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Hydrometallurgy

Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials.[1][2] Processing techniques that complement hydrometallurgy are pyrometallurgy, vapour metallurgy, and molten salt electrometallurgy. Hydrometallurgy is typically divided into three general areas:

  • Leaching
  • Solution concentration and purification
  • Metal or metal compound recovery

Leaching

Leaching involves the use of aqueous solutions to extract metal from metal bearing materials which is brought into contact with a material containing a valuable metal.[3] The first examples come from 11-12th centuries China where it was applied to extraction of copper and accounted for a significant share of total copper production.[4] In the 17th century it was used for the same purposes in Germany and Spain.[5]

The lixiviant solution conditions vary in terms of pH, oxidation-reduction potential, presence of chelating agents and temperature, to optimize the rate, extent and selectivity of dissolution of the desired metal component into the aqueous phase. Through the use of chelating agents, one can selectively extract certain metals. Such chelating agents are typically amines of schiff bases.[6]

The five basic leaching reactor configurations are in-situ, heap, vat, tank and autoclave.

In-situ leaching

In-situ leaching is also called "solution mining." This process initially involves drilling of holes into the ore deposit. Explosives or hydraulic fracturing are used to create open pathways within the deposit for solution to penetrate into. Leaching solution is pumped into the deposit where it makes contact with the ore. The solution is then collected and processed. The Beverley uranium deposit is an example of in-situ leaching and also Trojan Mine in Zimbabwe.[citation needed]

Heap leaching

In heap leaching processes, crushed (and sometimes agglomerated) ore is piled in a heap which is lined with an impervious layer. Leach solution is sprayed over the top of the heap, and allowed to percolate downward through the heap. The heap design usually incorporates collection sumps, which allow the "pregnant" leach solution (i.e. solution with dissolved valuable metals) to be pumped for further processing. An example is gold cyanidation, where pulverized ores are extracted with a solution of sodium cyanide, which, in the presence of air, dissolves the gold, leaving behind the nonprecious residue.

 
Ball-and-stick model of the aurocyanide or dicyanoaurate(I) complex anion, [Au(CN)2].[7]

Vat leaching

Vat leaching involves contacting material, which has usually undergone size reduction and classification, with leach solution in large vats.

Tank leaching

Stirred tank, also called agitation leaching, involves contacting material, which has usually undergone size reduction and classification, with leach solution in agitated tanks. The agitation can enhance reaction kinetics by enhancing mass transfer. Tanks are often configured as reactors in series.

Autoclave leaching

Autoclave reactors are used for reactions at higher temperatures, which can enhance the rate of the reaction. Similarly, autoclaves enable the use of gaseous reagents in the system.

Solution concentration and purification

After leaching, the leach liquor must normally undergo concentration of the metal ions that are to be recovered. Additionally, undesirable metal ions sometimes require removal.[1]

  • Precipitation is the selective removal of a compound of the targeted metal or removal of a major impurity by precipitation of one of its compounds. Copper is precipitated as its sulfide as a means to purify nickel leachates.
  • Cementation is the conversion of the metal ion to the metal by a redox reaction. A typical application involves addition of scrap iron to a solution of copper ions. Iron dissolves and copper metal is deposited.
  • Solvent Extraction
  • Ion Exchange
  • Gas reduction. Treating a solution of nickel and ammonia with hydrogen affords nickel metal as its powder.
  • Electrowinning is a particularly selective if expensive electrolysis process applied to the isolation of precious metals. Gold can be electroplated from its solutions.

Solvent extraction

In the solvent extraction a mixture of an extractant in a diluent is used to extract a metal from one phase to another. In solvent extraction this mixture is often referred to as the "organic" because the main constituent (diluent) is some type of oil.

The PLS (pregnant leach solution) is mixed to emulsification with the stripped organic and allowed to separate.[citation needed] The metal will be exchanged from the PLS to the organic they are modified.[clarification needed] The resulting streams will be a loaded organic and a raffinate. When dealing with electrowinning, the loaded organic is then mixed to emulsification with a lean electrolyte and allowed to separate. The metal will be exchanged from the organic to the electrolyte. The resulting streams will be a stripped organic and a rich electrolyte. The organic stream is recycled through the solvent extraction process while the aqueous streams cycle through leaching and electrowinning[clarification needed] processes respectively.[citation needed]

Ion exchange

Chelating agents, natural zeolite, activated carbon, resins, and liquid organics impregnated with chelating agents are all used to exchange cations or anions with the solution.[citation needed] Selectivity and recovery are a function of the reagents used and the contaminants present.

