adsorption equilibrium was described well by the DKR isotherm model, indicative of a cooperative process. The maximum adsorption capacity obtained with DKR model of 3.13 mol/g of Ni2+ on China vermiculite was higher than the value of 2.91 obtained for Piaui vermiculite. The kinetic experimental data were described using pseudo-first and pseudo-second order kinetic models, being well described by pseudo-second order model. The adsorption rate value in distilled water was the same with both vermiculites, 0.001 h(-1). Thermally exfoliated vermiculites type-2, as China, would be more suitable than vermiculites type-1, as Piaui, for recovering traces of Ni2+ in water because: a) its high mica-like content and therefore high degree of expansion, exfoliation and formation of larger pores; b) its maximum adsorption capacity. (C) 2016 Elsevier B.V. All rights reserved.