Published: Kem. Ind. 53 (4) (2004) 167–174
Paper reference number: KUI-42/2002
Paper type: Review
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Some Questions About Copper Extraction in Pre-Industrial Metallurgy
The modern methods of non-ferrous metal production from ores are not convinient for describing the extraction processes of these metals in past. Modern method for copper, described by processes from (1) to (5), could not be applied with simple furnaces used through the long history of metallurgy. The simple methods for reduction sulphide minerals of copper (chalcolite, covelin, and probably some sulphides with higher ratio of Cu to Fe that still has to be determinated by archeometallurgical experiments) to metal are described by reactions from (6) to (12) and could be provided in simple open hearths as such in fig. 1. These methods are known as roast – reaction. But for copper extraction in the past another mineral has to be considered; that was, as it is today, the mineral chalcopyrite. The extraction of copper from it by the method considering reactions above could be hardly possible because of sulphidization of copper during smelting by iron sulphide or, if repetitive smelting is considered as another option, because of the separation problems due to the low temperature in primitive furnaces. This could be explained by physical properties of principal products of smelting in table 1. So, metalurgist of the past would be in better position by applying the method of full oxidation of sulphide ore (“dead roasting”) and reduction of oxides by carbon to the metal. As it is shown in table 2, the partial pressure of CO for copper oxide reduction is much lower than for iron oxides (also present in roasted ore) which allow the extraction of copper and remaining the most of iron in oxide state. The devices for roasting the ores (for medižval time known from the pictures but probably very similar in ancient time), are shown in fig. 2. The history of metallurgy shows certain paradigm of metal extraction for major metals: for iron and copper (fig .3) which could be explained by low level of equipment during the most of the time. That does not oppose to the considerable amount of expiriences and discoveries of various metal obtaining processes that were accumulated during the long period of time.The change of paradigm (fig. 4) came with the technical development of metallurgical equipment in the late mediavel era, of which some transitional devices are shown in fig. 5 and fig. 6.
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copper, extraction processes, archeometallurgy, sulphide ores, roasting to oxides, selective reduction, roast reaction, matte