Challenges Associated with Using Retorts To Limit ... - ACS Publications

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Chapter 3

Challenges Associated with Using Retorts To Limit Mercury Exposure in Artisanal and Small-Scale Gold Mining: Case Studies from Mozambique, Ecuador, and Guyana Adam M. Kiefer,*,1 Kevin Drace,2 Caryn S. Seney,1 and Marcello M. Veiga3 1Department

of Chemistry, Mercer University, 1400 Coleman Avenue, Macon, Georgia 31207 2Department of Biology, Mercer University, 1400 Coleman Avenue, Macon, Georgia 31207 3Norman B. Keevil Institute of Mining Engineering, University of British Columbia, Vancouver, Canada *E-mail: [email protected].

Artisanal and small-scale gold mining (ASGM) is recognized as the number one source of anthropogenic mercury pollution in the world. Miners use mercury to amalgamate gold, then heat the amalgam to evaporate the mercury. This process, referred to by miners as burning, releases large quantities of mercury vapor that affects the health of miners and community members. A retort is a mercury capture device that provides a simple solution to reduce human exposure to mercury vapor during the burning process. In spite of the low cost, ease of use and numerous outreach programs that have introduced miners to this technology, miners have been reluctant to use retorts. This chapter provides a review of ASGM processes involving mercury, discusses the health effects of mercury vapor, and provides case studies on retort use in Mozambique, Ecuador and Guyana. The chapter concludes with a discussion on reasons why retorts have not been widely adopted in these countries, and it provides potential solutions to address miners concerns with the use of retorts.

© 2015 American Chemical Society Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Introduction Artisanal and small-scale mining (ASM) is a significant source of employment for men and women in developing nations around the world, with the majority of these miners processing ore to isolate and sell gold (1). The number of people employed in artisanal and small-scale gold mining (ASGM) tracks with the global price of gold, which increased over 400% from 2002-2012 (2). Unfortunately, the transient nature of miners involved in ASGM coupled with the fact that many miners are involved in illegal mining operations makes it difficult to estimate the total number of gold miners throughout the world. From 2002-2011, estimates have ranged from 13-30 million artisanal and small-scale miners globally (3–7), and in 2014 a study by Seccatore et al. estimated that ~16 million artisanal and small-scale gold miners are responsible for 17-20% of global gold production (2). ASM activities, which include ASGM, impact entire regions and communities, not just the miners themselves. In 2011, Hruschka and Echavarria estimated that there were 25 million artisanal miners, and 150-170 million people were indirectly involved in ASM-related activities (6). In 2013, Jønsson and coworkers estimated that there were 9 million people engaged in ASM in Africa, with 54 million people financially dependent on ASM (8). If correct, this estimate implies that ~5% of Africans are dependent on ASM activities for their livelihoods (9). Although gold mining is a viable option for people in developing nations seeking to escape poverty and unemployment, the dramatic increase in ASGM activities has led to numerous challenges to both human and environmental health (7, 10–21). Mining is an inherently dangerous profession for those without appropriate training. The lack of formal engineering training in this sector results in frequent mine collapses (22). In addition, the processing of ore often releases arsenic, cadmium, chromium, mercury and lead into the environment. For example, from 2010-2013, hundreds of Nigerian children died of lead poisoning directly linked to ASGM activities, in spite of the fact that lead was not being actively mined (23, 24). Lead sulfide was present in high concentrations in the ore and released during mining operations, heavily contaminating soil and drinking water in the local community. Perhaps the most notable of the human and environmental health effects are derived from the fact that the vast majority of ASGM workers use elemental mercury to amalgamate gold and silver (25). It is estimated that over 1,600 tonnes of metallic mercury are consumed in ASGM each year (26). The resulting chemical waste is emitted directly into the atmosphere and released into watersheds. ASGM represents 37% of anthropogenic atmospheric mercury emissions globally and is now recognized as the number one source of anthropogenic mercury emissions to the environment (2, 27). Mercury is a bioaccumulative toxin, and in its elemental form mercury is easily distributed throughout the environment. Over time it is oxidized to water-soluble inorganic mercury salts that are then modified by anaerobic bacteria and methylated. These highly toxic organomercury complexes accumulate in fish and are incorporated into higher order predators, including humans (28). For miners, the most immediate danger from elemental mercury during the mining process occurs when mercury is evaporated from the amalgam by heating (11). Miners directly inhale the mercury vapor. Exposure to these mercury vapors 52 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


results in a variety of health effects including tremors, short-term memory loss, kidney damage, and in high concentrations can lead to death (14, 25). A number of outreach programs have provided ASGM workers with retorts, which are a suitable, inexpensive technology that traps up to 95% of mercury during the burning process (8, 29–31). In spite of the low cost and health benefits attributed to retorts, this technology has not been widely adopted by miners (1, 31–36). This chapter will provide the reader with an overview of mercury usage in ASGM activities, a brief overview of programs related to the implementation of retorts in ASGM communities, and three case studies highlighting retort use and misuse in Ecuador, Guyana and Mozambique.

An Overview of ASGM Processing in Developing Nations This section will provide the reader with an understanding of the mining and processing of gold ore in Portovelo and Nambija, Ecuador; Mahdia, Guyana and the Manica Province, Mozambique. Gold mining in Ecuador and Mozambique rely on mechanical comminution (grinding) of hard rock. Mining in Guyana is largely relegated to the mining of colluvium, or geological material that has deposited at the base of a hill due to weathering over millions of years.

