Location of Ni2+ in nickel-intercalated vermiculites

In previous investigations on the magnetic properties of Ni2 +-vermiculite intercalation compounds from Santa Olalla, it was considered that each of the two anomalies in the real component of the ac magnetic susceptibility exhibited by these compounds could be related to the spin dynamics of the nickel ions located in different local environments in the intralayer and interlayer space of the structure. This paper reports a study of vermiculites containing intercalated Ni2 + cations, in order to verify whether the nickel enters not only the interlayer, but also the octahedral layer and to what extent. Nickel-intercalated vermiculites were prepared from vermiculite ore from Santa Olalla (Huelva, Spain) by means of an ion exchange process using an aqueous solution of Ni2 + acetate. Thermogravimetric, chemical and Mössbauer spectral studies were used to characterize the synthetic nickel-intercalated vermiculites and provide insight into the allocation of Ni2 + within the structure. The 3D structure was refined by X-ray powder diffraction, and the DIFFaX + code, based on a recursive description of faulted structures, was used to describe the structure of this compound. The results suggested the entry of Ni2 + into two positions of the structure: the interlayer space and the octahedral layer. This finding is important because it would imply greater retention of toxic metals by vermiculite in polluted environments compared to the case in which entry of the metal was limited to one single structural position. The disordered 3D structure of natural Mg- and intercalated Fe-vermiculites is maintained in Ni2 +-intercalated compounds.