what happened to the aluminum metal that was consumed in this reaction

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• Lippincott Williams & Wilkins Open Access
• PMC4131935

J Occup Environ Med. 2014 May; 56(5 Suppl): S23–S32.

The Aluminum Smelting Process and Innovative Culling Technologies

Abstract

Objective:

The industrial aluminum product process is addressed. The purpose is to give a short only comprehensive description of the electrolysis prison cell applied science, the raw materials used, and the health and safe relevance of the process.

Methods:

This article is based on a study of the extensive chemic and medical literature on primary aluminum product.

Results:

Now, there are two main technological challenges for the process—to reduce energy consumption and to mitigate greenhouse gas emissions. A futurity stride may be carbon dioxide gas capture and sequestration related to the electric ability generation from fossil sources.

Conclusions:

Workers' health and rubber take at present become an integrated part of the aluminum business. Piece of work-related injuries and illnesses are preventable, and the ultimate goal to eliminate accidents with lost-time injuries may hopefully exist approached in the time to come.

Industrial production of main aluminum is carried out past the Hall–Héroult process, named after its inventors, who independently of each other, in 1886, adult and patented an electrolytic procedure in which aluminum oxide (or alumina, Al₂O₃) is dissolved in an electrolyte consisting mainly of molten cryolite (Na₃AlF₆) and aluminum fluoride (AlF₃). In modern aluminum electrolysis cells, several prebaked carbon anodes are dipped into the electrolyte, and oxide ions from the dissolved alumina are discharged electrolytically onto the anodes as an intermediate production. Still, the oxide immediately reacts further with the carbon anodes and gradually consumes them by formation of gaseous carbon dioxide (CO₂). Below the electrolyte, there is a pool of molten aluminum, which is the cathode in the prison cell. Fresh aluminum is formed from aluminum-containing anions that are reduced at the electrolyte–aluminum interface.

AN ALUMINUM PRODUCTION PLANT (SMELTER)

The buildings where the electrolysis cells are located (the potrooms) are huge. They can be more than than ane km long, in some cases nigh 50 m wide, and perhaps twenty thousand high. In a potroom, between 100 and 400 electrolysis cells are arranged in series, with the cathode of one cell electrically continued to the anode of the adjacent cell, to grade a cell line (which in the industry jargon is called a potline). Series connexion allows the use of high-voltage rectifiers; and for modern potlines, the maximum voltage now may be well above 1500 5. Although the current of the potlines are kept constant, the cells take private voltage adjustments to satisfy special technological requirements, such as rut balance, cell-operating conditions, and the age and condition of the cathode. Figure i shows a modern potline.

A mod potline with high-amperage side-by-side prebake cells.

Modern potlines now typically take amperages from about 300 kA and up to most 600 kA, which are the largest cells in operation now. These cells are placed adjacent every bit shown in Figure 1, to reduce the adverse magnetic effects of the loftier electrical current and also to reduce the oestrus loss from the cells. Older cells, which tin can have amperages less than 200 kA, are often placed cease to cease, but not always.

Day and night, each of these cells produces this valuable metallic in large amounts, maybe 100 kg or more every hour. Added together, the aluminum production in the plant tin can be huge, and the largest aluminum plants in the earth now report an annual production close to or fifty-fifty more than i million metric tons.

The process is still far from fully automated. Cranes are moved back and forth for transportation and changing of anodes and for removal of aluminum from the cells. Big vehicles transport the metal out of the potline building. They bring the metallic to the cast house for farther handling and casting of aluminum products.

The upper role of the cell is called the prison cell superstructure. Aluminum hoods are at that place to facilitate collection of the anode gases and fluoride vapors from the electrolyte, and these are sent to the smoke-treatment institute. Large vertical aluminum bars (chosen anode risers) acquit the electric current from the negative cathode of the neighbor prison cell to the positive anode of the nowadays prison cell.

A layer of alumina plus solid electrolyte encompass the top of the anodes. In that location should preferably be open up holes in the crust along the center line between the two rows of anodes, where the alumina is added automatically to the electrolyte. Underneath the crust, at that place is a 15- to 20-cm deep layer of electrolyte, and with 10 to twenty cm of molten aluminum beneath. These 2 melts have different densities, and as such, they do not mix with each other. Alumina is dissolved in the electrolyte and is electrolyzed at the cathode to form molten aluminum.

There is a high ambience temperature in the potrooms, due to the heat emitted from the cells. Ambient temperature in potlines is poor if there is no designed natural ventilation arrangement, equally may be the case for Søderberg potlines. In hot regions, estrus exposure is a serious problem in the potrooms, and extensive programs for data, acclimatization, and preventive measures are set upward. It is, therefore, important to accept strict rules for fluid intake, remainder areas, and measures to exist taken when the operators show signs of heat stress and heat burnout. Some individuals are more than at risk than others; for example, high body mass alphabetize is a well-known hazard factor for reduced tolerance to estrus exposure.

The loftier electric current flowing through each cell creates stiff static magnetic fields, and because these cannot be felt by the human torso, the fields tin cause damage to watches and credit cards. People will not be immune to enter the potroom if they take a pacemaker, as these also can be afflicted.

In these huge systems, there are lots of joints that used to be packed with asbestos material, usually chrysotile. Previously, asbestos was likewise used to embrace metal that had leaked from the cells. Asbestos is a known carcinogen; even so, a study supported by the Norwegian Cancer Institute could not discover whatever asbestos-related lung cancer amid onetime and present operators in the Norwegian aluminum industry.ane

THE ALUMINUM Production PROCESS—FROM ART TO SCIENCE

Throughout the years since its invention in 1886, the industrial aluminum production has developed from art to scientific discipline. Steadily increased agreement of the process has been achieved equally a result of extensive research and development piece of work, especially in the latter half of the twentieth century, both in aluminum plants and in several universities and academic institutions. During monitoring and intervention of the process, the cell operators are constantly faced with decision-making situations. Theoretical and applied preparation of the operators and their supervisors and superintendents give them the skills and knowledge needed to improve steadily cell operation and work practices.

The overall electrochemical reaction for industrial production of molten aluminum may be written every bit follows:

[ane]

This reaction is simple and shows that the two primary raw materials are alumina and carbon and that there are 2 chemical products, molten aluminum, which we want, and gaseous CO_two, which nosotros actually do not want.

The amounts of raw materials used in the process are illustrated in Fig. two. Alumina is consumed according to the stoichiometric ratio predicted from Equation 1. The consumption of alumina theoretically amounts to ane.89 kg per kilogram of aluminum produced. Nevertheless, in practice, the real value for the specific alumina consumption in the industry is a little higher, typically 1.93 kg, because the alumina supplied is not 100% pure. It always contains pocket-sized amounts of impurity oxides like Na₂O, CaO, Fe₂O₃, and SiO₂. Furthermore, from the aforementioned chemical equation, we see that we produce three-fourth moles of CO₂ per mole of aluminum. One-half mole of alumina should then theoretically react with 0.33 kg of carbon and produce i kg of aluminum and i.22 kg of CO_two. Nonetheless, because of other reactions of carbon with both oxygen and CO₂, between 0.40 and 0.45 kg carbon are consumed per kilogram of aluminum in practice. This is chosen the net anode consumption, and this in plow produces about one.5 kg of CO₂ per kilogram of aluminum.

