Use and Misuse of Sorption Kinetic Data: A Common Mistake That Should Be Avoided

Abstract

Numerical simulation of sorption dynamics showed that the use of data recorded at (or very close to) equilibrium in the search for the kinetic equation that best describes the process frequently leads to incorrect conclusions. Notably, it has been demonstrated that the fit of the adsorption data at equilibrium (t/q t versus t) is a straight line irrespective of the sorption kinetics. In order to distinguish pseudo-first-order from pseudo-second-order sorption kinetics, the data near the equilibrium should be omitted from the least-squares fit and the result confirmed by a different method. A straightforward method based on ∆(q t /q e )/∆t versus 1 -q t /q e and versus (1 -q t /q e ) 2 plots is suggested. Some recent papers reporting incorrect sorption kinetic analyses are discussed.

Sorption of Organic Pollutants by Humic Acids: A Review

“…The "very high concentration" assumption of Azizian is poorly applicable in adsorption studies because requires that the solute concentration remains virtually constant over time [82]. Moreover, it is worth noting that also nowadays we find papers in highly authoritative journals containing a wrong analysis of sorption kinetic data [83]. A frequent mistake is to evaluate the applicability of the pseudo-second-order model from the linearity of the plot t/q vs. t without excluding adsorption data at (or very close to) equilibrium.…”

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“…Noticeably, better performance of the PSO model may also be an artifact from improper analysis of the data. In most cases this results from the application of Equation (30) in the following linearized form [17,93]:…”

“…According to Equation ( 31), if the data obey the pseudo-second order model, a plot of t/q vs. t should produce a straight line. The main drawback of this method is that for data points at (or very close to) equilibrium, the plot of t/q vs. t becomes linear independently of sorption kinetics [93]. The goodness of the results obtained by the plot of t/q vs. t may be verified by using a linearized form of the PSO model [17]:…”

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