178:
540:
504:) - converts cyanide to cyanate. Cyanate then hydrolyses to ammonium and carbonate ions. The Caro's acid process is able to achieve discharge levels of Weak Acid Dissociable" (WAD) cyanide below 50 mg/L, which is generally suitable for discharge to tailings. Hydrogen peroxide and basic chlorination can also be used to oxidize cyanide, although these approaches are less common. Typically, this process blows compressed air through the tailings while adding
189:
111:
74:, the process is controversial and its use is banned in some parts of the world. Cyanide can be safely used in the gold mining industry. A key feature for safe use of cyanide is to ensure adequate pH control at an alkaline pH level above 10.5. At industrial scale, pH control is mainly achieved using lime, as an important enabling reagent in gold processing.
1526:
555:
cyanide spills can have a devastating effect on rivers, sometimes killing everything for several miles downstream. The cyanide is soon washed out of river systems and, as long as organisms can migrate from unpolluted areas upstream, affected areas can soon be repopulated. According to
Romanian authorities, in the
554:
due to the toxic nature of cyanide. Although aqueous solutions of cyanide degrade rapidly in sunlight, the less-toxic products, such as cyanates and thiocyanates, may persist for some years. The famous disasters have killed few people â humans can be warned not to drink or go near polluted water, but
335:
slows leaching rate. Air or pure oxygen gas can be purged through the pulp to maximize the dissolved oxygen concentration. Intimate oxygen-pulp contactors are used to increase the partial pressure of the oxygen in contact with the solution, thus raising the dissolved oxygen concentration much higher
831:
Under
Article 14, companies must also put in place financial guarantees to ensure clean-up after the mine has finished. This in particular may affect smaller companies wanting to build gold mines in the EU, as they are less likely to have the financial strength to give these kinds of guarantees.
1346:
Al, Tom A.; Leybourne, Matthew I.; Maprani, Antu C.; MacQuarrie, Kerry T.; Dalziel, John A.; Fox, Don; Yeats, Phillip A. (2006). "Effects of acid-sulfate weathering and cyanide-containing gold tailings on the transport and fate of mercury and other metals in Gossan Creek: Murray Brook mine, New
495:
The Inco process can typically lower cyanide concentrations to below 50 mg/L, whereas the Caro's acid process can lower cyanide levels to between 10 and 50 mg/L, with the lower concentrations achievable in solution streams rather than slurries. Caro's acid â peroxomonosulfuric acid
520:
is added as a catalyst if there is insufficient copper in the ore extract. This procedure can reduce concentrations of WAD cyanide to below the 10 ppm mandated by the EU's Mining Waste
Directive. This level compares to the 66-81 ppm free cyanide and 500-1000 ppm total cyanide in the pond at
141:, Scotland, developed the MacArthurâForrest process for the extraction of gold from gold ores. Several patents were issued in the same year. By suspending the crushed ore in a cyanide solution, a separation of up to 96 percent pure gold was achieved. The process was first used on the
409:
The cyanide remaining in tails streams from gold plants is potentially hazardous. Therefore, some operations process the cyanide-containing waste streams in a detoxification step. This step lowers the concentrations of these cyanide compounds. The INCO-licensed process and the
525:. Remaining free cyanide degrades in the pond, while cyanate ions hydrolyse to ammonium. Studies show that residual cyanide trapped in the gold-mine tailings causes persistent release of toxic metals (e.g. mercury ) into the groundwater and surface water systems.
156:
in Utah, "the first mining plant in the United States to make a commercial success of the cyanide process on gold ores." In 1896, BodlÀnder confirmed that oxygen was necessary for the process, something that had been doubted by MacArthur, and discovered that
1028:
356:(prior to the introduction of cyanide) of the ore in water at high pH can render elements such as iron and sulfur less reactive to cyanide, therefore making the gold cyanidation process more efficient. Specifically, the oxidation of iron to
65:
for mineral processing to recover gold represents more than 70% of cyanide consumption globally. Other metals are recovered from the process include copper, zinc, and silver, but gold is the main driver of this technology. Due to the highly
828:", and at most all mines started after 1 May 2008 may not discharge waste containing over 10ppm WAD cyanide, mines built or permitted before that date are allowed no more than 50ppm initially, dropping to 25ppm in 2013 and 10ppm by 2018.
