A Green Approach to the Bio-based Synthesis of Selenium Nanoparticles from Mining Waste

This study deals with producing selenium nanoparticles (SeNPs) by an economical and reliable process using a mining waste that contains significant amounts of selenium (6.11%), silver (4.12%), lead (4.69%), copper (3.61%), antimony (4.97%) and barium sulfate (70.01%). For separation of valuable metals and obtaining a pure solution for Se synthesis, several steps need to be taken; (a) Barium sulfate removal by gravity separation; (b) Leaching of the concentrate by HNO3 (3M); (c) Precipitation of silver and lead as insoluble chloride salts and (d) removing of other impurities such as arsenic, tellurium and strontium. The solution of purified selenium stock was then utilized as a precursor for the green synthesis of SeNPs using fruit extracts via an eco-friendly approach. The different fruit extracts such as plum, grape, orange, pomegranate, tomatoes, and lime were examined, and orange extract was found to be an efficient, reducing agent as well as a stabilizer for green synthesis of SeNPs. The biosynthesized SeNPs were characterized by various techniques such as SEM, TEM, XRD, FTIR and EDX. The spherical morphology of SeNPs was confirmed by SEM and TEM analysis, and particle size of SeNPs was found between 70 and 80 nm on the basis of the Debye-Scherrer equation.