Removal of paraquat from water by an Algerian bentonite

The sorption–desorption of the cationic pesticide 1,1′-dimethyl-4,4′-bipyridinium dichloride (paraquat) on a bentonite from Maghnia (Algeria) desiccated at 110 °C (M), and calcined at 400 °C (M400) and 600 °C (M600) from aqueous solution at 25 °C has been studied using batch experiments. A complete characterization of the natural and heat activated bentonite samples has been carried out through the following techniques: X-ray fluorescence spectroscopy, FTIR, X-ray diffraction, thermogravimetric and differential thermogravimetric analysis and surface analysis. In order to have a better understanding of the variables affecting the sorption of this herbicide, factors such as the working temperature or the ionic strength of the solution have been investigated. The sorption experimental data have been fitted to the Langmuir equation in order to calculate the maximum sorption capacities (Xm) of the samples. The results show that the sorption capacity of the calcined samples greatly decreased with heat treatment. On the other hand, the sorption process is hardly affected by the working temperature, whereas the higher electrolyte concentration, the lower sorption of this pesticide. In addition to batch experiments, a decontamination continuous process (DCP) was designed by the authors using the natural clay to evaluate the potential application of this adsorbent for removing paraquat from water.