RARE -- CHAPTER 2 -- WHAT IS RARE?

CHAPTER 2 – WHAT IS RARE?

·         Chapter 2 starts off pointing out that the prices of metals like gold, standard of wealth, and silver have seen wide fluctuations over time.  Unlike gold, it is hard to keep with the value or price of rare earth metals.  The author then defines what these rare earth elements (REE) are:  they are a group of 17 elements that include scandium, yttrium and the 15 elements of the lanthanide series.  Of these, 5 are subclassified as light rare earth’s (lanthanum, cerium, praseodymium, neodymium, and samarium) and 10 as heavy rare earth’s (europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium).  Although the term “rare” is used, many of these are in fact not rare but exist in quantities comparable to that of metals considered common.  While not rare, it is known that, for many of these elements, it is difficult to extract a large amount of pure metal because they are thinly distributed occurring in milligram to gram amounts.  The chemical reactions used in the processing also results in loss of the pure metal to side reactions.  The author provides a simple explanation for why many metals appear gray or silver:  their outer electrons reside in closely spaced energy levels that affect the way to absorb and reflect visible light.  The author provides a simplified explanation of the unique magnetic properties of lanthanides arise from the atypical contraction of diameters of the ions formed as one moves from lanthanum down to lutetium.  These smaller trajectories impart special magnetic abilities to the electrons in atoms of the lanthanides useful in electronics and military applications.  What is the source of most of these rare earth elements? The author lists five species of minerals that contain REE’s:  monazite, tantalite, bastnasite, xenotime, and columbite.  The challenge of isolating pure individual REE’s is evidenced by the number of processing steps it takes to individually isolate the rare earth metals from monazite and bastnasite, 18 and 24 respectively.  One thing that makes extraction of REE’s more economically feasible is if deposits are found in ores mined largely for other more lucrative metals like copper in carbonatite.  The author ends the chapter with a short paragraph on the superconcentration of rare industrial metals in only two countries, an imbalance that can provide the impetus to serious conflicts, even war, later on over these rare resources.

·         FLUCTUATING VALUE:  Gold has seen numerous times when its value has swung wildly, starting as early as in the 14^th century.  Gold has been used as a standard of wealth for many years, only followed by wide margin by silver.  In ancient Rome, gold was worth 12 times the value of silver.  At the time of writing, an ounce of gold was worth 60 ounces of silver.  Unlike gold, silver, and platinum, it is difficult to place an up-to-date price on rare earth metals.

·         WHAT ARE THE RARE EARTH METALS?  There are 17 rare earth elements (REE).  The 15 elements after Yttrium and starting with lanthanum are collectively called the lanthanides.

o   Scandium                          Sc

o   Yttrium                             Y

o   Lanthanum                        La

o   Cerium                              Ce

o   Praseodymium                  Pr

o   Neodymium                      Nd

o   Promethium                       Pm

o   Samarium                          Sm

o   Europium                          Eu

o   Gadolinium                       Gd

o   Terbium                             Tb

o   Dysprosium                       Dy

o   Holmium                           Ho

o   Erbium                              Er

o   Thuluium                           Tm

o   Ytterbium                          Yb

o   Lutetium                           Lu

·         Although these elements are referred to as ‘rare”, some of them actually exist in about the same amount in the earth’s crust as some common metals.  Nd, Yb, Eu, Ho, and La exist in about the same quantity as Cu, Zn, Ni, or Co.

·         RARE VERSUS DIFFICULT TO ACQUIRE: The REE’s are thinly distributed in the earth’s crust, existing in milligram or gram amounts in certain places.  The term “rare earth” then derives from the trace quantities that exist for these 17 elements, making “extracting and accumulating useful, high purity quantities” difficult.  The basics of the chemical reactions involved in the processing also act as a “spanner” that further reduces the amount isolated due to loss to side reactions.

·         Why then the effort to isolate them?  Many of them are necessary for fabricating electronics.  The author likens them to vitamins: you do not need a lot of them but they are necessary.

·         ELECTRIC EXTERIORS AND THE CHARACTERISTICS OF RARE EARTH METALS:

·         The author gives some basic explanation of why most metals appear gray or silver:  The d electrons are constantly jumping back and forth between closely placed orbitals (in terms of energy levels).  When light impinges on the metal surface, these electrons in the outer orbital absorb only a small amount of the light.  The rest are reflected back in equal amounts across the wavelength spectrum in visible range.  But why is gold yellow?  The author answer this question in the following way: “The distance a given electron is jumping in an atom of gold is slightly smaller that it is in the silver-colored metals.  The electrons making the shorter jump absorb incoming light a little differently, emitting light with a wavelength corresponding to what we see as yellow”.