The amounts of raw materials needed to produce 1 kg of aluminum.

Alumina must exist added regularly to the electrolyte to continue the normal electrolytic production going on continuously. Older aluminum electrolysis cell designs had large and infrequent additions of alumina, while modernistic cells are equipped with so-chosen signal feeders. Alumina is so supplied automatically from an overhead bin or hopper, which is built into the superstructure of the cell. Two to six volumetric feeders successively add about 1 kg of alumina to the electrolyte every minute or so. These pocket-sized additions increase the ability for the alumina powder to dissolve, mix, and disperse rapidly in the electrolyte. The average alumina concentration in the electrolyte is usually kept within the narrow range of two to four wt% alumina. Higher concentrations may lead to the formation of excessive amounts of undissolved alumina, which in the manufacture is called sludge. Because of its higher density, the sludge is collected at the bottom of the molten metal. Sludge has no useful purpose in the cell, and it is unwanted, mainly because information technology contributes to increase the electrical resistance in the cell and thereby the cell voltage.

On the contrary, low alumina concentrations in the electrolyte tin can give a dramatic change in the anode process, which leads to a and so-called anode effect. An anode outcome causes a very high cell voltage, perhaps up to 30 to 40 V instead of the normal 4.0 to four.5 V, by forming an electrically insulating layer of gas underneath the anodes. The anode gas limerick then changes abruptly from nigh pure CO₂ (one thousand) to mainly CO (thou) and as well some gaseous perfluorocarbon compounds, CF_four (g) and smaller amounts of C₂F₆ (k). These are greenhouse gases with high global-warming potential and extremely long atmospheric life times (of the order of 10,000 years).

The formation of these gases can exist lowered by reducing the anode effect frequency (the number of anode effects per cell per day) and the anode upshot duration (given in minutes). All aluminum producers have now made significant progress in reducing their emissions of perfluorocarbon gases. Near modernistic prebake cells can at present be controlled to operate for more than 1 calendar week and even for several months without an anode upshot.

Before leaving the topic of anode effects, it should exist mentioned that 70% to 80% of the anode gas evolved is and so CO (g). In some cases, termination of anode effects may crave manual intervention, and the operators may and so exhale in this poisonous gas. All the same, even if this effect has probably not been studied in detail, the concentration of CO (g) in the working atmosphere in potlines may be and so low that information technology is not harmful to humans.

In add-on to being the raw material for product of aluminum, alumina also acts as a thermal insulator when it is placed on summit of the self-formed solid chaff higher up the electrolyte, thereby reducing heat losses. Alumina is besides used for covering the top of the anodes, which conserves heat and minimizes air burning of the carbon anodes. More frequently, a mixture of alumina pulverisation and crushed pieces of solid electrolyte is used.

The third major role fulfilled by alumina is a very important one. Alumina is used to capture fluoride emissions from the cells by anode gas cleaning, by utilize of the and so-called dry scrubbing method. Alumina powder adsorbs the hydrogen fluoride (HF) gas evolved, and information technology also entraps fluoride condensates, mainly particulate sodium tetrafluoroaluminate (NaAlF₄). The resulting alumina is called secondary alumina and is then used as feed material to the cells. The cleaned frazzle gas, containing CO₂ and smaller amounts of perfluorocarbon gases, is discharged to the temper.

Figure 3 shows a menstruum canvas of the industrial aluminum production process. The processes made before the metal is sent to the cast house are chosen upstream processes, while the processes in the cast house to make extrusion ingots, canvass ingots, primary foundry alloys, and/or wire rods are called downstream processes. A much more detailed clarification of the electrolysis process can be found in several textbooks, for example, in Grjotheim and Kvande2 and Thonstad et al.three

Menstruum sheet of the aluminum production process.

RAW MATERIALS USED IN THE ALUMINUM PRODUCTION Procedure

Bauxite Mining

Aluminum is the most arable metallic element (8 wt%) in the earth's chaff. Information technology is found in nature in a wide variety of minerals combined with oxygen, silicon, and other metals. Because all the aluminum compounds are very stable chemically, aluminum is never institute as a metal in nature.

Information technology is mainly bauxite that is used equally raw cloth for the aluminum industry. Bauxite contains typically between 40 and 60 wt% alumina, with smaller amounts of atomic number 26, silicon, and titanium compounds, also every bit many other trace impurities.2

Ane of these impurities is glucinium, the concentrations of which vary from less than 1 parts per million to several parts per 1000000 in different bauxite mines. Because beryllium is toxic to humans and can be found to some extent in the potroom atmosphere (usually in concentrations less than 100 ng/m³), some concerns accept been raised. Nevertheless, studies in various aluminum plants have found a very depression incidence of sensitization against beryllium amongst the potroom workers.4,5

Alumina

In alumina refineries, bauxite is processed into pure alumina. The Bayer process extracts alumina by caustic digestion of crushed bauxite at loftier temperature and loftier pressure in an autoclave, followed past clarification, precipitation, washing, and finally calcination to produce pure anhydrous alumina. This is a white powder that looks similar ordinary table salt. Alumina has a high melting point, more than 2050°C, and is chemically a very stable chemical compound. This is why so much energy is required to produce aluminum from alumina.

Electric Ability

A big amount of electrical energy is, therefore, required to reduce alumina to aluminum. The most modern aluminum smelters need close to 13 kWh to produce 1 kg of aluminum, while the world boilerplate value for the directly current energy consumption now may exist shut to fourteen kWh/kg Al.ii

Data for the mix of power sources for aluminum production in 2009 show the following percentages, when including Chinese aluminum product^*:

Coal	51%
Hydro	39%
Natural gas	8%
Nuclear	ii%

Whereas hydropower traditionally has been the dominant electricity source for aluminum production, we see that coal at present accounts for more than 50% of the globe production.

Energy typically counts for roughly xxx% of the aluminum product toll,^† and its price is, therefore, highly significant for the economic system of the process. Energy consumption of aluminum product has decreased in recent years by means of technological improvements of the process. All the same, with the global demand for electrical energy increasing steadily, energy savings in all parts of the production process will be a very important chore for aluminum producers in the coming years. New aluminum plants will exist congenital only in areas with bachelor and cheap electric ability.

Prebaked Carbon Anodes

Today, all aluminum smelters use carbon anodes in their electrolysis cells. Carbon is a reasonably good electrical usher, and more importantly, it is able to withstand the action of the corrosive fluoride-containing molten electrolyte at about 960°C. Furthermore, carbon is an agile part of the electrochemical reaction, and thereby, it contributes to reduce the cell voltage by 1.0 Five. Equally such, electrical energy is saved by burning carbon. On the ground of Equation 1, we may consider carbon as a raw material in aluminum production, because carbon is consumed by the anode reaction.

