IN-DEPTH INVESTIGATION INTO THE IDENTITY, MORPHOLOGY AND CRYSTALLINITY OF LOW-TEMPERATURE SULFIDE MINERALS OF TRANSITION METALS AT THE NANOSCALE THROUGH TRANSMISSION ELECTRON MICROSCOPY

The sulfide minerals of transition metals (TMe) such as zinc (Zn), copper (Cu), nickel (Ni) and cobalt (Co) can play important roles in mediating the natural biogeochemical cycling of elements throughout the Earth’s low temperature near-surface environments. However, these minerals remain poorly characterized due to the challenge in detecting and extracting nano-sized and poorly-crystalline minerals from complex matrix. Here, we present a detailed nanoscale characterization on the identity (i.e., phase and elemental composition), morphology and crystallinity of sulfide minerals of transition metals precipitated from low temperature, anoxic aqueous solutions. The metal sulfides are precipitated with/without sulfate-reducing bacteria (Desulfovibrio vulgaris) and at varying initial aqueous TMe-to-Fe(II) concentration ratios to capture the biogeochemical diversity of potential precipitation conditions in nature. The major technique for the analyses is high resolution transmission electron microscopy (HRTEM) coupled with selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS). Based on our work, we present a chart detailing the characteristics of transition metal sulfide nanoparticles as a function of different degrees of biological influence and initial aqueous TMe-to-Fe(II) concentration ratios. The results of our work are expected to pave the way towards a better constraint on the roles that these nanoparticles play in biogeochemical cycling throughout the Earth’s near surface environment.