Editing Gold cyanidation

{{Short description|Technique for extracting gold from low-grade ore}}

'''Gold cyanidation''' (also known as the '''cyanide process''' or the '''MacArthur–Forrest process''') is a [[hydrometallurgy|hydrometallurgical]] technique for extracting [[gold]] from low-grade [[ore]] through conversion to a water-soluble [[coordination complex]]. It is the most commonly used [[leaching (chemistry)|leaching]] process for [[gold extraction]].<ref name=Ullmann>{{cite book|doi=10.1002/14356007.a08_159.pub3 |chapter=Cyano Compounds, Inorganic |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2011 |last1=Gail |first1=Ernst |last2=Gos |first2=Stephen |last3=Kulzer |first3=Rupprecht |last4=Lorösch |first4=Jürgen |last5=Rubo |first5=Andreas |last6=Sauer |first6=Manfred |last7=Kellens |first7=Raf |last8=Reddy |first8=Jay |last9=Steier |first9=Norbert |last10=Hasenpusch |first10=Wolfgang |isbn=978-3-527-30385-4 }}</ref> Cyanidation is also widely used in [[silver]] extraction, usually after [[froth flotation]].<ref name=KO>{{cite book |chapter=Silver and Silver Alloys |title=Kirk-Othmer Encyclopedia of Chemical Technology |year=2010 |last1=Etris |first1=S. F. |pages=1–43 |isbn=978-0471238966 |doi=10.1002/0471238961.1909122205201809.a01.pub3}}</ref>

Production of [[reagent]]s for mineral processing to recover gold represents 70% of cyanide consumption globally. While other metals, such as [[copper]], [[zinc]], and silver, are also recovered using cyanide, gold remains the primary driver of this technology. <ref name=Ullmann/> The highly [[toxic]] nature of [[cyanide]] has led to controversy regarding its use in gold mining, with it being banned in some parts of the world. However, when used with appropriate safety measures, cyanide can be safely employed in gold extraction processes.<ref>{{Cite web |title=Cyanide Management |url=https://www.industry.gov.au/sites/default/files/2019-04/lpsdp-cyanide-management-handbook-english.pdf |publisher=Australian Government}}</ref> One critical factor in its safe use is maintaining an alkaline pH level above 10.5, which is typically controlled using [[lime (material)|lime]] in industrial-scale operations. Lime plays an essential role in gold processing, ensuring that the pH remains at the correct level to mitigate risks associated with cyanide use.<ref>{{cite journal |title=Lime use in gold processing – A review |year=2021 |last1=Du Plessis |first1=C. A. |last2=Lambert |first2=H. |last3=Gärtner |first3=R. S. |last4=Ingram |first4=K. |last5=Slabbert |first5=W. |last6=Eksteen |first6=J. J. |journal=Minerals Engineering |volume=174 |page=107231 |bibcode=2021MiEng.17407231D |s2cid=240128866 |doi=10.1016/j.mineng.2021.107231 |doi-access=free}}</ref>

==History==
In 1783, [[Carl Wilhelm Scheele]] discovered that gold dissolved in [[aqueous solution]]s of cyanide. Through the work of [[Peter Bagrationi|Bagration]] (1844), Elsner (1846), and [[Michael Faraday|Faraday]] (1847), it was determined that each gold atom required two cyanide ions, i.e. the [[stoichiometry]] of the soluble compound.

