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Open AccessArticle

Modified Vermiculite as Adsorbent of Hexavalent Chromium in Aqueous Solution

1
Departamento Geología e Instituto de Química Organometálica “Enrique Moles”, Universidad Oviedo, Jesús Arias de Velasco s/n, 33005 Oviedo, Spain
2
Laboratory of High-Resolution Transmission Electron Microscopy, Institute for Scientific and Technological Resources, Edificio Severo Ochoa s/n, Campus de El Cristo, 33006 Oviedo, Spain
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(9), 749; https://doi.org/10.3390/min10090749
Received: 23 July 2020 / Revised: 13 August 2020 / Accepted: 21 August 2020 / Published: 24 August 2020
(This article belongs to the Special Issue Environmental Applications of Chemically Modified Clay Minerals)
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. View Full-Text
Keywords: vermiculite; Cr6+ adsorption; thermo-exfoliation; microwaves vermiculite; Cr6+ adsorption; thermo-exfoliation; microwaves
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MDPI and ACS Style

Marcos, C.; Medoro, V.; Adawy, A. Modified Vermiculite as Adsorbent of Hexavalent Chromium in Aqueous Solution. Minerals 2020, 10, 749.

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