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Abstract: The development of modern technologies requests increasing demand for rare earth elements (REEs) and noble metals (NMs). That has spurred mining activities and has released metals into the environment as a consequence. Phytoextraction uses plants to accumulate metals into their shoots enabling metal removal from brownfields (phytoremediation) or recovery of valuable metals (phytomining). Nevertheless, the occurrence and distribution of NMs, REEs in biomass coming from contaminated lands have not been intensively investigated yet.
In this study, different types of woody biomass including root, trunk, branches, and leaf were collected from a metal-polluted location in Gyöngyösoroszi, Hungary. Afterward, the harvested plants were combusted at 500 °C to generate ashes for ICP (Inductively Coupled Plasma) analysis. Elemental analytical results show that a couple of NMs such as Ag, Au, Pt were found and distributed differently in various biomass ash samples. In specific, the highest Ag concentration is around 5.4 mg/kg achieved in the root ash. Meanwhile, the greatest number of Au and Pt is about 1.8 mg/kg obtained in the trunk and leaf ash respectively. Besides, several REEs with substantial quantities were identified in the contaminated biomass ashes. The significant results observed in the root ash are approximately 47.8 mg/kg Ce and 30.5 mg/kg Nd. The concentration of REEs in root ash is higher than in the above-ground biomass ash with the decreasing order of root ash, leaf ash, trunk, and branches ash. It can be explained by the distribution of REEs in root or leaf is usually greater than other plant parts. These valuable findings indicate that phytomining is a promising approach for recycling NMs, REEs from soils via plants. Moreover, solid residues obtained from polluted biomass are potential metal resources.
Keywords: Biomass, noble metals, rare earth elements, phytoextraction, phytomining
Introduction
Nowadays, in the context of industrialization and urbanization, the concentration of metals in soils has been increasing significantly resulting in environmental problems and brownfield lands [1]. According to the reported data, more than one-third of the global land is polluted [2]. The real number even could be greater than what has been unveiled so far. On the other hand, the growth of metals in soil surface simultaneously provides the opportunity for extracting metals from contaminated areas.
Phytoextraction using plants to accumulate metals from...