Assessment of the Ground and Plant Chemistry in an Area Affected by Rare Metal Ore Concentration Waste Storage


 This paper presents the results of an assessment of the ground and plant chemistry in disturbed areas exposed to impacts from adjacent rare metal ore concentration waste storage facilities.The focus of research were areas with sparse vegetation cover near the site of the first tailing storage facility (TSF), which is not exploited from 1985. In the summer of 2019, on three key plots within the study area, plant samples were collected at a small distance from the TSF and operating process transport routes (<1 km). Based on a bulk chemistry analysis of the ground samples, concentration values were measured above the background values adopted for the region’s soil parent rock materials, and in the absence thereof, the clarkes of elements in acidic (SiO2 >60%) rocks found in the earth's crust. Grounds were found to be rich in Ta, Ce, La, Th, Zr, Nb, which are also present in the loparite ores of various origins mined by the operation.The chemistry was examined of Salix spp. commonly found both in the study area and in the region as a whole and of wavy hair grass Avenella flexuosa L. An abnormally high level of zinc accumulation was observed in Salix lapponum (>850 mg/kg, biological absorption coefficient (BAC) >4), and technological transport influence was proposed as a possible cause. High paired correlation coefficients of rare and trace elements with Al and with each other (>0.9) in the bulk chemistry analysis of Salix spp. indicate the likelihood of deposition of minerogenetic dust particles. Based on the observed values of the BAC, the plants were classified into biological accumulation (BAC >1) and biological uptake (BAC <1) classes and the latter was found to be dominant.

Introduction reduction in the size of crushed ore, based on the difference in density between the main mineral -loparite and rock-forming minerals (its density is 1.7-2 times higher than the main rock-forming minerals, represented by feldspar, nepheline and aegirine). This is followed by the cleaning stage -apatite otation department. At the stage of nishing, light-colored minerals (nepheline, feldspar, aegirine) are removed using electrostatic and electromagnetic separation.
During the period of operation of the rst TSF site , the amount of ore concentration waste accumulated by the operation reached 6.7 million tons (Mesyats and Ostapenko, 2013). From 1985 to the present, tailings have been discharged to the second site of the mining operations tailings storage facility.
The study area is the industrial site of mining enterprise in the immediate vicinity of the rst TSF and process transport routes (Fig. 1). In the summer of 2019, ground samples were collected in the study area at three key locations. Samples were collected at a depth of 0-20 cm in accordance with the requirements of GOST 17.4.3.01-83. The collected samples were brought to an air-dry state and sieved through a 2 mm sieve.
Simultaneously with the sampling of grounds at the selected locations, three replicates of plant samples was collected. Plants of two genera were selected for the bulk analysis -wavy hair grass Avenella exuosa L., and woody plants of the willow genus Salix: S. phylicifolia, S. lapponum, and S. glauca. Willow leaves and the aboveground part of wavy hair grass were sampled in accordance with the international sampling guidelines for the ground vegetation cover to study the effect of air pollution on forest ecosystems (Manual…, 2007).
Bulk analysis after acid decomposition of the ground samples was carried out by inductively coupled plasma mass spectrometry (measuring instrument ELAN 9000 by PerkinElmer, USA) at the Shared Use Centre, Institute of Industrial Ecology of the North, Kola Science Centre at the Russian Academy of Sciences (INEP KSC RAS). This paper presents weighted average values of bulk ground chemistry.
Plant samples weighing 500 mg were placed in polypropylene tubes, to which concentrated HNO 3 was added. The mixture was kept in closed test tubes for 12 hours. Then the contents were transferred to the liners of DAC-100 autoclaves, placed in the microwave system MW 4 and decomposed in a single cycle (90 min). The solutions were returned to the test tubes and diluted to the mark with a 2% HNO 3  Based on the bulk ground chemistry analysis, the enrichment factor K o was calculated as the ratio of the concentration of the target element C i to its content in the parent rock C P : К о = С i / С P (Nikonov et al. 2004; Kabata-Pendias 2011). Gross content of the element in the C horizon of the region's native soils was taken as the background value (Nikonov et al. 2004). In the absence of background values, the comparison was based on the clarke content of the element in the earth's crust, determined for acid (SiO 2 > 60%) rocks as described in (Vinogradov 1962).
Based on the results of the bulk chemistry analysis of plants and ground, the biological absorption coe cient (BAC) was calculated as the ratio of the total content of an element in the plant material to its total content in the ground. Then the studied plants were classi ed into two groups: biological accumulation group (BAC > 1) and biological capture group (BAC < 1) (Avessalomova 1987; Perelman 1979).
To identify minerogenic particles in the dust deposited on the leaf blade, a correlation analysis was carried out of the bulk chemistry of the vegetative organs of Salix spp. Identi cation was carried out based on statistically signi cant correlation of the given element with the reference element aluminum (Reimann et al. 2001), as the most common (along with oxygen and silicon) element in the earth's crust.

