Non-ferrous extractive metallurgy

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Electrowinning of copper ELECTROWINNING REFINING PLANT, PART OF ARIZONA'S EXTENSIVE COPPER INDUSTRY - NARA - 544053.jpg
Electrowinning of copper

Non-ferrous extractive metallurgy is one of the two branches of extractive metallurgy which pertains to the processes of reducing valuable, non-iron metals from ores or raw material. [1] [2] [3] Metals like zinc, copper, lead, aluminium as well as rare and noble metals are of particular interest in this field, [4] while the more common metal, iron, is considered a major impurity. [5] [6] Like ferrous extraction, non-ferrous extraction primarily focuses on the economic optimization of extraction processes in separating qualitatively and quantitatively marketable metals from its impurities (gangue). [7]

Contents

Any extraction process will include a sequence of steps or unit processes for separating highly pure metals from undesirables in an economically efficient system. Unit processes are usually broken down into three categories: pyrometallurgy, hydrometallurgy, and electrometallurgy. In pyrometallurgy, the metal ore is first oxidized through roasting or smelting. The target metal is further refined at high temperatures and reduced to its pure form. In hydrometallurgy, the object metal is first dissociated from other materials using a chemical reaction, which is then extracted in pure form using electrolysis or precipitation. Finally, electrometallurgy generally involves electrolytic or electrothermal processing. The metal ore is either distilled in an electrolyte or acid solution, then magnetically deposited onto a cathode plate (electrowinning); or smelted then melted using an electric arc or plasma arc furnace (electrothermic reactor). [8]

Another major difference in non-ferrous extraction is the greater emphasis on minimizing metal losses in slag. This is widely due to the exceptional scarcity and economic value of certain non-ferrous metals which are, inevitably, discarded during the extraction process to some extent. [9] Thus, material resource scarcity and shortages are of great concern to the non-ferrous industry. Recent developments in non-ferrous extractive metallurgy now emphasize the reprocessing and recycling of rare and non-ferrous metals from secondary raw materials (scrap) found in landfills. [10] [11]

History

Prehistory of non-ferrous extractive metallurgy

In general, prehistoric extraction of metals, particularly copper, involved two fundamental stages: first, the smelting of copper ore at temperatures exceeding 700 °C is needed to separate the gangue from the copper; second, melting the copper, which requires temperatures exceeding its melting point of 1080 °C. [12] Given the available technology at the time, accomplishing these extreme temperatures posed a significant challenge. Early smelters developed ways to effectively increase smelting temperatures by feeding the fire with forced flows of oxygen. [5]

Copper extraction in particular is of great interest in archeometallurgical studies since it dominated other metals in Mesopotamia from the early Chalcolithic until the mid-to-late sixth century BC. [13] [14] There is a lack of consensus among archaeometallurgists on the origin of non-ferrous extractive metallurgy. Some scholars believe that extractive metallurgy may have been simultaneously or independently discovered in several parts of the world. The earliest known use of pyrometallurgical extraction of copper occurred in Belovode, eastern Serbia, from the late sixth to early fifth millennium BC. [12] However, there is also evidence of copper smelting in Tal-i-Iblis, southeastern Iran, which dates back to around the same period. [15] During this period, copper smelters used large in-grown pits filled with coal, or crucibles to extract copper, but by the fourth millennium BC this practice had begun to phase out in favor of the smelting furnace, which had a larger production capacity. From the third millennium onward, the invention of the reusable smelting furnace was crucial to the success of large-scale copper production and the robust expansion of the copper trade through the Bronze Age. [5]

The earliest silver objects began appearing in the late fourth millennium BC in Anatolia, Turkey. Prehistoric silver extraction is strongly associated with the extraction of the less valuable metal, lead; although evidence of lead extraction technology predates silver by at least 3 millennia. [16] [17] Silver and lead extractions are also associated because the argentiferous (silver-bearing) ores used in the process often contains both elements.

In general, prehistoric silver recovery was broken down into three phases: First, the silver-lead ore is roasted to separate the silver and lead from the gangue. The metals are then melted at high temperature ( greater than 1100 °C) in the crucible while air is blown over the molten metal (cupellation). Finally, lead is oxidized to form lead monoxide (PbO) or is absorbed into the walls of the crucible, leaving the refined silver behind.

