The electrolytic reduction process requires the use of fluorides compounds, namely sodium fluoride and aluminium fluoride in order to improve properties of the electrolytic bath. The addition of fluoride generates energy savings in the order of 50% since it allows for the electrolytic process to be operated at a temperature of approximately 960°C.
Source: Ministère de l'Environnement et de la Faune du Québec
Given the high temperature inside the electrolytic pot, some of the fluoride is released to the atmosphere. Two methods are used to reduce fluoride emissions. In older smelters, the addition of lithium in the electrolytic bath reduces the quantity of fluoride. It is treated in wet scrubbers before being exhausted to atmosphere. The water used in the scrubbers is processed and re-circulated.
In modern smelters, exhaust from pots is captured by an advanced exhaust system and routed to be taken to gas treatment centres where alumina is injected into the gas stream and the fluoride is adsorbed by the alumina. This fluoride-enriched alumina is recovered and distributed to the electrolytic pots. Continuous monitors are used to measure the efficiency of gas treatment centres. These centres achieve an exhaust removal performance of over 99%.
The smelters also implement strict monitoring of both flora and fauna within a radius of several kilometres from the facilities. Monitoring of the local environment indicate that fluoride concentrations in forage are below the limit in all locations
Minimising the Damage of Mining
Bauxite, the ore that is processed into Aluminium, is extracted from open mine sites located in tropical and subtropical areas of the globe. About four tonnes of bauxite are needed to produce one tonne of Aluminium. The mining extraction of large quantities of bauxite leaves marks that need to be corrected when the mine ceases to be operated.
In order to minimise consequences of mining activity on the ecosystems, producers use operating methods that foster full site restoration. Once a site is mined-out, the affected area is graded and covered with a topsoil cover, often the same one that was removed at the beginning of mining operations. This allows for restoration of the land to its original or other beneficial use, depending of the requirements of local communities.
The results achieved are truly remarkable, from Australia to Jamaica: new forests are born, wildlife are recovered or, alternatively, dairy farms are being operated over former mining sites. Such results are possible thanks to the involvement of local communities.
This is a true example of sustainable development.
Aluminium Recycling Example: Aluminium Cans
Any comprehensive solution to the problem of solid waste disposal must include recycling, reusing materials, extracting resources from waste products and producing less material in the first place.
The recycling of Aluminium beverage cans not only reduces waste, it saves energy, conserves natural resources, lessens use of municipal landfills and provides recyclers and municipalities with considerable revenue. In short, the Aluminium can performs well in two of the world's major problem areas: It is good for the environment and good for the economy.
One cannot discuss protecting the environment without talking about recycling and resource recovery. In fact, it is nearly impossible to contemplate a global solution to the elimination of waste without thinking in terms of the selection and reuse of recyclable materials, efficient packaging or reduced energy consumption. In any such discussion, the recycling of Aluminium, which uses 95% less energy than the production of primary metal from raw materials, constitutes a choice solution in addressing today's environmental concerns. More so, when one considers that, because of its nature and unlike more fragile materials, Aluminium can be recycled almost indefinitely.
The Aluminium can is 100% recyclable; there are no labels or covers to be removed. Recycling one kilogram of Aluminium can save about eight kilograms of bauxite, four kilograms of chemical products and fourteen kilowatt-hours of electricity.
Each year, in Canada alone, 1.5 billion Aluminium cans are recovered, shredded, cleaned and re-melted to produce new cans. This results in the country saving enough energy to cover the energy needs of 15,000 homes for one year.
In Canada, each person on average produces more than 600 kilograms of household solid waste a year. The Aluminium industry encourages and supports curb-side recycling programs as a way of reducing solid waste, and fosters the "3 R’s" of environmentally sensitive solid waste management: Reduce, Re-use and Recycle.
Today's Aluminium can requires about 40% less metal than the can made 25 years ago; this means less need of both energy and raw materials per can.
Number of 12-ounce cans fabricated from one pound of 484 grams of Aluminium*
1972 21,75 cans
1975 23,00 cans
1980 24,23 cans
1985 26,60 cans
1990 30,00 cans
1995 30,50 cans
* Source: Aluminium Recycling - The Aluminium Association
Even though Aluminium cans represent less than 1% of solid waste, they are so valuable they should all be recycled. An 8,000 kilogram sheet ingot makes over half-a-million cans!