A typical prebaked anode is made from a mixture of petroleum coke, coal tar pitch, and butts. An anode barrel is the rest of the used anode removed from the cell during anode changing. The butts content in the new anodes tin vary, just commonly it is betwixt fifteen% and 25%.two

The main constituent of prebaked carbon anodes is calcined petroleum coke. When crude oil is refined, there is a residue of about xxx% from the distillation unit. This balance is treated at virtually 450°C and 4 to 5 bar force per unit area to form what we telephone call green coke. The process is known equally delayed coking. This implies that coking is used to upgrade waste products from oil refineries that would otherwise have to exist sold as low-value fuels.

The coke residuum from petroleum refining is quite pure, and therefore, information technology has been the major source of carbon for anodes. This coke requires calcining at about 1200°C to remove volatile constituents and increase its density, strength, and porosity earlier information technology is blended into the anode mix. The product, now chosen calcined petroleum coke, is and so gear up to exist shipped to the anode production plant in the aluminum smelter.

In improver, the carbon anodes contain 13 to 16 wt% coal tar pitch to be used every bit a folder textile, thus bounden the coke and butts particles together in the anode.2 The pitch is distilled from the coal tar produced when coke for the iron and steel industry is made from coking of bituminous coal. Coal tar pitch is a circuitous hydrocarbon mixture consisting of thousands of compounds, of which only a few hundred have been identified chemically. Liquid pitch can be kept at most 200°C and transported by send to the aluminum smelters.

In the anode product procedure, the petroleum coke and the recycled anode fabric (butts) are crushed and sieved into fractions, which are so composite to obtain an optimum particle size composition. This blend is mixed with sufficient coal tar pitch (usually between xiii and xvi wt%) to allow molding into green anode blocks past pressing or by vibrating. Before these greenish anodes tin can be used in the electrolysis cells, they have to be prebaked in a special anode baking furnace at about 1150 to 1200°C, causing the pitch to carbonize and forming strong and dumbo anode blocks.

To provide electric contact and physical support, an aluminum or copper rod with an atomic number 26 yoke and from i to six fe stubs are attached to the anode. The stubs are placed into cavities on the top of the carbon anode and are fastened by applying molten cast atomic number 26 around the stubs. The purpose of the cast iron is to brand a good mechanical and electrical connection between the carbon anode and the stubs. This process is called anode rodding.

The Søderberg Anode

There are two basic anode designs soon in use. Prebaked anodes are the dominating type now. The other primary anode type is the Søderberg anode, invented past the Norwegian engineer Carl Wilhelm Søderberg (1876 to 1955). The Søderberg anode can be characterized as a monolithic, continuous, and cocky-blistering anode. This type of anode is as well made from a mix of petroleum coke and coal tar pitch, but hither the mix typically contains betwixt 25 and 28 wt% pitch,2 which is about twice the pitch content used for making prebaked anodes. Small-scale briquettes of Søderberg anode paste are and then fabricated, and these are added regularly to the peak of the Søderberg anode.

Although the anode paste passes slowly downward through a rectangular steel casing, it is broiled into an electrically conducting solid blended by pyrolysis of the pitch from the waste rut generated in the electrolyte and in the anode itself. The baked portion of the anode extends by the steel casing and into the molten electrolyte. The briquettes added on the top supersede the function of the anode that is beingness consumed at the working surface on the bottom.

Electric current usually enters the Søderberg anode through vertical spikes or studs, although in some older Søderberg cells, side-entry horizontal studs are used. These spikes are pulled and reset to a college level when they approach the lower anode surface. Søderberg anodes take an electrical resistivity that is about 30% higher than that of prebaked anodes. Søderberg anodes suffer from resulting lower efficiency and peachy difficulty in collecting and disposing of anode baking fumes, especially polycyclic aromatic hydrocarbons (PAHs). These hydrocarbons are mainly volatiles from the pitch used in the anode paste, but the PAH emissions tin can too depend on the conditions of the anode top. Polycyclic effluvious hydrocarbons consist of many unlike organic compounds, which have been shown to exist carcinogenic. Benzo(a)pyrene is considered as the most dangerous compound here. Its concentration is, therefore, measured regularly both in the working atmosphere and in the air exterior of the Søderberg potroom.

In Søderberg plants, epidemiological studies have found an increased incidence of bladder cancer, which is considered to exist caused by PAH exposures. Some studies have also found an increment in lung cancer among Søderberg potroom workers. This is also believed to exist caused by PAH exposures.one,6

The trend now is that Søderberg cells are gradually existence replaced by prebaked anode cells, even though the erstwhile relieve the upper-case letter cost, labor, and energy required to industry the latter. Particularly in the contempo v to 10 years, many Søderberg potlines take been shut downward, because they cannot cope with the new stringent emissions limit values to air for total fluorides, gaseous hydrogen fluoride, particulate fluorides, and grit. Nevertheless, there are still several Søderberg plants in performance in Russia, Europe, Brazil, and the United States.

ELECTROLYTE MATERIALS

The 4 main functions of the electrolyte are every bit follows:

• To be the solvent for alumina to enable its electrolytic decomposition, forming molten aluminum and CO_ii

• To laissez passer electricity from the anode to the cathode

• To provide a physical separation between the cathodically produced aluminum metal and the anodically evolved CO₂ gas

• To provide a heat-generating resistor that allows the cell to be self-heating

Cryolite unremarkably comprises 75 to 80 wt% of the molten electrolyte, which typically also contains excess aluminum fluoride (9% to 12%), calcium fluoride (four% to seven%), and alumina (2% to 4%). These three additives lower the melting point of the electrolyte, as well equally the cell operating temperature, and they increase the efficiency of the process.

Cryolite

The mineral cryolite is a double fluoride of sodium and aluminum and has a stoichiometric composition very shut to the formula Na₃AlF_half-dozen and a melting point of almost 1011°C. It has been found in substantial quantities only in Greenland. Cryolite was mined extensively there in the early twentieth century, but the mine is at present substantially exhausted. Cryolite, thus, has to be made synthetically now. It can be produced past reacting hydrofluoric acrid with an alkaline sodium aluminate solution co-ordinate to the overall reaction:

[2]

Aluminum Fluoride

Aluminum fluoride, AlF_iii, may comprise equally much every bit nine to 12 wt% of the electrolyte, when it is recorded in excess of the corporeality represented past the cryolite composition. Aluminum fluoride is consumed during normal functioning past three major mechanisms. Outset and foremost, aluminum fluoride reacts with sodium oxide that is e'er added as an impurity fabric in alumina. This amount has to be replaced, and it requires addition of about xx kg of aluminum fluoride per metric ton of aluminum produced to keep the AlF₃ concentration in the electrolyte abiding.

