Sources, behaviour, and environmental and human health risks of high-technology rare earth elements as emerging contaminants.

The increasing number of rare earth elements (REEs) studies in the past decade has been induced by their wider applications in industry, including electronics and high technology. This review presents the brief characteristics of REE, their occurrence in abiotic and biotic systems, and their possible detrimental effects on the environmental quality and human health. This also outlines the REE behavior in different geochemical interactions and the potential for tracing anthropogenic pollution sources.

The Characteristics, Occurrence, and Geochemical Behavior of Rare Earth Elements in the Environment: A Review

Rare earth elements (REE) are indispensable to infrastructure, technology, and modern lifestyles, which has led to an increasing demand for these elements. The current global rare earth oxides (REO) market is dominated by Chinese production, which peaked in 2006 at 133,000 tonnes REO per year, accounting for some 97.1% of global production, causing concern about the long-term supply of REE resources. Although the REE consist of 17 individual elements (15 lanthanides plus scandium and yttrium) that are hosted by numerous types of mineralization, the relatively modest scale of the global REE mining sector has limited our knowledge of REE mineral resources and mineralizing systems compared to metals such as copper and iron, which are produced in much larger quantities.

In order to quantitatively analyze the mineralogy, concentrations, and geologic types of REE deposits, we compiled a global dataset of REE mineral resources based on the most recently available data (2013–2014). This compilation yields minimum global contained total rare earth oxides plus yttrium oxide (TREO + Y) resources of 619.5 Mt split between 267 deposits. Deposits with available grade and tonnage data (260 of the 267 deposits in our database) contain some 88,483 Mt of mineral resources at an average concentration of 0.63% TREO + Y, hosting 553.7 Mt TREO + Y. Of the 267 total deposits in our database, some 160 have mineral resources reported using statutory mining codes (e.g., JORC, NI43-101, SAMREC), with the remaining 107 projects having CRIRSCO-noncompliant mineral resources that are based on information available in the industry literature and peer-reviewed scientific articles.

Approximately 51.4% of global REO resources are hosted by carbonatite deposits, and bastnasite, monazite, and xenotime are the three most significant REE minerals, accounting for >90% of the total resources within our database. In terms of REE resources by individual country, China dominates currently known TREO + Y resources (268.1 Mt), accounting for 43% of the global REO resources within our database, with Australia, Russia, Canada, and Brazil having 64.5, 62.3, 48.3, and 47.1 Mt of contained TREO + Y resources, respectively. Some 84.3 Mt TREO + Y is hosted within tailings (dominated by tailings from Bayan Obo but with smaller resources at Palabora, Steenkampskraal, and Mary Kathleen) and 12.4 Mt TREO + Y is hosted by monazite within heavy mineral sands projects, illustrating the potential for REO production from resources other than traditional hard-rock mining.

Global REE resources are dominated by the light REE, having an average light REO (LREO; La-Gd) to heavy REO (Tb-Lu and Y) ratio of 13:1. These REE deposits contain an average of 81 ppm Th and 127 ppm U, indicating that radioactive waste associated with REE extraction and refining could be a concern. Modeling the 2012 global production figures of 110 kt TREO + Y combined with an assumed 5% annual growth in REE demand indicates that known REE resources could sustain production until 2100 and that geologic scarcity is not an immediate problem. This suggests that other issues such as environmental, economic, and social factors will strongly influence the development of REE resources.

A Detailed Assessment of Global Rare Earth Element Resources: Opportunities and Challenges

Environmental fate and ecotoxicity of lanthanides: are they a uniform group beyond chemistry?

Rare earth elements (REE) are a homogenous group of 17 chemical elements in the periodic table that are key to many modern industries including chemicals, consumer electronics, clean energy, transportation, health care, aviation, and defense. Moreover, in recent years, they have been used in agriculture. One of the consequences of their worldwide use is the possible increase of their levels in various environmental compartments. This review addresses major topics concerning the study of REE in the soil environment, with special attention to the latest research findings. The main sources of REE to soils, the contents of REE in soils worldwide, and relevant information on the effects of REE to plants were explored. Ecological and human health risk issues related to the presence of REE in soils were also discussed. Although several findings reported positive effects of REE on plant growth, many questions about their biological role remain unanswered. Therefore, studies concerning the actual mechanism of action of these elements on cellular and physiological processes should be further refined. Even more urgent is to unveil their chemical behavior in soils and the ecological and human health risks that might be associated with the widespread use of REE in our modern society.

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Yonghe Zhang

Papers

A human health risk assessment of rare earth elements in soil and vegetables from a mining area in Fujian Province, Southeast China.