805:(Directive 80/68/EEC) which bans any discharge of a size which might cause deterioration in the quality of the groundwater at the time or in the future. The Groundwater Directive was largely replaced in 2000 by the
744:. Challenges include reagent cost and the efficiency of gold recovery. Thiourea has been implemented commercially for ores containing stibnite. Yet another alternative to cyanidation is the family of glycine-based
824:
on the management of waste from extractive industries. Article 13(6) requires "the concentration of weak acid dissociable cyanide in the pond is reduced to the lowest possible level using
384:
In order of decreasing economic efficiency, the common processes for recovery of the solubilized gold from solution are (certain processes may be precluded from use by technical factors):
716:
Although cyanide is cheap, effective, and biodegradable, its high toxicity has incentivized to alternative methods for extracting gold. Other extractants have been examined including
1303:
Maprani, Antu C.; Al, Tom A.; MacQuarrie, Kerry T.; Dalziel, John A.; Shaw, Sean A.; Yeats, Phillip A. (2005). "Determination of
Mercury Evasion in a Contaminated Headwater Stream".
801:(82/501/EEC brought in after the 1976 dioxin disaster. "Free cyanide and any compound capable of releasing free cyanide in solution" are further controlled by being on List I of the
787:
1614:
Directive 2000/60/EC of the
European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy (the
1381:"Long Term persistence of cyanide species in mine waste environments", B. Yarar, Colorado School of Mines, Tailings and Mine Waste '02, Swets & Zeitlinger,
1026:, MacArthur, John Stewart; Forrest, William & Forrest Robert, Robert, "Process of Obtaining Gold and Silver from Ores", published 1889-05-14
821:
782:
rejected a proposal for such a ban, noting that existing regulations (see below) provide adequate environmental and health protection. Several attempts to ban
563:, the plankton returned to 60% of normal within 16 days of the spill; the numbers were not confirmed by Hungary or Yugoslavia. Famous cyanide spills include:
802:
1669:
165:(1869â1956) and his engineer Thomas Bennett Crowe improved the treatment of the cyanide leachate, by using vacuum and zinc dust. Their process is the
1565:
1227:
Teixeira, Luiz
Alberto Cesar; Montalvo, Javier Paul; Yokoyama, Andia, LĂdia; da Fonseca AraĂșjo, Fabiana ValĂ©ria; Sarmiento, Cristian Marquez (2013).
861:
1491:
1273:
1702:
996:
Gray, J. A.; McLachlen, J. (Jun 1933). "A history of the introduction of the MacArthur-Forrest cyanide process to the
Witwatersrand goldfields".
1290:
1173:
1630:
Directive 2006/21/EC of the
European Parliament and of the Council of 15 March 2006 on the management of waste from extractive industries.
1602:
Council
Directive 80/68/EEC of 17 December 1979 on the protection of groundwater against pollution caused by certain dangerous substances.
786:
were rejected by the
Romanian Parliament. There are currently protests in Romania calling for a ban on the use of cyanide in mining (see
927:
2172:
129:. The gold could not be extracted from this compound with any of the then available chemical processes or technologies. In 1887,
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Council Directive 96/82/EC of 9 December 1996 on the control of major-accident hazards involving dangerous substances.
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245:
Gold is one of the few metals that dissolves in the presence of cyanide ions and oxygen. The soluble gold species is
2336:
1645:
International Cyanide Management Code For The Manufacture, Transport, and Use of Cyanide In The Production of Gold
145:
in 1890 and, despite operational imperfections, led to a boom of investment as larger gold mines were opened up.
859:
Rubo, Andreas; Kellens, Raf; Reddy, Jay; Steier, Norbert; Hasenpusch, Wolfgang (2006). "Alkali Metal Cyanides".
1802:
1797:
1688:
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Greenwood, N. N. & Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.), Oxford:Butterworth-Heinemann.
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1962:
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270:
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Council Directive 82/501/EEC of 24 June 1982 on the major-accident hazards of certain industrial activities.
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839:" that aims to reduce environmental impacts with third party audits of a company's cyanide management.