The second consumption mechanism is that aluminum fluoride can be depleted by hydrolysis due to moisture in different forms in the cell:

[3]

Gaseous hydrogen fluoride is extremely hazardous. Fortunately, fume capture and gas scrubbing efficiencies have been improved strongly in aluminum smelters, and very trivial HF (g) is emitted now to the potroom and the surrounding atmosphere.

Finally, losses of aluminum fluoride by vaporization from the electrolyte are appreciable. The almost volatile species evolved from the electrolyte is sodium tetrafluoroaluminate vapor, NaAlF_iv (m). It has a partial pressure of 400 to 600 Pa over the operating electrolyte, depending on its composition and temperature. Fortunately, more than than 98% of the fluorides, including HF (thou), are collected by the gas cleaning procedure in the smoke-treatment plant and are returned to the cell together with the secondary alumina.

Exposures to grit and fluorides in the prebake potrooms are typically over curt periods with extremely high exposures for sure tasks, followed by longer periods with very depression exposures. HF (g) may achieve high concentrations, upwards to 100 parts per 1000000, during short episodes during certain job procedures. These peak exposures are considered to exist a risk factor in causing occupational asthma. Occupational asthma among smelter workers has been extensively reported in several epidemiological studies. Recent reports from Australia and Norway, however, have shown a considerable decrease in the incidence of occupational asthma among potroom workers.7,8 Recent methods of simultaneous exposure measures and video surveillance when the operators carry out their jobs visualize the exposure during piece of work performance and help to mitigate exposure through work practise changes.9

Calcium fluoride is seldom added intentionally to the electrolyte. Because of the small amount of calcium oxide impurity in the alumina (typically only about 0.035 wt%), it attains a stable steady-state concentration of calcium fluoride of 4 to 7 wt% in the melt. At this level, a minor amount of calcium is codeposited into the aluminum, while some is emitted as a calcium compound, perchance CaCO_iii vapor, in the off-gas at a rate equal to its rate of introduction with the alumina.

Finally, a few words are needed nigh safety when working with molten cryolite. Many reactive substances can result in danger past contact with electrolyte and metal, and moisture is the most hazardous. The molten electrolyte tin give splashes and must be treated with respect and awareness. The electrolyte and also the metal take a temperature of about 950°C. In addition, the fluoride-containing electrolyte is corrosive. Remember that electrolyte burns must be cooled immediately with temperate h2o for at least an hr.

THE CATHODE AND CATHODE MATERIALS

In the prison cell, the electrolyte and the molten aluminum are independent in a preformed carbon lining that has refractory and thermally insulating materials within a steel shell. Graphitic or semigraphitized materials are now used extensively as prebaked carbon cathode blocks. The other materials used are silicon carbide (SiC) sidewall bricks and carbonaceous ramming paste. Several steel current collector bars are embedded in the carbon cathode and bear the electric electric current away from the jail cell. Effigy iv shows a schematic drawing of an aluminum electrolysis prison cell.

Schematic drawing of an aluminum electrolysis cell.

Insulation bricks are used to insulate the cathode thermally. These bricks are porous and vulnerable to penetration of electrolyte components through the cathode blocks. The insulation materials are protected past using refractory bricks, and sometimes a special bulwark material made of steel, glass, or other materials can exist added. Refractory bricks also have some insulating event, then that the temperature in the insulation materials does non go too high.

It should exist noted here that the word cathode is used in the aluminum industry to depict the whole container of electrolyte and metal. Nevertheless, the real acting cathode from an electrochemical betoken of view is the top surface of the molten aluminum pool. Thus, the aluminum atoms are formed from aluminum-containing ions that are reduced at the electrolyte–aluminum interface.

Cells are now typically 9 to 18 m long, 3 to 5 thousand wide, and ane to i.5 m deep. The depth of the operating jail cell cavity is relatively low, still, only 0.four to 0.5 m. Although carbon is the material known to withstand best the combined corrosive action of molten fluorides and molten aluminum, even carbon would have a very express life fourth dimension in contact with the electrolyte at the sides of the prison cell if it was not protected by a layer of frozen electrolyte. Now silicon carbide is used as sidewall material, but this material is also corroded by the electrolyte and needs to be protected.

TECHNOLOGICAL Central OPERATIONAL PARAMETERS FOR THE ALUMINUM SMELTING Process

Electric current efficiency (CE) is a very of import technological parameter used to depict the performance of the procedure. One may just say that current efficiency is the function of the current that is used to produce aluminum. Co-ordinate to Faraday'due south first law, ane kAh of electric electric current should theoretically produce 0.335 kg of aluminum, simply only 90% to 96% of this amount can be obtained in industrial cells. Loss in metal product is typical for all electrolytic processes and is, therefore, very hard to avoid completely. The master loss mechanism in aluminum electrolysis is recombination of the anodic and cathodic products, the so-called "back reaction," where aluminum dorsum-reacts with CO_ii to grade alumina and carbon monoxide.

To business relationship for these losses and to measure out the electrochemical efficiency of the process, the concept of current efficiency has been introduced in the industry as the ratio between measured and theoretical production rates:

[4]

Here, p is the measured production rate (kg/h), and p _o is the theoretical production charge per unit (kg/h), calculated from Faraday's first law.

In addition to the "back reaction," there are several other mechanisms bookkeeping for boosted small losses in electric current efficiency. A new jail cell lining will absorb sodium. Fortunately, the cell lining becomes saturated early in the cell'southward life, merely until this occurs, current efficiency will exist low. When a metal dissolves in a molten salt, it commonly imparts electronic electrical conductivity to the cook, thereby lowering the current efficiency. This is because the electrons "steal" current without producing any metal. Some investigators have constitute a pocket-sized electronic electrical conductivity for cryolite-based melts in contact with molten aluminum in laboratory cells, while others have not; so more than studies are needed hither. In any case, this contribution is small compared to the "back reaction."

Energy consumption (EC) is given in kWh/kg Al and can be calculated by the following equation:

[5]

Here Voltage is the operational cell voltage given in volts (V), and CE is current efficiency given as a fraction (and non in percent here). Energy consumption is the best technological parameter in aluminum production, considering it also includes current efficiency.

Energy efficiency is defined as the office of the electrical energy (amperage multiplied by voltage) that is used to produce aluminum. Typical values are but between 45% and 50%, even in modern cells. The remainder of the free energy produces rut, which is lost to the surround. 1 important job for the manufacture in the time to come is to reduce the energy consumption and thereby increment energy efficiency.

Cell OPERATION

The following operational procedures accept to be performed regularly, although at different time intervals in the potlines:

• Alumina feeding

• Anode change and anode covering

• Metallic borer

• Addition of aluminum fluoride

• Rack raising

Alumina feeding is present automatic through the utilize of point feeders, and therefore, anode irresolute is now the near labor-intensive manual routine performance. Prebaked anodes must be replaced at regular intervals when they have reacted down to well-nigh one fourth of their original size. This occurs afterwards 25 to xxx days. Considering each prison cell may have between 16 and 40 prebaked anodes, this ways that ane anode in average has to be changed approximately each day in every jail cell. Mod potlines are equipped with sophisticated overhead cranes that permit the operator to sit in an air-conditioned cabin and perform the anode-changing performance by manipulating robotic artillery. Alternatively, the employ of anode-irresolute vehicles is also common in many plants.

