Review of Barriers to Reduce Mercury Use in Artisanal Gold Mining

Home , Borax

The Extractive Industries and Society 1 (2014) 351–361

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The Extractive Industries and Society

jou rnal homepage: www.elsevier.com/locate/exis

Review Article

Review of barriers to reduce mercury use in artisanal gold mining

Marcello M. Veiga *, Gustavo Angeloci-Santos, John A. Meech

Norman B. Keevil Institute of Mining Engineering, University of British Columbia, Vancouver, Canada

A R T I C L E I N F O A B S T R A C T

Article history: This article reviews the use of amalgamation in artisanal gold mining (AGM) and the barriers to reducing

Received 5 January 2014

mercury use and emissions from the sector. In 2012, AGM accounted for approximately 12% of all the

Received in revised form 31 March 2014

gold produced in the world. The main method of extraction used is gold amalgamation, a process which

Available online 26 April 2014

accounts for the release of between 1000 and 1600 tonnes of metallic mercury every year. The

availability of mercury is expected to decline since the international market is shrinking as a result of

Keywords:

international policies. Major producers and traders are discontinuing efforts to market the metal.

Mercury

Unfortunately, gold amalgamation is still in wide use around the world, despite its elevated price in a

Gold

restricted market. Alternative gold extraction methods for artisanal miners have been attempted, but

Artisanal mining

Pollution with limited success. This paper brings to light the perceptions of different stakeholders, including

Myths governments, communities, academics, and the artisanal gold miners themselves, all of whom have

impeded progress towards improved gold processing practices. Capacity building, education, and the

presence of trainers prior to introducing a new approach are keys to facilitating change.

Contents

1. Introduction and background ...... 351

2. Gold amalgamation: an overview ...... 352

3. Interventions to reduce mercury pollution in AGM ...... 353

4. Micro-credit ...... 354

5. Formalization of artisanal miners ...... 355

6. Gold concentration to reduce mercury pollution ...... 356

7. Treatment of gravity concentrates ...... 357

7.1. Borax ...... 357

7.2. Cyanide ...... 357

7.3. Alternative lixiviants...... 358

7.4. Retorts ...... 358

8. Conclusion ...... 359

Acknowledgements ...... 359

References ...... 359

1. Introduction and background the metal has increased three fold over the past 10 years. Its

extraction on a small scale, however, induces extremely high levels

Approximately 30 million individuals spread over virtually all of river siltation, mercury pollution, and many other environmen-

developing countries are involved in extracting over 30 different tal and social problems (Velasquez-Lopez et al., 2010).

minerals using rudimentary techniques (Veiga and Baker, 2004). In 2004, annual gold production from Artisanal Gold Mining

Gold is the predominant product being worked since the price of (AGM) was estimated at 20–30% (500–800 tonnes) of total

global production (Swain et al., 2007). A more recent study

(Seccatore, 2012) placed production from AGM at about

392 tonnes/a or 12.2% of total output (2828 from organized mines

* Corresponding author. Tel.: +1 6048224332; fax: +1 6048225599.

E-mail addresses: [email protected], [email protected] (M.M. Veiga). (WGC, 2013) + 392 tonnes from AGM = 3220 tonnes).

http://dx.doi.org/10.1016/j.exis.2014.03.004

352 M.M. Veiga et al. / The Extractive Industries and Society 1 (2014) 351–361

Annual mercury releases to the environment from AGM the amalgamation process, they virtually all answer, ‘‘almost

operations based on UNEP (2013) and Swain et al. (2007) is nothing’’. However, when they are asked how much mercury they

1400 tonnes and 1000 tonnes, respectively giving a global range of buy every month, they reveal the real mercury losses, since they

average ratio of tonnes of Hglost to tonnes of Auproduced between 2.5 would not buy mercury if they did not need it (Veiga and Baker,

and 3.5. Recently, Koekkoek (2013) projected the annual amount of 2004).

mercury released by AGM in 70 countries to be 1608 tonnes. This Amalgamation is not complicated, but gold must be liberated

estimate represents 93% of the countries that use mercury in AGM. from the gangue for the process to be effective. Mercury combines

The environmental and health impacts of mercury pollution with gold to form a wide range of compounds, from AuHg2 to

from AGM have been well-documented in different parts of the Au8Hg (Taggart, 1945). When amalgamating a concentrate,

world (Pfeiffer et al., 1989; Malm et al., 1990, 1995; Ikingura and mercury losses occur mainly because of ‘‘mercury sickening’’

Akagi, 1996; Veiga, 1997; Lacerda, 1997; Olivero and Solano, 1998; and loss of coalescence (or ‘‘ﬂouring’’). ‘‘Sickening’’ is caused by

Malm, 1998; Harada et al., 1999; Akagi et al., 2000; Drake et al., mercury oxidation or impurities such as oil, grease, clay minerals,

2001; Wasserman et al., 2003; Eisler, 2004; Castilhos et al., 2006; sulfates, and sulﬁdes on the mercury surface while ‘‘ﬂouring’’ is the

Bo¨se-O’Reilly et al., 2008; Cordy et al., 2011, 2013). It seems that dispersion of mercury into small drops caused by ‘‘sickening’’ or by

the health effects of mercury vapour emissions in workers and mechanical forces such as grinding (Beard, 1987). It is believed by

families living in mining towns is much more evident and dramatic the miners in most AGM regions of the world that addition of

than the effects of methylmercury by ﬁsh ingestion in mining ‘‘amalgamation-aiding reagents’’ avoids complete mercury sick-

communities (van Straaten, 2000; Drasch et al., 2001; Ogola et al., ening and ﬂouring, therefore eliminating mercury losses. In many

2002; Feng et al., 2006; WHO, 2013; Sieber and Brain, 2014). The parts of the world, miners add lemon juice, brown sugar, caustic

main cause of environmental problems related to mercury releases soda, quicklime, tooth paste, baking powder, guava leaves, urea,

is amalgamation of the whole ore (Spiegel and Veiga, 2010) cyanide, urine, or detergent to reduce ‘‘ﬂouring’’ (Veiga et al.,

whereas the main health problem is caused by inhalation of 2006). There is no study proving that such reagents increase the

metallic mercury vapours when amalgams are thermally decom- capacity of mercury to hold together and avoid formation of

posed without using a condenser or ﬁlter (Veiga and Baker, 2004). droplets. Neither are there studies about how these reagents work,