·         Why these REE are’s useful?  The author begins this section by providing a simple description of the unique electronic properties of the lanthanides:

·         The 15 elements of the lanthanide series, according to the author, share a subatomic level property of being able to “hide electrons better than the rest of the elements on the periodic table”.  In most cases of the elements, the outer electrons follow an elliptical trajectory, speeding past each other at 2,000 km/s, nearly 6,000 times the speed of sound, such high speeds that electrons are best viewed as forming a cloud of electrical charge around the nucleus.  The trajectories of these electrons follow different shapes around the nucleus, the shape of which and other properties define it as either being an s, p, d, f, g, etc type of orbital.  In the next paragraph describing the lanthanides in particular, the author presents the following basis for the uniqueness of their electronic structure:  “The electrons added to the rare earth elements as we move left to right along the row enter a quirky scenario, one that leads to an interesting phenomenon in the rare earth elements.  When the new electron is added to its set (one electron for each element after lanthanide), another set of electrons is left unprotected to the positive pull of protons in the nucleus.”  The author then goes on to use a football analogy that was lost on me.  In the end, however, he simplified it by saying that when an electron is added, the arrangement of the original electrons is altered in such a way as to remove to expose electrons in another area to the nuclear attractive force.  Because of this extra pull from the nucleus, when an atom of a lanthanide loses an electron to form an ion, the resulting particle contracts more so than what is expected from an atom with the given number of protons [lanthanide contraction]. 

·         As a result, ions of lanthanide àlutetium decrease in diameter.  This is opposite what is observed for other elements in the periodic table where the ions of elements typically increase in diameter going from left to right.

·         Because the ions are smaller, “the electrons travelling along their unique path bestow on the elements interesting magnetic abilities” that make them useful in the electronics industry and in military applications.

·         BREAKING DOWN THE MINERALS:

·         Because the term “mineral” is loosely used in different contexts (minerals in cereal, in our water, minerals in mining, etc.), the author offers the following definition: “a mineral is a solid, stable material that is found within the earth’s crust”.  They normally contain many different elements.  Gold and silver are an exception in that they are generally found in their native metallic form, needing very little processing.  On the other hand, most other metals, occurring in varying amounts, need to be extracted from the mineral deposits they are found in:

o   aluminum in bauxite

o   tantalum and niobium in the coveted ore coltan

o   cerium, lanthanum, praseodymium, and neodymium in the crystalline mineral monazite

·         5 species of minerals containing the rare earth metals:

o   Columbite

o   Tantalite

o   Monazite

o   Xenotime

o   Bastnasite

o   (Columbite and tantalite are often found together in the ore coltan.  An ore, according to the kindle dictionary is a “naturally occurring solid material from which a metal or valuable mineral can be profitably extracted”.)

·         The ore coltan contains large deposits of tantalum and niobium (two of the most sought after rare metals).  [The element niobium is not on the list of REE’s but the author simply refers to it as a rare metal.]  Large amounts of coltan are concentrated in Central Africa.

·         Monazite, xenotime, and bastnasite are relatively inexpensive mineral rocks.  They contain small deposits of various rare earth metals.  “Sizable deposits” of these three minerals are found in North America.

·         Most samples of the ore containing monazite are radioactive because it contains large deposits of radioactive thorium.

·         18 steps are required before the individual rare earth metals can be isolated from monazite.

·         24 steps are needed for bastnasite to do the same.

·         Carbonatite is a mineral prized for primarily because of large deposits of copper but it also contains small deposits of REE’s.

·         NOT ALL RARE EARTHS ARE CREATED EQUAL:

·         Light rare earth’s (LREE’s):  lanthanum, cerium, praseodymium, neodymium, and samarium.

·         Heavy rare earth’s (HREE’s): europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium. 

·         As a rule of thumb, the HREE’s are harder to find in usable quantities than the LREE’s and this more valuable.

·         Distribution in the universe:

o   The vast majority of matter in the universe is made from four elements: hydrogen, heliu, oxygen, and carbon.

o   Heavier elements and rare earth’s were not formed after the big bang.

o   Hydrogen, helium, lithum, and beryllium existed a few seconds after the universe was formed.

o   In general, lighter atoms are more abundant than heavier ones; hydrogen and helium are two of the most abundant in the universe.

·         At the time of writing, 90% of the supply of rare industrial metals come from two countries, a fact that the author claims reinforces the real possibility of conflict due to this monopoly.