Anode changing causes the largest operating disturbance in cells with prebaked anodes. When a new, cold anode is inserted, weighing almost 1 ton, a layer of solid electrolyte rapidly freezes on the underside of the anode, and it can take upward to 24 hours to cook this layer completely. This reduces the temperature of the electrolyte locally, as the new anode draws very little current during this remelting procedure. The solid electrolyte layer is a poor electrical conductor. It too disturbs the anodic current distribution in the cell. Several aluminum plants are now irresolute ii anodes simultaneously, and this introduces an even larger thermal and electrical disturbance in the cell.

There will unavoidably be some dust nowadays in the air inside the potrooms. This potroom dust consists both of alumina and fluorides from the electrolyte and gives exposure of fine particulates to operators. The presence and compositional nature of these airborne particles have been discussed recently by Wong et al.ten

Especially during anode change, significant densities of nanoparticles with a median particle size smaller than 20 nm tin can exist recorded in the vicinity of the cells. They are possibly produced when the molten mass is exposed to the colder surround. The surface of these particles is large, and HF, SO₂, Be, and other particles on the surface represent potential wellness hazards of which at that place is express noesis at present. After existence released into the air, the nanoparticle manner is bailiwick to ageing, leading to a shift in the size distribution toward larger particles.xi

Private droplets particles of aluminum oxide/cryolite with a high cryolite content immediately become surrounded by a surface water film when exposed to relative high humidity (such as in the upper respiratory tract). Because gaseous HF and So_two are highly soluble in water, the aerosol particles may act as carrier for these gases into the lower respiratory tract.12

Anode covering is ordinarily done nearly 4 hours subsequently anode changing. Because the anodes are hot, we need a method of protecting them from air oxidation (air burn) and estrus loss. The anode embrace material must not introduce whatever metal contagion, and hence a mixture of alumina and recycled electrolyte is used. The composition of the anode comprehend can play an important part by reacting with the fume and fusing the under surface of the crust. Poor anode cover practise tin outcome in air burn of the anodes.

The spent anodes, the butts, are cleaned outside the cell in a separate butts-cleaning station. First the adhering electrolyte and alumina are removed and are recycled to the cells. The cleaned butts are and then crushed and reused as a carbon raw material in the manufacture of new prebaked anodes.

Removal of molten aluminum from the cells is called tapping, and this is also a labor-intensive routine manual performance. The spout of a vacuum ladle, or crucible, is dipped into the metal pad in the cell, and the metal is then siphoned out and into the crucible by the suction from an air ejector system. The molten metallic is and so weighed and transported to the cast firm. Although overhead cranes are usually used to assist the manual tapping work practices, too specially synthetic motorized vehicles can be used. But otherwise, these tapping procedures are identical.

Add-on of aluminum fluoride is performed automatically in modernistic cells. One or more silos for aluminum fluoride are built into the superstructure of the cell, and the addition is done through the hole in the chaff made by the point feeder breakers for alumina addition.

The final manual routine performance in the aforementioned list is called rack raising or anode axle raising. Considering the anodes are consumed, the anode axle, which is holding all the anodes in position, has to exist gradually lowered downward into the cell to maintain a abiding anode–cathode distance. The cathode, which is the metallic surface, is kept approximately at the same position by regular tapping. Finally, the position of the anode beam becomes and then low that information technology reaches a stopping device that tin can be electronic or physical. The beam so has to exist raised by use of a special anode beam–raising car carried past an overhead crane. All anodes are first continued electrically to this motorcar and are held in their correct positions in the electrolyte, while the anode clamps are loosened and the anodes are electrically disconnected from the anode beam. The beam is and so raised to its upper position, the anodes are refastened to the anode axle in their right position over again, and the car is finally removed from the top of the cell superstructure. This operation is carried out every two to 3 weeks for each cell, and information technology so raises the anode axle by about 20 cm.

If potline operators are asked what they recollect is the most risky or hazardous work they do on the cells, the respond will probably be axle raising. The reason for this is that sparks can occur through electric arcing, if the electrical contact with the anodes is not satisfactory. The possible loss of electric continuity during axle raising if an anode consequence occurs on the prison cell is the underlying reason for operators' business organisation hither. A potline open excursion, with explosive consequences, tin can and has indeed occurred, with a high take a chance of fatality for those in the proximity.

The extensive work to run the potrooms, as well as continuous maintenance, causes much noise at times, and the operators commonly accept to wear devices for noise protection. In spite of this, hearing loss is a risk that has to exist managed by the industry.

CELL PREHEATING AND START-Up

Before a new cell can be started, information technology has to be preheated. In that location are two main preheating methods that are used now. One is based on electric resistance preheating with a thin bed of small coke or graphite particles (2 to 5 mm unremarkably) between the anodes and the cathode. The other master method is flame preheating, where gas burners are used. Resistance preheating is the oldest method here, but both methods are now frequently in utilize in the aluminum industry.

The objective of preheating is to oestrus the prison cell materials as close as possible to the operating temperature of a normal prison cell, which really means 960°C for the cathode surface and the underside of the anodes. This provides a careful transition from the common cold jail cell to the operating temperature, and it contributes to avoid thermal shock of the cathode materials when the molten electrolyte is added. The higher the preheat temperature, the easier is the cell start-up. Nevertheless, this target is difficult to reach in practice, because unwanted hot spots on the cathode surface may and then be difficult to avoid. The target for the average cathode surface temperature at the end of the preheating is, therefore, commonly effectually 900°C.

The actual showtime-upwardly is done past adding molten electrolyte to the jail cell and raising the anodes carefully when the electric electric current is cut in. Then the electrolysis process starts. The temperature preferably should be kept less than grand°C in the first few hours and then lowered gradually to increase the aluminum production efficiency.

During the commencement-up and early operation of the cell, many of the hoods are removed so that the operators will be able to observe the movement of the molten electrolyte. In this period, there is germination of fluoride vapors and besides HF (g), which can crusade asthma-like symptoms for the operators when this gas in inhaled. The employ of proper respiratory protection is, therefore, very important during this type of work, and certainly also in other piece of work where people are exposed to fluoride vapors from the electrolyte.

MAGNETOHYDRODYNAMICS

The large electrical currents used in mod aluminum electrolysis cells (300 to 600 kA) generate strong magnetic fields, both outside and within the cell. These magnetic fields interact with the high electrical currents and exert then-chosen Lorentz forces. These forces are strong enough to produce move of liquid conductors. Molten aluminum, which in itself is nonmagnetic, is influenced by these strong magnetic fields. The reason is that molten aluminum then acts as a movable electric current usher.

