Zinc Structural Coordination and Sorption Characteristics in Phyllosilicate Clays.

The study of zinc’s role in soil-plant and soil-water interfaces has been very popular in reference to developing a better understanding of plant toxicities and deficiencies or to minimize water contamination due to heavy metal loading from anthropogenic wastes, disposals and spills. The soil-plant interface has been of particular interest because zinc is a necessary micronutrient in plants and is used as a fertilizer to decrease deficiencies for crops grown in high pH soils, soils of low zinc parent material concentration or soils high in phosphates such as those derived from phosphatic Ordovician limestones. Very little attention however, has been paid to the effect of zinc loading on the solid phase of soils. It has been suggested that Zn can incorporate into the mineral structures of phyllosilicate clays. This is especially important to note for Zn deficiencies in soils high in hydroxyl-interlayered minerals such as those of the Bluegrass Region of Kentucky. These soils, combined with their high phosphate content have the potential to fix Zn, which may help explain the area’s common corn zinc deficiency. The objective of this study was to determine the potential of Zn to substitute via isomorphic substitution into the octahedral layer of phyllosilicate minerals derived from the Karnak, Vertrees, Nicholson and Pulaski soil series of Kentucky, as well as from saponite, sauconite, vermiculite and montmorillonite standards. This study used XRD, thermogravimetic analysis, FTIR-DRIFT, as well as pH and zeta potential shifts from zinc sorption isotherms on soils of varying clay mineral composition and pHs to show that zinc incorporates into both the interlayer of Fe-laiden and hydroxy-interlayered minerals and into the octahedral layers of Mg-saturated phyllosilicate clays.