The objective of this paper is to provide a review of mercury use although some do appear to be effective. Alteration of mercury’s

in AGM identifying perceptions from different stakeholders surface tension or adsorption of such reagents to act as a surfactant

(governments, NGOs, academics and artisanal gold miners) around is a possible way of enhancing mercury coalescence.

the world that may have created barriers to introducing Hg-free An experiment conducted by Veiga et al. (2009) demonstrated

practices or to reduce mercury pollution from artisanal gold to Ecuadorian miners that amalgamation extracted only 26% of the

miners. The data and comments presented in this article are the gold from a gravity concentrate, whereas cyanidation extracted

result of over 35 years of practical experience of the authors in the more than 90%. The low efﬁciency of gold extraction was attributed

ﬁeld of mercury and artisanal mining. to the oxidation of the mercury. Pantoja and Alvarez (2000)

recommended using an electrolytic process to remove mercury

oxidation layers and form sodium-amalgam, which is more

2. Gold amalgamation: an overview efﬁcient in gold amalgamation than mercury alone. Their results

were impressive, showing an increase of recovery of around 60%

Amalgamation is one of the oldest gold extraction methods. (using regular mercury) to 92% (using ‘‘activated’’ mercury).

When mercury is added to gold and silver ores, it forms an Mercury is activated in an electrolytic process with a 10% NaCl

amalgam (or paste) following contact with these metals. Mercury solution. Metallic mercury is connected via a copper wire to the

amalgamates all metals except iron and platinum. The heavy mass negative pole of a 12-V motorbike battery and a rod of graphite that

of liquid mercury with the solid amalgam inside can be separated can be obtained from an old radio battery connected to the positive

from other minerals through panning. The amalgam is then pole for 15 min (Fig. 1). ‘‘Activated’’ mercury is much more

squeezed by hand in a piece of fabric to eliminate the excess liquid coalescent than ‘‘sick’’ mercury. As mercury salts are soluble at

mercury not bound to gold. The resulting amalgam consisting of high pH values (Meech et al., 1998) and sodium-amalgam forms

40–50% mercury can be separated from the gold by decomposition sodium hydroxide in water, this is likely the mechanism by which

using a propane or gasoline torch at temperatures around 460 8C. the surface of metallic mercury is cleaned from oils and mercury

This process produces a gold dore´ containing about 2–5% residual oxide. This process is similar to the industrial process used to

mercury, depending on the effectiveness of the evaporation manufacture caustic soda. Actually, the use of ‘‘charged mercury’’,

process (Veiga and Hinton, 2002). In some cases, such as those as this process is popularly known, is recommended by the Nevada

observed in some African countries, when amalgams are burned in Prospectors Association (Ralph, 2013).

low-temperature bonﬁres, the dore´ will contain as much as 20% Whole ore amalgamation is the oldest technique, culminating

mercury (Veiga et al., 2006). in the greatest environmental damage in gold processing. Mercury

Two methods are used by operators to extract gold with is introduced into a sluice box directly, the ore pulp is allowed to

mercury: ﬂow over copper-plates or the mercury is poured into small ball

mills prior to grinding. This latter technique results in the greatest

(1) amalgamation of a gravity concentrate; Hg loss since mercury droplets are formed during grinding, and are

(2) amalgamation of the whole ore. then dragged into the tailings that end up in the environment or

are sent for cyanide leaching and then to the environment.

The ﬁrst method dramatically reduces mercury releases (losses) There is a general perception in the public domain that the main

to the environment since only a small amount of material source of mercury pollution from AGM is amalgam burning (Veiga

(concentrate) is amalgamated. The second method is responsible and Hinton, 2002). Amalgams usually contain 40–50% of Hg and

for the largest losses of mercury to the environment (Veiga and 40–60% of gold and silver. Thus, the emission level from amalgam

Hinton, 2002). burning is restricted to the amount of gold produced. In contrast,

Most operators have the wrong perception that amalgamation amalgamation of the entire ore requires the addition of much more

is very efﬁcient at extracting gold and that no mercury is lost in the mercury. Based on mass balances of 15 artisanal mining plants,

process. When a miner is asked how much mercury he or she lost in Cordy et al. (2011) demonstrated that mercury losses when the

M.M. Veiga et al. / The Extractive Industries and Society 1 (2014) 351–361 353

Fig. 1. Miners applying mercury activation process in the Amazon.

whole ore is amalgamated in ball mills is 10–15 times higher than Micro-miners have neither the education nor the capital to work

when amalgam is decomposed in open pans by heating. On the properly. Furthermore, they are not in any way tried to stop their

other hand, amalgam-burning likely triggers the main health activities for training or formalization (Spiegel and Veiga, 2010). In

problems. fact, the general public has the perception that all artisanal miners

Amalgamation of the whole ore is a result of ignorance and/or are those panning for gold in the river banks. There is a wide variety

‘‘tradition’’. It is also a convenient manner for the owners of of miners that can be classiﬁed as ‘‘artisanal’’, ranging from those

processing centres to quickly produce gold for their clients (the processing 5000 tonnes of ore per day to those panning 20 kg of

miners). The concept of processing centres began to spread around gravel per day. The solution for the small-panner using mercury is

the world in the 1990s, with the idea that this would prevent very complicated as they are dispersed in the ﬁeld and are mining

dispersing mercury used by individual miners. These centres for gold as a seasonal or temporary activity due to a lack of

extract a fraction (30% or less) of the gold by rudimentary process employment in rural areas (Hentschel et al., 2002). It is difﬁcult to

usually associated with amalgamation and they retain the tailings convince miners to adopt a ‘‘cleaner’’ procedure since their

with its residual gold as payment from the miners to the processing panning activities are compatible with their low income and

plant owner. This gold is then leached by the processing plant knowledge. As Hilson (2007) explains, there is a poor understand-

using cyanide. Worldwide, these centres are proliferating at ing of artisanal mining dynamics and so, international organiza-

artisanal mining and processing sites since they provide operators tions try to implement inappropriate support schemes and

with a means to quickly process their ores for free or for a nominal interventions. Usually they are not sustainable.