The magnetic motion of the metal may give rise to loftier metallic velocities, metallic height variations, and metallic instabilities. To minimize the adverse consequences of these effects, it is desirable to compensate for the magnetic forces by a special arrangement of the interconnecting electric current usher organization.

Calculation of the magnetic fields and electric electric current flow patterns is complicated. All the same, for many years now, at least iv decades, powerful computer programs accept been designed to make these calculations and describe the fluid-dynamic consequences. These calculations have been refined to the point where cells with amperages up to 600 kA have been designed and such cells are at present in operation.

Even if these static magnetic fields usually range from 5 to xv mT in the potrooms, there is no indication that that they cause any serious wellness effects.thirteen,fourteen Nonetheless, during maintenance work in the rectifiers where the static fields may be even higher, at that place are some operators who feel magnetophosphenes (visual blurring or calorie-free flashes) and some operators who have dental fillings with mercury, describe metallic taste in the rima oris.

Safe IN ALUMINUM PRODUCTION PLANTS

Safe is number 1 priority for all aluminum producers. This area has received considerable attending in the last decades and rightly so. Workers' health and safety have get an integrated part of the aluminum business. Protection of the employees is disquisitional, because in that location are numerous possible exposures to the employees in this industry. Nothing is more of import than to send the employees habitation safely at the end of the working day. Proficient working surround is crucial, and good housekeeping is a prerequisite here.

In principle, all accidents at work can be avoided. The expression "Accidents don't happen; they are caused" is a good philosophy. Thus, piece of work-related injuries and also illnesses are preventable. The ultimate goal to eliminate accidents with lost-time injuries will hopefully be approached in the hereafter.

ALUMINUM IN THE Human BODY

Aluminum is a metallic that is all around us. People wear it, cook in it, and eat and potable it. Much food is packaged in aluminum foil, and beverage cans are usually made from aluminum. Daily intake of aluminum may range from 10 to 100 mg, the bulk beingness through oral routes. Nevertheless, about of this will be excreted. Still the corporeality of aluminum in the human torso ranges betwixt fifty and 150 mg, with an average value of about 65 mg. About half of the aluminum in the human body is stored in the basic, and virtually 1 quarter in the lungs.

Measurements of aluminum in serum of industrial workers accept always been difficult because so much sampling equipment contains aluminum, and thus, contamination of the sample may easily occur. Healthy subjects usually accept less than ten μg/L aluminum in serum. Postshift serum aluminum will increment to some extent in potroom workers. With normal renal function, aluminum is readily excreted in the urine. So far, there are no consistent findings of an increased incidence of either aluminum-induced diseases or neurological disorders amid potroom workers.

INNOVATIVE Culling ALUMINUM PRODUCTION TECHNOLOGIES

Electrolysis Cells With Inert Anodes

The concept of inert anodes for aluminum electrolysis is by no means a new thought. Information technology was suggested first past Charles Martin Hall already in his famous patent from 1886. Hall tried to employ copper anodes, but he soon found out that they did not work in do. Copper dissolved chop-chop in the electrolyte, and he had to surrender this idea. Carbon anodes accept since then been the simply possible practical solution for the anode material in industrial alumina reduction cells.

Nevertheless, in 2000, Alcoa announced that it was working hard with inert anodes, and 2 years later, Alcoa's chief executive officer Alain Belda stated that "the science is proved, and so we have an inert anode, simply we have not proved the commercial aspects." Of grade, this led to highly increased interest, curiosity, and activities, and information technology inspired several aluminum companies and research institutions to start work to try to notice an inert anode material. Much of this piece of work is surely unpublished and will probably remain so for proprietary reasons. Still, the open up literature at present offers a vast amount of individual publications and patents on inert anode materials. A comprehensive literature review of inert anodes was given by Galasiu et al15 in 2007.

So what is actually meant past an inert anode? The give-and-take inert means chemically nonreactive, and a completely inert anode volition, therefore, not react chemically or electrochemically in the electrolysis process. This means that it would ideally non exist consumed by the anode reaction. An inert anode has been given many names, like dimensionally stable anode, nonconsumable anode, and passive anode.

With inert anodes in the electrolysis cell, the full jail cell reaction volition be very simple:

[half-dozen]

We meet immediately that this reaction is dissimilar from Equation 1. Here, oxygen is formed at the anode, which environmentally is a highly favorable gas, compared with CO₂.

The dream would of course be to have anodes that lasted as long as the cell life, which now may be upward to 5 years or longer. Anode changes would then non be necessary afterwards the cell has been started. Nevertheless, it is a chemic fact that all materials have a finite solubility in the very corrosive cryolitic melts at well-nigh 960°C, so a totally inert anode volition probably never be found for use in these electrolytes. Thus, what we actually are looking for is a slowly consumable anode. Simply how slow a consumption rate tin can we tolerate?

The potential inert anode material must accept depression solubility and low reactivity in the electrolyte and also show good chemical resistance against the anodically produced hot oxygen gas. In addition, the anode material should be physically stable at the operating temperature, mechanically robust and resistant to thermal shock. In that location will be extreme requirements for keeping the wear rates of these anodes depression. A wear rate of the order of x mm/y may perhaps be sufficient, merely lower values would certainly be beneficial.

There are ii chief challenges in the development of inert anode materials. In addition to the requirement that the anode material should survive sufficiently long in the electrolyte, the metallic produced must be of adequate purity. The impurity metal content in the aluminum tin indeed exist very significant for the customers, and the need for making pure aluminum will get more stringent in coming years. The corrosion products, caused by the dissolution of the anode material into the electrolyte, predominantly will end upwardly in the metal phase and thereby contaminate the aluminum produced. Hence, the anode corrosion should be depression enough to give impurity contents corresponding to the nowadays specifications for smelter grade aluminum.

There are three master potential advantages in favor of developing a new cell technology with inert anodes:

1. Cost reduction. All costs straight associated with the consumable carbon anode volition then be eliminated, including the capital saving and raw materials costs past eliminating the need for the carbon anode fabrication, baking, and also the anode rodding plant. These cost savings may exist significant. Information technology has been indicated that there might be 25% to thirty% lower capital costs for a new potline with inert anode cell technology.3

2. Ecology friendliness. Inert anodes would eliminate all greenhouse gas generation and emissions from the electrolysis cells. Smelters would no longer generate CO₂, carbon monoxide, or perfluorocarbon gases (CF₄ and C_iiF₆), considering carbon would no longer be used as anode fabric. Carbon residues (butts) will of form disappear. In addition, the fluoride and dust emissions during anode change will besides be eliminated.

3. Improved occupational health issues. Inert anodes would reduce the work practices associated with the present prebaked carbon anode change. The frequency of anode changes will certainly exist drastically reduced with inert anodes. Working conditions in the potrooms would also exist improved by avoiding all anode furnishings.

