What kind of harmful chemicals are used for anodizing and whether or not anodizing increases the burden on the environment?
Or
What is the energy cost to anodize one kilogram of aluminum, and what is the amount of different harmful chemicals used for this process?
Taken with courtesy from Aluminum Anodizers Council website the following should be said:
The environmental friendliness of anodizing is among its best properties.
Anodizing uses simple water-based chemicals, such as sodium hydroxide, sulfuric acid, soap and nitric acid all in diluted solutions. They can be treated easily and release no harmful by-products. The liquid by-products are recycled and returned to the process. Solid by-products can be isolated and diverted for use in the manufacture of alum, baking powder, cosmetics, newsprint, fertilizer and water purification systems.
The U.S. Environmental Protection Agency (EPA), which heavily regulates the production and use of solvent-based paints and flouropolymer finishes containing volatile organic compounds (VOCs), regards anodizing as an environmentally friendly process.
The by-product anodizing creates is composed primarily of aluminum hydroxide, some aluminum sulfate and water. It is harmless because it contains no significant amounts of heavy metals. In some cases, municipal sewerage treatment plants benefit from these by-products by using them as filters in the secondary treatment of sewage.
If processes like bright dip, some inorganic coloring processes and nickel acetate sealing are introduced in the anodizing process, then more caution should be taken regarding the waste water treatment.
The aluminum oxide layer formed during the Anodizing process is a degradation/corrosion of aluminum back to its original form found in the earth crust. The original form of Aluminum oxide is found as corundum, sapphires and rubies. Rubies are characterized by their deep red color, which comes from traces of chromium. The sapphires are all the rest of the colored corundum's, where the different colors come from impurities such as iron and titanium.
When recycling anodized aluminum the aluminum oxide will melt without any emissions of organic substances. Other surface finishes contains various amount of organic materials, as for example in paints, lacquers, greases and oils.
The anodizing process uses energy to form the aluminum oxide and it is important to invent and/or use already well-known knowledge to decrease this energy consumption. Pulse anodizing is one of the energy reducing processes, reducing energy in other steps in the anodizing process are other places to search. All this for improving and growing the anodizing industry, showing the world that anodizing is the "green" or environmental friendly surface finishing process for aluminum.
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