304:) is added to the extracting solution to ensure that the acidity during cyanidation is maintained over
162:
1023:
825:
806:
418:, which is not as toxic as the cyanide ion, and which can then react to form carbonates and ammonia:
398:
361:
166:
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of South Africa began to slow down in the 1880s, as the new deposits being found tended to contain
1849:
1180:
944:
Du Plessis, C. A.; Lambert, H.; GĂ€rtner, R. S.; Ingram, K.; Slabbert, W.; Eksteen, J. J. (2021).
903:
411:
1198:"The absorption of gold cyanide onto activated carbon. I. The kinetics of absorption from pulps"
1971:
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114:
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European Commission rejects proposed ban on using cyanide in extractivism|extractive industry
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Such spills have prompted fierce protests at new mines that involve use of cyanide, such as
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minimizes loss of cyanide from the formation of ferrous cyanide complexes. The oxidation of
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La Brooy, S.R.; Linge, H.G.; Walker, G.S. (1994). "Review of gold extraction from ores".
817:
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544:
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consumed during cyanidation, accepting the electrons from the gold, and a deficiency in
265:
using grinding machinery. Depending on the ore, it is sometimes further concentrated by
2022:
1919:
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1417:
La politica es la politica: "After cyanide spill, can First Majestic clean up its act?"
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98:(1847), it was determined that each atom of gold required two cyanide ions, i.e. the
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The chemical reaction for the dissolution of gold, the "Elsner equation", follows:
91:
87:
1213:
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speed and quantity recovered, particularly in processing partially oxidized ores.
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In the EU, industrial use of hazardous chemicals is controlled by the so-called
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2001:
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Truck leaked 200 liters of cyanide solution into the Piaxtla River in Durango
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The Citizens Initiative banning of cyanide mining in the State of Montana, US
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54:. Cyanidation is also widely used in the extraction of silver, usually after
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177:
133:, working in collaboration with brothers Robert and William Forrest for the
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1987:
1977:
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249:. from which it can be recovered by adsorption onto activated carbon.
188:
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was formed as an intermediate. Around 1900, the American metallurgist
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1982:
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110:
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2014:
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1202:
Journal of the Southern African Institute of Mining and Metallurgy
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Journal of the Southern African Institute of Mining and Metallurgy
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Despite being used in 90% of gold production: gold cyanidation is
1899:
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1844:
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775:
763:
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328:
138:
71:
62:
1291:"UN assessment mission â Cyanide Spill at Baia Mare, March 2000"
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In some ores, particularly those that are partially sulfidized,
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1787:
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compounds to sulfate ions avoids the consumption of cyanide to
369:
324:
126:
67:
1022:
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1814:
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A different commercial method that does not use toxic cyanide
1345:
2285:
1642:
35:
1302:
379:
277:. The basic ore slurry can be combined with a solution of
117:
developed the cyanide process for gold extraction in 1887.
1760:
258:
39:
788:
2013 Romanian protests against the RoÈia MontanÄ Project
192:
Cyanide leaching "heap" at a gold mining operation near
305:
858:
184:
of the aurocyanide or dicyanoaurate(I) complex anion,
740:), iodine/iodide, ammonia, liquid mercury, and alpha-
543:
Sodium cyanide drum at the abandoned Chemung Mine in
1547:
Zöld siker: törvényi tilalom a cianidos bånyåszatra!
1632:
For the modifications see the consolidated version.
1620:
For the modifications see the consolidated version.
1580:
For the modifications see the consolidated version.
1428:
1285:
1283:
340:. Oxygen can also be added by dosing the pulp with
1229:"Oxidation of cyanide in effluents by Caro's Acid"
1527:"Czech Senate bans use of cyanide in gold mining"
894:Etris, S. F. (2010). "Silver and Silver Alloys".
797:(Directive 96/82/EC, which replaced the original
2318:
1280:
404:
16:Technique for extracting gold from low-grade ore
896:Kirk-Othmer Encyclopedia of Chemical Technology
516:is added to maintain the pH at around 8.5, and
347:
242:are sometimes used in place of sodium cyanide.