What types of materials are the most promising for inert anodes? Ii main paths accept emerged so far:

1. The cermet conducting electrodes, which is used by Alcoa. The word cermet ways a combination of ceramics and metals and consists of a mixture of oxides and metals, NiFe_twoO₄ + NiO + Cu + Ag

2. The so-called "metal anodes" were previously adult by Moltech. These were metal alloys fabricated of Ni + Fe + Cu

Both these groups have reported large-scale trials retrofitting the conventional jail cell design. In reality, these two types of the electrodes go extremely similar at the anode–electrolyte interface, because this electroactive surface necessarily has to be an oxide, irrespectively of what materials the anode substrate is made of.16

Present Decision on Inert Anodes

Several companies and research institutions accept studied inert anode materials actively in recent years. It is no doubt that substantial progress has been made in inert anode evolution during the terminal decade, especially regarding the two main challenges: anode clothing and metal purity in inert anode cells.

UC Rusal has at present started rig testing of a pocket-sized three kA jail cell with inert anodes. On success of the rig tests, the company plans to begin production tests on its inert anode cells in 2015 at the Krasnoyarsk aluminum smelter.17

Performance of inert anode cells will certainly be very challenging. The commercial aspects of inert anodes have non notwithstanding been proven. At nowadays, a number of technology problems remain to be solved. It is presently impossible to say when, or even if, this may be a proven technology. In whatsoever case, there will probably go several years before the issues mentioned previously volition be solved satisfactorily. Perhaps, prison cell retrofitting will not exist the preferred development path in the futurity, and information technology is possible that a completely new prison cell pattern will be necessary.fifteen

Carbothermic Production of Aluminum

History

The idea of carbothermic reduction of alumina to aluminum is also an old dream. Aluminum–copper alloys with nearly 15% aluminum were produced industrially by this method already in 1886,xviii the same year as the present industrial process was invented. In the 1920s, Al–Si alloys with 40% to 60% aluminum were produced in Frg, and nearly 10,000 tons of these alloys were produced annually up to 1945.

The first attempt to produce pure aluminum by carbothermic reduction of alumina was made around 1955. In French republic, Pechiney worked on the process from 1955 to 1967, only terminated the program for technical reasons. Reynolds worked on an electric arc furnace to produce aluminum from 1971 to 1984. Alcan acquired information from Pechiney and continued their research, but stopped in the early 1980s. Alcoa tried to develop the procedure to produce Al–Si alloys from 1977 to 1982.

Withal, in 1998, Alcoa started the carbothermic production projection again together with Elkem R&D in Norway. Elkem had a long-fourth dimension experience with modernistic silicon furnace technology and came upwardly with the idea to use their experience to design a new type of tailor-fabricated high-temperature electric reduction reactor for carbothermic production of aluminum. Alcoa had a strong cardinal understanding and a long-time experience with carbothermic product of aluminum from the piece of work in the 1960s, 1970s, and 1980s. Together Alcoa and Elkem so agreed to endeavour this over again, and the work is nevertheless going on, as we will come across later on.

But what is really meant by carbothermic aluminum production? As the name says, the carbothermic method is to utilize carbon and heat to reduce alumina to aluminum, according to the overall reaction:

[7]

The reaction proceeds shut to and higher than 2000°C and produces CO equally the primary gas. From Equation 7, it is easily seen that the carbothermic process is dissimilar from the nowadays electrolytic process. No electrolysis is involved here, just electrical free energy is of course required. In the carbothermic process, alternate current is used to heat upwardly the raw materials alumina and carbon.

The Three Main Steps in the Carbothermic Procedure

The reduction of alumina to aluminum must take place in three stages (see Kvande et al,xviii Bruno,19 and Johansen et al20), which are characterized by three different phase combinations:

[8]

[ix]

[10]

Nevertheless, reaction equations with pure condensed solid phases volition give only an estimate clarification of the chemical organization involved here. Therefore, these reactions exercise not give a correct description of the reactions that will really occur. Equations 8 and 9 will really requite production of a molten slag, which contains a molten mixture of alumina and aluminum carbide.

The molten aluminum phase will contain some dissolved carbon, and therefore, information technology can be considered chemically every bit an Al–C blend. Equation ten, therefore, actually gives product of a molten aluminum–carbon–(carbide) alloy rather than pure aluminum. This molten blend volition float on top of the molten slag. An additional reaction step required would so be the product of pure aluminum (refining) from the alloy containing aluminum–carbon–(carbide).

The ii most difficult steps hither are the production of the aluminum–carbon alloy and the subsequent refining of the alloy. In addition, a gas scrubber is needed for drove of all the aluminum-containing gases that volition evaporate from the furnace at these high temperatures. This is also an technology challenge. A simplified flowchart of the process is shown in Figure 5.

Flowchart of the aluminum carbothermic technology–advanced reactor process concept of Alcoa and Elkem.20,21

Greenhouse Gas Emissions From Carbothermic Aluminum Production

The carbothermic reaction produces CO as the primary gas, and the gaseous by-product is, therefore, different from the present industrial process. Equation 7 shows that theoretically 1.v mol of CO are formed per mole of aluminum, which on a mass basis means 1.56 kg of CO per kilogram of aluminum produced.

In the temper, CO generally has a lifetime of several months earlier it converts to CO₂ past natural atmospheric processes. Still it is obvious, from both health and environmental reasons, that poisonous CO gas cannot exist emitted direct into the atmosphere from the carbothermic aluminum production. The gas will have to be burnt to CO_ii, and this reaction tin can exist written as follows:

[eleven]

This means that one.56 kg of CO will form 2.44 kg CO_ii per kilogram of aluminum. This value does not include whatever CO₂ resulting from electrode consumption during carbothermic reduction, but this is expected to exist modest here. Thus, the theoretical production of CO_two is then increased by near 60% in the carbothermic process, compared with the nowadays procedure.

In practice, this means that the entire amount of CO produced has to be captured. In a recent article by White et al,21 it is reported that the CO generated from the process is more than than 90% pure and it tin can then potentially be collected and used as a chemical. The CO gas can, for example, be used industrially as raw material for several unlike chemical products. According to these authors,21 this can include utilize as a reductant for removing Fe₂O₃ from bauxite, or as a reductant in direct reduced iron processes. If CO is used as fuel, it would produce CO₂, which then will accept to be stored by carbon capture and sequestration.

The determination is and then that the carbothermic process itself will increase the specific greenhouse gas emissions by most 60%. Nevertheless, the procedure promises to reduce energy consumption from 13 to xi kWh/kg Al. For hydroelectric power, this does not matter much for the overall greenhouse gas emissions. Yet, if the energy used to produce aluminum is coal-fired power and if the free energy consumption tin be reduced from 13 to 11 kWh/kg Al, this in itself can contribute to reduce the overall greenhouse gas emissions past nigh xx%. Fifty-fifty if this reduction may be considered to be significant, information technology can be concluded that unless all the CO (g) is captured and used industrially, the carbothermic process is not the solution to minimize the carbon footprint from aluminum production.

