**5. Case studies of rare earth elements environmental impact because of mining, processing, and utilization**

Rare earth element mines differ from other mines, that is, rare earth element ores are not highly concentrated, and the quantity of tailings is frequently substantial compared to the quantity of rare earth elements recovered. Krasavtseva et al. [31] investigated heavy metals and rare earth elements at mine sites in the Kola Subarctic (Russia). Noting that finely dispersed materials from mine tailings exhibited from 1.5 to 3 times the heavy metal and rare earth element concentrations, they calculated pollution assessments using the (i) geoaccumulation index, (ii) enrichment factor, (iii) potential ecological risk factor, and the (iv) potential environmental hazard index. Increased mobilized heavy metal and rare earth elements were observed for mine tailing leachates. The heavy metal and rare earth element leachate concentrations were increased with (i) reduced pH levels, (ii) elevated organic carbon levels, and (iii) increased temperatures.

In China, Bai et al. [32] investigated six rare earth element mines for their environmental impact and conducted a cross-sectional comparison. Accurate resource and environmental carrying capacity (RECC) assessments are critical for ensuring that rare earth element exploration and extraction activities are appropriate and conducted with achieving multiple interests. The RECC assesses the ability of an ecosystem to resist external disturbances and maintain its original ecosystem services. The RECC considers multiple factors, including human activities, climate change, and energy structure and consumption. Except for the Bayan mine in inner Mongolia, the support index (evaluation of policies, inputs, and technologies to mitigate environmental impact) was greater than the pressure index (omission of policies, inputs, and technologies to mitigate environmental impact), implying limited environmental impact. The ratio of financial investment in pollution control was an important factor limiting environmental sustainability.

Wang and Liang [33] observed geochemical rare earth element fractionation involving the light and heavy rare earth elements in tailings of the Baotou mine in China. Using the NASC and PAAS values for normalization, the light rare earth elements showed greater normalized patterns. A map of the rare earth element PAAS normalized concentrations exhibited reduced concentrations at an increasing distance from the mine site. The total rare earth element concentrations (Σ REE) of surface samples varied from 156 to 57,000 mg kg−1, with a mean of 4700 mg kg−1. The enrichment factors for all of the rare earth elements displayed values suggesting very high to extremely high enrichment in the east, southeast, and south directions from the mine site, whereas enrichment factors in the northwest direction were indicative of only significant impact. In Baotou, China, Zhou et al. [34] investigated rare

#### *Evaluation of Rare Earth Element Mine Sites for Environmental Impact DOI: http://dx.doi.org/10.5772/intechopen.109161*

earth element concentrations in dust samples and subsequently expressed data using enrichment factors. The enrichment factors, when normalized to the local loess, indicated rare earth element contamination; that is, the igeo index indicated contamination and the HQ did not indicate contamination. In India, Humsa and Srivastava [35] investigated industrial waste from a titanium dioxide pigment industry. Soil resources in the impacted area demonstrated increased heavy metal (Fe, Cr, V, Ni, Cu, Zn, and Pb) concentrations, as well as increased concentrations of Sm, Tb, and Dy.

In Australia, Nkrumah et al. [36] investigated the rare earth element biogeochemical behavior in natural ecosystems to estimate their soil abundances. In addition to a slight HREE enrichment, key rare earth element concentrations were (i) Ce (2550 mg kg−1), (ii) La (645 mg kg−1), (iii) Gd (25 mg kg−1), and Lu (1.5 mg kg−1). Plant uptake showed variation among species, with broadleaf plants typically having greater rare earth element accumulation than greases. In Brazil, Cunha et al. [37] observed uranium-phosphate deposits and estimated the spatial rare earth element soil distribution. The soil rare earth element concentrations were closely correlated with the soil uranium and phosphate concentrations. In China, Zhao et al. [38] evaluated mine tailings from sites with and without phytoremediation. The Nd and Y hazard quotients (HQ ) were determined, with the concentration baselines for Nd and Y established at which 10% soil root length inhibition was observed. The HQs for wheat (*Triticum aestivum*) and mung bean (*Vigna radiata*) were less than 1; however, the geo-accumulation index was variably distributed as (i) uncontaminated (Igeo <0), (ii) uncontaminated to moderately contaminated (0 < Igeo <1), (iii) moderately contaminated (1 < Igeo <2), and (iv) moderately to strongly contaminated (2 < Igeo <3). Wang and Liang [39] assessed the environmental impact of rare earth elements in soils surrounding the Bayan Obo Mine. The Bayan Obo deposit is estimated to contain more than 100 million Mt. of rare earth reserves containing monazite and bastnaesite ores. The sum of the rare earth element concentrations in surface soil horizons varied from 150 to 18,900 mg kg−1. The distribution patterns of the individual rare earth elements were like those of the Bayan Obo ores.

MacDonald et al. [40] reviewed the development of pollution indices for freshwater ecosystems, noting that further research is warranted to guarantee accurate predictive environmental outcomes. Chamber [41] discussed "technologically enhanced naturally occurring radioactive material," noting that monazite mining will produce waste material having 232Th. 232Th will alpha decay slowly to 228Ra, which will more rapidly decay by beta emission to 228Ac (half-life of 5.75 years). Where the activity is substantial, appropriate actions to protect the environment and personnel are warranted. Aide and Aide [42] discussed the use of rare earth elements in identifying and assessing soil lithologic discontinuities. Aide and Aide also demonstrated that Fe-Mn masses (pedogenic nodules) in selected alluvial soils preferentially accumulated Ce and revealed a positive Ce anomaly, suggesting that alternating conditions of oxidation–reduction were important for glaebule (Fe-Mn nodules) synthesis and Ce incorporation.