Hard Rock Mining: Mozambique In the mining communities of Munhena and Tsetsera in the Manica Province of Mozambique, the majority of gold is mined from hard rock. Miners extract ore along quartz veins in the hills and mountainsides and then process the ore where they, and often their families, reside. While artisanal miners in Mozambique often extract the ore working within small groups, individual miners process their own ore. These miners will initially crush the ore into pieces of approximately 1-2” in diameter using a mortar and pestle. The crushed ore is then transferred into a ball mill, which is a cylinder equipped with stainless steel ball bearings (Figure 1). Often mercury is added to the ball mill at this stage. The mill is turned by hand for approximately one hour, and the ball bearings crush the ore while the mercury amalgamates the liberated gold in a process known as whole-ore amalgamation. Upon completion, the finely-ground contents are transferred to a large plastic basin for panning. The mercury-contaminated gangue is separated and placed on the ground or in small tailings pits, where over time it enters local waterways. Additional mercury is added to the heavier black sands, and after agitation, the mercury is strained through a fine mesh cloth producing a gold amalgam. While the excess mercury is collected and reused, a substantial portion has already been lost to the tailings. The amalgam is often heated or “burned” on a smoldering log. The temperature of the smoldering log is insufficient to rapidly vaporize the mercury; thus, miners resort to blowing on the log until the mercury has evaporated producing sponge gold, or doré (Figure 2). The miners directly inhale evolved mercury into their lungs. Because of the inefficiency of the burning process, the 53 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


sponge gold still contains mercury. The sponge gold can be sold on-site to people that provide the miners with mercury, who then purify the gold in populated areas. The mercury trapped in the sponge gold is released to the environment during this process.

Figure 1. A miner operates a ball mill in Munhena, Mozambique. A ball mill is a cylinder containing stainless steel ball bearings used to crush ore and liberate gold. (see color insert)

Figure 2. A) The amalgam is heated on a smoldering log. B) A miner blows on the log to increase the temperature to heat the amalgam more quickly. During this process he breathes in mercury vapor. (see color insert) 54 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


A few medium-scale mining operations in the region operate in much the same way; however, these operations often have automated jaw crushers and ball mills. Ball mills powered by motors allow for the continuous processing of ore as opposed to the batch processing found in the hand-powered ball mills that artisanal miners use. These ball mills increase throughput and yield, as the automated mills allow for better control of particle size and maximization of gold liberation. Under these conditions the gold is concentrated by panning or centrifugation prior to amalgamation, preventing both whole-ore amalgamation and the contamination of the tailings by mercury. We have previously reported on mercury-free technology being used in the region, but the practice of separating the black sands (magnetite and ball mill iron filings) from gold using magnets is not applicable in most regions of the Manica Province (37).

Hard Rock Mining: Ecuador Similar to Mozambique, in the mining communities of El Oro Province, Ecuador, the majority of gold is associated with sulfides in hard rock. However, the processing of ore rarely occurs at the mine, but rather in the city of Portovelo where more efficient and expensive equipment can be rented to process the ore (7, 38, 39). These processing centers offer miners access to techniques and equipment that they could not afford themselves. Most processing centers offer miners these services for a small fee on the condition that the processing center keeps all of the tailings. Miners extract the ore at their mine, and once a predetermined amount of ore has been collected, the ore is transferred via vehicle to a processing center in Portovelo. Miners select one of the 87 processing centers based on previous experience and the amount of ore that needs to be processed. Artisanal miners with a small amount of rich ore prefer to utilize one or more chanchas to carry out either whole-ore or concentrate amalgamation. Chanchas are small ball mills powered by an electric motor that operate on batch-scale as opposed to continuous flow (Figure 3A). Processing plant owners will often rent chanchas to miners by the hour or batch, with the understanding that the processing plant keeps the tailings. When a sufficient amount of tailings have been accrued, the processing plant owner then processes the tailings with cyanide and recovers the remaining gold. Because whole-ore amalgamation rarely results in more than 30% recovery of gold in ore (30), the processing plant owners often make a large profit from gold-containing tailings. For miners with large quantities of ore, Chilean mills are utilized for comminution (Figure 3B). These mills consist of three heavy cement wheels rimmed with steel that rotate in a circle on a steel plate. After being passed through a jaw crusher, the ore is shoveled into the mill and crushed. Water continuously passes over the material, which is then screened and passed down a sluice angled at ~5° containing nylon carpet. The heavier gold lodges in the carpet, while the lighter materials flow to a tailings pit. The carpet is rinsed approximately every hour into large buckets for amalgamation, and further concentrated by manual panning. Although Chilean mills are continuous throughput, they are still 55 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


inefficient, and a portion of the gold remains in the tailings. However, because only the concentrate is amalgamated the tailings from a Chilean mill can directly undergo cyanidation without the issue of solubilizing mercury as occurs after whole-ore amalgamation.