862:Ullmann's Encyclopedia of Industrial Chemistry
1696:
995:
528:
319:
1676:How gold is extracted by cyanidation process
1272:: CS1 maint: multiple names: authors list (
904:10.1002/0471238961.1909122205201809.a01.pub3
2231:
835:The industry has come up with a voluntary "
1703:
1689:
1080:The alumni quarterly and fortnightly notes
711:
42:by converting the gold to a water-soluble
1710:
1083:. University of Illinois. January 1, 1921
969:
854:
852:
676:Helicopter dropped crate into rainforest
946:"Lime use in gold processing â A review"
538:
273:. Water is added to produce a slurry or
187:
176:
109:
1516:regarding the use of cyanide in mining.
708:in Chile, and Bukit Koman in Malaysia.
380:Recovery of gold from cyanide solutions
2319:
1305:Environmental Science & Technology
991:
989:
849:
1684:
1122:
893:
172:
105:
1404:BBC: "Cyanide seeps into PNG rivers"
121:The expansion of gold mining in the
1179:. Multi Mix Systems. Archived from
986:
271:centrifugal (gravity) concentration
13:
1127:. Elsevier. pp. XXXVIIâXLII.
1060:Recent Advances in Gold Metallurgy
778:, have banned cyanide mining. The
86:discovered that gold dissolved in
14:
2348:
1724:Non-ferrous extractive metallurgy
1652:
887:
658:Collapse of containment dam (see
292:To prevent the creation of toxic
296:during processing, slaked lime (
289:, which is more cost effective.
90:of cyanide. Through the work of
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1369:10.1016/j.apgeochem.2006.08.013
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1190:
1166:
1149:
1125:Advances in Gold Ore Processing
1116:
1095:
414:process oxidise the cyanide to
152:had refined the process at his
46:. It is the most commonly used
1071:
1035:
1016:
937:
920:
751:
252:
1:
2077:Bottom-blown oxygen converter
1529:. Nl.newsbank.com. 2000-08-10
1123:Adams, Mike D. (2005-12-02).
842:
535:List of gold mining disasters
405:Cyanide remediation processes
336:than the saturation level at
148:By 1891, Nebraska pharmacist
1659:Efforts at a cleaner process
1469:Mining and Process Solutions
1451:10.1016/0892-6875(94)90114-7
1253:10.1016/j.mineng.2013.01.008
1043:"Methods to recover Gold II"
971:10.1016/j.mineng.2021.107231
814:2000 Baia Mare cyanide spill
660:2000 Baia Mare cyanide spill
611:Unrestrained waste discharge
348:Pre-aeration and ore washing
7:
1289:UNEP/OCHA Environment Unit
1208:(2): 50â54. February 1984.
784:gold cyanidation in Romania
94:(1844), Elsner (1846), and
10:
2353:
755:
532:
529:Effects on the environment
320:Effect of dissolved oxygen
163:Charles Washington Merrill
77:
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2125:
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2013:
2000:
1933:
1887:
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1730:
1718:
1616:Water Framework Directive
1494:October 21, 2007, at the
826:best available techniques
807:Water Framework Directive
626:Collapse of tailings dam
102:of the soluble compound.
34:technique for extracting
28:MacArthurâForrest process
1803:Underground in soft rock
1798:Underground in hard rock
933:. Australian Government.
871:10.1002/14356007.i01_i01
820:and the Council adopted
642:Truck drove over bridge
2337:Metallurgical processes
1564:International Mining -
865:. Weinheim: Wiley-VCH.
712:Alternatives to cyanide
594:Leakage from leach pad
308:10.5 - strongly basic.
1552:July 21, 2011, at the
1214:10520/AJA0038223X_1427
1174:"Technical Bulletin 1"
1010:10520/AJA0038223X_5033
547:
285:; many operations use
196:
185:
131:John Stewart MacArthur
118:
115:John Stewart MacArthur
2131:(by aqueous solution)
1963:Gravity Concentration
1712:Extractive metallurgy
1670:Cyanide Uncertainties
803:Groundwater Directive
542:
399:MerrillâCrowe process
191:
180:
167:MerrillâCrowe process
113:
2246:HallâHĂ©roult process
1925:Mechanical screening
1507:2001 Senate Bill 160
1465:"Glycine lixiviants"
1431:Minerals Engineering
1349:Applied Geochemistry
1347:Brunswick, Canada".