fee (Veiga et al., 2014). International development agencies rarely dedicate the time to

A major environmental problem linked to processing centres ﬁnd out about the needs of the miners (Siegel and Veiga, 2010).

results from the cyanidation of mercury-contaminated tailings This criticism was also put forward by Hilson (2005), who

(Guimara˜es et al., 2011). Soluble mercury cyanide species are suggested that any intervention must ﬁrst assess ‘‘the number

formed and released into the environment. How mercury cyanide of people operating in AGM regions, their origins and ethnic

complexes, such as Hg(CN)2(aq), bioaccumulate in aquatic backgrounds, ages, and educational levels’’. The main problem is

organisms is not well-studied, but one can presume that that when assistance is unwanted, it is not sustainable. Sirolli

methymercury formation is a possible step. At many sites where (1999) shouts with passion when he says: ‘‘if people do not wish to

mercury-contaminated tailings are leached with cyanide, nearby be helped, leave them alone. This should be the ﬁrst principle of aid.’’.

ﬁsh contain high levels of mercury (McDaniels et al., 2010). Interventions to deal with the owners of the Processing Centres

Worldwide, virtually all tailings left at processing centres are producing 0.5–3 kg of gold per day are badly needed, but are

leached with cyanide. In some cases, the process is conducted in unfortunately rare. These individuals are the main polluters. They

percolation vats, as been witnessed in Brazil, China, Colombia, have power and are in a ‘‘privileged position’’ that takes advantage

Ecuador, Mozambique, Nicaragua, Peru, Venezuela, Tanzania and of the ignorance and low capital of miners. This is at the very core of

Zimbabwe (Veiga et al., 2014). the problem. Mercury emissions cannot be reduced if these

Attention is needed to organize these centres so that they do not individuals do not change their poor practices of amalgamation

have a large impact on exposed populations. Contamination can be followed by cyanidation. A better division of labour and more

observed far from the mercury source as in the Tumbes River equitable participation of the miners in the process are required

system where mercury released in Ecuador travels to Peru, (Veiga et al., 2014).

hundreds of kilometres away (Adler-Miserendino, 2012) generat- Table 1 identiﬁes the steps needed to implement a technical

ing international tension. intervention programme in an artisanal mining community. First,

it is important to identify the community, how they are organized,

3. Interventions to reduce mercury pollution in AGM what they lack and what can be used as links to solve the identiﬁed

sources of problems. Being known and trusted before, during and

Many interventions have been made by governments, aca- after intervention is fundamental in order to have the proposed

demics, NGOs, and international agencies to reduce mercury solutions adopted and implemented by the miners in a sustainable

pollution. Without a clear deﬁnition of what the source of the fashion. Considering that artisanal miners usually have little

problem is, interventions have tended to focus on small artisanal education, it is important to understand that knowledge transfer

panners, or micro-miners – those producing 0.1–0.5 g of gold per will be slow. The most important reason for an artisanal miner to

day and releasing an equal amount of mercury to the environment. change their way of working is to produce more gold. One must

354 M.M. Veiga et al. / The Extractive Industries and Society 1 (2014) 351–361

Table 1

Suggested steps for successful technical intervention at an artisanal mining site.

Concept Action

Know the miners Identify the miners’ strength and weakness

Identify Problems Identify the main technical needs to improve production

Be known Create links of friendship and trust with miners and their community members

Promote technologies Demonstrate the efﬁciency of the ‘‘new’’ technology to extract gold from the miners’ tailings to create credibility

Educate patiently Start the education process slowly, explaining why the ‘‘new’’ technology works better

Do not complicate Use technical concepts and language familiar to local miners

Let miners decide Demonstrate more than one ‘‘new’’ technology and let the miners decide what is ‘‘best’’ for them

Be ﬂexible Check the receptivity to ‘‘new’’ technologies and be prepared to demonstrate more than one option

Pick the right people Train the trainers (select local leaders)

Gold is more important for them Show the economic advantages of ‘‘new’’ technologies ﬁrst and then show the reduction in environmental and health impacts

explore this aspect when introducing cleaner procedures (i.e., countries (Selin, 2013). The implications of this inter-government

extracting gold from their tailings). Trainers should always be agreement in artisanal mining communities are concerning, since

available to assist miners; ideally, they should also have a similar without training and enforcement, artisanal miners will not

cultural background to that of the miners. change their polluting techniques.

The introduction of technical improvements must coincide The artisanal miners have long resisted changing their

with constant presence of trainers (McDaniels et al., 2010). In fact, practices, based on belief that any modiﬁcation will lead to a

maintaining a presence in the community, promoting dialogue and reduction in their gold production (Hinton et al., 2003). Many

participation as a means of building trust are critical steps for any interventions in AGM have been delivered by those with no

community development work. experience in the ﬁeld. Recently, many ‘‘wannabe’’ experts have

Different approaches to intervening in mining communities are appeared with ‘‘magic’’ solutions aimed at eliminating mercury

taken by different groups, governments, and organizations around from AGM. Some of these solutions are usually poor adaptations of

the world to reduce mercury use, emissions and release. Some the methods used in large-scale mining. Hilson (2006) mentioned

believe legislation is the key while others think that introducing that many interventions ‘‘failed to identify appropriate mitigation

new technologies are the best solution. Government representa- measures, and has done little to advance understanding of why

tives, academics, and NGOs have concentrated their efforts on contamination persists’’. There is no generic solution. An interven-

solutions for mercury pollution based on political actions that can tion must be appropriate for a speciﬁc ore, a speciﬁc site, and in

reduce the availability of mercury to artisanal miners. In 2011, the accordance to the speciﬁc knowledge level of the artisanal miners.

