One-step simultaneous biomass synthesis of iron nanoparticles using tea extracts for the removal of metal(loid)s in acid mine drainage

Acid Mine Drainage (AMD) contains various metal/metalloid ions such as Fe, Cu, and As, which all impact seriously on mine ecosystems. Currently, the commonly used chemical methods for treating AMD may cause secondary pollution to appear in the environment. In this study, one-step simultaneous biomass synthesis of iron nanoparticles (Fe NPs) using tea extracts for the removal of heavy metals/metalloids in AMD is proposed. Characterizations revealed that the Fe NPs presented severely agglomerated particles with an average particle size of 119.80 ± 4.94 nm, on which various AMD-derived metal(loid)s, including As, Cu, and Ni, were uniformly dispersed. The biomolecules participating in the reaction in the tea extract were identified as polyphenols, organic acids, and sugars, which acted as complexing agents, reducing agents, covering/stabilizing agents, and promoted electron transfer. Meanwhile, the best reaction conditions (reaction time = 3.0 h, volume ratio of AMD and tea extract = 1.0:1.5, concentration of extract = 60 g/L, and T = 303 K) were obtained. Finally, the simultaneous formation of Fe NPs and their removal of heavy metals/metalloids from AMD was proposed, mainly involving the formation of Fe NPs and adsorption, co-precipitation, and reduction processes of heavy metals/metalloids.