Equilibrium data and its analysis with the Freundlich model in the adsorption of arsenic(V) on granular ferric hydroxide

Kenneth Walsh, Sebastian Mayer, Dirk Rehmann, Thomas Hofmann, Karl Glas

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53 Scopus citations


An accurate understanding of equilibrium conditions is an essential starting point for dimensioning and modelling efforts in adsorption systems. However, key assumptions and methodologies in the generation and analysis of adsorption data sets might be contributing to the error in the description of the equilibrium. This study investigates the potential impacts of the equilibration time, test adsorbent particle size selection, and the regression technique applied, on the fitted coefficients of the Freundlich equilibrium model in the adsorption of arsenate on Granular Ferric Hydroxide. The choice of regression algorithm was found to impact primarily the exponent describing the energetic heterogeneity of the adsorption surface and resulting non-linearity of the isotherm, nf. Non-linear regression with a hybrid error function on the observed solute concentration rather than loading was found to be a suitable approach. Insufficient equilibration time was found to impact predominantly the strength of adsorption, given by Kf, when applying a small adsorbent size fraction, and both coefficients when applying a coarser technical size fraction. Application of the small size fractions in lieu of the larger in accelerated trials appeared to over-estimate both coefficients, but is a reasonable alternative to long contact times.

Original languageEnglish
Article number116704
JournalSeparation and Purification Technology
StatePublished - 15 Jul 2020


  • Adsorption
  • Arsenic
  • Equilibrium
  • Granular ferric hydroxide
  • Linear regression
  • Non-linear regression
  • Statistical analysis


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