Modified Vermiculite as Adsorbent of Hexavalent Chromium in Aqueous Solution

Abstract

The aim of this study was to investigate the efficiency of removing Cr6+ from aqueous solutions using two exfoliated vermiculite: (1) heated abruptly at 1000 °C and (2) irradiated with microwave radiation. The effects investigated were contact time, adsorbate concentration and initial Cr6+ concentration. The adsorption with both exfoliated vermiculites was well described by the DKR isotherm, indicative of a cooperative process and with the pseudo second order kinetic model. The Kd value for the two exfoliated vermiculites was similar, 0.2 ·1010 μg/Kg. The maximum adsorption capacity of Cr6+ with thermo-exfoliated vermiculite, 2.81 mol/g, was much higher than with microwave irradiated vermiculite, 0.001 mol/g; both values were obtained with 0.5 g of vermiculite in contact with distilled water enriched with 1 ppm of Cr6+ for 24 h. Factors such as ion chemistry, the solution pH and ionic strength, influence the values of capacity, adsorption energy and initial adsorption rate values of the exfoliated vermiculite. In addition, these values depended on the exfoliation process, being the adsorption capacity highest with abrupt heating of vermiculite, while the adsorption energy and rate values showed just a slight increase with microwave irradiation. This aspect is important to select the most suitable vermiculite modification treatment to use it as an adsorbent.

Adsorption Performance of Modified Fly Ash for Copper Ion Removal from Aqueous Solution

“…To calculate the kinetic parameters, the equations presented in Table 4 were used [45]: Intraparticle diffusion q t = k i t 0.5 +c where q t (mg/g) is the amount of Cu(II) ions adsorbed at time t, q e (mg/g) is the amount of Cu(II) ions adsorbed at equilibrium, k 1 is the pseudo-first order rate constant (1/min), k 2 is the pseudo-second order rate constant (g/mg min), and k i is the intraparticle diffusion rate constant.…”

Structural Changes in Vermiculites Induced by Temperature, Pressure, Irradiation, and Chemical Treatments

“…For the experiments with Cr 3+ [54] and Cr 6+ [55], commercial vermiculite from China thermo-exfoliated at 900°C for 1 minute was used. With Ni 2+ , commercial from Piauí (Brazil) and China, vermiculites thermo-exfoliated at 1000°C for 1 minute were used [35].…”