Nickel, iron-containing clay minerals from Niquelandia deposit, Brazil: 2. Behaviour under reducing conditions

The reduction behavior of two Ni, Fe-rich dioctahedral smectite clays has been investigated by temperature-programmed reduction (TPR). For both clays, the reduction process of the transition metal elements occurs in two steps. At about 400°C, Fe3+ is first reduced to Fe2+. At higher temperatures, further reduction of iron and reduction of nickel are achieved. Samples reduced at 400°C and 700°C have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Mِssbauer spectroscopy (MS), and transmission electron microscopy (TEM). After a treatment at 700°C, metallic particles deposited on the silicates has been evidenced by TEM and confirmed with the other techniques.