European Union introduced restricted control for countries As a result, these ‘‘wannabes’’ tarnish the reputation of those trying

exporting mercury through a treaty signed with UNEP (United to work seriously and so, artisanal miners lose trust in any solution

Nations Environmental Programme). The US followed-up in 2013 coming from foreigners.

with similar restrictions on mercury commercialization. The Veiga et al. (1995) discussed the inefﬁciency of the armed, the

international price of mercury has increased sharply from US$ legal, the health, and the ecological approaches to the problem and

4.93/kg in 2003 to US$ 55.2/kg in 2011 to US$ 103.7/kg in 2014 concluded that education of miners is the most powerful way to

(Metal-Pages, 2014; USGS, 2009). Mercury at AGM sites sells at up reduce mercury pollution. This in fact was demonstrated by the UN

to twice the international price. This was recently observed in the Global Mercury Project where over 30,000 miners in six pilot

Department of Antioquia in Colombia. In September 2007, mercury countries were educated to adopt more efﬁcient methods to

in the gold ﬁelds of Antioquia was sold at US$ 35/kg and in recover gold and generating less pollution (McDaniels et al., 2010).

December 2009 at US$ 50/kg (Veiga, 2010; Garcia and Molina, Recently, Veiga (2014) reported ﬁndings from a small project

2011). In 2014, the price jumped to US$ 150/kg. In the Brazilian ﬁnanced by the US Department of State that led to the

Amazon, the price of mercury at AGM sites is close to US$ 300/kg. implementation of a demonstration gold processing plant in

The restrictions on mercury access have yielded better results Ecuador to train more than 600 artisanal miners and community

than legislation limiting its use, such as in Brazil and French members from Peru, Ecuador, Colombia and Bolivia. The project led

Guiana. Sousa et al. (2011) analyzed 20 laws, decrees, and to the construction of more than 40 improved plants. The reduction

resolutions in Brazil related to the use of mercury in AGM and of mercury releases and emissions were substantial, reaching 40%

concluded that these pieces of legislation ‘‘are stringent on paper in Portovelo, Ecuador, 50% in Piura, Peru, and up to 60% in Segovia,

and weak in their application and enforcement’’. In 141 artisanal Colombia.

mining sites visited from 2006 to 2008 in the Brazilian Amazon,

only one had an environmental license and mining permit to 4. Micro-credit

operate. French Guiana banned mercury in AGM in 2006 but

despite the law, mercury is still in wide use, as reported in the Technological education is not always sufﬁcient to induce

literature and observed in the ﬁeld (Veiga and Baker, 2004; signiﬁcant change in artisanal miners’ techniques. Capital is

Hammond et al., 2007; Telmer and Veiga, 2008; Howard et al., needed as well. When a relatively costly technology is considered,

2011). Similar to Brazil and Indonesia, the governments of the idea of offering micro-credits to miners is often suggested.

Philippines (Valencia, 2013), Guyana (Dillard, 2012; Guyana Micro-credits do not make any difference in the modernization of

Chronicles, 2013) and Colombia (Guiza-Sua´rez and Aristizabal, artisanal miners. They need a capital inﬂux of about US$ 10,000 per

2013) established or are establishing laws to prohibit or limit tonne of ore being processed per day to establish a cleaner and

mercury use in AGM. Without any type of enforcement, these laws proﬁtable processing facility (plus improvements in mining as

are a waste of valuable time and money that could be used to well). This is the main challenge here since banks and governments

educate miners about cleaner procedures. are not prepared to create lines of credits for these individuals.

An agreement involving governments from 92 countries was Artisanal miners usually do not measure geological gold reserves.

signed in October 2013. The Minamata Convention on Mercury They establish their production plan based on the day-by-day

intends to limit mercury trading, in particular in developing results. This is unacceptable to a bank. Even if the miners show a

M.M. Veiga et al. / The Extractive Industries and Society 1 (2014) 351–361 355

Table 2

minimum reserve that could guarantee the loan, banks are still

Fundamental differences between artisanal and conventional mining operations.

suspicious. This issue was thoroughly studied under the UNIDO

Global Mercury Project in 2006–2008 (McDaniels et al., 2010). It is Type of Mining Size Legal situation Mechanization

clear that without formalization, miners will not be able to access

Artisanal (rudimentary) Micro Illegal Manual

the most basic forms of micro-credit, but formalization is a process, Small Informal Semi-mechanized

not a product. Even the most elaborate policies to formalize mining Medium Legal Mechanized

Large

activities will fail if a government lacks the will to implement a

plan; if miners perceive licensing as a threat; or if miners cannot Conventional Small Legal Mechanized

afford the cost to join the legal economy (Siegel and Veiga, 2009). Medium

Large

Hilson (2011) conﬁrmed that the examples of microcredit

projects in African AGM sites were not successful. This is because,

for many reasons, artisanal miners are not fully legalized and

secondly, banks are very selective about which clients deserve the mineral title giving transferable capital to the miners (Siegel and

loan and demand collateral. Knowledge about the geological Veiga, 2009). In a practical sense, formalization is an intricate

reserves, businesses plans, and other requests that would be more process for artisanal miners. Not all miners can fulﬁl the legal

appropriate to organized large gold companies, is expected of requirements for formalization. It is important to note that, in most

artisanal miners. countries, formalization by the Ministry of Mines does not imply

Worldwide, not a single artisanal mine site is known that has that a legal condition is satisﬁed since environmental permits must

evolved into a responsible small-mining operation thanks to bank also be obtained from the Ministry of Environment (Sousa et al.,

ﬁnancing. Usually, the investors are private local capitalists. This 2011).

has been observed in Portovelo, Ecuador where about 40 good The numbers of formalized miners are usually too small to

small-scale plants processing 60–300 tonnes of ore/day are make a signiﬁcant difference in the disorganization and pollution

currently in operation because of private investors. observed at artisanal mining sites. For example, after three years of

promotion and planning, the formalization of 450,000 Peruvian

artisanal miners proved to be a ﬁasco due to the bureaucratic

5. Formalization of artisanal miners

procedures in the formalization process. Peruvian authorities

recognized that out of the 50,000 miners who applied to obtain a

There is a dominant perception from the governments of

formal mineral title, only 27,000 would be formalized in the short

countries impacted by AGM that mercury pollution can be

to medium term (Expreso Peru, 2012). A similar failure to formalize

controlled through formalization of the artisanal miners. The

artisanal miners is described by Guiza-Sua´rez and Aristizabal

formalization approach has been tried by the majority of federal

(2013) in Colombia, where 87% of all mining operations are illegal.

governments of developing countries that face problems with

Between 1993 and 2008, after government efforts to formalize the

informal or illegal artisanal mining. Chen (2007) suggests that

mines, of 3631 applications, only 23 mines were legalized – less

informal employment comprises 50–75% of non-agricultural

than 1%.

