NOTE THE USE OF NUCLEAR MAGNETIC RESONANCE (NMR) FOR THE DETERMINATION OF TETRAHEDRAL ALUMINIUM IN

The presence of smectite minerals in soils is of great importance because their cation-exchange capacity (CEC) and high surface area play a major role in determining the mechanical nd fertility properties of the soil. The CEC occurs because the cationic harge in the structure is insufficient to balance the charge of the structural anions. While the CEC and the relative number of the various cations in the structure are well-known for most clay minerals, an understanding of the specific ionic arrangements in the structure is limited because present knowledge is based primarily on results from powder X-ray diffraction (XRD) and elemental nalyses. The common practice is to measure the concentrations of important cations and to fit these, according to a set of empirical rules, into a structural framework of anions derived from XRD measurements. There are a number of dangers in this approach, the most obvious deriving from the absence of any determination f anion composition, the possible presence of cations not determined, and the compounding of errors from the cation determinations. Nevertheless, little work has been done to check the accuracy or even the validity of the structural assignments hat are conventionally made. One exception ha