Sorbent materials characterization based on mechanical or thermal pretreated montmorillonite modified by surfactant loading for improved chromium retention

FERNANDEZ MORANTES, C.; YARZA, FLORENCIA; MONTES, MARIA L.; MERCADER, C.; CURUTCHET, G.; TORRES SANCHEZ, R.

WATER AIR AND SOIL POLLUTION

SPRINGER

Lugar: Berlin; Año: 2020

0049-6979

To improve hexavalent chromium retention at pH 3, two montmorillonite (Mt) products were synthesized with different octadecyl trimethyl ammonium loading, 50% and 100% of Mt cation exchange capacity (CEC). Mt was subjected to different pretreatments: thermal ones at 600 °C or 950 °C for 2 h, or mechanical grinding for 300 s. The samples were characterized by several techniques at each stage. Differential thermogravimetric analysis (DTGA) performed on the products allowed determining the actual surfactant amount related to the internal or external surface by cation exchange and Van der Waals (VdW) mechanisms, respectively, taking into account the CEC of the thermal or mechanical pretreated Mt base sample used. X-ray diffraction (XRD) analyses reveal that the surfactant loading allowed the reversal of the collapsed interlayer after both pretreatments. The samples subjected to the thermal treatment at 600 °C and the raw Mt samples exhibit higher positive zeta potential values than the mechanical pretreated Mt ones with 100% of the CEC surfactant loaded at pH 3. This is evidence that zeta potential is directly related to the external surface covered by the surfactant. The agreement between the results of the surfactant coverage on the external surface and Cr(VI) removal at pH 3 indicates that the electrostatic mechanism is the main driving force for the sorption of Cr(VI). These synthesized sorbents achieve similar Cr(VI) retention using less than half the surfactant amount of already published studies