employment in developing countries. When the agricultural sector

Despite all legal restrictions, artisanal mining will occur,

is considered to be an informal activity, the proportion of informal

particularly in areas where law enforcement is nonexistent.

employment can be 93% of the total employment, as in India, for

Enforcement is not a simple matter since the majority of the

example. Why, then, are governments so interested in formalizing

artisanal operations are located in remote areas (Hilson, 2002).

informal miners and not other sectors of the economy? The answer

The formalization process is linked to another major hurdle:

is simple: the opportunity to tax. However, an artisanal miner,

awkward legislation related to artisanal mining. Artisanal mining

micro, small, medium, or large in size, will not pay a dollar to be

refers to a rudimentary type of mining and processing used to

formalized or to adopt a new cleaner procedure if they do not see

process gold and other minerals, whereas small mining refers only

two dollars as a result (Hinton et al., 2003). Unfortunately,

to the size of the operation (Veiga, 1997). A small mine may

governments usually do not have the technical capacity to deal

operate in a conventional or artisanal fashion. Alternatively, an

with unregulated artisanal miners. The absence of government

artisanal mining operation can process over 10,000 tonnes of ore

authorities in remote artisanal mining areas is a major part of the

per day, which should not be considered ‘‘small’’ (Table 2). The

problem (Hilson and Vieira, 2007). Without training and education,

main attribute of conventional and artisanal activities lies in the

miners do not know how to obtain legal mineral titles (McDaniels

technologies applied (Table 3).

et al., 2010) or how to improve their gold extraction methods.

Few countries have clear regulations or deﬁnitions of artisanal

Good examples of successful formalization are rare. While the

mining, but almost all relate the term to the size of the operation. In

approach has relative merit in dealing with small, medium and

Peru, Law 27651 of 1992 (Peru, 1992) provides deﬁnitions based on

large artisanal mining operations, it cannot work with micro-

production capacity. Here, a large mine is one that exploits and

miners–those millions of miners who pan the river banks to

processes more than 5000 tonnes of ore per day (tpd) while a

produce 0.1–0.5 g of gold per day. This activity is usually driven by

medium mine processes from 150 to 5000 tpd. The Ecuadorian

poverty and subsistence. Organized companies can be required to

Mining Law of Jan 29, 2009, deﬁnes three types of mining:

implement cleaner production methods and follow the laws.

Artisanal, Small, and Large-scale (Vergara, 2009). According to Ch.

However, it is rare to see governments enforcing the laws and

providing technical advice on how to apply cleaner techniques

Table 3

(MMSD, 2002; Song and Mu, 2012). Attributes of artisanal and conventional mining operations.

In theory, the formalization of artisanal miners is a step towards

Conventional Artisanal

cleaner production since this creates a sense of ownership of the

Geology, drilling Feeling, testing

1 Reserves Subsistence

Illegal mining is identiﬁed herein when the activity is conducted without a

Engineering Curiosity, feeling

proper title, authorization, or concession issued by the competent authorities, while

Control Results

informal mining is a set of deﬁciencies in environmental management, technical

Feasibility study Pay the bills

assistance and development, access to information and acceptable working

Sophisticated equipment Homemade devices

conditions (Hentschel et al., 2002).

356 M.M. Veiga et al. / The Extractive Industries and Society 1 (2014) 351–361

2, Art. 138 of this law, a small-scale mine has a capacity to exploit

and process up to 300 tonnes of ore per day. Everything above this Recovery

capacity is considered large-scale and subject to high taxes.

Artisanal miners are individuals, families, or cooperatives that

mine for subsistence (Delgado, 2009).

The lack of distinction between small-scale conventional

mining and artisanal mining is usually the source of formalization

problems. In addition, formalization cannot be implemented and Concentrate Grade

enforced at sites where artisanal miners are not organized.

Education is the ﬁrst step towards formalization; otherwise,

Mass of concentrate

governments can only formalize pollution since artisanal miners

will not change their way of operating.

Fig. 3. Hypothetical relationship between mass of concentrate, gold grade and gold

recovery.

6. Gold concentration to reduce mercury pollution

The main means for reducing mercury emissions is to introduce behaviour of gold recovery and concentrate grade. A large mass of

gold concentration methods. Concentration by gravity or ﬂotation concentrate implies that the gold grade is low but the recovery is

can also offer the beneﬁt of recovering additional values such as high and vice versa. The choice of an operating point on this curve

copper minerals. This is exactly what the artisanal miners in (where a concentrate from a sluice box or centrifuge is to be

Portovelo, Ecuador are doing. Capital and technology are helping discharged) is an economic decision.

artisanal miners to become more organized small-miners who Introducing concentration principles to artisanal miners is not

now produce more gold. More than 40 plants in Portovelo and 39 easy since many miners believe that concentration is a waste of time

plants in Antioquia, Colombia (Veiga, 2014) are concentrating gold and gold will be lost. In fact, this is true when gold is extremely ﬁne

and copper minerals by gravity separation and ﬂotation and but in the majority of cases, problems occur because of poor

eventually leaching only the pyrite (gold-bearing sulphide) grinding, classiﬁcation, and concentration operations. This is the

concentrate with cyanide, thus reducing the amount of material rationale behind amalgamation of the whole ore; it is cheap and the

to be leached. Old tailings are also being reprocessed. This miners immediately see gold in their hands. It is important to show

approach, together with the presence of local capitalists, have that in a well-developed concentration process, reducing the mass of

substantially reduced mercury pollution, since copper concentrate the material (e.g., to less than 10% of its original mass, will lower by a

with gold, are sold directly to smelters. large extent the cost of leaching and/or amalgamation of the

Even the best concentrator in the world will not work if the concentrate). At the end of the process – a well-conducted one –

operators do not have proper knowledge of how the gold is there will be more money generated when concentrating the ore. As

associated with other minerals in the ore as well as how ﬁne the a positive side-effect, less mercury or cyanide will be used. Although

gold is. A typical size distribution of gold in tailings from a quartz this is routine for mining engineers working in large companies, it is

vein artisanal mining operation is shown in Fig. 2. Fine gold a challenge to introduce these concepts to AGM workers, because of

particles are associated with the coarse fractions, usually the lack of education in the sector.

