Color removal by clays. Kinetic study of adsorption of cationic and anionic dyes

Abstract

Experiments were designed to study the kinetics of adsorption of two industrial dyes-methylene blue (cationic) and sulfur blue (anionic)-by kaolinite and montmorillonite clays. The cationic dye was removed from aqueous solution at a continuously decreasing rate from 10 mg/g min to 0.07 mg/g min by montmorillonite whereas kaolinite adsorbed the dye at a faster and uniform rate of 16 mg/g min. The anionic dye was removed at a uniform rate of 2.3 mg/g min by kaolinite and 2.6 mg/g min by montmorillonite. The apparent control of ion-exchange capacities and nature of exchange sites of the clays on the rates of color removal is pointed out.

Adsorption of methylene blue on Cu(II)-exchanged montmorillonite

“…1. The adsorption processes of MB molecules occurring on each of the tested adsorbents reached equilibrium after 2 h. This result is in agreement with the investigation of Sethuraman and Raymahashay [19]. However, Zhao and Wang [20] reported that the equilibrium in adsorption of MB on bentonite, which consists mainly of montmorillonite, was reached within 3 h. Some workers described the adsorption process of MB on montmorillonite particles as divided into two parts [15,21]: rapid adsorption on the external surface of the clay by ion exchange and aggregation, followed by deaggregation of the MB dimer and the monomer migrating to the interlamellar position of the clay.…”

Effect of acid activation of Saudi local clay mineral on removal properties of basic blue 41 from an aqueous solution

“…The clay minerals exhibit a high affinity for cationic dyes (Sethuraman, 1975). The adsorption takes place largely by the mechanism of cation exchange; exchangeable metallic cations are released from the clay mineral into the aqueous phase and organic cationic dye molecules are replaced (Sethuraman, 1975).…”

“…The adsorption takes place largely by the mechanism of cation exchange; exchangeable metallic cations are released from the clay mineral into the aqueous phase and organic cationic dye molecules are replaced (Sethuraman, 1975). The raw MtKhl was expected to remove the highest BB-41 amount, which was not the case, and the adsorption could occur only on surface.…”

Adsorption behavior of reactive dyes from aqueous solutions on chitosan

“…The Ðrst, sharper, portion (the dashed) is the external surface adsorption stage19 or instantaneous adsorption stage. 21 The second, gradual linear, portion is the gradual adsorption stage21 and the third, linear, portion is the Ðnal equilibrium stage. 20,21 In this model, the chitosan Ñakes are treated as being surrounded by a boundary layer Ðlm through which the dyes must di †use prior to external adsorption on chitosan surface.…”

“…21 The second, gradual linear, portion is the gradual adsorption stage21 and the third, linear, portion is the Ðnal equilibrium stage. 20,21 In this model, the chitosan Ñakes are treated as being surrounded by a boundary layer Ðlm through which the dyes must di †use prior to external adsorption on chitosan surface. The second sections of Figs 8 and 9, between about 10 and 40% dye adsorption are due to intraparticle di †usion being predominant in the ratecontrolling step.…”