Ground chemistry
The gross content of elements in the grounds (n = 9), plants, clarke and background values for the study area are shown in Table 1. No pronounced differences in the bulk ground chemistry under vegetation cover in the sampled area and that of the tailings on the rst TSF site (Krasavtseva 2020) were found for the measured elements, which suggests that these originate from same source. The current variability of the chemical composition can be explained by the differentiation of the particle size distribution of the tailings over a long period after the TSF was decommissioned. Note: * -data from (Nikonov et al. 2004); ** -data from (Vinogradov 1962 The biological absorption coe cients of most elements in the study area are less than 1, which indicates very low reserves of their bioavailable forms. This can be attributed to the coarse grounds and the resistance of ground minerals to weathering, including when exposed to plant root exudates. Figure 3 shows the biological absorption coe cients of those elements, for which a relatively high accumulation level in the vegetative organs of Salix spp. and is Avenella exuosa L. was found (> 100 mg/kg). Abnormal zinc accumulation is characteristic of Salix spp., which makes it possible to classify these tree species as belonging to the biological accumulation group. The gross zinc content in the vegetative organs of Salix spp. individuals varied between 560.2 and 856.6 mg/kg. The highest level of zinc accumulation was found in Salix lapponum (BAC 4.31). Avenella exuosa L. is classi ed in the biological capture group with a weak ability to accumulate Zn.
The high level of zinc accumulation in willow leaves can be associated with the effects of technological transport. For instance, (Avdoshchenko and Klimova 2020 a, b) showed the indicator role of willows in the monitoring of zinc and lead pollution in urban areas with maximum accumulation levels in areas with heavy tra c. Dust deposition of zinc on roadside vegetation is associated with the wear of tires containing zinc (Konczak et al. 2021).
With the observed low root absorption values of most elements, as indicated by the low BAC values in willows, clear differences in their chemical composition from European reference values indicate the impact of dust deposition on the vegetation cover in the study area. The reason may be the transfer of the ne waste fraction accumulated in the tailings storage facility. Based on the data on the current particle size distribution of the ore concentration waste stored at the rst site of the TSF (Goryachev et al. 2020), it was concluded that their surface layer should be classi ed as ne and medium-grained sands with a dusting during summer period.
Identi cation of dry deposition of dust particles on the willow leaf blade was carried out in this study based on the statistical signi cance of the "measured element -Al" correlation based on the results of the bulk chemistry analysis of willow leaves (Reimann et al. 2001). Correlation analysis data are shown in Table 2. Generally, plants growing in the study area are characterized by a low accumulation of the primary and secondary elements found in the ore concentration waste, which makes it possible to recommend these species for creating a sustainable man-made vegetation cover in the disturbed area. Based on our analysis of the collected data, one of the areas for further research will be to assess the compatibility of loparite ore concentration wastes with phytoremediation as a very promising, cost-effective solution that not only removes pollutants from the environment, but also helps restore lost biodiversity Conclusion 1. In the study area disturbed by a rare metal ore concentration tailings storage facility, elevated ground levels of Ta, Ce, La, Th, Zr, Nb present in the mined loparite ores of different genesis were found. 2. High pair correlation coe cients of rare metals with Al and with each other (r > 0.9) in the leaves of Salix spp. indicate the likelihood of deposition of minerogenic dust particles, which nding requires eld veri cation by installing sediment collectors and conducting a mineralogical analysis of the lter sediment. 3. Plants growing in the study area are characterized by a low accumulation of the primary and secondary elements found in the ore concentration waste, which makes it possible to recommend these species for creating a sustainable man-made vegetation cover in the disturbed area.

Declarations
Funding This study was carried out as part of the research project 0226-2019-0011 and partially funded by the grant 19-05-50065 Microcosm and by the Kolarctic CBC 2014-2020 programme, Project No. KO 1030 "Supporting Environmental Economic and Social Impacts of Mining Activity".

Figure 3
Biological absorption coe cients of Sr, Zn, Mn