Figure 3. A) Miners emptying a chancha in Portovelo, Ecuador. B) A Chilean mill in Portovelo, Ecuador. (see color insert)

Independent of the form of comminution, the amalgamation process occurs similarly to the process in Mozambique. The mercury and gold are strained through a tightly woven cloth, and the excess mercury is collected and reused. However, the resulting amalgam is typically significantly larger than amalgams found in Mozambique due to both improved processing practices and higher gold grade of the ore. The resulting spherical amalgam is then crushed flat, mixed with brown sugar and heated with a propane torch to evaporate the mercury. The role of brown sugar is not understood, although miners claim that it increases the rate of evaporation of mercury. Although this process is often performed outside in the open environment or under a makeshift fumehood without proper condensers or filters, occasionally mercury capture devices such as retorts are employed. The resulting doré is then sold to local gold shops in Portovelo and neighboring communities for further refinement. The owners of processing centers leach the collected tailings with cyanide. It has been suggested that cyanidation following whole-ore amalgamation results in the formation of water-soluble cyanomercury species that are more bioavailable than elemental mercury (16). Most final tailings containing these organomercury species and elemental mercury are ultimately disposed of in local streams and rivers. In Portovelo there are approximately 375 cyanidation tanks with capacities ranging from 14-40 m3 (16). In 2011 it was estimated that over 880,000 tonnes/a of tailings containing about 650 kg of Hg and 6000 tonnes of cyanide are discharged into the rivers (40). 56 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Colluvial Mining: Guyana As rock weathers over a period of millions of years, it travels down hillsides and is deposited as loose, unconsolidated sediment known as colluvium. The natural weathering results in the partial liberation of gold from the surrounding rock, and if the material reaches a stream the material (now alluvium) it is further separated from gangue. In essence, nature grinds the material and separates the gold. The mining community of Mahdia, Guyana, located in the Potaro-Siparuni region has numerous colluvial and alluvial deposits of gold (41, 42). Miners remove the overburden using heavy machinery or by hand, and then use highpressure water flow to loosen the colluvium (Figure 4a). The resulting slurry is then pumped to a carpeted sluice box, where water flow and gravity separate the gold and heavy minerals from the gangue (Figure 4b). The majority of gold is very fine and is not captured on the sluice bed. This practice has led to small-scale miners and “pork knockers” (43), as artisanal miners are referred to in Guyana, reworking the tailings from abandoned claims.

Figure 4. A) Miners created a slurry using high powered water hoses and the slurry is pumped to B) a sluice box. (see color insert)

Miners collect the heavy concentrate from the sluice box in large basins and approximately once a week add mercury to amalgamate the gold. The amalgam is separated from the excess mercury using a fine mesh cloth. The resulting amalgam is burned in open air using a propane torch or is wrapped in wet leaves and heated over a bonfire in close proximity to the miners’ encampment. At some of the medium-scale mines, miners will use a retort to condense and capture the mercury, which is then returned to the original mercury supply. Miners often sell the gold directly to gold shops licensed by the Guyanese government.

Mercury Vapor and Human Health Mercury has been used to amalgamate gold since 1000 BC (44), and mercury usage in ASGM activities remains ubiquitous today. ASGM workers use mercury for numerous reasons (30). First and foremost, mercury works for artisanal and 57 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


small-scale miners. It is both inexpensive and readily available for purchase in mining communities. Moreover, a miner with no formal training can learn to use mercury in ASGM within an hour oftentimes being trained by friends and family members. Although amalgamation is inefficient, and miners more often than not discard the majority of gold with the tailings, many miners can isolate gold from the rest of the ore in a matter of hours using mercury. This transformation translates to food on the table, and a higher quality of life in the short term. Although in some regions, such as in Portovelo, Ecuador, miners have access to mercury-free technologies such as cyanidation and flotation, many miners around the world do not have access to the training needed to operate these systems. In addition, these miners may not have the capital to establish and maintain them. Even when available, many artisanal and small-scale miners cannot collect enough ore to make these processes feasible and economical when they are available. The vast majority of gold miners that use mercury form and burn amalgams, and most do so without taking appropriate safety precautions. It is during the burning process that there is an immediate health risk to the individual miner as well as the mining community as a whole. The effects of chronic mercury exposure associated with gold mining are well documented, and extend not only to miners but their families and members of the surrounding community as well. For example, Bose-O’Reilly and coworkers demonstrated that in the Philippines children “just living” in gold mining areas contaminated by mercury have statistically significant higher levels of mercury in their bodies than the control group (13). Many of the children in this community displayed the symptoms of chronic mercury exposure, particularly ataxia and coordination problems. The authors attribute these symptoms to exposure to mercury vapor as opposed to organomercury species. Table 1 relates mercury concentrations in the air to potential human health effects. It is important to note that during the burning of amalgams, concentrations of mercury can exceed 6,000,000 – 60,000,000 ng/m3 when burned without a retort or at a gold shop (45, 46). Chronic exposure to mercury vapors results in a variety of debilitating impairments over time. Exposure to high concentrations of mercury during the burning process can lead to acute toxicity, to mercurial pneumonitis and to rapid death (51). For example, a manager of a Guyanese gold mine was treated for mercury poisoning after he was exposed to high concentrations of mercury vapor while burning an amalgam (52). Although he was discharged from the hospital after 9 days of chelation therapy with penicillamine, the damage to his lungs caused by acute chemical pneumonitis resulted in his inability to walk one flight of stairs without shortness of breath 11 months after treatment. In 1987, 11 Filipinos became ill and one died after burning a gold amalgam without appropriate ventilation (11). The effects of mercury vapor are not limited to the pulmonary system. The effects of mercury vapor on kidneys of miners are dramatic and cases of kidney failure followed by death are reported in Venezuela (53) and in Colombia, where a high incidence of kidney transplants is observed in towns with high concentrations of Hg-based atmospheric pollution (54). These examples clearly demonstrate that exposure to high concentrations of elemental mercury released during the burning process is a threat to human health in ASGM communities. 58 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Table 1. Potential Symptoms Due to Exposure to Mercury Vapor of Specific Concentrations