unliberated from the silicate gangue, while in the ﬁne fractions, There is also a perception that gold concentration equipment is

ﬁne gold is not trapped (or recovered) by the rudimentary expensive. Even a home-made wood zigzag sluice box can be very

concentration methods. The problem with concentration of fine efficient with insignificant cost (Veiga et al., 2006). A small

particles can be resolved by using centrifuges, ﬂotation, or even centrifuge, the most efﬁcient gold gravity concentrator, is also

cyanidation. The liberation problem must be solved with changes affordable and can pay back the investment very quickly. Flotation

in the grinding and classiﬁcation (screens or cyclones), which are has been widely used in AGM operations in Brazil, Ecuador,

the most expensive steps in gold processing. Colombia and Chile and there are many options in the market of

Most gravity concentration methods used in artisanal mining inexpensive ﬂotation cells.

are not continuous (i.e., they must be stopped to discharge the Concentration requires previous liberation of the gold particles.

concentrate). Miners working with alluvial ores control their Liberation of the mineral of interest (gold) from the gangue by

activities based on how ‘‘yellow is the concentrate’’. This is a very grinding is not part of the vocabulary of artisanal miners. This idea

common mistake. High gold grade in concentrates do not reﬂect is probably inherited from alluvial operations, where in most cases

high gold recoveries. Usually, the relationship is the opposite. Fig. 3 (but not always), gold is naturally liberated by abrasion in the

shows a hypothetical graph that exempliﬁes the antagonistic water stream. Working with secondary gold deposits (alluvial,

colluvial and eluvial), most miners believe that gold is always free.

However, for secondary deposits, gold particles are either partially

liberated or completely trapped within gangue minerals (Spiegel

and Veiga, 2010). The gold recoveries are very low as it is rare to see

any AGM grinding these types of ores. Ball mill grinding is the most

efﬁcient but also the most expensive step to liberate gold. It

requires high energy and high investment. However, even a

Chilean mill (also known as Muller pan), as observed in many

Andean countries (Velasquez-Lopez et al., 2010) or a hammer mill

can be an inexpensive and relatively efﬁcient solution to liberate

gold before concentration, if well operated.

Unlike other minerals, gold does not need to be completely free

to be concentrated by gravity methods. Gold associated with

quartz particles can increase the weight of a particle that reports to

the concentrate. Unliberated gold can be leached with cyanide if

Fig. 2. Typical Au grade distribution of artisanal mining tailings. the gold particle is exposed but cannot be trapped by mercury and

M.M. Veiga et al. / The Extractive Industries and Society 1 (2014) 351–361 357

so is lost to the amalgamation tailings. However, when the ore is for the centrifuge and 70% for the sluice box (to increase the gold

concentrated, the particles can then be reground (and the gold grade to 3330 ppm). In the best case scenario (84% of gold recovery

liberated) at a relatively low cost. in the smelting process), the global recovery would be about 41%.

When grinding ores, artisanal miners rarely use classiﬁcation Comparing direct smelting to the current amalgamation method,

(screens or cyclones) which can improve grinding efﬁciency. It is the gold recovery might be slightly better with direct smelting, but

common to ﬁnd miners believing that a circulating load in a ball impractical and costly (energy-wise) to be conducted on 175 kg of

mill is a bad practice. They believe that returning between 100 and concentrate per day. In addition, the slag must be recycled back for

400% of the material to the ball mill feed is a waste of equipment. cyanidation.

However, a high circulating load can maximize output rates at a The process seems useful for a narrow range of artisanal miners

narrower range of product size (Mular et al., 2002) and thus, a and types of ores (e.g. those without sulphides). It may be useful for

higher degree of liberation is generated. micro-miners producing very small amounts of gold per day and

working with alluvial ores in water streams. But they must have

7. Treatment of gravity concentrates resources to melt gold and access to the ﬂux.

Once a concentrate is obtained, there are many methods to 7.2. Cyanide

extract gold from it. The mining companies usually extract the

relatively coarse gold by gravity separation. The gravity concen- Almost all industrial gold mining companies no longer use

trate is then, re-concentrated in a shaking table to obtain a very amalgamation to extract gold. Instead, they carry out cyanidation

rich concentrate to be directly smelted with a ﬂux such as borax. of the whole ore (when gold is very ﬁne) or concentration (gravity

All tailings are either ﬂoated and/or leached with cyanide. and/or ﬂotation) followed by cyanidation of the concentrate.

The public thinking about cyanide is the main hurdle to accept

7.1. Borax gold cyanidation as a technique cleaner than amalgamation. The

general perception is that cyanide is much more toxic than

The use of borax (Na2B4O7Á10H2O) as a ﬂux to melt gold mercury, as the acute effects of cyanide are much more dramatic

concentrates is a very old technique to reduce the melting point of than mercury (which is an accumulated chronic threat over time).

the mixture of minerals, bringing the silicate and oxide impurities Most cyanide complexes can be decomposed to less toxic species

to the slag. The use of borax alone has been publicized recently as a (ammonia and carbon dioxide). This cannot happen with mercury

way to replace amalgamation of gravity concentrates (Amankwah species. The neurological chronic effects of mercury and its

et al., 2010). This borax method is only efﬁcient with very low compounds are many times more serious than the chronic effects

sulphide content concentrates and in materials that are not ground of cyanide-derived compounds (Veiga and Baker, 2004).

too ﬁne (Appel and Na-Oy, 2013). The technique emphasizes the Public perception about cyanide has its roots in judicial

use of borax to lower the melting point of the minerals (impurities executions, suicidal acts, or death by ingestion of cyanogenic

in the concentrate) to about 1064 8C, which is the gold melting plants. Bitter cassava can contain up to 400 mg/kg and it is not rare

point and a temperature reachable using charcoal and a blower, or to hear of fatal incidents with inadvertent consumption (Akin-

a butane/propane torch (Appel and Na-Oy, 2011). Their studies tonwa and Tunwashe, 1992; Kwok, 2008).

indicate that for the process to be effective, the concentration In Guyana, two incidents made cyanide an even greater villain.

process must achieve high gold grades (>30,000 ppm Au or 3% Au). The ﬁrst was the mass suicide in 1978 of 909 members of a

