NEODYMIUM

Chemical properties

grey metal ingot

Physical properties

Neodymium is the third most abundant rare-earth element in the Earth’s crust (24 ppm). Itis reactive with moist air and tarnishes in dry air, forming a coating of Nd₃O₃, an oxide witha blue tinge that flakes away, leaving bare metal that then will continue to oxidize.
Its melting point is 1,021°C, its boiling point is 3,074°C, and its density is 7,01 g/cm³.

Isotopes

There are 47 isotopes of neodymium, seven of which are considered stable.Together the stable isotopes make up the total abundance in the Earth’s crust. Twoof these are radioactive but have such long half-lives that they are considered stablebecause they still exist on Earth. They are Nd-144 (half-life of 2.29×10⁺¹⁵ years) andNd-150 (half-life of 6.8×10⁺¹⁵years). All the other isotopes are synthetic and havehalf-lives ranging from 300 nanoseconds to 3.37 days.

Origin of Name

Derived from the two Greek words neos and didymos. When combined, they mean “new twin.”

Occurrence

Although neodymium is the 28th most abundant element on Earth, it is third in abundanceof all the rare-earths. It is found in monazite, bastnasite, and allanite ores, where it isremoved by heating with sulfuric acid (H₂SO₄). Its main ore is monazite sand, which is amixture of Ce, La, Th, Nd, Y, and small amounts of other rare-earths. Some monazite sandsare composed of over 50% rare-earths by weight. Like most rare-earths, neodymium can beseparated from other rare-earths by the ion-exchange process.

History

In 1841 Mosander extracted from cerite a new rose-colored oxide, which he believed contained a new element. He named the element didymium, as it was an inseparable twin brother of lanthanum. In 1885 von Welsbach separated didymium into two new elemental components, neodymia and praseodymia, by repeated fractionation of ammonium didymium nitrate. While the free metal is in misch metal, long known and used as a pyrophoric alloy for light flints, the element was not isolated in relatively pure form until 1925. Neodymium is present in misch metal to the extent of about 18%. It is present in the minerals monazite and bastnasite, which are principal sources of rare-earth metals. The element may be obtained by separating neodymium salts from other rare earths by ion-exchange or solvent extraction techniques, and by reducing anhydrous halides such as NdF3 with calcium metal. Other separation techniques are possible. The metal has a bright silvery metallic luster. Neodymium is one of the more reactive rare-earth metals and quickly tarnishes in air, forming an oxide that splits off and exposes metal to oxidation. The metal, therefore, should be kept under light mineral oil or sealed in a plastic material. Neodymium exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at 863°C. Natural neodymium is a mixture of seven isotopes, one of which has a very long half-life. Twenty-seven other radioactive isotopes and isomers are recognized. Didymium, of which neodymium is a component, is used for coloring glass to make welder’s goggles. By itself, neodymium colors glass delicate shades ranging from pure violet through wine-red and warm gray. Light transmitted through such glass shows unusually sharp absorption bands. The glass has been used in astronomical work to produce sharp bands by which spectral lines may be calibrated. Glass containing neodymium can be used as a laser material to produce coherent light. Neodymium salts are also used as a colorant for enamels. The element is also being used with iron and boron to produce extremely strong magnets. These are the most compact magnets commercially available. The price of the metal is about $4/g. Neodymium has a low-to-moderate acute toxic rating. As with other rare earths, neodymium should be handled with care.

Characteristics

As an element, neodymium is a soft silver-yellow metal. It is malleable and ductile. It canbe cut with a knife, machined, and formed into rods, sheets, powder, or ingots. Neodymiumcan form trivalent compounds (salts) that exhibit reddish or violet-like colors.
Neodymium reacts with water to form Nd(OHO)₃ and hydrogen (H₂), which can explodeif exposed to a flame or spark. It is shipped and stored in containers of mineral oil.

The Uses of NEODYMIUM

Neodymium salts, electronics, alloys, colored glass, (especially in astronomical lenses and lasers), to increase heat resistance of magnesium, metallurgical research, yttrium-garnet laser dope, gas scavenger in iron and steel manufacture

The Uses of NEODYMIUM

Misch metal is composed of about 18% neodymium, from which cigarette-lighter flints aremade. Because neodymium absorbs the yellow “sodium” line in the visible light spectrum, itcan be added to glass to produce violet-, red-, or gray-colored glass. Neodymium glass is usedto calibrate spectrometers and other optical devices in astronomical and laboratory observationinstruments. It is also used in the production of artificial rubies used in lasers. Its salts areused as pigments for ceramic enamels and glazes.
Neodymium is magnetic and is used in many of the most powerful magnets in the world.Some types of steel contain up to 18% neodymium as an alloy. It is also used as a color forTV tubes and as a tint for eyeglasses.

The Uses of NEODYMIUM

Neodymium, plasma standard solution is used as a standard solution in analytical chemistry and atomic absorption spectroscopy. It is also used as a single-element standard solution for plasma emission spectrometry.

Definition

Metallic element having atomic number 60, group IIIB of the periodic table, aw 144.24, valence of 3. A rare-earth element of the lanthanide (cerium) group. There are seven isotopes

Definition

A toxic silvery element belonging to the lanthanoid series of metals. It occurs in association with other lanthanoids. Neodymium is used in various alloys, as a catalyst, in compound form in carbon-arc searchlights, etc., and in the glass industry. Symbol: Nd; m.p. 1021°C; b.p. 3068°C; r.d. 7.0 (20°C); p.n. 60; r.a.m. 144.24.