[Hg0] (ng/m3)

Symptoms

Reference

200

ATSDRa minimal risk level

(47)

25,000

Gingivitis, stomatitis, vision changes, hearing loss, kidney effect, teratogenic effects, tremors, emotional instability and irritability, peripheral neuropathy, reproductive effects (ACGIHb Threshold Limit Value, time weighted average for 8-h work day)

(48, 49)

50,000

Kidney damage, erethism (irritability, weakness, sensitivity to stimulation, shyness, depression, insomnia, and eventually memory loss and tremors), micromercurialism, respiratory effects, chest pains, coughing, dermatitis, damage to lens of eye (NIOSHc Recommended exposure limit, time weighted average for 8-h work day)

(48)

100,000

Mercurial pneumonitis and all of the above (OSHAd Ceiling limit)

(48, 49)

200,000

24-h emergency exposure guidance level (EEGL)

(50)

10,000,000

Immediately dangerous to life

(50)

Agency for Toxic Substances and Disease Registry (ATSDR); American Conference of Governmental Industrial Hygienists(ACGIH); c National Institute for Occupational Safety and Health(NIOSH); d Occupational Safety and Health Administration (OSHA). a

b

Retorts in ASGM There is a simple solution for limiting human exposure to mercury vapor during the amalgam burning process. A retort is a mercury capture device that allows for the safe heating of an amalgam using a propane torch or campfire. As the amalgam is heated, mercury is vaporized, condensed and captured in a secondary container. Retorts must be constructed of materials that will not amalgamate when exposed to mercury vapor; if a retort is constructed of metal, steel must be used (1). Three examples of retorts are shown in Figure 5. Retort A and B are two styles of retort from Mozambique. Retort A consists of a chamber that holds the amalgam that screws into the condenser. It is very similar to the most common “water-pipe” retort designed by Raphael Hypolito (8, 55) but possesses a small, refillable water jacket is welded onto the condenser to ensure more efficient condensation of the mercury vapor. Liquid mercury is captured at the end of the pipe in a secondary container. This style of retort is made locally from discarded pipefittings and costs ~$35 USD. Miners report that it works best with larger amalgams. Retort B is 59 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


referred to as a “kitchen-bowl retort” and is constructed from materials available in many village markets (56–59). The operation of this retort is simple: the amalgam is placed in a stainless steel cup inside a larger salad bowl. If cast iron or steel are used the retorted gold turns brown, but the gold remains yellow when in contact with stainless steel or when the retort is lined with clay (1). This surface brown color should not reduce the gold grade and is easily removed when the gold is hammered, but many gold buyers fool the miners paying less for brown gold. The cup is surrounded by sand in order to facilitate heat transfer. A second inverted bowl is placed on top, and the seam between the two large bowls is sealed using wet sand. The top bowl is initially made of a glass salad bowl that allows visual inspection of the burning process by the miners. The glass bowl can later be replaced by a stainless steel or enameled bowl that cools down faster than the glass when the retorting process ends. The lower bowl is then heated using either a campfire or a propane torch. As the mercury vaporizes, it is condensed on the cooler top bowl and is captured by the sand on the bottom of the bowl. Retort C is one of many designs available in and around Portovelo, Ecuador (60). It is similar in operation to retort A, except it has a built in burner that is directly attached to a propane tank. In addition, the water jacket around the condenser is much larger and allows for a continuous flow of water to ensure more efficient cooling of the mercury vapor.

Figure 5. A) A water-pipe retort in Munhena, Mozambique. B) A miner demonstrates the operation of a kitchen-bowl retort in Munhena, Mozambique. C) A retort in Portovelo, Ecuador with a built-in propane torch. (see color insert)

Retorts such as these have been introduced in many mining communities, and have been demonstrated to capture up to 95% of mercury vapor (8, 30). The kitchen bowl retort can be made for less than $5 USD (57), and yet many miners seem adverse to using them regardless of their low cost, the training they receive and the safety benefits inherent in using retorts. The explanation for this surprising behavior is complex and interwoven through the culture of ASGM. In the next section three independent case studies from Ecuador, Guyana and Mozambique that highlight some of the barriers and prohibitive perceptions to implementing retorts in ASGM communities will be examined. 60 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Case Study #1: Mozambique In 2005, a team from the University of British Columbia (UBC) developed and implemented an educational pilot-program for miners in the Munhena region of the Manica province in Mozambique (57–59). This program was specifically designed to instruct miners how to use retorts when burning amalgams. Prior to intervention, amalgams were burned in open air in bonfires. This program was organized and delivered by experts and was supported by the local mining association. At the time of the educational session, the mining association represented 3,764 miners in the Munhena region, and it was estimated that over 12,000 people in the surrounding area were dependent on ASGM activities. Mining in Munhena was exclusively artisanal in 2005. Ore was extracted at the top of the hill in open pit mines angled into the hillside. The ore was processed in the lowest part of the valley where there were year-round streams that aided in processing. Miners exclusively amalgamated the concentrate after comminution and panning. Between the mines and the processing area was a village where some miners and their families lived. The village was comprised of ~25% women, some of whom processed ore but never collected ore from the mine. Children under 15 years of age were also seen processing ore, although they too were excluded from collecting ore in the mines. Because the mines were open, unreinforced pits dug into the hillside, death from collapses and landslides were common. Due to the dangers associated with the mine, miners started reprocessing tailings and waste rock to glean remaining gold from processing as opposed to mining new ore. Amalgams formed during processing were burned both in the village and at the processing site. Air concentrations of mercury were so high during the initial visit (>50,000 ng/m3) that the Lumex spectrometer used to measure mercury became contaminated and required repair work and recalibration. For these reasons, the UBC team developed an educational experience that included three workshops highlighting chemical hygiene and the appropriate use of retorts. These workshops were attended by a select group of miners, who were then tasked with training the community as a whole. This model, referred to as “training-the-trainer”, engages members of the community in active participation in their own education and provides miners with a sense of purpose and inclusion. The first workshop in 2005 introduced miners to the hazards of working with mercury. Miners were taught about the dangers of inhaling mercury vapor during the burning process, and an informal evaluation of exhaled air using the Lumex spectrometer demonstrated to miners that they were inhaling tremendous amounts of mercury during processing. Of 25 miners sampled, the average miner’s exhaled breath had a concentration of 8,200 ng/m3 (57, 59). Three miners that identified they recently burned amalgams had breath concentrations of 50,000 ng/m3, 60,000 ng/m3 and 27,000 ng/m3. The miner with a breath concentration of 27,000 ng/m3 was identified by the team as a child of less than 15 years of age. It is important to note that although the best way to analyze human exposure to elemental mercury is through urinalysis (12, 13, 61), breath analysis has been demonstrated to provide a reasonable approximation of mercury exposure (62). Given the remoteness of the mining village, breath analysis was used exclusively for demonstration purposes to show miners in real-time their exposure to mercury vapor. 61 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