1233:Minerals Engineering
950:Minerals Engineering
928:"Cyanide Management"
822:Directive 2006/21/EC
758:Gold cyanidation ban
506:sodium metabisulfite
338:atmospheric pressure
182:Ball-and-stick model
84:Carl Wilhelm Scheele
44:coordination complex
1968:Magnetic separation
1915:Cyclonic separation
1736:(by physical means)
1721:Metallurgical assay
1443:1994MiEng...7.1213L
1361:2006ApGC...21.1969A
1317:2005EnST...39.1679M
1245:2013MiEng..45...81T
962:2021MiEng.17407231D
818:European Parliament
812:In response to the
795:Seveso II Directive
780:European Commission
545:Masonic, California
508:, which releases SO
22:(also known as the
2049:Refractory linings
1920:Gyratory equipment
1732:Mineral processing
1512:2006-10-10 at the
1065:2008-03-30 at the
548:
197:
186:
173:Chemical reactions
119:
106:Industrial process
32:hydrometallurgical
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2220:Electrometallurgy
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2173:Gold chlorination
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2007:
1996:
1995:
1958:Jig concentrators
1756:Natural resources
1751:Geological survey
1737:
1437:(10): 1213â1241.
1406:, March 23, 2000.
1355:(11): 1969â1985.
1325:10.1021/es048962j
1134:978-0-444-51730-2
898:. pp. 1â43.
762:The US states of
694:
693:
673:Papua New Guinea
607:Papua New Guinea
376:(SCN) byproduct.
342:hydrogen peroxide
312:can improve gold
298:calcium hydroxide
283:potassium cyanide
236:Potassium cyanide
159:hydrogen peroxide
150:Gilbert S. Peyton
88:aqueous solutions
2344:
2229:
2228:
2224:(by electricity)
2223:
2206:Pan amalgamation
2178:Gold cyanidation
2168:In situ leaching
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2005:
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333:dissolved oxygen
302:sodium hydroxide
294:hydrogen cyanide
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20:Gold cyanidation
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1943:Froth flotation
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360:and subsequent
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287:calcium cyanide
267:froth flotation
255:
240:calcium cyanide
228:
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222:
216:
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208:
204:
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135:Tennant Company
108:
80:
56:froth flotation
52:gold extraction
38:from low-grade
24:cyanide process
17:
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2002:Pyrometallurgy
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1781:Precious metal
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1653:External links
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1421:
1415:Wilson, T. E.
1408:
1395:
1374:
1338:
1295:
1279:
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1189:
1186:on 2009-10-23.
1165:
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1015:
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913:978-0471238966
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880:978-3527306732
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809:(2000/60/EC).
772:Czech Republic
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596:
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518:copper sulfate
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394:Electrowinning
391:
389:Carbon in pulp
381:
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366:iron hydroxide
349:
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327:is one of the
321:
318:
279:sodium cyanide
254:
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79:
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61:Production of
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2183:Bayer process
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2171:
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2163:Tank leaching
2161:
2159:
2158:Dump leaching
2156:
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2153:Heap leaching
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2023:Iron smelting
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1045:. 2013-05-14.
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363:
362:precipitation
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247:dicyanoaurate
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201:
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183:
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168:
164:
160:
155:
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103:
101:
100:stoichiometry
97:
93:
89:
85:
75:
73:
69:
64:
59:
57:
53:
49:
45:
41:
37:
33:
29:
25:
21:
2233:Electrolysis
2193:Amalgamation
2177:
1948:Jameson cell
1905:Hydrocyclone
1637:
1625:
1615:
1609:
1597:
1585:
1573:
1568:, July, 2010
1560:
1542:
1531:. Retrieved
1521:
1502:
1484:
1472:. Retrieved
1468:
1459:
1434:
1430:
1424:
1411:
1398:
1391:Google Books
1377:
1352:
1348:
1341:
1308:
1304:
1298:
1268:cite journal
1256:. Retrieved
1236:
1232:
1222:
1205:
1201:
1192:
1181:the original
1168:
1151:
1124:
1118:
1106:. Retrieved
1103:"Mercur, UT"
1097:
1085:. Retrieved
1079:
1073:
1037:
1018:
1001:
997:
953:
949:
939:
922:
895:
889:
860:
837:Cyanide Code
836:
834:
830:
811:
792:
761:
742:cyclodextrin
715:
700:in Romania,
695:
559:river below
549:
494:
408:
383:
351:
323:
310:Lead nitrate
291:
274:
256:
244:
234:
198:
194:Elko, Nevada
147:
120:
81:
60:
50:process for
27:
23:
19:
18:
2269:Co-products
2103:Calcination
2067:Cupellation
1983:Dry washing
1972:Magnetation
1895:Ore sorting
1860:Pebble mill
1827:Comminution
752:Legislation
718:thiosulfate
706:Pascua Lama
639:Kyrgyzstan
587:Summitville
412:Caro's acid
374:thiocyanate
300:) or soda (
253:Application
154:Mercur Mine
127:pyritic ore
2321:Categories
2306:Stamp sand
2256:Downs cell
1988:Buddle pit
1978:Rocker box
1835:Stamp mill
1776:Base metal
1744:Extraction
1533:2013-01-03
1402:BBC News,
956:: 107231.
