Humic acid retention by Cetyl Trimethyl Ammonium-montmorillonite

M. A. FERNÁNDEZ, R. M. TORRES SÁNCHEZ

Rosario Sta. Fe-Argentina

Workshop; 1st Argentinean Workshop in Environmental Science at Rosario; 2009

Faculty of Biochemistry and Pharmaceutical Science National University at Rosario

Many of the remediation technologies are based on pollutant retention by adsorption in a solid medium attaining easy handle and possibility the materials recovery. Clays modified with quaternary ammonium salts are obtained by replacing the inorganic exchangeable cations, highly hydrated, by organic cations less hydrated. The exchange of these cations modifies the hydrophilic nature of the montmorillonite to hydrophobic, and consequently enables them to adsorb organophilic compounds. Such exchanges modify the specific area, porosity and surface electric charges of the clay. The objective pursued by this work is to extend the adsorption capacity of montmorillonite, by exchanging its interlayer cations with a quaternary ammonium salt, and study their application in the retention of humic acid. The montmorillonite used (Rio Negro Province, denoted MMT), contains 84% montmorillonite and quartz and feldspar (4 and 12% respectively) as impurities. The humic acid used was commercial type (Aldrich) and further purified (AH) and the quaternary ammonium salts was Bromide Cetyl trimethyl Ammonium (Sigma) (CTMA). The samples were characterized by XRD, specific surface determination (Sw) and apparent diameter (Dapp) with ionic strength (FI = 10-2M) and without FI. The HA adsorption isotherms were determined on MMT and CTMA-MMT, with and without FI. Montmorillonite and the complexes formed with CTMA and AH were examined by differential thermal analysis (DTA) and Zeta potential. XRD spectra for CTMA-MMT showed a shift of the reflection d(001), respect to MMT, indicating the CTMA incorporation in the interlayer of the montmorillonite. The Sw values obtained were 573, 156 and 218 m2/g for MMT, CTMA-MMT and CTMA-MMT + AH, respectively. While, the Dapp values determined were: 580, 3753, 2335, 540, 4233, and 1053 nm, for MMT, CTMA-MMT and CTMA-MMT + AH, with and without FI, respectively. The adsorption isotherms showed a significant increase of HA adsorption on the sample CTMA-MMT (80 mg HA / g clay) on the MMT sample (10 mg HA / g clay). While the FI presence produced a lower HA adsorption in the MMT showing a modification of the electrostatic sites surface. The ATD showed a variation of weight loss between samples MMT, CTMA-MMT and CTMA-MMT + AH indicating the presence of CTMA and AH. The curves of zeta potential versus pH showed a change in the surface charge on the MMT samples and CTMA-MMT+AH, indicating the positively charged surface generated both: the exchange cations CTMA in the interlayer and by the subsequent adsorption of HA on the CTMA-MMT+AH.