The second workshop introduced miners to both the kitchen-bowl retort and water-pipe retort. This group of miners was taught the underlying principles of how retorts work, how to safely use retorts and the advantages of using retorts properly. The retorts were demonstrated, and the surrounding air analyzed for mercury content. The kitchen-bowl retort was particularly well accepted, because miners could watch the amalgam as mercury was driven off and the gold revealed. During eight trials of the kitchen bowl retort, it was demonstrated that air concentrations two meters away from the retort (the approximate distance from a miner’s face to the retort) never exceeded 1,000 ng/m3. The third workshop introduced miners to mercury-free magnetic sluice boxes and other mercury-free technologies. In addition, miners were taught how to build retorts from locally sourced materials. Upon completing these three workshops in 2005, the miners then relayed their knowledge to other miners in the community under the observation of the UBC team. In spite of the success of the program, the UBC team unequivocally noted that future fieldwork was needed to assess the miners’ health and that continued monitoring of the miners’ usage of retorts was necessary to ensure that safe and appropriate techniques were being used. The team also suggested isolating one area away from the village to burn amalgams (59). Due to lack of funding, follow-up on the implementation of retorts did not occur until 2010-2011 when a team from Mercer University evaluated the mine at Munhena. Since the initial report of mining activities at the Munhena mine in 2005, many changes occurred within the mining community that led to dramatic reductions of mercury in the ambient air. This reduction in mercury occurred for two reasons: 1) the splitting of the mine into two distinct entities and 2) the utilization of locally made retorts. Shortly after discovery of gold at Munhena, an association of miners was formed to monitor gold production on site. When the pilot-project occurred in 2005, little had changed at Munhena, with the majority of gold being collected by ~3,700 independent and largely unregulated miners. During the pilot-project, it was noted that miners were forced to reprocess tailings and waste rock because the mine itself was unstable. In many ways, the mine itself was inoperable because new ore could not be safely collected. Shortly after the pilot-project in Munhena, the local mining association sought external investment in the mine (63, 64). The formalization of mining at Munhena resulted in two distinct mining zones, referred to as “Upper Munhena” and “Lower Munhena.” Upper Munhena was converted into a highly organized mining operation with 108 salaried employees. Each was assigned a specified job at the mine. The majority of employees were responsible for extracting ore. In order to improve both the efficiency and safety of the mining process, it was necessary to tunnel into the hill. The miners were provided with appropriate safety equipment, and the shafts were ventilated. The mine also purchased a jaw crusher and a continuousflow ball mill (Figure 6A). The gold was separated on a sluice box, the concentrate was amalgamated, and the tailings were collected in tailings ponds. In 2011, a cyanidation plant was being constructed on site, but progress was slowed due to the difficulty of purchasing the equipment and having it delivered to the site. 62 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Figure 6. A) Miners crush ore at Upper Munhena in a jaw crusher. A ball mill is located to the right of the miners. B) A miner in Lower Munhena reprocesses tailings. (see color insert)

The Upper Munhena mine employed retorts to capture mercury vapor during the burning process. Amalgams were burned at one location, once a week, as had been suggested in 2005. Only two employees were allowed to burn the amalgams. Both employees were able to demonstrate the appropriate use of the water-pipe retort, which was of the same design introduced in 2005. A cursory inspection of the retort revealed that it was often used. When the lower chamber was removed, the concentration of mercury 1 m away exceeded 20,000 ng/m3. Although the two employees were able to explain the operation of the kitchen bowl retort, it was unused at Upper Munhena because the amalgams were large and more easily burned using the pipe retort. In 2010 and 2011 at Upper Munhena, the concentration of mercury detected never exceeded 200 ng/m3 except for the burning area, which never exceeded 5,000 ng/m3. Shandro and coworkers noted that ambient concentrations in Munhena in 2005 were recorded as high as 30,000 ng/m3 (58). Lower Munhena remains largely unchanged from 2005. The organization of Upper Munhena led to a dramatic decrease in both mercury emissions and exposure of miners to mercury but it also led to a dramatic decrease in the number of miners in Lower Munhena. At a peak of ~3,700 miners at Munhena in 2005, there are now fewer than 100 miners in Lower Munhena. Lower Munhena operates independently of Upper Munhena, and miners still process tailings and waste rock using communal hand-operated ball mills (Figure 6B). Of the miners at Lower Munhena and Upper Munhena in 2010 and 2011, none had been present at the original pilot-project. A representative of the local mining association stated that many miners left Lower Munhena and had moved on to other mining sites in the region. 63 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


