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Granulation of Filter Lime from Ceramic Coatings
The process of manufacturing ceramic coatings creates harmful gases that can be released into the environment. Variable amounts of fluorine, that are found in certain clays (raw materials) are released during firing in the form of a fluoride ion (F). This reacts with the water vapor in the atmosphere of the furnace, forming hydrofluoric acid (HF), which is conducted by the flow of gases into the chimney. The resulting emissions can cause serious harm to the health of people, plants and animals.
To reduce the release of such gases into the atmosphere and subsequent penalties imposed by environmental organizations, industries have an obligation to install specific filters.
Passing through the filtering system, the fluoride ion reacts with the introduced gases composed of calcium hydroxide to form the element CaF2, known as "Ceramic Fluorite" or "filter lime", as per the reaction below:
When suitably granulated, this by-product of ceramic coating production can replace metallurgical fluorite, which is used in the formation of slag in Ferrous Metallurgy processes.
The amount of filter lime generated by ceramic coating and flooring companies varies according to the type of clay used, the sintering temperature and the combustion cycle.
For every thousand square meters (1,000 m2) of ceramic coating produced, between 2 to 20 kg of filter lime residue can be extracted.
In the production of steel from ferrous waste in a conventional steel mill, 1 kg of fluorite is consumed on average to obtain 1 ton of steel.
The use of ceramic industry residues as a raw material for the Ferrous Metallurgy industry is beneficial due to two factors:
1. Technical: Ceramic fluorite is relatively similar to metallurgical fluorite;
2. Economical: The price of ceramic fluorite (once granulated) averages $100-200 per ton. While metallurgical fluorite, due to being increasingly scarce in the world, reaches an average value of $250 per ton.