Dynamics of reversible sorption of anthocyanins on the surface of bentonite clays

Abstract

Using examples of sorption of anthocyanins of black garden nightshade (known as the Sunberry) fruits on bentonite clay «Bentakon», it was shown that when applying the Lagergren’s equation, it is necessary to exclude the results obtained at the beginning and at the end of the experiment from the set of experimental data. Lagergren’s equation modified for the use of direct measurements is associated with the time τ from the beginning of the sorption by the linear equation lg(A_τ - A_e) = a0 – a1τ, where Aτ and Ae are the absorbance of anthocyanins in solutions at the time τ and at the end of the sorption. The previously proposed correction to the equation for the dynamics of irreversible sorption on sorbents without intradiffusion inhibition, taking into account changes in the concentration of sorbate in the solution during the sorption of ln(Aτ/(Aτ – Ae)) = a0 + a1τ allows the inclusion of all the starting points into the data set processed by the equation, the data at the end of the sorption curve were located above the obtained trend line. It was suggested that this was due to the reversibility of the sorption of anthocyanins under experimental conditions. MS Excel was used for the numer-ical simulation of reversible sorption. The study presents a simulation algorithm, which shows that even in the case of the reversibility of sorption, the linearity of the corrected equation for irreversible sorption is preserved until the 70-80% completion of sorption is reached, which sets the limits of applicability of the corrected equa-tion: R2 for a linear dependence was at least 0.99.