===Industrial process===
[[File:Jsmacarthur-X-007r.jpg|thumb|upright|[[John Stewart MacArthur]] developed the cyanide process for gold extraction in 1887.]]
The expansion of gold mining in the [[Witwatersrand|Rand]] of South Africa began to slow down in the 1880s, as the new deposits found tended to contain [[pyrite|pyritic ore]]. The gold could not be extracted from this compound with any of the then available chemical processes or technologies.<ref name="Gray">{{ cite journal |first1=J. A. |last1=Gray |first2=J. |last2=McLachlen
|title=A history of the introduction of the MacArthur-Forrest cyanide process to the Witwatersrand goldfields |journal=Journal of the Southern African Institute of Mining and Metallurgy |volume=33 |issue=12 |date=Jun 1933 |pages=375–397 |hdl=10520/AJA0038223X_5033}}</ref>
In 1887, [[John Stewart MacArthur]], working in collaboration with brothers Robert and William Forrest for the [[Charles Tennant|Tennant Company]] in [[Glasgow]], Scotland, developed the MacArthur–Forrest process for the extraction of gold from gold ores. Several patents were issued in the same year.<ref>{{cite patent
|inventor1-last=MacArthur |inventor1-first=John Stewart |inventor2-last=Forrest |inventor2-first=William |inventor3-last=Forrest Robert |inventor3-first=Robert |pubdate=1889-05-14 |title=Process of Obtaining Gold and Silver from Ores |country=US |number=403202}}</ref> By suspending the crushed ore in a cyanide solution, a separation of up to 96 percent pure gold was achieved.<ref>{{cite web |title=Methods to recover Gold II |date=2013-05-14 |url=https://suertegold.wordpress.com/in-the-beginning-there-was-gold-1/day-52/}}</ref>
The process was first used on the [[Witwatersrand|Rand]] in 1890 and, despite operational imperfections, led to a boom of investment as larger gold mines were opened up.<ref name="Recent Advances in Gold Metallurgy">Habashi, Fathi [http://www.ucv.ve/cifi/16%5CArticuloh.htm Recent Advances in Gold Metallurgy] {{webarchive|url=https://web.archive.org/web/20080330234816/http://www.ucv.ve/cifi/16%5CArticuloh.htm |date=2008-03-30}}</ref><ref name="Gray"/>

By 1891, Nebraska pharmacist [[Gilbert S. Peyton]] had refined the process at his [[Mercur, Utah|Mercur Mine]] in Utah, "the first mining plant in the United States to make a commercial success of the cyanide process on gold ores."<ref>{{cite book |title=The alumni quarterly and fortnightly notes |author=<!--Staff writer(s); no by-line.--> |date=January 1, 1921 |publisher=University of Illinois |url=https://books.google.com/books?id=HGDnAAAAMAAJ&q=Gilbert+Peyton+cyanide&pg=RA1-PA102 |access-date=May 1, 2016}}</ref><ref>{{cite web |title=Mercur, UT |author=<!--Staff writer(s); no by-line.--> |url=http://silverstateghosttowns.com/mercurut.html |access-date=May 1, 2016}}</ref> In 1896, Bodländer confirmed that oxygen was necessary for the process, something that had been doubted by MacArthur, and discovered that [[hydrogen peroxide]] was formed as an intermediate.<ref name="Recent Advances in Gold Metallurgy"/>
Around 1900, the American metallurgist [[Charles Washington Merrill]] (1869–1956) and his engineer Thomas Bennett Crowe improved the treatment of the cyanide leachate, by using vacuum and zinc dust. Their process is the [[Merrill–Crowe process]].<ref>{{cite book |last=Adams |first=Mike D. |title=Advances in Gold Ore Processing |date=2005-12-02 |publisher=Elsevier |pages=XXXVII–XLII |isbn=978-0-444-51730-2 |issn=0167-4528}}</ref>

==Chemical reactions==
[[File:Dicyanoaurate(I)-3D-balls.png|thumb|right|[[Ball-and-stick model]] of the aurocyanide or dicyanoaurate(I) complex anion, [Au(CN)<sub>2</sub>]<sup>−</sup><ref>Greenwood, N. N. & Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.), Oxford:Butterworth-Heinemann. {{ISBN|0-7506-3365-4}}.</ref>]]
[[File:Gold heap leaching.jpeg|thumb|Cyanide leaching "heap" at a gold mining operation near [[Elko, Nevada]]]]
The chemical reaction for the dissolution of gold, the "Elsner equation", follows:
: 4{{nbsp}}Au + 8{{nbsp}}NaCN + O<sub>2</sub> + 2{{nbsp}}H<sub>2</sub>O → 4{{nbsp}}Na[Au(CN)<sub>2</sub>] + 4{{nbsp}}NaOH

[[Potassium cyanide]] and [[calcium cyanide]] are sometimes used in place of sodium cyanide.

