RARE EARTH ELEMENTS

Rare earth elements (REE) were initially found in 1788, but their production and consumption worldwide remained below 5000 metric tons of rare earth oxides (REO) until the 1950s. In fact, they were seldom utilized in our daily lives until the 1960s. However, starting from the 1960s, rare earth applications began to extend to various aspects of everyday life, including television screens, the petroleum industry, and computer systems. Consequently, global production and consumption of REE experienced a significant surge in the subsequent decades.

The rare-earth elements (REEs), also known as rare-earth metals or rare earths, are a group of shiny silvery-white heavy metals. They are sometimes referred to as rare-earth oxides or lanthanides, which include yttrium and scandium. Compounds that contain rare earths are used in various applications such as electrical components, electronic devices, lasers, glass, magnets, and industrial processes.

It is important to mention the use of rare earths in renewable energy technologies like wind turbines, batteries, catalysts, and electric cars. It also covers the current state of mining, processing, and sustainability aspects. The availability of rare earths is currently declining due to certain quotas on exports and actions against illegal mining operations. This reduction in availability, combined with increasing demand, has caused rare earth prices to rise. Although prices have recently decreased, the situation is expected to remain volatile until new sources are found or closed mines are reopened.

Despite there being approximately a thousand identified deposits worldwide, there are only a few operating mines. The processing of rare earths contributes significantly to the greenhouse gas footprint, with hydrochloric acid being the largest contributor at around 38%, followed by steam use at 32% and electricity at 12%. Water and energy consumption throughout the life cycle of rare earths are also much higher compared to other metals.

Periodic Table of Elements

The rare earth elements encompass the lanthanide series on the periodic table, which ranges from atomic number 57 to 71 and includes elements such as lanthanum (La), lutetium (Lu), scandium (Sc), and yttrium (Y). These elements are in limited supply globally, with China holding significant control over their production and trade. The criticality level of REEs has been assessed as high, receiving a score of 29, based on multiple reports and three key factors for criticality analysis. The score mentioned was determined by adding up the individual scores for each REE in recent studies on material criticality conducted in the UK, EU, US, South Korea, and Japan.

Promethium (Pm), a member of the lanthanide series, is both radioactive and extremely rare. It is typically obtained through nuclear transformations. Rare earth elements are categorized as either light rare earth elements (LREE) or heavy rare earth elements (HREE), with the division occurring between the unpaired and paired electrons in the 4f shell. The classification of LREE and HREE is somewhat arbitrary, but the industry convention includes lanthanum to europium, as well as scandium, in the LREE category. The HREE category includes gadolinium to lutetium, as well as yttrium. However, the International Union of Pure and Applied Chemistry (IUPAC) definition includes gadolinium in the LREE category and considers all HREE to have paired electrons. There is inconsistency in the reporting of REEs, with some companies classifying lanthanum to neodymium as LREE and occasionally including samarium, while others consider samarium as the starting point for HREE. Additionally, rare earth oxides are sometimes grouped as LREE (La to Nd or Ce), medium REEs (Sm to Gd), and HREEs (Tb to Lu and Y), or referred to as yttric.

The Origin of REE

In comparison to other abundant elements like copper, lead, and tin, the global production of rare earth elements is significantly lower. However, despite their limited availability, rare earth elements are essential for various technologies crucial to clean energy initiatives and are found in everyday gadgets and electronics that have become prevalent in modern society. They are utilized in small but essential quantities in numerous technologies, materials, and chemicals across various sectors, including commerce, industry, society, medicine, and the environment.

These elements, known as REEs, are commonly found together in the Earth's crust due to their shared trivalent charge (+3) and similar ionic radii. Unlike individual elements like gold or copper, REEs occur in minerals either as minor or major components. Typically, these minerals are dominated by either light or heavy REEs, although both types can be present. It is worth noting that cerium and europium are exceptions to the trivalent charge, with cerium occasionally occurring in a Ce4+ valence state and europium existing as Eu2+.

The lanthanides (lanthanum to lutetium) display a distinctive characteristic where, as the atomic number increases within the group, an electron is added to an incomplete subshell within the nucleus rather than to an outer level. This selective filling of inner levels leads to a gradual decrease in the ionic radius of the trivalent lanthanide ions from La3+ to Lu3+, commonly known as the "lanthanide contraction."

In tropical areas with moderate to high rainfall, there is a formation of thick clay deposits containing relatively low levels of rare earth elements (REEs), ranging from approximately 0.04 to 0.25 percent of total REE oxides. This process occurs in three steps:

• Groundwater leaches REEs from the underlying granite bedrock.
• Clay-rich soils with significant thickness are formed above the granites.
• The mobilized REEs in the soils are loosely attached (through ion adsorption) to the clays.

There has been much speculation in recent decades about the concept of "peak oil," which refers to the point at which oil production will start to decline. This concept is now being discussed in relation to other elements in the periodic table that are experiencing rapidly increasing demand but limited supply. Two such elements are phosphorus (P) and indium (In). Phosphorus is essential for intensive farming practices to sustain a growing global population, but the limited supply of phosphorus suggests a potential crisis in the future. Indium is a crucial component in the displays of mobile phones and newer-generation computers. While it is relatively abundant in the Earth's crust, there are only a few mineral deposits with high concentrations of indium, meaning that the known reserves that can be economically mined may only last around 10 years. The increasing demand for rare earth elements and the limited reserves for certain rare earths also lead to speculation about their future availability.

Wind energy and electric vehicles are likely to be considered as part of the solution for a more sustainable future. Currently, these technologies rely heavily on dysprosium (Dy) and neodymium (Nd) for rare-earth magnets. However, the future widespread adoption of these technologies will lead to an increased demand for these elements. It is expected that recycling and recovery methods will help meet the demand for rare earth elements, but the current rates of recycling and recovery are very low (less than 1%), presenting significant challenges in terms of collection, processing, and recovery due to the low concentration of these elements in products. Some studies have listed environmental impact indicators for rare earths and reported results, but there is currently no comprehensive life cycle assessment of all relevant environmental impacts for specific rare earth products.

There is a lack of comprehensive information available in the public literature regarding the current state of rare earth elements (REEs). This is partly due to the fact that China was the main source of REEs during the growth of industries that rely on them, and the rest of the world has only recently begun actively seeking out new reserves. The recycling aspects of REEs have also been discussed. The content of this study can be considered a review, as it contains a significant amount of gathered, organized, compiled, and analyzed information. However, a small case study has been included to demonstrate the environmental impact, rather than providing specific and certain results, in order to highlight the importance of considering this aspect in the rare earth industry.