LEGISLACIÓN AMBIENTAL

3.4.38

Magnesium

Magnesium is a light, chemically reactive metal, belonging to the alkaline earth group. It is known as the lighter structural metal in the industry, due to its low weight and its capability of forming mechanically resistant alloys. Magnesium alloys are used in beverage cans, as structural components of automobiles and machinery. Magnesium compounds, primarily magnesium oxide, are used mainly as refractory material in furnace linings for producing iron and steel, nonferrous metals, glass and cement. Magnesium oxide and other compounds are also used in agricultural, chemical and construction industries.

11_{See sections3.4.41and3.4.4for details about the assumptions done for wulfenite and boulan-}

Magnesium is among the eight most abundant elements. It usually occurs in crustal rocks mainly as the insoluble carbonates and sulfates and less accessibly as silicates. Important magnesium-containing minerals are dolomite C aM g(CO₃)₂, magnesite

M g CO3, carnallite K2M g C l4· 6H2O, olivine(M g, Fe)2SiO4, talc M g3Si4O10(OH)2

or spinel M gAl₂O4.

Fifty-five magnesium-containing minerals have been considered in our model.

3.4.39

Manganese

Manganese is a grey-white chemically active metal. It resembles iron and is essential in the iron and steel production by virtue of its sulfur-fixing, deoxidizing and alloy- ing properties. It is also widely used in aluminium alloys. Further applications for manganese and its compounds are as additive in gasoline to boost octane rating, as a reagent in organic chemistry, as a colorizing and decolorizing agent for glass, as a paint, as a disinfectant and in batteries.

Manganese is found over 300 different and widely distributed minerals of which about twelve are commercially important. It occurs in primary deposits as the sili- cate metal. Of more commercial importance are the secondary deposits of oxides and carbonates such as pyrolusite M nO₂ and to a lesser extent as rhodochrosite

M nCO3. Vast quantities of manganese exist in manganese nodules (manganese, iron

and other metal-containing agglomerates) of the ocean floor. But no economically viable methods of harvesting manganese nodules have been found yet.

The M n-containing minerals included in Grigorev’s model are: rhodochrosite, pyro- lusite, chloritoid, ankerite, todorokite, vernadite, spessartine, wolframite, jacobsite, cryptomelane, manganite, tephroite, braunite, rhodonite, samsonite, psilomelane, hollandite, neptunite, helvite, eudyalite, lavenite and nordite. The quantity of the nine latter minerals is fixed by their W , Ag, Ba, Li, Be, Z r and S r contents. The rest minerals are assumed to have in our model the relative proportions given by Grigor’ev.

3.4.40

Mercury

Mercury is the only common metal which is liquid at ordinary temperatures. Because of its high density it is used in barometers and manometers. It is extensively used in thermometers thanks to its high rate of thermal expansion that is fairly constant over a wide temperature range. Amalgams of silver, gold and tin (alloys of mercury) are used in dentistry. Most mercury is used for the manufacture of industrial chemicals and form electrical and electronic applications.

Cinnabar, H gS is the only important ore and source of mercury, being the deposits at Almaden in Spain the most famous and extensive ones.

Grigor’ev records two minerals of mercury: cinnabar and metacinnabar. Both mine- rals will be kept in our model, maintaining their respective proportions.

3.4.41

Molybdenum

Molybdenum is a refractory metal able to withstand extreme temperatures without significantly expanding or softening. Those properties make M o useful in applica- tions that involve intense heat, including aircraft parts, electrical contacts and fila- ments. Molybdenum is used in alloys, mainly in steel, cast iron and superalloys. It is also used in electrodes, lubricants, pigments and catalysts.

The most important ore of molybdenum is the sulphide molybdenite M oS₂, which can be found in tungsten and copper ores, being molybdenite a byproduct of W and

Cuproduction. Less important ores are wulfenite P bM oO₄ and powellite C aM oO₄. All three minerals are considered in Grigorev’s model and will be considered in our model, keeping Grigorev’s relative proportions.

3.4.42

Neodymium

Neodymium is a member of the lanthanide series and hence has few properties which distinguish it from the other members of the series. Like lanthanum and other REE, it can be found in houses equipment such as televisions, lamps and glasses. Neodymium forms an important alloy (neodybium), found to produce very high magnetic field strengths with small masses.

