4. ANÁLISIS DE VIABILIDAD DE LA PLANTA DE BIOMETANIZACIÓN
4.2 VIABILIDAD ECONÓMICA
4.2.4 CÁLCULOS ECONÓMICOS
Aluminium is a light, malleable, ductile, easily machined and strong metal used for many different applications. It has excellent corrosion resistance and durability. Some of the many uses for aluminium are in transportation (automobiles, aircraft, trucks railcars, marine vessels, etc.), packaging (cans, foil, etc.), transmission lines, machinery, mirrors, cooking utensils, water treatment, etc.
Aluminium is the most abundant metal in the earth’s crust. It is a major constituent of many common igneous minerals, including feldspars and micas. Aluminim is a very reactive metal and it requires a lot of energy to extract it from its ore bauxite, which is composed mainly of the minerals gibbsite Al(OH)3, diaspore AlO(OH) and
boehmite AlO(OH). Therefore, recovery of this metal from scrap has become so important and about 50% of its production comes from recycled Al.
In our model of continental crust, we have considered 84 Al-containing minerals, one more than in Grigorev’s analysis. Their abundance in the earth’s crust will be determined applying the constraints explained above.
5A mineral is considered to be important here, especially when it constitutes an ore of a certain
element.
6Note that when we refer to percentages in the optimization process, they are always based on a
3.4.4
Antimony
Antimony is a semimetallic chemical element increasingly being used in the semicon- ductor industry. As an alloy, it increases lead’s durability and mechanical strength. Antimony compounds are used to make flame-proofing materials, paints, glass and pottery.
Stibnite S b2S3 is the most important ore of antimony and it occurs in large quanti-
ties in China, South Africa, Mexico, Bolivia and Chile. Other sulfide ores include ullmanite N iS bS, livingstonite H gS b4S8, boulangerite P b5S b4S11 or jamesonite
FeP b4S b6S14 and small amounts of oxide minerals formed by weathering are also
known. Considerable amounts of S b are also obtained as a byproduct in lead and copper refining, especially from galena.
Grigorev’s S b minerals are stibnite, boulangerite, tetrahedrite and the silver mine- rals samsonite, freibergite, stephanite and pyrargirite. Since stibnite is by far the most important mineral of S b, the quantity of that mineral on earth should presu- mably account for a very important part of S b in the crust. The quantity of antimony in stibnite considered by Grigor’ev is about four orders of magnitude smaller than Rudnick’s S b estimations in the upper crust. Therefore, we will ignore Grigorev’s estimations about stibnite and assume that most S b comes at equal rates from stib- nite and in solution with galena P bS. Grigorev’s estimation for boulangerite and tetrahedrite will be assumed to be correct. The quantity of the S b-Ag-containing minerals are fixed by their silver content.
3.4.5
Arsenic
Arsenic is a semi-metallic poisonous element. Its compounds are used as insecticides of fruit trees, as wood preservatives, in making special types of glass and lately, in the semiconductor gallium arsenade, which has the ability to convert electric current to laser light. Many other arsenic compounds used in the past have fallen out of use due to their toxicity and reactivity.
Arsenic minerals are widely distributed throughout the world and small amounts of the free element have also been found. Most arsenic is found in conjunction with sulphur such as realgar As4S4and orpiment As2S3, and the oxidized form arsenolite
As2O3. But non is mined as such because it is produced as a byproduct of refining
ores of other metals such as iron, copper, cobalt or nickel. The main economic source of As is arsenopyrite FeAsS. But it can be also recovered from loellingite
FeAs2, safflorite C oAs, nickeline N iAs, cobaltite C oAsS, gersdoffite N iAsS, enargite
Cu3AsS4, etc.
The arsenic-containing minerals considered by Grigor’ev are: the sulphides ar- senopyrite, orpimnet, realgar, freibergite and the sulfosalt group “fahlerz group”, which will be assumed to be represented by the mineral tennantite Cu11Fe2+As4S13.
Less abundant N i, Fe and C o arsenides recorded in his model are nickeline, gers- dorffite, loellingite and cobaltite. In addition to the minerals considered by Grigor’ev, the cobalt arsenide smaltite7 is also included. Due to the importance of its oxidized form, arsenolite will be also taken into account, assuming that it is responsible for the same quantity of As on earth as realgar. The relative proportions given by Grigor’ev will be kept in our model. The abundance of cobaltite, smaltite and freibergite are fixed by their C o and Ag contents.