From 2005-2010, gold processing at Lower Munhena changed greatly. In 2005 there was virtually no whole-ore amalgamation at Munhena, but in 2011 every single hand-operated ball mill registered mercury concentrations greater than 20,000 ng/m3, indicating the use of mercury during comminution. This process, referred to as whole-ore amalgamation, is environmentally destructive and unnecessary, as mercury is pulverized and lost to the tailings (65). When questioned about why miners were performing whole-ore amalgamation, miners responded that this practice was common in Zimbabwe (66). Because of the continual turnover in ASGM communities and political turmoil in Zimbabwe, there has been an increase in the number of unregistered Zimbabwean miners in the Manica Province. Zimbabwe borders Mozambique, and a major border crossing is less than 20 km away from the city of Manica. Zimbabweans and Mozambicans on both sides of the border share a common language and culture. Lower Munhena had a designated area for burning amalgams, but miners continued to burn amalgams in public and residential areas. One such miner proudly showed us his domicile constructed of wood and mud, where he burned his amalgams on the floor over an open fire. Upon being asked why he chose to burn his amalgams in his hut, he stated he did so due to security concerns. The concentration of mercury exceeded 50,000 ng/m3 of mercury outside of his house after burning an amalgam. In 2011 an information-gathering session in Lower Munhena consisting of ~30 miners was conducted. The majority of miners were unfamiliar with the use of retorts. Those miners who were familiar with them chose not to use them. Miners reported that: 1) gold was lost during the burning of amalgams using retorts; 2) the gold turned brown when using retorts; and 3) their amalgams were not large enough to warrant the use of retorts. Miners were informed that gold was not lost during the burning process, but this remains a common misconception in ASGM communities. Gold can turn brown when inappropriate metals are used for the construction of a retort. Upon further inquiry, the miner stating this issue had not experienced the color change himself but heard about it from another miner. Finally, miners were convinced that small amalgams contained insufficient mercury to warrant the use of retorts. A few miners who were familiar with the use of retorts stated that no mercury was captured when the retort was used. In 2014, we published a paper on mercury content in amalgams purchased directly from miners at Munhena and demonstrated that the amalgams contained between 40-60% mercury by mass (67). This number translated to less than 0.63 g of mercury evolved from the most mercury-rich amalgam. It is unlikely that miners would adequately recover this amount of mercury using a retort of any design. However, lack of recovery of mercury does not equate to lack of exposure to mercury vapor. The local miners trained in 2005 have not transferred their knowledge to other mining sites in the Manica Province. Approximately 50 km away from Munhena, Tsetsera is a mining community where miners are largely unaware of the benefits of using retorts. Most miners in Tsetsera refer to mercury as “silver”, perform whole-ore amalgamation and never received formal training of any kind in mining. All processing activities occurred in the village itself, and amalgams were burned throughout the village. Because of a lack of education on the dangers 64 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


of mercury, miners stored their elemental mercury inside their living quarters. Even huts where the inhabitants clearly stated they did not burn amalgams recorded mercury concentrations between 5,000 and 100,000 ng/m3. These huts were mostly stick and mud buildings with thatched roofs. An interesting phenomenon arose in measuring mercury both inside and outside of these huts. Mercury concentrations increased dramatically when the Lumex analyzer was moved from the floor to the roof of the hut. Mercury vapor condenses and adsorbs onto a variety of materials, and it was initially assumed that the increase in concentration was due to the normal evaporation and condensation of mercury during burning. Upon closer inspection, however, the thatched roof seemed to trap mercury more efficiently than the smooth walls. It is assumed that because the thatch has significantly more surface area than the walls, the thatch acts like theoretical plates in a distilling column, allowing for increased condensation of elemental mercury. If this is the case, it follows that the problems of burning amalgams in a hut are compounded by the design and construction of the hut itself. This may lead to increased concentrations of mercury in the air due to inappropriate storage of elemental mercury. Case Study #2: Ecuador Although retorts were introduced during training sessions in the Portovelo region when the Government of Switzerland initiated a Swiss Technical Cooperation (COTESU) project in 1993 (68), many miners continue to burn amalgams in the open air. The district of El Pache in Portovelo has been studied extensively due to the high concentration of mercury vapor in the air (39); however, as part of an air quality assessment from 2013-2015, the concentration of mercury on the main street that runs through the district was determined to rarely exceed 200 ng/m3. For security reasons, the processing plants have built large walls separating themselves from the main street that blocked the flow of air from the processing plants to the street. However, when miners or processing plant workers burn amalgams without using a retort, the concentration of mercury on the street rapidly exceeds 50,000 ng/m3. Within one particular processing plant, the levels of mercury concentration 12-18 h after the last amalgam was burned remained in excess of 100,000 ng/m3, and exceeded 1,000,000 ng/m3 10 m away from the burning area when an amalgam was being heated. Ecuadorian miners routinely state two reasons why they choose not to use retorts. First off, miners do not like losing sight of their gold during the burning process. Because miners’ weekly or monthly salaries are often exclusively based off of the amount of gold they are able to collect, the thought of losing any gold to the retort is terrifying. Second, miners also routinely invoke loss of time as a major factor for why they burn amalgams without using a retort. In order to use a retort effectively, the amalgam must be heated for a set amount of time to ensure all of the mercury is liberated from the sponge gold. Depending on the design, this may exceed an hour. The retort must then be allowed to cool prior to opening the chamber. If the chamber is not cool, copious amounts of mercury will be released and inhaled by the miner when he/she opens the warm retort. Burning an amalgam in the open air using a propane torch often takes less than 15 min. A 30-g amalgam 65 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