Metal recovery

Metal recovery is the final step in a hydrometallurgical process. Metals suitable for sale as raw materials are often directly produced in the metal recovery step. Sometimes, however, further refining is required if ultra-high purity metals are to be produced. The primary types of metal recovery processes are electrolysis, gaseous reduction, and precipitation. For example, a major target of hydrometallurgy is copper, which is conveniently obtained by electrolysis. Cu2+ ions reduce at mild potentials, leaving behind other contaminating metals such as Fe2+ and Zn2+.

Electrolysis

Electrowinning and electrorefining respectively involve the recovery and purification of metals using electrodeposition of metals at the cathode, and either metal dissolution or a competing oxidation reaction at the anode.

Precipitation

Precipitation in hydrometallurgy involves the chemical precipitation of either metals and their compounds or of the contaminants from aqueous solutions. Precipitation will proceed when, through reagent addition, evaporation, pH change or temperature manipulation, any given species exceeds its limit of solubility.

References

  1. ^ a b Brent Hiskey "Metallurgy, Survey" in Kirk-Othmer Encyclopedia of Chemical Technology, 2000, Wiley-VCH, Weinheim. doi:10.1002/0471238961.1921182208091911.a01
  2. ^ Habashi, F. (2009). "Recent Trends in Extractive Metallurgy". Journal of Mining and Metallurgy, Section B: Metallurgy. 45: 1–13. doi:10.2298/JMMB0901001H.
  3. ^ Um, Namil (July 2017). Hydrometallurgical recovery process of rare earth elements from waste: main application of acid leaching with devised diagram. INTECH. pp. 41–60. ISBN 978-953-51-3402-2.
  4. ^ Golas, Peter J. (1995). "A Copper Production Breakthrough in the Song: The Copper Precipitation Process". Journal of Song-Yuan Studies. 25: 153.
  5. ^ Habashi, Fathi (2005). "A short history of hydrometallurgy". Hydrometallurgy. 79 (1–2): 15–22. doi:10.1016/j.hydromet.2004.01.008.
  6. ^ Tasker, Peter A.; Tong, Christine C.; Westra, Arjan N. (2007). "Co-extraction of cations and anions in base metal recovery". Coordination Chemistry Reviews. 251 (13–14): 1868–1877. doi:10.1016/j.ccr.2007.03.014.
  7. ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.