However, Aluminium recycling is not limited to cans; anything made of Aluminium can be recycled indefinitely. Also included is the recovery and re-smelting of various items, construction materials, automobile parts or process scrap. Aluminium foil, plates and pie moulds, window frames, garden furniture, are melted down and used to make the same products again. Soon we will have automobiles that can be recycled entirely!
Aluminium should be considered a raw material and never waste material. The energy needed to produce each tonne of primary Aluminium has been reduced by over 30% in the last 35 years.
For any aluminium anodising needs, please don't hesitate to contact us!
While the chemical anodising process remains the same for all applications, the mechanical methods vary according to the two physical types and shapes of metals used:
Batch Anodising - Involves racking parts and immersing them in a series of treatment tanks. Extrusions, sheets or bent metal parts, castings, cookware, cosmetic cases, flashlight bodies, and machined aluminium parts are just a few of the items that are batch anodized.
Continuous Coil Anodising - Involves continuous unwinding of pre-rolled coils through a series of anodising, etching and cleaning tanks, and then rewinding for shipment and fabrication. This method is used for high volume sheet, foil and less severely formed products such as lighting fixtures, reflectors, louvers, spacer bars for insulated glass, and continuous roofing systems.
Appearance options and quality are improved through the use of dyes and special pre-treatment procedures. This makes the aluminium look like pewter, stainless steel, copper, brushed bronze or polished brass and can also be coloured with brilliant blues, greens, reds, and many varieties of metallic gold and silver.
The unique dielectric properties of an anodized finish offer many opportunities for electrical applications.
The surface of the aluminium itself is toughened and hardened to a degree un-matched by any other process or material.
The coating is 30 percent thicker than the metal it replaces, since the volume of oxide produced is greater than that of the metal replaced.
The resulting anodic coating is porous, allowing relatively easy colouring and sealing.
Hard Anodising is a term used to describe the production of anodic coatings with film hardness or abrasion as their primary characteristic. They are usually thick by normal anodising standards (greater than 25 microns) and they are produced using special anodising conditions (very low temperature, high current density, special electrolytes). They find application in the engineering industry for components which require a very wear resistant surface such as piston, cylinders and hydraulic gear. They are often left unsealed, but may be impregnated with materials such as waxes or silicone fluids to give particular surface properties.
BATCH AND COIL ANODISING
Batch and coil anodising are accomplished in five carefully controlled, calibrated, quality-tested stages:
1. Cleaning - Alkaline and/or acid cleaners remove grease, and surface dirt.
Etching - An appealing matte surface finish is created with hot solutions of sodium hydroxide to remove minor surface imperfections. A thin layer of aluminium is removed to create a matte or dull finish.
Brightening - A near mirror finish is created with a concentrated mixture of phosphoric and nitric acids which chemically smooths the aluminium's surface.
3. Anodising - The anodic film is built and combined with the metal by passing an electrical current through an acid electrolyte bath in which the aluminium is immersed. The coating thickness and surface characteristics are tightly controlled to meet end product specifications.
4. Colouring - Colouring is achieved in one of four ways:
Electrolytic Colouring (The two-step method) - After anodising, the metal is immersed in a bath containing an inorganic metal salt. Current is applied which deposits the metal salt in the base of the pores. The resulting colour is dependent on the metal used and the processing conditions (the range of colours can be expanded by over dyeing the organic dyes). Electrolytic colours can be specified from any AAC member. Commonly used metals include tin, cobalt, nickel, and copper. This process offers colour versatility and the most technically advanced colouring quality.
Integral Colouring - This so-called one-step process combines anodising and colouring to simultaneously form and colour the oxide cell wall in bronze and black shades while more abrasive resistant than conventional anodising. It is the most expensive process since it requires significantly more electrical power.
Organic Dyeing - The organic dyeing process produces a wide variety of colours. These dyes offer vibrant colours with intensities that cannot be matched by any other paint system in the market. They can also provide excellent weather-fastness and light-fastness. Many structures built with these finishes have lasted more than 20 years. The colour range can be broadened by over-dyeing the electrolytic colours with the organic dyes for a wider variety of colours and shades. This method is relatively inexpensive and involves the least amount of initial capital of any other colouring process.
Interference Colouring - An additional colouring procedure, recently in production, involves modification of the pore structure produced in sulphuric acid. Pore enlargement occurs at the base of the pore. Metal deposition at this location produces light-fast colours ranging from blue, green and yellow to red. The colours are caused by optical-interference effects, rather than by light scattering as with the basic electrolytic colouring process. Further development will produce a greater variety of colours.
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