Gold is one of the few metals that dissolves in the presence of cyanide ions and oxygen. The soluble gold species is [[dicyanoaurate]].<ref>{{cite web |title=Technical Bulletin 1 |publisher=Multi Mix Systems |url=http://www.multimix.com.au/DOCUMENTS/Technical%20Bulletin1.PDF |url-status=dead |archive-url=https://web.archive.org/web/20091023235047/http://www.multimix.com.au/DOCUMENTS/Technical%20Bulletin1.PDF |archive-date=2009-10-23}}</ref> from which it can be recovered by adsorption onto activated carbon.<ref>{{cite journal |title=The absorption of gold cyanide onto activated carbon. I. The kinetics of absorption from pulps |journal=Journal of the Southern African Institute of Mining and Metallurgy |date=February 1984 |volume=84 |issue=2 |pages=50–54 |hdl=10520/AJA0038223X_1427 |url=https://journals.co.za/doi/abs/10.10520/AJA0038223X_1427}}</ref>

==Application==
The [[ore]] is [[comminution|comminuted]] using grinding machinery. Depending on the ore, it is sometimes further concentrated by [[froth flotation]] or by [[mineral processing#Gravity concentration|centrifugal (gravity) concentration]]. Water is added to produce a slurry or ''pulp''. The basic ore slurry can be combined with a solution of [[sodium cyanide]] or [[potassium cyanide]]; many operations use [[calcium cyanide]], which is more cost effective.

To prevent the creation of toxic [[hydrogen cyanide]] during processing, slaked lime ([[calcium hydroxide]]) or soda ([[sodium hydroxide]]) is added to the extracting solution to ensure that the acidity during cyanidation is maintained over [[pH]] 10.5 - strongly basic.
[[Lead(II) nitrate|Lead nitrate]] can improve gold [[tank leaching|leaching]] speed and quantity recovered, particularly in processing partially oxidized ores.<!--how?--><!--why?, probably some sort of reduction reaction-->

===Effect of dissolved oxygen===
[[Oxygen]] is one of the [[reagent]]s consumed during cyanidation, accepting the electrons from the gold, and a deficiency in [[oxygen saturation|dissolved oxygen]] slows leaching rate. Air or pure oxygen gas can be purged through the pulp to maximize the dissolved oxygen concentration. Intimate oxygen-pulp contactors<!--huh?--> are used to increase the partial pressure of the oxygen in contact with the solution, thus raising the dissolved oxygen concentration much higher than the saturation level at [[atmospheric pressure]]. Oxygen can also be added by dosing the pulp with [[hydrogen peroxide]] solution.

===Pre-aeration and ore washing===
In some ores, particularly those that are partially sulfidized, [[aeration]] (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 [[iron (III) oxide]] and subsequent [[precipitation (chemistry)|precipitation]] as [[iron hydroxide]] minimizes loss of cyanide from the formation of ferrous cyanide complexes. The oxidation of [[sulfur]] compounds to sulfate ions avoids the consumption of cyanide to [[thiocyanate]] (SCN<sup>−</sup>) byproduct.

==Recovery of gold from cyanide solutions==
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):
* [[Carbon in pulp]]
* [[Electrowinning]]
* [[Merrill–Crowe process]]
<!--wasn't there one which uses mercury? NONE-->

==Cyanide remediation processes==
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 [[peroxymonosulfuric acid|Caro's acid]] process oxidise the cyanide to [[cyanate]], which is not as toxic as the cyanide ion, and which can then react to form carbonates and ammonia:
<ref>{{cite journal |last1=Teixeira |first1=Luiz Alberto Cesar |last2=Montalvo |first2=Javier Paul |last3=Yokoyama |first3=Andia, Lídia |last4=da Fonseca Araújo |first4=Fabiana Valéria |last5=Sarmiento |first5=Cristian Marquez |title=Oxidation of cyanide in effluents by Caro's Acid |journal=Minerals Engineering |year=2013 |volume=45 |pages=81–87 |bibcode=2013MiEng..45...81T |doi=10.1016/j.mineng.2013.01.008 |url=https://www.sciencedirect.com/science/article/abs/pii/S0892687513000101 |access-date=2 May 2021|url-access=subscription }}</ref>