3.4.6
Barium
Barium is an alkaline-earth metal that is chemically similar to calcium. Barium and its compounds have many industrial uses. For instance barite BaSO4is extremely im- portant for the petroleum industry, which accounts for more than 85% of the barite consumption in the world. It is used as a weighting agent in petroleum well-drilling mud. Barium-nickel alloys are used for spark-plug electrodes and in vacuum tubes as drying and oxygen-removing agents. Barium nitrate and chlorate give fireworks a green color. Other compounds of barium are used to make bricks, tiles, glass or rubber.
Barium is rather abundant in the earth’s crust. The chief mined ore is barite. A subsidiary mineral is barium carbonate witherite, BaCO3.
Barium-containing minerals analyzed by Grigor’ev are barite, psilomenane, hollan- dite and lamprophyllite. We take into account in our model all four minerals given by Grigorev’s analysis and include additionally witherite, for being an important Ba ore. It will be assumed that witherite accounts for about 10% of the Ba content of all barite in the crust. The relative concentrations of the minerals in Grigor’ev model will be kept. Nevertheless, the quantity of lamprophyllite is fixed as a result of the strontium mass balance8.
3.4.7
Beryllium
Beryllium is a light alkaline-earth metal and has one of the highest melting points of any light metal. It is used as an alloying agent in the production of beryllium-copper. Thanks to their electrical and thermal conductivity, high strength and hardness, good stability over a wide temperature range, Be− Cu alloys are used in many applica- tions. Some of them are in the defense and aerospace industries, in the field of X-ray detection diagnostic and in the manufacture of computer equipment.
Beryllium is relatively unabundant in the earth’s crust. It occurs as bertrandite
Be4Si2O7(OH)2, beryl Be3Al2Si6O18, chrysoberyl BeAl2O4 and phenakite Be2SiO4. Precious forms of beryl are aquamarine and emerald.
7See section3.4.18for details about the assumptions done for cobaltite and smaltite.
Grigor’ev accounted in his model for beryl, phenakite, bertrandite and helvite
M n4Be3(SiO4)3. In addition to those minerals, chrysoberyl is included in our model,
assuming that it has the same Be content as beryl. The relative proportions of the minerals given by Grigor’ev will be kept and the concentrations of each mineral will be obtained assuring that constraint 1 is satisfied.
3.4.8
Bismuth
Bismuth is a metal used for metallurgical additives for castings and galvanizing, in the manufacture of low melting solders and fusible alloys as well as low toxicity bird shot and fishing sinkers. Additionally, it finds some application in the pharmaceutical industry.
The most important ores of bismuth are bismuthinite Bi2S3, bismutite(BiO)2CO3
and bismite B2O3. It occurs naturally also as the metal itself and is found as crystals
in the sulphide ores of nickel, cobalt, silver and tin. The main commercial source of the element is as a byproduct from lead-zinc and copper plants.
Grigor’ev takes into account four minerals containing bismuth: bismutite, bismuthi- nite, native bismuth and tetradymite. Because of its importance, we include in our model bismite as well, assuming that it accounts for the same quantity of Bi as bismuthinite. Nevertheless, the relative proportions of bismutite, bismuthinite and native bismuth as well as the quantity of tetradymite9given by Grigor’ev will be kept in our model.
3.4.9
Boron
Boron is a non metallic element and the only non-metal of the group 13 of the peri- odic table. The most economically important compound of boron is borax, used for insulating fiberglass and sodium perborate bleach. Boric acid is also an important compound used in textile products. Other uses of boron are in synthetic herbicides and fertilizers, porcelain enamels, detergents, soaps, cleaners and cosmetics, cata- lysts or corrosion control.
More than 200 minerals contain boron, but only a few of commercial importance. Boron is usually found combined in tincal N a2B4O7·10H2O(natural borax), sassolite
H3BO3 (natural boric acid), colemanite C a2B6O11· 5H2O, kernite N a2B4O7· 4H2O,
ulexite N aC aB5O9· 8H2Oand boracite M g3B7O13C l. Only four minerals make up
almost 90% of the borates used by industry worldwide: borax, kernite, colemanite and ulexite.
