## 1 Introduction
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Element**} & \multicolumn{2}{c}{**[PERSON] and**} & \multirow{2}{*}{**[PERSON]**} & \multirow{2}{*}{**[PERSON] and**} & \multirow{2}{*}{**[PERSON]**} & \multirow{2}{*}{**[PERSON] and**} & \multirow{2}{*}{**[PERSON]**} & \multirow{2}{*}{**[PERSON]**} & **Earth** \\  & **Love 1963** & & & & & & **Crust** \\  & [34] & & & & & & **Crust** \\ \hline Sc & 10 & - & - & 16 & 10 & 5–10 & 22 & \\ Y & 28 & - & 29 & 24 & 28 & 28–70 & 33 & \\ La & 18 & 18.3 & 29 & 30 & 18 & 5–18 & 39 & 30 \\ Ce & 46 & 46.1 & 70 & 60 & 46 & 20–46 & 66.5 & 60 \\ Pr & 5.5 & 5.53 & 9 & 6.7 & 5.5 & 3.5–5.5 & 9.2 & 6.7 \\ Nd & 24 & 23.9 & 37 & 27 & 24 & 12–24 & 41.5 & 27 \\ Sm & 6.5 & 6.47 & 8 & 5.3 & 6.5 & 4.5–6.4 & 7.05 & 5.3 \\ Eu & 0.5 & 1.06 & 1.3 & 1.3 & 0.5 & 0.14–1.1 & 2 & 1.3 \\ Gd & 6.4 & 6.36 & 8 & 4 & 6.4 & 4.5–6.4 & 6 & 4 \\ Tb & 0.9 & 0.91 & 2.5 & 0.7 & 0.9 & 0.7–1 & 1.2 & 0.7 \\ Dy & 5 & 4.47 & 5 & 3.8 & 5 & 4.5–7.5 & 5.2 & 3.8 \\ Ho & 1.2 & 1.15 & 1.7 & 0.8 & 1.2 & 0.7–1.2 & 1.3 & 0.8 \\ Er & 4 & 2.47 & 3.3 & 2.1 & 4 & 2.5–6.5 & 3.5 & 2.1 \\ Tm & 0.4 & 0.2 & 0.27 & 0.3 & 0.4 & 0.1–1 & 0.52 & 0.3 \\ Yb & 2.7 & 2.66 & 0.33 & 2 & 2.7 & 2.7–8 & 3.2 & 2 \\ Lu & 0.8 & 0.75 & 0.8 & 0.7 & 0.8 & 0.8–1.7 & 0.8 & 0.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Presence of elements in the Earth’s crust in parts per million. Until the 1970s, the production of REEs was testimonal. However, the development of electronics increased the production of such metals. In the mid-1980s, China started trading rare earths, taking advantage of the fact that they were a by-product in some of its most bulky iron ore deposits [14]. China's entry into the market of REEs eventually affected the rest of the world's production, since the lower wages of their workers and the lower levels of environmental control increased its competitiveness. In 2011, China was producing 97% of world's REEs [47; 48; 49]; however, this had decreased to 80% in 2017 [42]. Figure 1 shows the current situation of the market [42]. China retains the dominant position, and their production levels did not vary between 2016 and 2017; however, Australia and Russia have increased their production of REEs. By September 2017, Chinese exports had grown 10% compared with the same period in 2016, and its consolidation into the six major industrial entities continued [32]. Market forecasts imply that the findings of new deposits along with new techniques of recovery, recycling, and reuse of REE will enable world production to continue increasing. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Country** & **Gupta [32]** & **Schüler [45]** & \
\begin{tabular}{c} **U.S. Geological** \\ **Survey 2012 [46]** \\ \end{tabular} &
\begin{tabular}{c} **U.S. Geological** \\ **Survey 2018 [42]** \\ \end{tabular} \\ \hline US & 13,000,000 & 13,000,000 & 13,000,000 & 1,400,000 \\ Australia & 5,800,000 & 5,400,000 & 1,600,000 & 3,400,000 \\ Brazil & 310,000 & - & 48,000 & 22,000,000 \\ Canada & 1,000,000 & - & - & 830,000 \\ China & 89,000,000 & 36,000,000 & 55,000,000 & 44,000,000 \\ India & 1,300,000 & 3,000,000 & 3,100,000 & 6,900,000 \\ Malaysia & 35,000 & - & 30,000 & 30,000 \\ South Africa & 400,000 & - & - & 860,000 \\ Sri Lanka & 13,000 & - & - & - \\ Former USSR & 21,000,000 & 19,000,000 & 19,000,000 & 18,000,000 \\ Other countries & 21,000,000 & 22,000,000 & 22,000,000 & 23,600,000 \\ Total & 154,258,000 & 98,400,000 & 110,000,000 & 120,000,000 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: World reserves of rare earth elements (REEs). Figure 1: Rare earth production by country [33]. Given the booming market for REEs and the future forecasts that report a significant increase in demand, which is estimated to reach 6% per annum (p.a.) for 2020 [50], as well as their specific function, alternative sources will be essential in the future [2; 51; 52; 53; 54; 55; 56; 57; 58; 59]. In particular, waste mining can be an adequate source in many ways.