As explained in Fig. 3, there is a balance between grade and religious cult conducted using a solution of cyanide in Kool-Aid.

recovery. The higher the concentrate grade, the lower the gold The second incident occurred in 1995 when 1.25 million cubic

recovery. Enrichment to a 3% Au concentrate grade is much too metres of gold mine tailings from the Canadian company Omai

high and will compromise gold recovery to an unacceptable level. Gold Mine spilled into the Essequibo River (Davidson, 1995). As a

A site-speciﬁc investigation was conducted with a sulphide ore consequence, the Guyanese Government banned cyanide use in

from Portovelo, Ecuador (Angeloci-Santos, 2013). A sample of gold mines. However, mercury is freely used by artisanal miners.

centrifuge-sluice box concentrate with 3330 ppm of gold and The Government of Costa Rica recently banned cyanide in gold

1170 ppm silver was used. Using 50 g of concentrate to be melted mining (Friends of the Earth, 2010), however, artisanal miners still

with 50 g of borax the amounts of gold and silver were low: 0.165 g use mercury to extract gold.

and 0.06 g respectively. Several tests of direct smelting with borax Nowadays, all conventional gold mines destroy cyanide by

were conducted with no to little success. This series of tests, oxidation and follow regulations to achieve release levels less than

following the method described by Appel and Na-Oy (2011), was 1 mg/L of total cyanide (MMER, 2002). In contrast, processing

unsuccessful because there was no separation of the gold and slag centres at artisanal mine sites rarely destroy cyanide (Velasquez-

due to the high amount of sulphides in the concentrate sample. In Lopez et al., 2011).

all tests, it was clear that the mass of gold was really too small to One of the limitations to the wider use of cyanide replacing

carry all gold particles to the bottom of the crucible. The only amalgamation of concentrates is the slow rate of coarse gold

successful test involved adding a mixture of KNO3, SiO2 and dissolution which is controlled by the low dissolved oxygen

NaHCO3 to oxidize sulphides and reduce slag viscosity. A recipe of a content in the leach solution (Marsden and House, 2006). Some

mixture of ﬂuxes in the following proportion: 1:1:1:0.25:0.25 companies have developed pieces of equipment for gold extraction

concentrate:borax:KNO3:SiO2:NaHCO3 was used. Formation of a using intensive cyanidation. Veiga et al. (2009) proposed an

well-deﬁned interface between slag and gold bead was noticed intensive cyanidation method for small-miners using a simpliﬁed

while the slag was more vitreous, indicating that a higher amount methodology that does not require expensive equipment. The

of metal was separated. Around 84% of the gold was recovered; the methodology suggests that the concentrate generated by a small-

rest was lost in the slag. In fact, the assay of slag showed a high scale plant could be intensively leached by cyanide, by adding an

1 1

grade of gold (840 ppm) and the gold bead contained 6935 ppm Au oxidizing agent such as H2O2 or Vanish or Oxiclean which has

that still needed further treatment. around 16–21% of H2O2 in 50–66% of sodium percarbonate

It is important to note that gold recovery must also account for (Bracken and Tietz, 2005) in a small ball mill (the same used for

losses in the concentration step as well. In the case of the whole ore amalgamation) with a sturdy, perforated, plastic capsule

Ecuadorian concentrate tested, the gold recovery was around 70% ﬁlled with activated charcoal inside a nylon screen. The

358 M.M. Veiga et al. / The Extractive Industries and Society 1 (2014) 351–361

concentration of H2O2 and NaCN are usually 0.3 g/L and 20 g/L, An electro-chlorination or electro-leaching process has been

respectively. The amount of activated carbon is equal to 60 g per proposed by Barbosa et al. (2002) as a potential candidate to

gram of Au contained in the concentrate feed. substitute cyanide and amalgamation in AGM. The idea is to: a)

Sousa et al. (2010) achieved a gold extraction of 95% in 24 h produce chlorine from sodium chloride solution; b) oxidize

using the method described above in an AGM operation in Brazil to sulphides that trap the gold c) leach the gold in an agitated pulp;

recover gold from old tailings previously concentrated at lower and d) plate it on the cathode. Angeloci-Santos (2013) conducted

recovery with a centrifuge. This process was also successfully about 30 tests of electro-leaching at pH 1.5, using 30 g/L of NaCl

demonstrated to miners in Ecuador and Colombia (Angeloci- and 1 g/L of NaBr to leach an Ecuadorian centrifuge concentrate

Santos, 2013). This process can, therefore, be easily adapted by containing 1118 ppm of gold. Due to the high grade of copper and

processing centres and even artisanal miners. The capital cost iron sulphide minerals in the concentrate, gold extraction, even for

comprises acquisition of an efﬁcient gravity concentrator (e.g. 24 h, was very low (<10%). Greaves et al. (1990) investigated

centrifuge) and a small-ball mill already in use by many processors. chlorine as a substitute for cyanide on several different types of

gold ores. Their recoveries in high-sulphide ores were 10.2% for a

7.3. Alternative lixiviants 35% sulphide content ore and 6.4% for a 20% sulphide content ore.

When pre-oxidized, these values increased to 20.4 and 70%,

Researchers have been calling for the use of thiourea (Eisele respectively. Chlorination seems to be complicated for unskilled

et al., 1988) or thiosulphate (Rath et al., 2003) to leach gold for miners and applicable only in the case of simple gold ores (i.e. low

some time. Despite being less toxic and environmentally safer than sulphides content).

mercury and cyanide, the reagents are not generally available in In all cases of alternative lixiviants, the core of the problem is

remote regions and the leaching process requires strict control of obtaining a gold concentrate to be leached. This is critical, as it

parameters such as pH and Eh which are complicated for unskilled reduces substantially the mass of material in the gold leaching

miners. Many manufacturers also offer different alternatives to process with any type of reagent.

mercury and cyanide as a ‘‘green’’ gold-leaching agent. Commercial

products are available as a ‘‘panacea’’ for mercury pollution. Their 7.4. Retorts

compositions are rarely disclosed so it is difﬁcult to investigate

their real efﬁciencies and impacts. In addition, it seems that the A large majority of artisanal miners separate mercury from gold

strategy of these companies is to keep the miners as their perpetual in amalgam by heating in an open pan. They do not use methods to

clients using their proprietary reagents. condense mercury such as ‘‘retorts’’ because they do not believe