Non of these minerals are included in Grigorev’s model. However, boron element is present in his analysis as the borate silicates tourmaline, kornerupine, axinite
and dumortierite. Nevertheless, we cannot forget the four most important boron- containing minerals for industrial applications. Therefore, we keep in our model the concentrations of the borates given by Grigor’ev and assume that the rest quantity of boron in the crust is in form of borax, kernite, colemanite and ulexite having all of them the same boron content.
3.4.10
Bromine
Bromine is a brownish-red liquid at ambient temperature and is used in industry to make organobromo compounds. These compounds find application as insecticides, fire extinguishers, water purification, flame retardants, pharmaceuticals, fumigants, dyes or photography.
Like chlorine, the largest amount of bromine is the oceans. Salt lakes and brine wells are also rich sources of bromine, and these are usually richer in bromine than the oceans. It occurs in nature as bromide salts in very diffuse amounts in crustal rock, which are accumulated in sea water after leaching processes.
Grigor’ev does not include any bromine-containing minerals. We will account for them in our model as “dispersed Br”.
3.4.11
Cadmium
Cadmium is used as a protective coating for iron and steel, as a pigment, and as a stabilizer for plastics. But its main application (about three-fourths of its production) is used in Ni-Cd batteries.
No cadmium ore is mined for the metal, because more than enough is produced as a byproduct of the smelting of zinc from its ore, sphalerite (Z nS), in which greenockite
C dSis a significant impurity making up as much as 3%.
No cadmium ores are recorded by Grigor’ev. We will assume in our model that greenockite is the only ore containing C d.
3.4.12
Calcium
Calcium is a silvery white metal belonging to the alkaline earth group. The metal is used as a reducing agent in the extraction of other metals, as a deoxidizer, desulfur- izer and decarbonizer in the manufacture of many steels, as separating material for gaseous mixtures, as an alloying agent used in the production of aluminium, beryl- lium, copper, lead and magnesium alloys as well as in the making of cements and mortars to be used in construction. Calcium compounds are used in a wide variety of applications such as insecticides, manufacture of plastics, as an additive in food and vitamin pills, as a disinfectant, as a fertilizer, in paints lights and X-rays, etc.
Calcium is the fifth most abundant element in the earth’s crust and the third most abundant metal after Al and Fe. Vast sedimentary deposits of C aCO3, which repre- sent the fossilized remains of earlier marine life, occur over large parts of the earth’s surface. Other important minerals are gypsum C aSO4· 2H2O, anhydrite C aSO4,
fluorite C aF2and apatite C a5(PO4)3F.
Sixty-six minerals contain C a in our model. The mass balance between elements and species for carbon in Grigorev’s model gives a quantity of C a greater than the accepted value for C a in the earth’s crust in Rudnick et al. [292]. Probably, Grigor’ev
overestimated the quantity of some calcium-containing minerals in the upper crust.
3.4.13
Carbon
Carbon is a non metallic element that forms more chemical compounds than any other element except hydrogen. The major economic use of carbon not in living material or organisms is in the form of hydrocarbons. The free element has a lot of uses, including jewelry (as diamonds), as a black fume pigment in automobile’s rims, printer’s ink, for pencil tips, dry cell and arch electrodes and as a lubricant. Carbon compounds have also plenty of uses. Carbon dioxide is used in drinks, in fire extinguishers and in solid state, as a cooler. Carbon monoxide is used as a reduction agent in many metallurgic processes. Other carbon compounds are used as solvents, cooling systems, for welding and cutting materials.
Carbon occurs both as the free element (graphite, diamond) and in combined form mainly as the carbonates of C a, M g, and other electropositive elements. It also occurs as CO2, a minor but very important constituent of the atmosphere, because of its important contribution to the greenhouse effect. Additionally, carbon is widely distributed in the organic form of coal and petroleum.