Definition

neodymium: Symbol Nd. A soft silverymetallic element belonging tothe lanthanoids; a.n. 60; r.a.m.144.24; r.d. 7.004 (20°); m.p. 1021°C;b.p. 3068°C. It occurs in bastnasiteand monazite, from which it is recoveredby an ion-exchange process.There are seven naturally occurringisotopes, all of which are stable, exceptneodymium–144, which isslightly radioactive (half-life10¹⁰–10¹⁵ years). Seven artificial radioisotopeshave been produced. Themetal is used to colour glass violetpurpleand to make it dichroic. It isalso used in misch metal (18%neodymium) and in neodymium–iron–boron alloys for magnets. Itwas discovered by Carl von Welsbach(1856–1929) in 1885.

Production Methods

Neodymium is recovered mostly from mineral monazite and bastnasite, thetwo most abundant rare-earth minerals. Monazite is a rare earth-thorium phosphate usually containing between 9 to 20% neodymium. Bastnasite is a rare earth fluocarbonate ore containing 2 to 15% neodymium. Both ores are first cracked by heating with concentrated sulfuric acid or sodium hydroxide. The recovery process from monazite ore using sulfuric acid is described below:
Heating the ore with sulfuric acid converts neodymium to its water soluble sulfate. The product mixture is treated with excess water to separate neodymium as soluble sulfate from the water-insoluble sulfates of other metals, as well as from other residues. If monazite is the starting material, thorium is separated from neodymium and other soluble rare earth sulfates by treating the solution with sodium pyrophosphate. This precipitates thorium pyrophosphate. Alternatively, thorium may be selectively precipitated as thorium hydroxide by partially neutralizing the solution with caustic soda at pH 3 to 4. The solution then is treated with ammonium oxalate to precipitate rare earth metals as their insoluble oxalates. The rare earth oxalates obtained are decomposed to oxides by calcining in the presence of air. Composition of individual oxides in such rare earth oxide mixture may vary with the source of ore and may contain neodymium oxide, as much as 18%.
The oxalates obtained above, alternatively, are digested with sodium hydroxide converting the rare earth metals to hydroxides. Cerium forms a tetravalent hydroxide, Ce(OH)₄, which is insoluble in dilute nitric acid. When dilute nitric acid is added to this rare earth hydroxide mixture, cerium(IV) hydroxide forms an insoluble basic nitrate, which is filtered out from the solution. Cerium also may be removed by several other procedures. One such method involves calcining rare earth hydroxides at 500°C in air. Cerium converts to tetravalent oxide, CeO₂,while other lanthanides are oxidized to trivalent oxides. The oxides are dissolved in moderately concentrated nitric acid. Ceric nitrate so formed and any remaining thorium nitrate present is now removed from the nitrate solution by contact with tributyl phosphate in a countercurrent
After removing cerium (and thorium), the nitric acid solution of rare earths is treated with ammonium nitrate. Lanthanum forms the least soluble double salt with ammonium nitrate, which may be removed from the solution by repeated crystallization. Neodymium is recovered from this solution as the double magnesium nitrate by continued fractionation.
Three alternative methods may be mentioned here, which give high purity material and are less tedious than the one described above. These are (1) ion exchange, (2) metallothermic reduction, and (3) electrolysis
In the ion exchange process, the nitric acid solution of the rare earth oxides obtained above is passed through a sulfonated styrene-divinylbenzene copolymer or other cation exchange resin in the hydrogen form. The rare earths are selectively eluted by flowing down a chelating solution of ethylenediamine tetraacetic acid (EDTA), or citric acid, or nitrilotriacetate (NTA) through the loaded column. The most stable complexes are eluted first. Metal ions are selectively stripped out in successive stages.
In the metallothermal reduction, the mixture of rare earth oxides obtained above is first converted to their halide salts. This is done by heating the oxidesat 300 to 400°C with dry and purified hydrogen fluoride, or preferably, by allowing dry hydrogen fluoride to pass over rare earth oxides and ammonium fluoride at 300-400°C. If chloride salt is desired, the oxides must be heated with ammonium chloride. For example, neodymium oxide may be converted to its fluoride or chloride:
Nd₂O₃ + 6NH₄F?HF → 2NdF₃ + 6NH₄F↑ + 3H₂O↑
Nd₂O₃ + 6NH₄Cl → 2NdCl₃ + 6NH₃↑ + 3H₂O↑
Neodymium, along with lanthanum, cerium and praseodymium, has low melting points and high boiling points. The fluorides of these and other rare earth metals are placed under highly purified helium or argon atmosphere in a platinum, tantalum or tungsten crucible in a furnace. They are heated under this inert atmosphere or under vacuum at 1000 to 1500°C with an alkali or alkaline earth metal. The halides are reduced to their metals:
2NdF₃ + Ca → 2Nd + 3CaF₂
NdCl₃ + 3Li → Nd + 3LiCl
The crucible is allowed to cool and is held at a temperature slightly above the melting point of neodymium for a sufficient time to allow separation of the metal.
In the electrolytic process, a fused mixture of anhydrous rare earth chlorides (obtained above) and sodium or potassium chloride is electrolyzed in an electrolytic cell at 800 to 900°C using graphite rods as the anode. The cell is constructed of iron, carbon or refractory linings. Molten metal settles to the bottom and is removed periodically.

Hazard

(Salts) Irritant to eyes and abraded skin

Hazard

Many of the compounds (salts) of neodymium are skin irritants and toxic if inhaled oringested. Some are explosive (e.g., neodymium nitrate [Nd(NO₃)₃]).

Safety Profile

Human systemic effects by intracerebral route: blood changes. It may be an anticoagulant lanthanoid. Care in handling is advised. Flammable in the form of dust when exposed to heat or flame. Slight explosion hazard in the form of dust when exposed to flame. Can react violently with air, halogens, N2.Violent reaction with phosphorus above 4OOOC. Many of its compounds are poisons.