The silver-lead cupellation method was first used in Mesopotamia between 4000 and 3500 BC. Silver artifacts, dating around 3600 BC, were discovered in Naqada, Egypt. Some of these cast silver artifacts contained less than 0.5% lead, which strongly indicates cupellation. [16]

Early to late Anglo-Saxon cupellation

Medieval smelting plant Fotothek df tg 0000582 Metallurgie ^ Probierkunst.jpg
Medieval smelting plant

Cupellation was also being used in parts of Europe to extract gold, silver, zinc, and tin by the late ninth to tenth century AD. Here, one of the earliest examples of an integrated unit process for extracting more than one precious metal was first introduced by Theophilus around the twelfth century. First, the gold-silver ore is melted down in the crucible, but with an excess amount of lead. The intense heat then oxidizes the lead which reacts quickly and binds with the impurities in the gold-silver ore. Since both gold and silver have low reactivity with the impurities, they remain behind once the slag is removed. The last stage involves parting, in which the silver is separated from the gold. First the gold-silver alloy is hammered into thin sheets and placed into a vessel. The sheets were then covered in urine, which contains sodium chloride (NaCl). The vessel is then capped and heated for several hours until the chlorides bind with the silver, creating silver chloride (AgCl). Finally, the silver chloride powder is then removed and smelted to recover the silver, while the pure gold remains intact. [6]

Hydrometallurgy in Chinese antiquity

During the Song Dynasty, Chinese copper output from domestic mining was in decline and the resulting shortages caused miners to seek alternative methods for extracting copper. The discovery of a new “wet process” for extracting copper from mine water was introduced between the eleventh and twelfth century, which helped to mitigate their loss of supply.

Similar to the Anglo-Saxon method for cupellation, the Chinese employed the use of a base metal to extract the target metal from its impurities. First, the base metal, iron, is hammered into thin sheets. The sheets are then placed into a trough filled with “vitriol water” i.e., copper mining water which is then left to steep for several day. The mining water contains copper salts in the form of copper sulfate CuSO
4. The iron then reacts with the copper, displacing it from the sulfate ions, causing the copper to precipitate onto the iron sheets, forming a "wet" powder. Finally, the precipitated copper is collected and refined further through the traditional smelting process. This is the first large-scale use of a hydrometallurgical process. [18]

See also

Related Research Articles

<span class="mw-page-title-main">Metallurgy</span> Field of science that studies the physical and chemical behavior of metals

Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys. Metallurgy encompasses both the science and the technology of metals; that is, the way in which science is applied to the production of metals, and the engineering of metal components used in products for both consumers and manufacturers. Metallurgy is distinct from the craft of metalworking. Metalworking relies on metallurgy in a similar manner to how medicine relies on medical science for technical advancement. A specialist practitioner of metallurgy is known as a metallurgist.

<span class="mw-page-title-main">Smelting</span> Use of heat and a reducing agent to extract metal from ore

Smelting is a process of applying heat to an ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a chemical- reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind. The reducing agent is commonly a fossil fuel source of carbon, such as coke—or, in earlier times, charcoal. The oxygen in the ore binds to carbon at high temperatures as the chemical potential energy of the bonds in carbon dioxide is lower than the bonds in the ore.

Extractive metallurgy is a branch of metallurgical engineering wherein process and methods of extraction of metals from their natural mineral deposits are studied. The field is a materials science, covering all aspects of the types of ore, washing, concentration, separation, chemical processes and extraction of pure metal and their alloying to suit various applications, sometimes for direct use as a finished product, but more often in a form that requires further working to achieve the given properties to suit the applications.

<span class="mw-page-title-main">Crucible</span> Container in which substances are heated

A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. Although crucibles have historically tended to be made out of clay, they can be made from any material that withstands temperatures high enough to melt or otherwise alter its contents.

<span class="mw-page-title-main">Slag</span> By-product of smelting ores and used metals

Slag is a by-product of smelting (pyrometallurgical) ores and recycled metals. Slag is mainly a mixture of metal oxides and silicon dioxide. Broadly, it can be classified as ferrous, ferroalloy or non-ferrous/base metals. Within these general categories, slags can be further categorized by their precursor and processing conditions.

<span class="mw-page-title-main">Copper extraction</span> Process of extracting copper from the ground

Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper ores consists of a series of physical, chemical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors.

<span class="mw-page-title-main">Cupellation</span> Refining process in metallurgy

Cupellation is a refining process in metallurgy in which ores or alloyed metals are treated under very high temperatures and subjected to controlled operations to separate noble metals, like gold and silver, from base metals, like lead, copper, zinc, arsenic, antimony, or bismuth, present in the ore. The process is based on the principle that precious metals do not oxidise or react chemically, unlike base metals. When they are heated at high temperatures, the precious metals remain apart, and the others react, forming slags or other compounds.

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Liquation is a metallurgical method for separating metals from an ore or alloy. The material must be heated until one of the metals starts to melt and drain away from the other and can be collected. This method was largely used to remove lead containing silver from copper, but it can also be used to remove antimony from ore minerals, and refine tin.

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Archaeometallurgical slag is slag discovered and studied in the context of archaeology. Slag, the byproduct of iron-working processes such as smelting or smithing, is left at the iron-working site rather than being moved away with the product. As it weathers well, it is readily available for study. The size, shape, chemical composition and microstructure of slag are determined by features of the iron-working processes used at the time of its formation.