in a kitchen-bowl retort with steel covering bowl and thin stainless steel cup can be retorted and cooled down in 30 min, but this is still a long time for an anxious miner. In addition to the time required to burn the amalgam, mercury condensed during the retorting process is less effective at amalgamating gold due to oxidation and the fact that it condenses as small droplets and loses its coalescence. The mercury can be reactivated through an electrolytic process, but this process is also time consuming (1). In spite of outreach and educational programs teaching miners why retorting is important, miners continue to choose convenience over safety. Urban centers such as Portovelo are prime locations for educational outreach on mining safety because miners routinely come to the region in order to process their ore. However, there remain numerous small, hard rock mining settlements throughout Ecuador that continue to process ore at the mine site, which is often located in close proximity to their encampment. These sites are routinely overlooked for training because of their remoteness and lack of easy access. The mining community of Nambija, located in the Zamora-Chinchipe province of Southeastern Ecuador, is one such community. Although mining in the region had occurred for over 500 years, a major gold strike in Nambija caused the town to grow from a population of 100 to 8,000 miners seemingly overnight (69). In spite of the fact that this was a major ASGM site in Ecuador, its illegal status and inaccessibility coupled with excessive violence in the community prevented the effective training of miners in safety protocols. Partial and incomplete training is often more detrimental than no education. In 1995 the Ecuadorean Institute of Mining designed a pilot program to train miners in Nambija to use retorts (68). The program was abandoned prior to completion, and in 2003 Ramirez Requelme and coworkers reported that retorts were either sparsely used or not used at all in Nambija (70). In 2013, a research team from Mercer University traveled to Nambija and were surprised when a miner offered to demonstrate the use of a retort of the miner’s own design (Figure 7). The miner placed his amalgam on a raised iron platform in the middle of a steel bowl. Water was then added to the steel bowl until the water level was only ~1 cm from the top of the platform. A tuna can was then heated for two min using a propane torch and allowed to cool. The miner explained that this was to remove any remnants of plastic sealer from the inside of the can, which caused the gold to be discolored if it wasn’t removed. The can was then floated over the amalgam and heated with the propane torch. In less than 1 min, the air concentration of mercury went from ~200 ng/m3 to 20,000 ng/m3 as measured by a Lumex RA-915M mercury analyzer. After one min, the concentration exceeded the 50,000 ng/m3 maximum detection limit of the instrument, and the Lumex was removed from the area in order to prevent damage to the detector. The instrument was still registering over 50,000 ng/m3 over 9 m from the burning site. It is clear that this modified retort was ineffective. The design is similar to what is referred to as a “tin-fish-tin” retort design (31, 45). However, the tin-fish-tin retort is heated from the bottom, and the fish-tin top is not floated on water. In the case of the Ecuadorian design, when heat is applied to the top of the tuna can that is floated on the water, it breaks the seal between the upper container and the water. This releases a large amount of mercury vapor into the environment. The miner who demonstrated the use of this retort explained that he could complete 66 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


the process in less than 10 min. When the water was removed by the miner, there was elemental mercury that had indeed condensed and dropped to the bottom of the large steel bowl. The miner was informed that although he was able to collect mercury evolved during the burning process, his retort was ineffective at preventing him from breathing in mercury. The miner simply smiled, grabbed a large pan, scooped soil from the ground of the processing area and proceeded to pan the soil. In less than one minute the miner revealed that the dirt alone held multiple grams of elemental mercury.

Figure 7. A) The amalgam is placed on a raised platform surrounded by water. B) The amalgam is covered with a tuna can and heated using a propane torch. C) The sponge gold after heating. (see color insert)

Case Study #3: Guyana Guyana is a small, independent South American country with vast mineral resources and a long history of mercury use in ASGM activities (33, 41, 71–75). The interior of the country is difficult to access and sparsely populated. The PotaroSiparuni region (region 8) has an area of 20,000 km2, with a population in 2012 of only 10,000 residents. The region has numerous, independent small-scale colluvial mining operations that rely on amalgamation to concentrate the gold. The usage of retorts is mandated by law in Guyana, but enforcement of this law is not feasible considering the huge geographic area and sparse population. In 2015 seven mining sites were visited and monitored for airborne mercury concentrations using a Lumex RA-915M AAS. Five of these sites were classified as “small-scale” by the Guyanese government, and the remaining two were classified as “mediumscale”. Artisanal mining is not a recognized term in Guyana; however, small-scale operations in Guyana are comparable to artisanal mining in other nations. All seven sites used land dredges and sluice boxes to concentrate their gold and then amalgamated the concentrate. All mining camps were located within 100 m of mining operations, with miners living in canvas tents on site. Of the seven mining sites evaluated in Potaro-Siparuni, five operations were able to present retorts for inspection, and one mining operation did not possess a retort. The seventh site was not fully operational at the time of the visit, and the mine operators were not present. The largest operation visited clearly used the retort on site. The air concentration of mercury in the encampment never exceeded 67 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