External links

hydrometallurgy, technique, within, field, extractive, metallurgy, obtaining, metals, from, their, ores, involve, aqueous, solutions, recovery, metals, from, ores, concentrates, recycled, residual, materials, processing, techniques, that, complement, hydrometa. Hydrometallurgy is a technique within the field of extractive metallurgy the obtaining of metals from their ores Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores concentrates and recycled or residual materials 1 2 Processing techniques that complement hydrometallurgy are pyrometallurgy vapour metallurgy and molten salt electrometallurgy Hydrometallurgy is typically divided into three general areas Leaching Solution concentration and purification Metal or metal compound recoveryContents 1 Leaching 1 1 In situ leaching 1 2 Heap leaching 1 3 Vat leaching 1 4 Tank leaching 1 5 Autoclave leaching 2 Solution concentration and purification 2 1 Solvent extraction 2 2 Ion exchange 3 Metal recovery 3 1 Electrolysis 3 2 Precipitation 4 References 5 External linksLeaching EditLeaching involves the use of aqueous solutions to extract metal from metal bearing materials which is brought into contact with a material containing a valuable metal 3 The first examples come from 11 12th centuries China where it was applied to extraction of copper and accounted for a significant share of total copper production 4 In the 17th century it was used for the same purposes in Germany and Spain 5 The lixiviant solution conditions vary in terms of pH oxidation reduction potential presence of chelating agents and temperature to optimize the rate extent and selectivity of dissolution of the desired metal component into the aqueous phase Through the use of chelating agents one can selectively extract certain metals Such chelating agents are typically amines of schiff bases 6 The five basic leaching reactor configurations are in situ heap vat tank and autoclave In situ leaching Edit In situ leaching is also called solution mining This process initially involves drilling of holes into the ore deposit Explosives or hydraulic fracturing are used to create open pathways within the deposit for solution to penetrate into Leaching solution is pumped into the deposit where it makes contact with the ore The solution is then collected and processed The Beverley uranium deposit is an example of in situ leaching and also Trojan Mine in Zimbabwe citation needed Heap leaching Edit In heap leaching processes crushed and sometimes agglomerated ore is piled in a heap which is lined with an impervious layer Leach solution is sprayed over the top of the heap and allowed to percolate downward through the heap The heap design usually incorporates collection sumps which allow the pregnant leach solution i e solution with dissolved valuable metals to be pumped for further processing An example is gold cyanidation where pulverized ores are extracted with a solution of sodium cyanide which in the presence of air dissolves the gold leaving behind the nonprecious residue Ball and stick model of the aurocyanide or dicyanoaurate I complex anion Au CN 2 7 Vat leaching Edit Vat leaching involves contacting material which has usually undergone size reduction and classification with leach solution in large vats Tank leaching Edit Stirred tank also called agitation leaching involves contacting material which has usually undergone size reduction and classification with leach solution in agitated tanks The agitation can enhance reaction kinetics by enhancing mass transfer Tanks are often configured as reactors in series Autoclave leaching Edit Autoclave reactors are used for reactions at higher temperatures which can enhance the rate of the reaction Similarly autoclaves enable the use of gaseous reagents in the system Solution concentration and purification EditAfter leaching the leach liquor must normally undergo concentration of the metal ions that are to be recovered Additionally undesirable metal ions sometimes require removal 1 Precipitation is the selective removal of a compound of the targeted metal or removal of a major impurity by precipitation of one of its compounds Copper is precipitated as its sulfide as a means to purify nickel leachates Cementation is the conversion of the metal ion to the metal by a redox reaction A typical application involves addition of scrap iron to a solution of copper ions Iron dissolves and copper metal is deposited Solvent Extraction Ion Exchange Gas reduction Treating a solution of nickel and ammonia with hydrogen affords nickel metal as its powder Electrowinning is a particularly selective if expensive electrolysis process applied to the isolation of precious metals Gold can be electroplated from its solutions Solvent extraction Edit In the solvent extraction a mixture of an extractant in a diluent is used to extract a metal from one phase to another In solvent extraction this mixture is often referred to as the organic because the main constituent diluent is some type of oil The PLS pregnant leach solution is mixed to emulsification with the stripped organic and allowed to separate citation needed The metal will be exchanged from the PLS to the organic they are modified clarification needed The resulting streams will be a loaded organic and a raffinate When dealing with electrowinning the loaded organic is then mixed to emulsification with a lean electrolyte and allowed to separate The metal will be exchanged from the organic to the electrolyte The resulting streams will be a stripped organic and a rich electrolyte The organic stream is recycled through the solvent extraction process while the aqueous streams cycle through leaching and electrowinning clarification needed processes respectively citation needed Ion exchange Edit Chelating agents natural zeolite activated carbon resins and liquid organics impregnated with chelating agents are all used to exchange cations or anions with the solution citation needed Selectivity and recovery are a function of the reagents used and the contaminants present Metal recovery EditMetal recovery is the final step in a hydrometallurgical process Metals suitable for sale as raw materials are often directly produced in the metal recovery step Sometimes however further refining is required if ultra high purity metals are to be produced The primary types of metal recovery processes are electrolysis gaseous reduction and precipitation For example a major target of hydrometallurgy is copper which is conveniently obtained by electrolysis Cu2 ions reduce at mild potentials leaving behind other contaminating metals such as Fe2 and Zn2 Electrolysis Edit Electrowinning and electrorefining respectively involve the recovery and purification of metals using electrodeposition of metals at the cathode and either metal dissolution or a competing oxidation reaction at the anode Precipitation Edit Precipitation in hydrometallurgy involves the chemical precipitation of either metals and their compounds or of the contaminants from aqueous solutions Precipitation will proceed when through reagent addition evaporation pH change or temperature manipulation any given species exceeds its limit of solubility References Edit a b Brent Hiskey Metallurgy Survey in Kirk Othmer Encyclopedia of Chemical Technology 2000 Wiley VCH Weinheim doi 10 1002 0471238961 1921182208091911 a01 Habashi F 2009 Recent Trends in Extractive Metallurgy Journal of Mining and Metallurgy Section B Metallurgy 45 1 13 doi 10 2298 JMMB0901001H Um Namil July 2017 Hydrometallurgical recovery process of rare earth elements from waste main application of acid leaching with devised diagram INTECH pp 41 60 ISBN 978 953 51 3402 2 Golas Peter J 1995 A Copper Production Breakthrough in the Song The Copper Precipitation Process Journal of Song Yuan Studies 25 153 Habashi Fathi 2005 A short history of hydrometallurgy Hydrometallurgy 79 1 2 15 22 doi 10 1016 j hydromet 2004 01 008 Tasker Peter A Tong Christine C Westra Arjan N 2007 Co extraction of cations and anions in base metal recovery Coordination Chemistry Reviews 251 13 14 1868 1877 doi 10 1016 j ccr 2007 03 014 Greenwood N N amp Earnshaw A 1997 Chemistry of the Elements 2nd Edn Oxford Butterworth Heinemann ISBN 0 7506 3365 4 External links EditHydrometallurgy BioMineWiki Archived 2017 12 22 at the Wayback Machine Retrieved from https en wikipedia org w index php title Hydrometallurgy amp oldid 1133331998, wikipedia, wiki, book, books, library,

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