An in Situ ATR-FTIR Investigation of Sulfate Bonding Mechanisms on Goethite

✍ Scribed by Derek Peak; Robert G Ford; Donald L Sparks

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 141 KB
• Volume: 218
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1999.6405

✦ Synopsis

The mechanism of sulfate adsorption on goethite was investigated in situ using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Sulfate adsorption was investigated at ionic strengths between 0.005 and 0.1 M, reactant concentrations between 5 and 500 M, and pH values between 3.5 and 9.0. It was determined that sulfate forms both outer-sphere and inner-sphere surface complexes on goethite at pH less than 6. At pH values greater than 6, sulfate adsorbs on goethite only as an outer-sphere complex. The relative amount of outer-sphere sulfate surface complexation increased with decreasing ionic strength. The spectrum of sulfate adsorbed on goethite was also compared to the infrared spectrum of synthetic schwertmannite, an iron(III) oxy-hydroxy-sulfate. It was determined that in situ spectra of both schwertmannite and adsorbed sulfate are quite similar, suggesting that a continuum of outer-and inner-sphere sulfate occurs in both cases.