| http://www.w3.org/ns/prov#value | - In a preferred variant, it is useful selectively (8b) to extract the greatest possible part of a volatilizable compound during the heat treatment described hereinafter and for example in the case of a high-temperature heat treatment, the sulfates are usefully extracted in the form of useful gypsum (8b), so as to limit the volatilization of SO2.
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