Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/6/2006
Publication Date: 6/6/2006
Citation: Pereira, T.R., Laird, D.A., Johnston, C., Teppen, B., Li, H., Boyd, S. 2006. Sorption of dinitrophenol herbicide on K and CA saturated smectites in aqueous suspensions [abstract]. Joint Meeting of the Clay Mineral Society and the French Clay Group Meeting Abstracts. p. 216. Interpretive Summary:
Technical Abstract: 4, 6-dinitro-o-cresol (DNOC) is a nitro aromatic pesticide. Because DNOC is a weak acid (pKa = 4.4) we hypothesized that pH would be the dominant state variable controlling sorption on reference smectites (SAz-1 and SWy-2). Our results demonstrate that DNOC sorption on K-SAz-1 decreased from about 90% at pH 3 to 30% at pH 7. About 80% of added DNOC was sorbed by Ca-SWy-2 at pH 3 but sorption decreased abruptly to about 15% between pH 4 and pH 7. Ca-SAz-1 sorbed about 15% of added DNOC over the entire pH range. Elemental analysis of the filtered supernatants of K-SAz-1-DNOC systems revealed co-adsorption of DNOC with K+ over the entire pH range. Elemental analysis of the filtered supernatants of Ca-SWy-2-DNOC systems suggests little or no co-adsorption of Ca2+ with DNOC. FTIR analyses of smectite films showed a cation influenced spectral shift of the vsym (NO) band of DNOC indicating that the NO2 group of DNOC formed a stronger bond with K+ compared to Ca2+. XRD analysis of the smectite suspensions suggest that DNOC is primarily adsorbed on the external surfaces of suspended K- and Ca-smectite colloids. XRD analysis of air-dried and oven-dried K-smectite films revealed peak shifts and asymmetric peaks suggesting the presence of DNOC in the interlayer of K+-smectites, however these quasicrystals with DNOC in the interlayers were largely formed when the suspensions were dried. Overall the results indicate that pH was not a dominant state variable as hypothesized, because the DNOC was adsorbed as a complex with K. The results also reveal that DNOC is primarily adsorbed on external surfaces of suspended colloids but may become trapped in the interlayers of newly formed quasicrystals when the suspensions are dried.