CONCLUDING REMARKS

The outlook of the primary aluminum manufacture may be summarized equally follows: This is at present a mature industry, which before long (2013) suffers severely from low aluminum prices and a very challenging market state of affairs.

Technologically, the nowadays aluminum production procedure can be a shut-to-zero greenhouse gas producer. The commencement step, which is actually ongoing, is to focus on lower specific energy consumption, and too to eliminate the occurrence of anode effects. Furthermore, it is possible to reduce the inherent production of CO₂ past reducing the net carbon anode consumption, although this reduction tin just be perhaps 10% or even less with the existing carbon anode technology. Here, an inert anode, if such a material can exist found and adult for utilize in industrial aluminum product, would represent a remarkable technological breakthrough, because then oxygen is formed at the anodes instead of CO_ii. On the contrary, another alternative process, carbothermic production of aluminum, would increase the CO₂ emissions if the produced CO is not captured and stored.

A natural pace to save energy in the present electrolysis procedure would exist to recover energy from the main rut loss sources of the cells, the cathode sidewalls and the anode gas exhaust systems. A future step may be CO_two gas capture and sequestration related to the electric power generation. Finally, drove and cleaning of the CO₂ from the electrolysis process itself may peradventure be a technical possible scenario in the future.

^*Data reported to the International Aluminium Institute in 2009.

^† Source: CRU, based on boilerplate weighted global aluminum production.

The authors declare no conflicts of involvement.

REFERENCES

1. Romundstad P, Haldorsen T, Andersen A. Lung and bladder cancer among workers in a Norwegian aluminium reduction plant. Occup Environ Med. 2000;57:495–499 [PMC free commodity] [PubMed] [Google Scholar]

2. Grjotheim K, Kvande H, eds. Introduction to Aluminium Electrolysis—Understanding the Hall–Héroult Procedure. 2nd ed. Düsseldorf, Germany: Aluminium-Verlag; 1993:199–217 [Google Scholar]

iii. Thonstad J, Fellner P, Haarberg GM, et al. Aluminium Electrolysis—Fundamentals of the Hall–Héroult Process. 3rd ed. Düsseldorf, Germany: Aluminium-Verlag, Marketing and Kommunikation GmbH; 2001:1–359 [Google Scholar]

4. Nilsen AM, Vik R, Behrens C, et al. Glucinium sensitivity among workers at a Norwegian aluminium smelter. Am J Ind Med. 2010;53:724–732 [PubMed] [Google Scholar]

five. Taiwo OA, Slade MD, Cantley LF, et al. Beryllium sensitization in aluminum smelter workers. J Occup Environ Med. 2008;50:157–162 [PubMed] [Google Scholar]

vi. Armstrong B, Hutchinson Due east, Fletcher T. Cancer Risk Post-obit Exposure to Polycyclic Aromatic Hydrocarbons (PAHs): A Meta-Assay. Inquiry Study 068. London, England: London School of Hygiene and Tropical Medicine for the Health and Safety Executive; 2003. ISBN 0-7176-2604-0. [Google Scholar]

7. Kongerud J, Grønnesby JK, Magnus P. Respiratory symptoms and lung function of aluminum potroom workers. Scand J Work Environ Health. 1990;16:270–277 [PubMed] [Google Scholar]

8. Donoghue AM, Frisch N, Ison M, et al. Occupational asthma in the aluminum smelters of Australia and New Zealand: 1991–2006. Am J Ind Med. 2011;54:224–231 [PubMed] [Google Scholar]

9. Rosen G, Andersson I-K, Walsh PT, et al. A review of video exposure monitoring equally an occupational hygiene tool. Ann Occup Hyg. 2005;49:201–217 [PubMed] [Google Scholar]

10. Wong DS, Tjahyono NI, Hyland MM. Visualising the sources of potroom grit in aluminium smelters. In: Suarez CE, ed. Light Metals 2012. Orlando, FL: TMS (The Minerals, Metals and Materials Club); 2012:833–838 [Google Scholar]

11. Thomassen Y, Kock Westward, Dunkhorst Westward, et al. Ultrafine particles at workplaces of a primary aluminium smelter. J Environ Monit. 2006;8:127–133 [PubMed] [Google Scholar]

12. Weinbruck S, Benker North, Kock W, et al. Hygroscopic backdrop of the workroom aerosol in aluminium smelter aerosols: a case for ship of HF and And so₂ into the lower airways. J Environ Monit. 2010;12:448–454 [PubMed] [Google Scholar]

xiii. Moen Be, Drabløs PA, Pedersen South, et al. Symptoms of the musculoskeletal arrangement and exposure to magnetic fields in an aluminium plant. Occup Environ Med. 1995;52:524–527 [PMC free article] [PubMed] [Google Scholar]

xiv. Moen BE, Drabløs PA, Pedersen S, et al. Absence of relation between sick leave caused by musculoskeletal disorders and exposure to magnetic fields in an aluminium establish, Bioelectromagnetics. 1996;17:37–43 [PubMed] [Google Scholar]

xv. Galasiu I, Galasiu R, Thonstad J. Inert Anodes for Aluminium Electrolysis. Düsseldorf, Frg: Aluminium-Verlag, Marketing & Kommunikation GmbH; 2007:ane–207 [Google Scholar]

16. Welch B. Inert anodes—the status of the materials scientific discipline, the opportunities they nowadays and the challenges that need resolving before commercial implementation. In: Bearne Chiliad, ed. Calorie-free Metals 2009. Orlando, FL: TMS (The Minerals, Metals and Materials Society); 2009:971–977 [Google Scholar]

17. 4-Traders. AlCircle Newsletter. Feb 7, 2013 [Google Scholar]

18. Kvande H, Huglen R, Grjotheim Thousand. Carbothermal production of aluminium—technically possible, but today economically impossible? In: Kvande H, ed. Proceedings of the International Symposium Arranged in Honour of Professor Ketil Motzfeldt. Trondheim, Norway: NTH; 1991:75–102 [Google Scholar]

19. Bruno M J. Aluminum carbothermic technology comparison to Hall–Héroult process. In: Crepeau PN, ed. Light Metals 2003, San Diego, CA: TMS (The Minerals, Metals and Materials Order); 2003:395–400 [Google Scholar]

twenty. Johansen K, Aune JA, Bruno M, et al. Aluminum carbothermic technology Alcoa–Elkem advanced reactor process. In: Crepeau PN, ed. Low-cal Metals 2003. San Diego, CA: TMS (The Minerals, Metals and Materials Society); 2003:401–406 [Google Scholar]

21. White CV, Mikkelsen Ø, Roha D. Status of the Alcoa carbothermic aluminum project. In: Downey JP, Battle TP, White JF, eds. International Smelting Technology Symposium (Incorporating the 6th Advances in Sulfide Smelting Symposium). San Antonio, TX: TMS (The Minerals, Metals and Materials Social club); 2012:81–88 [Google Scholar]

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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4131935/

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