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<span class="mw-page-title-main">Lead smelting</span> Process of refining lead metal

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<span class="mw-page-title-main">Bottom-blown oxygen converter</span> Smelting furnace

The Bottom-blown Oxygen Converter or BBOC is a smelting furnace developed by the staff at Britannia Refined Metals Limited (“BRM”), a British subsidiary of MIM Holdings Limited. The furnace is currently marketed by Glencore Technology. It is a sealed, flat-bottomed furnace mounted on a tilting frame that is used in the recovery of precious metals. A key feature is the use of a shrouded lance to inject oxygen through the bottom of the furnace, directly into the precious metals contained in the furnace, to oxidize base metals or other impurities as part of their removal as slag.

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References

  1. ↑ Gosh, A., and H.S. Ray. Principles of Extractive Metallurgy. 2nd Ed. New Delhi: New Age International Ltd, 1991. pp 1-10.
  2. ↑ Reardon, Arthur C. Metallurgy for the Non-Metallurgist. 2nd Ed. U.S.: ASM International, 2011. Pp. 11.
  3. ↑ Habashi, F. (2005). "Mining, Metallurgy, and the Industrial Revolution Part 3". CIM Bulletin. 98 (1091): 81–82.
  4. ↑ Gosh, A., and H.S. Ray. Principles of Extractive Metallurgy. 2nd Ed. New Delhi: New Age International Ltd, 1991. pp 1-10.
  5. 1 2 3 Potts, D. T. (2012). A Companion to the Archaeology of the Ancient Near East. John Wiley & Sons. pp. 300–302. ISBN   978-1-4051-8988-0.
  6. 1 2 Nakamura, Takashi (2007). "Present Status and Issues of Non-Ferrous Extractive Metallurgy". Journal of MMIJ. 123 (12): 570–574. doi: 10.2473/journalofmmij.123.570 . ProQuest   33106898.
  7. ↑ Waseda, Yoshio.The Structure and Properties of Oxide Melts: Application of Basic Science to Metallurgical Processing. Singapore: World Scientific Publishing, 1998. Pp. 174.
  8. ↑ Mathur, V.N.S.. "Waste Management in Mineral Industries-Some Considerations." Precedings of the International Conference on Environmental Management in Metallurgical Industries: EMMI 2000. Ed. R.C. Gupta. New Delhi: Allied Publisher Ltd., 2000. 87. Web. 21 Apr. 2013.
  9. ↑ Waseda, Yoshio.The Structure and Properties of Oxide Melts: Application of Basic Science to Metallurgical Processing. Singapore: World Scientific Publishing, 1998. Pp. 174.
  10. ↑ Gordon, R. B.; Bertram, M.; Graedel, T. E. (31 January 2006). "Metal stocks and sustainability". Proceedings of the National Academy of Sciences of the United States of America. 103 (5): 1209–1214. doi: 10.1073/pnas.0509498103 . PMC   1360560 . PMID   16432205.
  11. ↑ Djokic, Sasa; Djokic, Biljana (February 2005). Metallic secondary raw materials recycling strategy in Serbia. EPD Congress 2005 as held at the 2005 TMS Annual Meeting. San Francisco. ProQuest   28530773.
  12. 1 2 Radivojević, Miljana; Rehren, Thilo; Pernicka, Ernst; Šljivar, Dušan; Brauns, Michael; Borić, Dušan (November 2010). "On the origins of extractive metallurgy: new evidence from Europe". Journal of Archaeological Science. 37 (11): 2775–2787. Bibcode:2010JArSc..37.2775R. doi:10.1016/j.jas.2010.06.012.
  13. ↑ Killick, David (December 2009). "Cairo to Cape: The Spread of Metallurgy Through Eastern and Southern Africa". Journal of World Prehistory. 22 (4): 399–414. doi:10.1007/s10963-009-9025-3. S2CID   162458882.
  14. ↑ Forbes, R.J. Studies in Ancient Technology:Volume 4 of Studies in Ancient Technology Series. Vol 9. The Netherlands: Brill, 1964. 84-104.
  15. ↑ Thornton, C.P.; Rehren, Th. (January 2007). "Report on the First Iranian Prehistoric Slag Workshop". Iran. 45 (1): 315–318. doi:10.1080/05786967.2007.11869198. S2CID   192248709.
  16. 1 2 Gale, N. H.; Stos-Gale, Z. A. (November 1981). "Cycladic Lead and Silver Metallurgy". The Annual of the British School at Athens. 76: 169–224. doi:10.1017/S0068245400019523. JSTOR   30103034. S2CID   137377867.
  17. ↑ Yener, K.A., and H. Ozbal. "Bolkardağ Mining District Survey of Silver and Lead in Ancient Anatolia." Proceedings of the 24th International Archaeometry Symposium, (1986), pp. 309-317 Published by: The Smithsonian Institution Press.
  18. ↑ Needham, Joseph, and Peter J. Golas. Science and Civilization in China. Vol. 13. Cambridge: Cambridge University Press, 1999, pp. 88,378-382. ISBN   978-0521580007
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