The composition of nanoparticulate nickel sulfide

The initial nickel sulfide precipitated in normal Earth surface aqueous environments is nanoparticulate hydrated NiS with the general formula Ni1.1S·1.5H2O. The water content was determined by thermogravimetric mass spectroscopic analysis, and the chemical composition was determined by inductively coupled plasma-optical emission spectrometer (ICP-OES), back titration of CuCl2, ion chromatography (IC) and energy dispersive X-ray (EDX) spectrometry. Together with the structural characterization of the material, the results suggest that the NiS nanoparticles may be modelled as 4 nm spheres with a 1 nm anhydrous crystalline NiS core and a hydrated disordered outer shell layer containing 24 ± 3 H2O molecules per nm3. Thermogravimetric results suggest that the water is an integral part of the shell layer configuration analogous to the intralayer H2O of some clays. The results suggest that this phase determines the aqueous solubility of nickel in low temperature sulfidic systems. It also provides a novel route for the nucleation and growth of nickel sulfides in aqueous solutions.