Chlorine leaching has been studied as a replacement for both that mercury vapours are harmful. However, few people in AGM

mercury and cyanide processing. This method was applied sites have clear knowledge about the relative toxicity of metallic

extensively in the 1800s with cyanidation replacing it in the mercury. Veiga et al. (1995) described an episode in 1987 where

1890s because of effectiveness and safety concerns. These early environmentalists were trapped in a theatrical performance when

procedures were conducted in wooden tanks by pumping chlorine an artisanal mining leader ingested metallic mercury in front of TV

gas through the ore inside a covered vat for 12–18 h (Eissler, 1888). cameras to show that the mercury used in gold mining is

The main problem faced by the engineers in the 1800s was the inoffensive. The truth of the matter is that when metallic mercury

difﬁculty in conducting the leach process in agitated steel tanks is ingested, the body can excrete most of it within about 30 days.

because of corrosion. This is completely different from methylmercury ingested with

MINTEK, a South African research centre, has developed a contaminated ﬁsh. Over long time periods, metallic mercury can

method to extract gold from gravity concentrates based on result in a health problem but this derives from breathing mercury

chlorine leaching. The iGoli gold extraction system is intended vapour.

for artisanal use as a substitute for amalgamation. A small (30 L) The assessment study by Jønsson et al. (2009) investigated use

agitated leach tank is used to which a 1:1 mixture of HCl @ 33% and of a water-pipe steel retort (Veiga et al., 1995) with miners for ﬁve

bleach (sodium hypochlorite @ 16%) is added. After the gold is months and solved the problems they faced when using the

recovered, calcium chloride, sodium hydroxide, and apatite are equipment. The authors stressed that miners usually stop using

added to the efﬂuent to precipitate the other metals in solution to retorts when they face any kind of problem.

an inert form. Recoveries as high as 98% were achieve by Mahlatsi Veiga et al. (2006) have given several reasons why miners do

and Guest (2003). On the other hand, the process is chemically not adopt retorts sustainably (Table 4). The main argument

complicated and technical knowledge is crucial to solve extraction encountered is the lack of being able to inspect the burning

problems that might appear using different ore concentrates. There process. Hilson and Pardie (2006) described the UNIDO project in

is also no recovery of silver in this system, since chlorination of this Ghana which introduced a glass retort to make the mercury

metal generates an insoluble compound (AgCl). Storage of sodium distillation process more visible. With a cost of US$ 520, low

hypochlorite also brings additional problems as this solution is not capacity, highly breakable, and unavailable spare parts,

stable in hot climates. this initiative was unsuccessful. This was eventually solved by

Table 4

Arguments and reasons given by artisanal miners to not use a retort.

Arguments Reasons

Mercury is inoffensive Miners do not see immediate health issues when exposed to Hg vapours

Retorts are expensive Miners do not know inexpensive options

It takes time (sometimes miners are Retorting temperature is too low

vulnerable to bandits)

Inexperience in operating a retort Lack of assistance in operation

Gold is lost during retorting With iron retorts, the amalgam is not visible so miners believe it has been lost

Gold sticks to the retort crucible Occurs when the temperature is too high or when crucible is not lined with a thin layer of clay, talc or soot

Recovered mercury loses coalescence Sometimes condensed Hg disperses into ﬁne droplets

Gold comes out brown from steel retorts Cause is unknown; it is probably due to a superﬁcial reaction with iron

M.M. Veiga et al. / The Extractive Industries and Society 1 (2014) 351–361 359

Fig. 4. Kitchen-bowls retort in Colombia.

convinced that policy and legislative variations are deterring

environmental management efforts in the region’’. Complex legisla-

tion creates a jungle of bureaucracy that is pushing the miners even

farther away from formalization. In addition, formalization

without enforcement is just formalizing more pollution.

Many perceptions are also created internationally by different

sectors interested in selling equipment, consulting or ‘‘magic

solutions’’ to artisanal miners. There are many methods available

to reduce and eliminate mercury in artisanal gold mining, but the

most important one is to amalgamate a gold concentrate, not the

whole ore. Extraction of gold from a small mass of concentrate with

intensive cyanidation is the most realistic process that does not

require high investment and extensive knowledge since artisanal

miners are already familiar with using cyanide (Veiga et al., 2009).

Fig. 5. AGM in Zimbabwe using improvised bellows to increase the temperature of

Any method to replace mercury should ﬁrst address the needs and

the ﬁre during amalgam retorting.

beliefs of the miners. It is important to bring technological options

Photo: S. Metcalf.

to miners. They must be comfortable in selecting what is right for

them. Financial assistance and education can help avoid the need

Veiga et al. (2006) using cheap and easily accessible salad bowl for ‘‘quick money’’ from amalgamation. The mercury-cyanide

retorts (Fig. 4). A large bowl of stainless or enamelled steel, found contamination generated by the processing centres is a far more

in any kitchen store, is perforated to accommodate a small bowl to complex problem with signiﬁcant social roots. A deeper investiga-

hold the amalgam. The set is covered with a glass bowl and tion and intervention in processing centres is needed to organize

sealed with wet sand. This allows the miners to follow the the business to operate in a less-environmentally harmful and

amalgam burning process and witness when the process is more equitable way.

complete. This unit has been successfully introduced into over

20 countries. The main drawback is that the glass cover cools Acknowledgements

slowly and miners do not want to wait to have the gold dore´ in

their hands. In this case after some initial experiments with the The authors would like to acknowledge the ﬁnancial support of

glass cover, an enamelled steel cover can be used which can be the NSERC Discovery Grant #217089 and the US Department of

quickly cooled with water. State. The assistances in the ﬁeld of the eng. Wilmer Niquen in

Another perception that creates resistance to retorts is that it Ecuador and eng Oseas Garcia in Colombia are acknowledged. We

takes too much time to eliminate mercury from the amalgam. also express our gratitude to Professor Gavin Hilson and two

Retort crucibles can be made with thinner steel walls that take less anonymous reviewers for comments on an early version of this

time to heat up. As many miners burn amalgams in bonﬁres, a manuscript.

manual air-blower bellows can also be built using a piece of pipe

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