The carbon-containing substances included in Grigorev’s model are graphite, organic carbon, moissonite and the carbonates calcite, dolomite, siderite, aragonite, magne- site, dawsonite, cancrinite, strontianite, bismutite, bastnasite, smithsonite cerussite, azurite, malachite, ankerite and rhodocrossite. Additionally, we have included in our model the barium carbonate witherite, for being an important Ba ore. It must be pointed out, that the mass balance between elements and species for carbon in Grigorev’s model gives a quantity of C greater than the accepted value for C in the earth’s crust in Rudnick et al. [292]. Probably, Grigor’ev overestimated the quantity
of some carbon-containing minerals in the upper crust.
3.4.14
Cerium
Cerium is a silvery metallic element, belonging to the lanthanide group. The metal is used as a core for the carbon electrodes of arc lamps, in incandescent mantles for gas lighting, in aluminium and iron alloys, in stainless steel as a hardening agent and to make permanent magnets.
Although cerium is part of the REE, it is not rare at all. In fact it is the most com- mon rare earth and is more abundant than lead. It is commonly found in orthite, monazite, bastnaesite, rhabdophane or in zircon.
Further Ce-containing minerals considered in Grigor’ev model are miserite, loparite, rhabdophane, chevkinite, tanteuxenite, euxenite rinkolite, polycrase, gadolinite, nordite britholite and fergusonite. In addition to those minerals, the cerium included in the crystal structure of other minerals such as zircon, gadolinite or bastnasite is accounted in our model as “diadochic C e”. The quantity of it will be calculated as the difference between the cerium content in the crust and the cerium content of the minerals included in the model. Except for miserite, which will be assumed to have the same concentration on earth than the one given by Grigor’ev, all other
C e-containing minerals are fixed by their REE, U, Z r, Ba and Ta contents.
3.4.15
Cesium
Cesium is the most electropositive and least abundant of the five naturally occur- ring alkali metals. The most important use for cesium has been in research and development, primarily in chemical and electrical applications.
Cesium occurs as the hydrated aluminosilicate pollucite, Cs0.6N a0.2Rb0.04Al0.9Si2.1O6·
(H2O), but the world’s only commercial source is at Bernic Lake, Manitoba. Cesium
is mainly obtained as a byproduct of the Li industry.
Cesium is not included in any of the minerals given by Grigor’ev. We will account for it in our model in the form of pollucite, assuming that it is the only main Cs ore.
3.4.16
Chlorine
Chlorine is the most common element of the halogens. In pure form, it is a green- yellow diatomic gas. Chlorine is very reactive and combines with nearly all other elements. It is used in water purification, disinfectants, in bleach and in mustard gas. Chlorine is also used extensively in the manufacture of many products directly or indirectly, i.e. in paper product production, antiseptics, food, insecticides, paints, petroleum products, plastics, medicines, etc.
In nature it the upper continental crust it is found in the form of halite N aC l, but also in carnallite KC l and sylvite K M g C l3· 6(H2O). Nevertheless, it is so abundant
in the ocean, that it is extracted mainly from the sea and underground brine deposits for commercial uses.
In addition to the minerals mentioned above, Grigor’ev considers also the following
C l-containing minerals: apatite, scapolite, sodalite, bischofite, eudialyte and chlo- rargirite. The mass balance between elements and species for chlorine in Grigorev’s model gives a quantity of C l grater than the accepted value for C l in the earth’s crust in Rudnick et al.[292]. Probably, Grigor’ev overestimated the quantity of halite. All
of them are included in our model keeping their relative proportions. The quantity of eudyalite and chlorargirite are however fixed by the Z r and Ag mass balance.
3.4.17
Chromium
Chromium is a hard transition metal. In iron, steel and nonferrous alloys it imparts hardness and resistance to corrosion and oxidation. The use of chromium to produce stainless steel and nonferrous alloys are two of its more important applications. It finds also applications as dyes and paints to produce synthetic rubies, as a catalyst in dyeing and in the tanning of leather or to make molds for the firing bricks. The only ore of chromium of any commercial importance is chromite FeC r2O4. Other
less plentiful sources are crocoite P bC rO4and chrome ochre C r2O3, while the gem-
stones emerald and ruby owe their colors to traces of chromium. Like in Grigorev’s analysis, we include chromite as the main chromium-containing mineral, since the other C r ores can be assumed to be insignificant when compared to chromite. Di- etzeite C a2(IO3)2(C rO4) is the other C r-containing mineral considered but its con-