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Thermodynamics of Organic Acid Sorption to Goethite.

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Title: Thermodynamics of Organic Acid Sorption to Goethite.
Authors: Konrad, Alexander1 (AUTHOR) alexander.konrad@umwelt.uni‐giessen.de, Mulder, Ines1,2 (AUTHOR), Hofmann, Diana3 (AUTHOR), Lang, Friederike4 (AUTHOR), Stutz, Kenton P.4 (AUTHOR), Siemens, Jan1 (AUTHOR)
Source: European Journal of Soil Science. Jan/Feb2026, Vol. 77 Issue 1, p1-10. 10p.
Subjects: Goethite, Sorption, Thermodynamics, Salicylic acid, Oxalic acid, Isothermal titration calorimetry, Citric acid
Abstract: Adsorption to minerals is a key mechanism in stabilizing organic carbon in soils. We used isothermal titration calorimetry (ITC) to quantify the thermodynamics of binding of citric acid, oxalic acid, and salicylic acid to four goethites with different specific surface areas (SSA, 14–120 m2 g−1). Thermodynamic parameters could be determined for sorption of citric and salicylic acids, while flocculation of particles prevented their quantification for sorption of oxalic acid. For citric acid adsorption, ∆H shifted from −23.5 ± 0.57 to −27.0 ± 0.47 kJ mol−1 and ∆S from −8.8 ± 1.54 to −29.9 ± 0.13 J mol−1 K−1 with increasing SSA and broader (110) diffraction peaks of goethite, thus reducing ∆G from −20.7 ± 0.02 to −18.0 ± 0.03 kJ mol−1. Salicylic acid adsorption was more exothermic (∆H −40.53 ± 1.93 kJ mol−1) and accompanied by a larger loss of entropy (∆S −65.1 ± 1.91 J mol−1 K−1), possibly due to chelation of its ortho hydroxyl and carboxyl groups to single iron atoms on the mineral surface. These results demonstrate that ITC can decipher adsorption thermodynamics of organic ligands to mineral surfaces, but ligand‐induced flocculation can render the interpretation of results difficult. Crystallite size and lattice defects of adsorbent minerals influence the thermodynamics of sorption by determining the conformation of organic molecules sorbed to goethite surfaces. Highlights: First complete assessment of ΔH, ΔS, and ΔG of sorption of organic acids to goethites.Flocculation of mineral particles must be prevented to obtain meaningful ITC data.Goethite particle size & crystallinity modulate the thermodynamics of citric acid sorption.Sorption of organic acids to goethite does not present an energetic barrier for their mineralization. [ABSTRACT FROM AUTHOR]
Copyright of European Journal of Soil Science is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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DbLabel: Engineering Source
An: 191727393
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PubType: Academic Journal
PubTypeId: academicJournal
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  Label: Title
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  Data: Thermodynamics of Organic Acid Sorption to Goethite.
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  Data: <searchLink fieldCode="AR" term="%22Konrad%2C+Alexander%22">Konrad, Alexander</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> alexander.konrad@umwelt.uni‐giessen.de</i><br /><searchLink fieldCode="AR" term="%22Mulder%2C+Ines%22">Mulder, Ines</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Hofmann%2C+Diana%22">Hofmann, Diana</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Lang%2C+Friederike%22">Lang, Friederike</searchLink><relatesTo>4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Stutz%2C+Kenton+P%2E%22">Stutz, Kenton P.</searchLink><relatesTo>4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Siemens%2C+Jan%22">Siemens, Jan</searchLink><relatesTo>1</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22European+Journal+of+Soil+Science%22">European Journal of Soil Science</searchLink>. Jan/Feb2026, Vol. 77 Issue 1, p1-10. 10p.
– Name: Subject
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  Data: <searchLink fieldCode="DE" term="%22Goethite%22">Goethite</searchLink><br /><searchLink fieldCode="DE" term="%22Sorption%22">Sorption</searchLink><br /><searchLink fieldCode="DE" term="%22Thermodynamics%22">Thermodynamics</searchLink><br /><searchLink fieldCode="DE" term="%22Salicylic+acid%22">Salicylic acid</searchLink><br /><searchLink fieldCode="DE" term="%22Oxalic+acid%22">Oxalic acid</searchLink><br /><searchLink fieldCode="DE" term="%22Isothermal+titration+calorimetry%22">Isothermal titration calorimetry</searchLink><br /><searchLink fieldCode="DE" term="%22Citric+acid%22">Citric acid</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Adsorption to minerals is a key mechanism in stabilizing organic carbon in soils. We used isothermal titration calorimetry (ITC) to quantify the thermodynamics of binding of citric acid, oxalic acid, and salicylic acid to four goethites with different specific surface areas (SSA, 14–120 m2 g−1). Thermodynamic parameters could be determined for sorption of citric and salicylic acids, while flocculation of particles prevented their quantification for sorption of oxalic acid. For citric acid adsorption, ∆H shifted from −23.5 ± 0.57 to −27.0 ± 0.47 kJ mol−1 and ∆S from −8.8 ± 1.54 to −29.9 ± 0.13 J mol−1 K−1 with increasing SSA and broader (110) diffraction peaks of goethite, thus reducing ∆G from −20.7 ± 0.02 to −18.0 ± 0.03 kJ mol−1. Salicylic acid adsorption was more exothermic (∆H −40.53 ± 1.93 kJ mol−1) and accompanied by a larger loss of entropy (∆S −65.1 ± 1.91 J mol−1 K−1), possibly due to chelation of its ortho hydroxyl and carboxyl groups to single iron atoms on the mineral surface. These results demonstrate that ITC can decipher adsorption thermodynamics of organic ligands to mineral surfaces, but ligand‐induced flocculation can render the interpretation of results difficult. Crystallite size and lattice defects of adsorbent minerals influence the thermodynamics of sorption by determining the conformation of organic molecules sorbed to goethite surfaces. Highlights: First complete assessment of ΔH, ΔS, and ΔG of sorption of organic acids to goethites.Flocculation of mineral particles must be prevented to obtain meaningful ITC data.Goethite particle size & crystallinity modulate the thermodynamics of citric acid sorption.Sorption of organic acids to goethite does not present an energetic barrier for their mineralization. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of European Journal of Soil Science is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.1111/ejss.70278
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 10
        StartPage: 1
    Subjects:
      – SubjectFull: Goethite
        Type: general
      – SubjectFull: Sorption
        Type: general
      – SubjectFull: Thermodynamics
        Type: general
      – SubjectFull: Salicylic acid
        Type: general
      – SubjectFull: Oxalic acid
        Type: general
      – SubjectFull: Isothermal titration calorimetry
        Type: general
      – SubjectFull: Citric acid
        Type: general
    Titles:
      – TitleFull: Thermodynamics of Organic Acid Sorption to Goethite.
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            NameFull: Konrad, Alexander
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            NameFull: Mulder, Ines
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            NameFull: Hofmann, Diana
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            NameFull: Lang, Friederike
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            NameFull: Stutz, Kenton P.
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            – D: 01
              M: 01
              Text: Jan/Feb2026
              Type: published
              Y: 2026
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              Value: 77
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