Processing Refractory Ores By Atomic Weight

Mine to Magnet : Silver Investor Blog

The rare earths are a group of 17 elements comprising Scandium, Yttrium, and the Lanthanides. The Lanthanides are a group of 15 (Cerium, Dysprosium, Erbium, Europium, Gadolinium, Holmium, Lanthanum, Lutetium, Neodymium, Praseodymium, Samarium, Terbium, Thorium, Thulium, Ytterbium) chemically similar elements with atomic numbers 57 through 71, inclusive.

Yttrium, atomic number 39, isn’t a lanthanide but is included in the rare earths because it often occurs with them in nature – it has similar chemical properties. Scandium, atomic number 21 is also included in the group although it usually occurs only in minor amounts.

The most abundant rare earth elements (REE) are each found in the earth’s crust in amounts equal to nickel, copper, zinc, molybdenum, or lead – Cerium is the 25th most abundant element of the 78 common elements in the Earth’s crust. Even the two least abundant REEs (Thulium, Lutetium) are nearly 200 times more common than gold. Overall Rees have an abundance greater than silver and similar amounts to copper and lead.

The “rare” in rare earth elements came from frustrated 19th century chemists who decided they were uncommon after trying to isolate these chemically related elements. REES are also very hard to find in economic concentrations.

The Lanthanides are divided into light rare elements, LREE, and heavy rare earth elements, HREE. Light REE’s are made up of the first seven elements of the lanthanide series -  Lanthanum (La, atomic number 57), Cerium (Ce, atomic number 58), Praseodymium (Pr, atomic number 59), Neodymium (Nd, atomic number 60) Promethium (Pm, atomic number 61) and Samarium (Sm, atomic number 62).

HREEs are made up of the higher atomic numbered elements – Europium (EU, atomic number 63), Gadolinium (Gd, atomic number 64), Terbium (TB, atomic number 65), Dysprosium (Dy, atomic number 66), Holmium (Ho, atomic number 67), Erbium (Er, atomic number 68), Thulium (Tm, atomic number 69), Ytterbium (Yb, atomic number 70) and Lutetium (Lu, atomic number 71).

The principal economic sources of LREE are the minerals bastnasite and monazite. In most rare earth deposits, the first four REE – La, Ce, Pr, and Nd – constitute 80 to 99 percent of the total.

Deposits of bastnäsite in China and the United States represent the largest percentage of the world’s Rare Earth economic resources.

The second largest percentage of the world’s LREE Rare Earth economic resources is monazite. Monazite contains less La, more Nd and some HREE with usually elevated levels of thorium compared to bastnasite.

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