Sorbent Materials Characterization Based on Mechanical or Thermal Pretreated Montmorillonite Modified by Surfactant Loading for Improved Chromium Retention

Abstract

To improve hexavalent chromium (Cr(VI)) retention of montmorillonite (Mt) at pH 3, Mt sample was subjected to different treatments: thermal ones at 600 °C or 950 °C, 2 h, or mechanical grinding for 300 s. Then, the obtained products were loaded with different octadecyl trimethyl ammonium loading and 50% and 100% of Mt cation exchange capacity (CEC). 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 revealed that the surfactant loading allowed the reversal of the collapsed interlayer after both treatments. 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 was 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.

One-Pot Green-Synthesis of Supported Reductive Biogenic Iron-Based Materials for the Removal of Cr(VI)

“…Total chromium (Cr Total ) concentration in solution was measured by using a flame atomic absorption spectrometer (FAAS) (Sens AA dual GBC Scientific Equipment). The difference between Cr Total and Cr­(VI) was considered as Cr­(III) . Unless otherwise indicated, all data shown are the mean values from two replicate experiments.…”

“…The difference between Cr Total and Cr(VI) was considered as Cr(III). 7 Unless otherwise indicated, all data shown are the mean values from two replicate experiments. The typical experimental error was less than 5% for all results.…”

“…Despite the popularity of some of the technologies mentioned above, there are some disadvantages related to operational costs, operational scales, or wastes produced. Moreover, adsorption processes for chemical species as Cr­(VI) are more challenging as aqueous Cr­(IV) occurs mainly as a negatively charged species in a wide range of pH and most cost-effective adsorbents have negative net charge on their surfaces, representing an additional constraint; only some adsorbent materials like activated carbon or montmorillonite were reported to directly adsorb Cr­(VI) species or were involved in its reduction and adsorption of Cr­(III) species simultaneously. , …”

“…Despite the popularity of some of the technologies mentioned above, there are some disadvantages related to operational costs, operational scales, or wastes produced. Moreover, adsorption processes for chemical species as Cr(VI) are more challenging as aqueous Cr(IV) occurs mainly as a negatively charged species in a wide range of pH and most cost-effective adsorbents have negative net charge on their surfaces, representing an additional constraint; 6 only some adsorbent materials like activated carbon or montmorillonite 7 were reported to directly adsorb Cr(VI) species or were involved in its reduction and adsorption of Cr(III) species simultaneously. 8,9 As an alternative, the use of Fe 0 or Fe(II) for the removal of these type of contaminants in water was addressed by several authors through the use of nanoscale zerovalent iron (nZVI) particles as reducing agents 10−15 or also through the use of engineered iron materials for photoreduction of Cr(VI) to Cr(III).…”

Removal of Trihalomethanes from Water using Modified Montmorillonite

“…Also, MMT and its modified forms were used to adsorb the sulfamethoxazole and tetracycline, 18 chromium(IV) retention, 19 cationic dyes, 20 tetracycline antibiotics, 21 acid Red 17, 22 calcium ion and bisphenol A, 23 bisphenol A, 24 rhodamine and hexavalent chromium, 25 thiabendazole, 26 and soil humic acid. 27 In this study, the effects of MMT and its modified forms with the chlorosulfonic acid (SMMT) were evaluated for the adsorption of the THMs.…”