Vanadium in Phyllosilicates

Abstract

Microscopic characterization of V-illites and V-chlorites investigated the role of V occurrence and V valence in the highly variable recovery of V from phyllosilicates in acid leaching. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS) were used to analyze V distribution on a nanometer scale and directly measure V redox state in silicate minerals, and the results were compared to the results of acid leaching experiments. EDS results show that V-illites are heterogenous in metal content. EELS measurements of V-illites identified a distinct nanometer scale V-oxide phase and showed that V in chlorites is more reduced vs. illites. V-chlorites have a more homogeneous V distribution and lacked a separate V-oxide phase. We suggest that the presence of nanoscale V-oxides in V-illites is responsible for variable, but sometimes higher V recovery of illite-rich ores vs. chlorite-rich ores. More generally, the presence of distinct microscopic phases within phyllosilicates is poorly understood yet may have significant economic impacts in mining, such as affecting metal extraction from phyllosilicate ores or gangue acid consumption.