Neodymium is the second most abundant of the REE after cerium. It is found in minerals that include other lanthanide elements such as monazite and bastnasite.

N d is included in the empirical formula of the minerals fergusonite, britholite and monazite given by Grigor’ev. In addition to those minerals, we include the rest of

N d in the upper continental crust as “diadochic N d” in our model, which should account mainly for N d found as an ion solution in bastnaesite.

3.4.43

Nickel

Nickel is a transition metal that belongs to the iron group. It is mainly used in the preparation of alloys, giving to them good strength, ductility and resistance to corrosion properties. About 65% of the nickel consumed in the western world is used to make stainless steel. The remaining is divided between alloy steels, rechargeable batteries, catalysts, coinage, foundry products and plating.

The bulk of the nickel mined comes from two types of ore deposits. The first are laterites where the principal ore minerals are nickeliferous limonite12and garnierite

N i3M gSi6O15(OH)2· 6(H2O). The second are magmatic sulfide deposits where the

principal ore mineral is pentlandite Fe_4.52+N i_4.5S₈. Arsenide ores such as nickeline

12_{Nickeliferous limonite is the term used to describe poorly crystalline nickel-bearing ferric oxides}

N iAsor gersdorffite N iAsS can be also found. N i appears as well in the crystalline structure of many other minerals including pyrrhotite, chalcopyrite, pyrite, ilmenite or magnetite.

The laterites group is represented in Grigorev’s model by garnierite, while the sec- ond by pentlandite. Other arsenides and sulphides of N i considered are violarite

Fe2+N i₂3+S4, vaesite N iS2, cooperite P t0.6P d0.3N i0.1S, nickeline and gersdorffite.

Additionally to those, we will include in our model “diadochic N i”, which should account for the whole N i appearing in small quantities in the crystal lattice of the minerals mentioned before. It will be assumed that diadochic N i contributes to the same N i amount than pentlandite. The relative proportions given by Grigor’ev will be maintained, although cooperite13, nickeline and gersdorffite14 are fixed by their

P d, and As contents.

3.4.44

Niobium

Niobium, sometimes called columbium, is a rare soft transition metal, used mainly for the production of high-temperature resistant alloys and special stainless steels. Small amounts of niobium impart greater strength to other metals. The applications of those alloys are in nuclear reactors, jets, missiles, cutting tools, pipelines, super magnets, surgical implants and welding rods. Niobium is additionally used as a superconductor when lowered to cryogenic temperatures.

Niobium has been mainly mined as columbite FeN b2O6. Two other important N b-

containing minerals are euxenite (Y, Ca, Ce, U, Th)(N b, Ta, Ti)₂O₆ and pyrochlore

N a1.5C a0.5N b2O6(OH)0.75F0.25 the latter is now its most important ore. Due to its

similarities to tantalum, minerals that contain niobium also contain tantalum, so that columbite gets the name of tantalite when tantalum preponderates.

Besides of columbite, pyrochlore and tantalite, other N b-containing minerals in- cluded in Grigorev’s model are ilmenorutile, murmanite, loparite, tanteuxenite, lavenite rinkolite, wohlerite, polycrase, blomstrandite and fergusonite. No addi- tional minerals will be included in our model. It will be assured the satisfaction of the mass balance, keeping the relative proportions of the different minerals given by Grigor’ev.

3.4.45

Nitrogen

Nitrogen is a common inert gas and an essential element in most of the substances that make up living organisms, including proteins. Its main application is as a com- ponent in the manufacture of ammonia, subsequently used as fertilizer and to pro- duce nitric acid. It can be used also as a refrigerant for freezing and transporting food products.

13_{See section3.4.47for details about the optimization method used for cooperite.}

Despite its ready availability in the atmosphere, constituting 78% of the air by vo- lume, nitrogen is relatively unabundant in the continental crust. The only major minerals are K N O₃ (nitre, salpetre) and N aN O₃ (sodanitre, nitratine). Both occur widespread.

Grigor’ev did not consider any of both minerals. We will assume that they are the only carriers of Nitrogen in the upper continental crust at equal relative proportions.