843:References
756:See also:
746:lixiviants
702:Lake Cowal
684:San Dimas
583:1985â1991
533:See also:
344:solution.
263:comminuted
70:nature of
2148:Lixiviant
2113:Liquation
2006:(by heat)
1867:Ball mill
1810:Recycling
1239:: 81â87.
1143:0167-4528
1024:US 403202
980:240128866
768:Wisconsin
670:Tolukuma
651:Baia Mare
578:Incident
561:Baia Mare
523:Baia Mare
92:Bagration
82:In 1783,
68:poisonous
2276:Tailings
2140:Leaching
2108:Roasting
2059:Refining
2043:ISASMELT
2015:Smelting
1872:Rod mill
1855:SAG mill
1840:Arrastra
1550:Archived
1510:Archived
1492:Archived
1474:23 April
1333:15819225
1063:Archived
730:thiourea
655:Romania
575:Country
354:aeration
329:reagents
314:leaching
211:NaCN + O
63:reagents
48:leaching
2301:Red mud
2291:Clinker
2045:furnace
1953:Panning
1910:Trommel
1900:Vanning
1877:IsaMill
1850:AG mill
1845:Crusher
1793:Surface
1771:Mineral
1664:Yestech
1439:Bibcode
1357:Bibcode
1313:Bibcode
1241:Bibcode
958:Bibcode
776:Hungary
764:Montana
687:Mexico
623:Guyana
603:Ok Tedi
416:cyanate
139:Glasgow
96:Faraday
78:History
72:cyanide
30:) is a
26:or the
2281:Gangue
2082:Poling
1888:Sizing
1788:Mining
1385:
1331:
1159:
1141:
1131:
1108:May 1,
1087:May 1,
1030:
978:
910:
877:
816:, the
770:, the
732:(SC(NH
635:Kumtor
370:sulfur
325:Oxygen
269:or by
229:
227:Na + 4
225:
217:
209:
207:Au + 8
205:
2096:Other
1815:Scrap
1672:(PDF)
1641:ICMI
1258:2 May
1184:(PDF)
1177:(PDF)
976:S2CID
931:(PDF)
681:2018
667:2000
647:2000
631:1998
620:Omai
617:1995
572:Mine
569:Year
557:SomeÈ
432:+ â
223:O â 4
2327:Gold
2296:Chat
2286:Slag
1476:2021
1383:ISBN
1329:PMID
1274:link
1260:2021
1157:ISBN
1139:ISSN
1129:ISBN
1110:2016
1089:2016
908:ISBN
875:ISBN
766:and
514:Lime
455:+ 2
275:pulp
257:The
238:and
231:NaOH
143:Rand
123:Rand
36:gold
1761:Ore
1447:doi
1365:doi
1321:doi
1249:doi
1210:hdl
1006:hdl
966:doi
954:174
900:doi
867:doi
790:).
728:),
591:US
470:HCO
446:OCN
434:OCN
364:as
281:or
261:is
259:ore
215:+ 2
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720:(S
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512:.
500:SO
496:(H
482:NH
480:+
468:â
423:CN
306:pH
169:.
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1974:)
1970:(
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1697:t
1690:v
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510:2
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498:2
487:3
475:3
466:O
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457:H
221:2
219:H
213:2
203:4
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