Interlayer expansion of dimethyl ditallowylammonium montmorillonite as a function of 2-chloroaniline adsorption

Abstract

The expansion behaviour of an organically modified montmorillonite during the adsorption of increasing amounts of an organic pollutant: 2-chloroaniline (2-CA). The organophilic montmorillonite, a commercial product, was obtained exchanging the inorganic cation with dimethyl ditallowylammonium ions (DMDTA). 2-CA was added to the organoclay, starting from 193.9 ppm up to 23,531.7 ppm going through twenty-two steps of growing quantities of 2-CA. For each of these twenty-two steps – corresponding to a range of adsorbed 2-CA ( C s) between 0.029 mol/kg (grams of 2-CA per kg of organoclay) and 2.763 mol/kg – the basal spacings were determined. The adsorption isotherm was performed according to ASTM D 4646-87 Standard and, by comparing the experimental C s data with the corresponding d 001 values, the basal expansion of the polluted organoclay is characterized by a steep rise for the first steps of adsorption of 2-CA (concentration in water at equilibrium C w < 0.00373 mol/L), then the d 001 remains almost constant up to the higher amounts of pollutant adsorbed. The 001 reflections are sharper, their intensity higher, and up to four orders of 00 l reflections are observed as the uptake of 2-CA increased. Since in aqueous solution the staking of organoclay platelets is poorly ordered, the observed behaviour may be partially explained by the 2-CA sorbed on the external surface of the clay mineral particles, which brings the silicate layers together. Finally, a tentative interpretation of the adsorption phenomena was carried out by fitting the experimental data according to the most common theoretical models: Freundlich, Langmuir, Dual Mode and Dual Langmuir Model.