Use of organo-montmorillonite for the nitrate retention in water: influence of alkyl length of loaded surfactants

JAWORSKI, MARIA A.; FLORES, FEDERICO M.; FERNÁNDEZ, MARIELA A.; CASELLA, MÓNICA; TORRES SÁNCHEZ, ROSA M.

SN Applied Sciences

Springer Link

Año: 2019 vol. 1

2523-3963

The removal of NO3− from water was performed and compared among four organo-montmorillonites (OMt) with quaternaryamine surfactants of different chain lengths [octadecyl trimethyl-(ODTMA),hexadecyl trimethyl-(HDTMA), tetradecyl trimethyl-(TDTMA) and dodecyltrimethyl-ammonium (DDTMA)] and loadings [100%, 200%, 400% of the Mt cationexchange capacity (CEC)]. The maximum adsorption of NO3− was attained by the long chainlength surfactants (64 and 100 mg NO3− ions per gram of OMt, for HDTMA and ODTMA,respectively) with initial loading of 400% with respect to the CEC of Mt. Theshort chain length surfactants (DDTMA and TDTMA) did not show adsorption of NO3− except for TDTMA400 sample. The NO3− adsorption produced a slight expansion of theinterlayer thickness of the OMt samples loaded with long-chain surfactants thatwas assigned to the entrance of NO3− by a synergic effect with these surfactants. The decrease of the negative zeta potential, found for OMt samples relative to thatof Mt sample, was attributed to the surfactant chain length rather than to theactual surfactant loaded amounts, which allowed attaining positive zeta potentialvalues for the OMt loaded with long-chain surfactants. The NO3− adsorption onOMt samples caused a slight decrease in the positive zeta potential values,reflecting the external surface coating by NO3−. For long-chain molecules, thisbehaviour also indicated the formation of greater interactions such as ionpairs between the positive polar group of the surfactant and NO3− ions.