:{{chem|CN|-}} + [O] → {{chem|OCN|-}}
:{{chem|OCN|-}} + 2 {{chem|H|2|O}} → {{chem|H|C|O|3|-}} + {{chem|N|H|3}}
The Inco process can typically lower cyanide concentrations to below 50&nbsp;mg/L, whereas the Caro's acid process can lower cyanide levels to between 10 and 50&nbsp;mg/L, with the lower concentrations achievable in solution streams rather than slurries. Caro's acid – peroxomonosulfuric acid (H<sub>2</sub>SO<sub>5</sub>) - 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&nbsp;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 [[sodium metabisulfite]], which releases SO<sub>2</sub>. [[Lime (material)|Lime]] is added to maintain the pH at around 8.5, and [[copper sulfate]] 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 [[Baia Mare]].<ref name="Baia Mare report"/> 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.<ref>{{cite journal |title=Determination of Mercury Evasion in a Contaminated Headwater Stream |journal=Environmental Science & Technology |volume=39 |issue=6 |pages=1679–1687 |year=2005 |last1=Maprani |first1=Antu C. |last2=Al |first2=Tom A. |last3=MacQuarrie |first3=Kerry T. |last4=Dalziel |first4=John A. |last5=Shaw |first5=Sean A. |last6=Yeats |first6=Phillip A. |bibcode=2005EnST...39.1679M |pmid=15819225 |doi=10.1021/es048962j}}</ref><ref>{{cite journal |title=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 Brunswick, Canada |journal=Applied Geochemistry |volume=21 |issue=11 |pages=1969–1985 |year=2006 |last1=Al |first1=Tom A. |last2=Leybourne |first2=Matthew I. |last3=Maprani |first3=Antu C. |last4=MacQuarrie |first4=Kerry T. |last5=Dalziel |first5=John A. |last6=Fox |first6=Don |last7=Yeats |first7=Phillip A. |bibcode=2006ApGC...21.1969A |doi=10.1016/j.apgeochem.2006.08.013}}</ref>

==Effects on the environment==
{{See also|List of gold mining disasters}}

[[File:Chemung mine-sodium cyanide.jpeg|thumb|Sodium cyanide drum at the abandoned Chemung Mine in [[Masonic, California]]]]
Despite being used in 90% of gold production:<ref>"Long Term persistence of cyanide species in mine waste environments", B. Yarar, Colorado School of Mines, Tailings and Mine Waste '02, Swets & Zeitlinger, {{ISBN|90-5809-353-0}}, pp.&nbsp;197 ([https://books.google.com/books?id=PPTL9-lM78AC&dq=world+cyanide+consumption&pg=PA197 Google Books]).</ref> gold cyanidation is [[controversy|controversial]] due to the toxic nature of cyanide. Although aqueous solutions of cyanide degrade rapidly in sunlight<!--sunlight? or just air?-->, the less-toxic products, such as cyanates and thiocyanates, may persist for some years. The famous disasters have killed few people — humans can be warned not to drink or go near polluted water, but cyanide spills can have a devastating effect on rivers, sometimes killing everything for several miles downstream. The cyanide could be washed out of river systems and, as long as organisms can migrate from unpolluted areas upstream, affected areas can soon be repopulated. Longer term impact and accumulation of cyanide in riparian or limnological benthos and environmental fate is less clear.   According to Romanian authorities, in the [[Someș]] river below [[Baia Mare]], the plankton returned to 60% of normal within 16 days of the spill; the numbers were not confirmed by Hungary or Yugoslavia.<!-- but what about larger creatures?--><ref name="Baia Mare report">UNEP/OCHA Environment Unit [https://reliefweb.int/report/romania/cyanide-spill-baia-mare-romania-unepocha-assessment-mission-advance-copy "UN assessment mission – Cyanide Spill at Baia Mare, March 2000"].</ref>
Famous cyanide spills include:
{|style="margin:auto;" class="wikitable"
|-
!style="text-align:left;" |Year
!style="text-align:left;" |Mine
!style="text-align:left;" |Country
!style="text-align:left;" |Incident
|-
|1985–1991
|[[Summitville mine|Summitville]]
|US
|Leakage from leach pad
|-
|1980s–present
|[[Ok Tedi Mine|Ok Tedi]]
|Papua New Guinea
|[[Ok Tedi environmental disaster|Unrestrained waste discharge]]
|-
|1995
|Omai
|Guyana
|Collapse of tailings dam
|-
|1998
|[[Kumtor Gold Mine|Kumtor]]
|Kyrgyzstan
|Truck drove over bridge
|-
|2000
|[[Baia Mare]]
|Romania
|Collapse of containment dam (see [[2000 Baia Mare cyanide spill]])
|-
|2000
|Tolukuma
|Papua New Guinea
|Helicopter dropped crate into rainforest<ref>BBC News, [http://news.bbc.co.uk/1/hi/world/asia-pacific/687913.stm BBC: "Cyanide seeps into PNG rivers"], March 23, 2000.</ref>
|-
|2018
|San Dimas
|Mexico
|Truck leaked 200 liters of cyanide solution into the Piaxtla River in Durango<ref>Wilson, T. E. [https://www.lapoliticaeslapolitica.com/2018/04/after-cyanide-spill-can-first-majestic.html La politica es la politica: "After cyanide spill, can First Majestic clean up its act?"] April 21, 2018.</ref>
|-
|2024
|Eagle Mine
|Canada (Yukon)
|Heap Leach failure, cyanide spill into surrounding waterways, ecological damage and company bankruptcy 
|}

