In the Arburese mine district (SW Sardinia, Italy), centuries of mine exploitation addressed to the extraction of Zn and Pb from sulphides and non-sulphides (calamine) deposits, left a widespread metal pollution. The Juncus acutus, a halophyte pioneer plant, was able to adapt in this extreme environment and to affect metal mobility thanks to its capacity to stabilize them in the external roots and rhizosphere. A method for evaluating the potential of reuse of biomasses for economic purposes is here presented starting from the specific case study of Juncus acutus. For this purpose, plants and rhizospheres, collected from the banks of two streams (Rio Naracauli and Rio Irvi) impacted by past mining activity, were used to perform Thermogravimetry and Differential Thermal analyses combined with X-ray Diffraction (XRD) carried out on raw samples and on samples heated ex-situ (by a conventional diffractometer) or in-situ (by synchrotron-based diffraction). Results showed the presence of mainly quartz, phyllosilicates, and feldspars with minor amounts of sulphides, sulphates, and Fe, Pb, and Zn carbonates concentrated in the rhizosphere of raw samples. The mineral phases, Zn and Fe oxides and willemite, detected in internal roots and stems samples after heating, indicated the presence of metals in the plant tissues. The ex-situ heating was found to be useful in determining the occurrence of metal-bearing phases in plants especially if combined with thermal analyses in order to reveal the temperature stages at which the significant reactions occur. Despite the high resolution proper of a synchrotron light source, the in-situ heating resulted less effective in revealing minor phases in organic samples, maybe due to the scarcity of oxygen within the sample holder that avoid sulphides oxidation and the degradation of organic compounds (Fancello et al., 2019). This method, if further developed, could be a useful tool in different application fields. The recognition of metals in plant tissues, and the mineralogical form in which they transform after thermal treatment, is an essential information for phytomining by hyperaccumulator plants. Likewise, biochar production from vegetal masses would benefit from the knowledge of the mineral assemblage attainable under different thermal conditions, to find the optimum temperature.
Potential recovery of metal from plants: a combined XRD-Thermal study on Juncus acuts
Fancello DarioPrimo
;Scalco Jessica;Medas Daniela;Dore Elisabetta
2022-01-01
Abstract
In the Arburese mine district (SW Sardinia, Italy), centuries of mine exploitation addressed to the extraction of Zn and Pb from sulphides and non-sulphides (calamine) deposits, left a widespread metal pollution. The Juncus acutus, a halophyte pioneer plant, was able to adapt in this extreme environment and to affect metal mobility thanks to its capacity to stabilize them in the external roots and rhizosphere. A method for evaluating the potential of reuse of biomasses for economic purposes is here presented starting from the specific case study of Juncus acutus. For this purpose, plants and rhizospheres, collected from the banks of two streams (Rio Naracauli and Rio Irvi) impacted by past mining activity, were used to perform Thermogravimetry and Differential Thermal analyses combined with X-ray Diffraction (XRD) carried out on raw samples and on samples heated ex-situ (by a conventional diffractometer) or in-situ (by synchrotron-based diffraction). Results showed the presence of mainly quartz, phyllosilicates, and feldspars with minor amounts of sulphides, sulphates, and Fe, Pb, and Zn carbonates concentrated in the rhizosphere of raw samples. The mineral phases, Zn and Fe oxides and willemite, detected in internal roots and stems samples after heating, indicated the presence of metals in the plant tissues. The ex-situ heating was found to be useful in determining the occurrence of metal-bearing phases in plants especially if combined with thermal analyses in order to reveal the temperature stages at which the significant reactions occur. Despite the high resolution proper of a synchrotron light source, the in-situ heating resulted less effective in revealing minor phases in organic samples, maybe due to the scarcity of oxygen within the sample holder that avoid sulphides oxidation and the degradation of organic compounds (Fancello et al., 2019). This method, if further developed, could be a useful tool in different application fields. The recognition of metals in plant tissues, and the mineralogical form in which they transform after thermal treatment, is an essential information for phytomining by hyperaccumulator plants. Likewise, biochar production from vegetal masses would benefit from the knowledge of the mineral assemblage attainable under different thermal conditions, to find the optimum temperature.
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