Canadian Prime Minister Justin on social media on the morning of May 11, 2018 A share of Tredeau came to the fore : Alcoa , Rio Tinto , Apple and the Quebec local government signed a collaboration that would create new jobs for thousands of Canadians , reduce Canada’s carbon footprint and strengthen the North American Aluminum industry. The project eliminates all greenhouse gas emissions from traditional primary aluminum production and instead produces oxygen – not yazım yes spelling error “but“ oxygen-generating ”- and as a“ revolution isinde in primary aluminum production technology, as well as a decisive step to tackle global climate change was introduced.
American primary aluminum producer ALCOA ( Aluminum) for the industrialization of the project, ie its commercialization Company of America ), Rio Tinto (Former ALCAN- Aluminum) The Company ofCanada ) and ELYSIS formed a joint venture and the budget of the project, planned to be realized in two phases, was declared as 558 million Canadian Dollars (approximately 435 million US Dollars).
If the project can go into industrial practice, Canada will reduce its annual greenhouse gas production by 6.5 million tons. This is equal to the greenhouse gas emissions produced by approximately 1.8 million automobiles in a year.
The domestic aluminum production volume of the Canadian aluminum industry is 4.6 billion Canadian dollars (approximately 3.59 billion US Dollars) and the annual aluminum export volume to the US is 9.5 billion Canadian dollars (approximately 7.41 billion US Dollars).
Government of Canada, this project, 1.26 billion Canadian dollars (980 million US dollars) to support high-quality business investment budget with and Canada, aimed at economic growth and Canadian firms to prioritize to improve the strength of the economy “Strategic Innovation (Innovation) Fund” to support in. The project is expected to become applicable on an industrial scale by 2024.
Traditional Primary Aluminum Production
There is no information about this technological revolution in the explanations, but those familiar with primary aluminum technologies will immediately see that this revolution is an “ inert anode revolution..
The recovery of metallic aluminum from ores containing aluminum is a complex and costly process .
Due to the aluminum in nature only oxide and oxide mixtures form and in that ore also contain more easily reduced by a number of other mixed oxides of aluminum oxide, direct ore reduction way of aluminum obtained by technically to be useful is that of impure. Aluminum should reach over 2000 OC for reduction with carbon such as iron ore. Aluminum is also one of the rare light metals carbide forming with calcium and titanium . Similarly, reduction of aluminum oxide with hydrogen gas is not possible. Due to the oxidation potential of -1.66 V in the EMF series , only hydrogen gas is released from the cathode when it is tried to be reduced from its aqueous solutions . Many other alkali and alkaline earth metals such as chlorinated salts can not be produced by electrolysis, because AlCl3 evaporates at 186OC . Although it may theoretically be possible to produce from AlF3, there is not enough fluoride aluminum ore to meet the world’s primary aluminum requirement .
The removal of the foreign oxides in the bauxite ore, especially iron and silicon, and obtaining pure aluminum oxide alone is a prerequisite for going to the metal.
As is known, conventional primary aluminum production consists of three independent processes :
1. Bauxite mining
2. Production of alumina from bauxite ores with Bayer Process,
3. Production of metallic aluminum by Elek Melted Salt Electrolysis ( Hall-Herault Process) Al from alumina,
In particular, the molten salt electrolysis step is an “energy intensive” step.
The unit unit where primary aluminum production takes place is defined as the “aluminum electrolysis cell”.
The deep cell chamber holds the electrolyte and the liquid metallic aluminum produced. Electrical energy comes to the cell with the busbar system and passes to the next cell with the busbar system. Each of the electrolysis cells, which vary in size, type and number according to the plants, are independent production units and are electrically connected in series. Cell components common to cells in all plants:
– anode equipment,
– cathode equipment,
– anode and cathode busbar systems,
– Aluminum metal reserve and
– cell control panel.
Among these construction elements is the ANOT , which defines both the cell type as well as the technology and technology level, mechanically carrying systems installed for cell services, in particular in modern technologies, and most importantly determining the cell regimen to a large extent . Industrial cells are divided into two categories according to their anodes:
– Söderberg anodized cells and
-Pre-baked (prebaked) anode cells
Söderberg anode cells are continuous anode type cells in which the coking process occurs on the cell, which is now being abandoned. Such cells are self- boiling anodes . Anode paste anode the desired shape and dimensions that are installed in a metal casing. The coking of the anode, that is, its conversion into a durable, monolithic block with the necessary electrical conductivity, takes place by means of heat. As the anode is exhausted from the base, new cake is added.
Söderberg anodes are composed of 25-28% hard coal pitch and petro- coke aggregate as binders . The anode firing takes place on the cell during electrolysis at about 960 ° C, and as the anode is consumed, new anodes in block form are added.
Due to the coking on the anode of the cell, and stabilization of business operations is more difficult than prebaked cells. The opportunity to apply automatic control is limited and the unit electricity consumption is higher than prebaked cells. Again , due to operational stabilization , pollutant gas release is greater.
Prebaked = pre-baked anode cell of the coking process that occurred in another unit used in blocks elektrolizhane brought to the pre-baked type of anode cells.
The pre-cooked anodes consist of hard coal tar and petro- coke as binders between 13-16% . They are cooked in 1150-1200 ° C in special anode baking ovens and take the form of anode. They can be connected to an anode bar in groups of one, two, three, four, five or six. Cast iron or carbon-based forged and paste-form binders are used to connect to the anode rod. Depending on the cell current intensity, they are replaced with new ones between 22-30 days.
Operation operation and stabilization is better because the anodes are prepared externally . Automatic control and point alumina feeding systems can be applied very easily and consequently their consumption of electricity and raw materials is lower. CO2 emission values are better than Soderberg cells.