Such spills have prompted fierce protests at new mines that involve use of cyanide, such as [[Roşia Montană]] in Romania, [[Lake Cowal]] in Australia, [[Pascua Lama]] in Chile, and Bukit Koman in Malaysia.

==Alternatives to cyanide==
Although cyanide is cheap, effective, and biodegradable, its high toxicity & increasingly poor impact on a mine's political and social license to operate, has incentivized alternative methods for extracting gold. Other extractants have been examined including [[thiosulfate]] (S<sub>2</sub>O<sub>3</sub><sup>2−</sup>), [[thiourea]] (SC(NH<sub>2</sub>)<sub>2</sub>), iodine/iodide, ammonia, liquid mercury, and alpha-[[cyclodextrin]]. Challenges include reagent cost and the efficiency of gold recovery, although some chlorination process using sodium hypochlorite (household bleach) have shown promise in terms of reagent regeneration.  These technologies are at a pre-commercialisation stage and compare favourably to equivalent cyanidation methods, including gold recovery percentage. Thiourea has been implemented commercially for ores containing stibnite.<ref>{{cite journal |title=Review of gold extraction from ores |journal=Minerals Engineering |volume=7 |issue=10 |pages=1213–1241 |year=1994 |last1=La Brooy |first1=S.R. |last2=Linge |first2=H.G. |last3=Walker |first3=G.S. |bibcode=1994MiEng...7.1213L |doi=10.1016/0892-6875(94)90114-7}}</ref> Yet another alternative to cyanidation is the family of glycine-based [[lixiviant]]s.<ref>{{cite web |title=Glycine lixiviants |website=Mining and Process Solutions |url=https://www.mpsinnovation.com.au/ |access-date=23 April 2021}}</ref>

