Phytomining: Powering the Circular Future of Silver Extraction

Phytomining offers a sustainable and environmentally benign strategy for recovering valuable metals from contaminated or low-grade substrates. In this study, Agrostis capillaris, Mentha spicata, and Lavandula angustifolia were assessed for their phytomining potential when exposed to silver nitrate and a commercial silver-containing waste stream. Quantitative X-ray fluorescence (XRF) analysis revealed species-specific differences in silver uptake and translocation; L. angustifolia exhibited the highest tissue silver concentrations under both treatments, reaching 5980 parts per million (ppm) following silver nitrate exposure and 91 ppm following commercial waste exposure. These higher tissue concentrations may partly reflect differences in plant biomass and species-specific uptake or retention characteristics. In contrast, A. capillaris exhibited the highest bioaccumulation factor (BAF) with a value of 2.15 under nitrate treatment and 0.78 under commercial waste exposure, indicating comparatively greater accumulation relative to the corresponding substrate conditions. Ultramicrotomy and scanning electron microscopy with energy-dispersive X-ray spectroscopy and backscattered electron (SEM-EDS-BSE) imaging confirmed the in vivo biosynthesis of silver nanoparticles (Ag-NPs), with distinct morphologies and spot analyses of silver weight percentages (Wt%) ranging from 16.7–72.6 Wt%. These findings underscore the dual capacity of selected herbaceous plants to extract bioavailable ionic silver and mediate the intracellular formation of Ag-NPs. The integration of XRF and SEM-EDS-BSE techniques provides a robust framework for evaluating phytomining systems, highlighting the potential of these species as biorefineries for noble metal nanoparticle recovery. Such approaches align with emerging circular economy principles and bio-nanotechnology development.