Pre-cooked anode cells are multi- anode cells. The anode numbers vary depending on the current strength. The anodes are suspended in the frame formed by aluminum busbars that conduct current and carry the anode system. Exhausted anodes are replaced with new ones.
Both pre-cooked and Soderberg The cells with anodes are similar in cathode structure and the surface area is about 4/3 greater than the anode surface area. However, the effective (liquid metal) surface area of the cathode is adjusted to be equal to the surface area of the anode. This adjustment is achieved by forming some solid electrolyte layer on the top and side surfaces of the cell.
Cells commonly used today are pre-cooked anode cells.
Aluminum molten salt electrolysis is the process of de-ionizing aluminum and oxygen by dissolving alumina in the molten cryolite bath under electric current .
The resulting positively charged aluminum ions are collected at the cathode acting as a negative electrode, and the negatively charged oxygen ions are collected at the anode acting as a positive electrode, reacting with the anode carbon and leaving the system by forming CO2. Therefore, the anode is continuously consumed and needs to be re-fed (in Söderberg cells) or regenerated (in pre-cooked cells) atregular intervals .
The framework of the electrolysis event can be summarized as follows:
In an environment in which there is no water (or rather hydrogen), an electric arc with low voltage and high current strength is formed between the carbon-based reservoir-cathode and the carbon-based anode, while keeping the charge liquid while doing electrochemical work.
Thus, to use the reaction medium as both electrolysis cell and direct current arc furnace … ( İ.Duman , 2nd Aluminum Symposium Opening Presentation)
The chemical reactions taking place in the electrolysis of cryolite -alüm the melt, due to the separation of compounds in many ways electrolyte ions it is diverse and complex. However, as a result, the release of aluminum at the cathode base and oxygen at the anode causes the reactions to be perceived as simple. In reality, not all reactions are fully known.
While the electric flow through the aluminum bars is carried out by electron movement (electronic), the electric flow in the electrolyte is realized by the movement of Na + and F- ions (ionic). The electrical flow on the electrode surface is electrochemical. In other words, as a result of the electrochemical reaction, the ionic mechanism becomes the electronic mechanism.
If the following reactions do not occur, the flow of electricity stops:
At the anode:
Al2O3 + 6NaF + 3 / 2C 2AlF3 + 3/2 CO2 + 6Na + 6e
At the cathode:
2AlF3 + 6Na- + 6e 2Al + 6NaF
Al2O3 + 3 / 2C 2Al + 3/2 CO2 commercial cell may have up to 700 kA and higher amperage than 60 female and daily production of 450 kg per cell can be up to 5500 kg.
Aluminum production by molten salt electrolysis is an energy intensive process . Therefore, when electrolysis plants are installed, the places where sufficient, long-term and reliable electrical energy can be provided should be selected.
More than 99% of the aluminum produced is commercial grade aluminum with an aluminum content between 99.0% and 99.80%.
One of the most important problems of the traditional molten salt electrolysis method is the ot anode effect .. Depending on the alumina feed technology, the amount of dissolved alumina in the electrolyte is kept between 2-3.5%. However, when the alumina dissolved concentration falls below the critical point of 2%, the anode effect occurs. Although the anode effect is random, it can be predicted.
During anode action, the anode carbon reacts with fluorine in the electrolyte bath to form perfluorocarbon (PFC) gases , since there is not enough oxygen in the environment due to the low aluminaconcentration .
Perfluorocarbon gases, CF4 and C2F6, are formed only during the anode action in the electrolysis process. However, although these gases are less than 0.5% in the atmosphere, their lifespan is approximately 6 000 years and the CO2 equivalent is 6 000.
Inert Anode Technology
In today’s world, commercially all primary aluminum production is carried out in aluminum electrolysis cells. Instead of the aluminum production process by electrolysis, known as the Hall-Heroult method,even if alternative methods have been studied for a long time and even some pilot plants have been established, all the hopes that these methods will find an industrial application area have been lost and the research has been intensified to improve the performance of this method. .
As it is known, the production of precious metals such as rare earth elements, silicon, manganese, sodium, calcium, lithium depends to a great extent on the availability of energy. In terms of sustainability, as much as verimli clean ”and“ cheap ”energy supply, it is important to consume energy efficiently and without polluting the environment. Advances in aluminum production technologies can pave the way for the sustainable production of all precious metals on a global scale.
With the use of inert anode in the specialty of primary aluminum production technologies ;
– CO2 emissions can be reduced or completely eliminated,
– Anode effect can be eliminated and
– The release of PFC ( perfluorocarbon ) gases can be prevented.
On the other hand, since the use of inert anodes does not require carbon anode production, investment costs of new primary aluminum plants and production costs will be reduced as anode replacement and production will not be necessary. At the same time with the use of the inert anode, the high surface area will increase productivity, the quality of the metal will increase due to the absence of carbon anode-based impurities, the process will be easier to control and thus the cell life will be prolonged. As described by ELYSIS , oxygen output as a by-product will be one of the important advantages of the process .
The most critical point in inert anode technology is the anode material. Because anode material should be able to conduct electricity, have high oxidation resistance and should not dissolve in cryolite based electrolyte bath.
Approximately 1% of global greenhouse gas emissions are caused by CO2 produced during the primary aluminum production process and PFC gases released during the anode impact. This new technology is likely to reset the aluminum metal to its carbon footprint, even to produce oxygen as a semi-product, and to make it negative.
Our technical knowledge of the new technology is limited. However, two major Canadian state funds and technological institutions in this partnership with a reputable manufacturer of primary aluminum isenough to excite alüminyumcu.
Hoping to share the technical information available in the coming days ümüzdeki
1. https: //.pm.gc.ca/eng/news
5. Modernization of Prebake Cells Restaurant Reviews , Halvor Kvande , Hydro Aluminum
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