==Legislation==
{{See also|Gold cyanidation ban}}
The US states of [[Montana]]<ref>[http://www.meic.org/mining/cyanide_mining/ban-on-cyanide-mining/i-137 The Citizens Initiative banning of cyanide mining in the State of Montana, US] {{webarchive |url=https://web.archive.org/web/20071021031827/http://www.meic.org/mining/cyanide_mining/ban-on-cyanide-mining/i-137 |date=October 21, 2007}}</ref> and [[Wisconsin]],<ref>[https://docs.legis.wisconsin.gov/2001/related/proposals/sb160.pdf 2001 Senate Bill 160] {{Webarchive|url=https://web.archive.org/web/20061010052437/http://www.legis.state.wi.us/2001/data/SB-160.pdf |date=2006-10-10}} regarding the use of cyanide in mining.</ref> the [[Czech Republic]],<ref>{{cite web |title=Czech Senate bans use of cyanide in gold mining |publisher=Nl.newsbank.com |date=2000-08-10 |url=http://nl.newsbank.com/nl-search/we/Archives?p_product=NewsLibrary&p_multi=BBAB&d_place=BBAB&p_theme=newslibrary2&p_action=search&p_maxdocs=200&p_topdoc=1&p_text_direct-0=0F97DD15035650A1&p_field_direct-0=document_id&p_perpage=10&p_sort=YMD_date:D&s_trackval=GooglePM |access-date=2013-01-03}}</ref> [[Hungary]],<ref>[http://greenpeace.hu/hirek/p1/rkezdo/i202 Zöld siker: törvényi tilalom a cianidos bányászatra!] {{webarchive |url=https://web.archive.org/web/20110721105032/http://greenpeace.hu/hirek/p1/rkezdo/i202 |date=July 21, 2011}}</ref> have banned cyanide mining. The [[European Commission]] rejected a proposal for such a ban, noting that existing regulations (see below) provide adequate environmental and health protection.<ref>International Mining - [https://im-mining.com/2010/07/06/european-commission-rejects-proposed-ban-on-using-cyanide-in-extractive-industry/ European Commission rejects proposed ban on using cyanide in extractivism|extractive industry], July, 2010</ref> Several attempts to ban [[gold cyanidation in Romania]] were rejected by the Romanian Parliament. There are currently protests in Romania calling for a ban on the use of cyanide in mining (see [[2013 Romanian protests against the Roșia Montană Project]]).

In the EU, industrial use of hazardous chemicals is controlled by the so-called [[Seveso II Directive]] (Directive 96/82/EC,<ref>[https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:31996L0082 Council Directive 96/82/EC of 9 December 1996 on the control of major-accident hazards involving dangerous substances.] For the modifications see the consolidated version.</ref> which replaced the original [[Directive 82/501/EC|Seveso Directive]] (82/501/EEC<ref>[https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:31982L0501 Council Directive 82/501/EEC of 24 June 1982 on the major-accident hazards of certain industrial activities.] Not in force.</ref> 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 [[Directive 80/68/EEC|Groundwater Directive]] (Directive 80/68/EEC)<ref>[https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:31980L0068 Council Directive 80/68/EEC of 17 December 1979 on the protection of groundwater against pollution caused by certain dangerous substances.] Not in force.</ref> 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 [[Water Framework Directive]] (2000/60/EC).<ref>[https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32000L0060 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 ''Water Framework Directive'').] For the modifications see the consolidated version.</ref>

In response to the [[2000 Baia Mare cyanide spill]], the [[European Parliament]] and the Council adopted [[Directive 2006/21/EC]] on the management of waste from extractive industries.<ref>[https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32006L0021 Directive 2006/21/EC of the European Parliament and of the Council of 15 March 2006 on the management of waste from extractive industries.] For the modifications see the consolidated version.</ref> Article 13(6) requires "the concentration of weak acid dissociable cyanide in the pond is reduced to the lowest possible level using [[best available techniques]]", 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.

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.

The industry has come up with a voluntary "''Cyanide Code''"<ref>ICMI [https://cyanidecode.org/ cyanidecode.org] International Cyanide Management Code For The Manufacture, Transport, and Use of Cyanide In The Production of Gold</ref> that aims to reduce environmental impacts with third party audits of a company's cyanide management.

==References==
{{Reflist}}

==External links==
{{Commons category|Gold mining}}
*[http://www.abc.net.au/science/news/enviro/EnviroRepublish_351793.htm Efforts at a cleaner process]
*[https://www.yestech.com/tech/gold1.htm Yestech] A different commercial method that does not use toxic cyanide
*[https://web.archive.org/web/20121021155525/http://www.earthworksaction.org/files/publications/cyanideuncertainties.pdf Cyanide Uncertainties] (PDF)
*[https://refreshscience.com/how-gold-is-extracted-by-cyanidation-process/ How gold is extracted by cyanidation process]

{{Extractive metallurgy}}

{{Authority control}}
[[Category:Gold|Cyanidation]]
[[Category:Cyano complexes]]
[[Category:Metallurgical processes]]