the 1,000 ng/m3, except when the manager opened his mercury storage area and the retort for inspection. Within 3-m of the opened retort, the air concentrations exceeded 20,000 ng/m3, indicating that the retort was recently used. The other medium-scale operation also had a dedicated area for burning amalgams away from living quarters; however, this operation burned amalgams in a stainless steel box with a chimney. This setup is also common in processing plants and gold shops in Ecuador and relies on the heat of the propane torch to carry the mercury vapor through the chimney and away from the face of the miner doing the burning. While this does partly protect the miner burning the amalgam, the mercury vapor is distributed by the wind throughout the camp and is not captured. In addition, the chimney had been moved under a canvas tent to keep it out of the rain. Although the encampment self-reported they burned no more than once a week under the open air, the tent containing the chimney exceeded 20,000 ng/m3 3 m away from the opening. Of the three remaining small-scale sites with retorts, all miners insisted that retorts were used when burning amalgams. However, all living quarters and food preparation areas registered greater than 5,000 ng/m3. It was common for the miners to open the chamber of the retort and the Lumex to register lower readings than that of the rest of the tent, indicating that the retort had not been used. Physical inspection of the retorts showed no heating marks on the outside. All of these sites used the same style and make of retort, similar to retort A (Figure 5) but without a cooling jacket. The condensation tube is very short, and miners had been trained to dip the open end of the retort in a bucket of water to aid in condensation. When pushed for a response as to why the retorts were not used in the field, most miners continued to insist that they were. However, two miners provided the following explanations. First and foremost, the miners stated that the chamber of the retort was too large for the amalgams their operation produced. When used, they never recovered mercury, and the short condenser meant that plastic water buckets intended to trap the mercury melted near the heat source. Even after heating for over an hour, the miners were never able to remove the mercury entirely and had to reheat the amalgam to drive off the remaining mercury. One miner said that it was faster and more efficient to heat the amalgam over a campfire, and it produced better results. The manager at the site without a retort stated that he wrapped his amalgam in wet leaves and burned the amalgam in a campfire directly outside of his living area. Not surprisingly, the campfire area exceeded 10,000 ng/m3, but the fire itself was downwind from the camp’s living area, which registered less than 500 ng/m3.

Conclusion In spite of the fact that retorts can be used to prevent miners’ exposure to elemental mercury, they have repeatedly been dismissed by miners in ASGM communities around the world. The case studies presented herein highlight many of the reasons why. Table 2 highlights the problems associated with retorts in Ecuador, Guyana and Mozambique and provides potential solutions to these issues. 68 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Table 2. Potential and Perceived Problems with the Use of Retorts and Potential Solutions Country


Problems or perceived problems associated with retorts and their implementation

Potential Solution

Mercury not recovered, miners do not recognize that small amounts of mercury are dangerous

Mozambique, Guyana

Use a retort designed for the burning of small amalgams, use a retort with a cooling jacket, appropriate educational intervention and follow-up.

Not all mercury is eliminated when using a retort

Guyana

Use improved heating techniques

It takes too long to use a retort

Guyana, Ecuador, Mozambique

Use improved heating techniques, select a more efficient retort, ensure retorts are constructed properly

Miners do not like to lose sight of gold when burning amalgam

Mozambique, Guyana, Ecuador

Kitchen-bowl retort with clear glass cover allows miners to monitor burning

Homemade modifications made to retorts to improve time needed for heating

Ecuador

Follow-up visits to sites to ensure appropriate research use

Relatively high cost for a retort vs. safety

Mozambique

Kitchen-bowl retort

Influx of new and untrained miners

Mozambique

Local, permanent training centers

Security concerns, burning amalgams in public

Mozambique

Develop burning centers in mining communities away from populated areas

Gold is lost during the burning process

Mozambique, Ecuador

This is a fallacy spread by miners when they cannot see the burning process inside the retort. Education and kitchen-bowl retorts. Continued on next page.

69 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Table 2. (Continued). Potential and Perceived Problems with the Use of Retorts and Potential Solutions Country


Problems or perceived problems associated with retorts and their implementation

Potential Solution

Gold turns brown in retort

Mozambique

Use stainless steel cups or make a bed of clay inside the retort

Condensed mercury loses coalescence which decreases its ability to form an amalgam

Ecuador

Re-activate the mercury using electrolytic process

Getting miners to use retorts begins with appropriate design and construction. A retort that is not designed for the size of the amalgams being heated will invariably lead to problems. A retort that does not have an appropriate condensation tube will prevent miners from using it appropriately. Training is essential. In spite of their simplicity, using a retort incorrectly is often as dangerous as not using a retort at all. Appropriate technique is essential for successfully volatilizing the mercury and condensing the vapor. For example, miners in Guyana and Mozambique complained that using a retort took too long over a campfire. A prepared trainer can address this problem during training by working with miners to increase the temperature of the fire used to heat the amalgam. In Zimbabwe, miners developed inexpensive bellows (referred to as a mvuto) constructed from a steel pipe and bag that reduced the burning time considerably simply by increasing airflow to the coals (1). Although this is a simple solution, if this concept is not taught to miners during their initial training, miners will choose to discard the retort as opposed to solving the problem. It is also important to distinguish between training and practice. Miners must practice using the retort in front of trainers in order to address potential future issues and to ensure bad habits and “shortcuts” are not developed. Miners are remarkably efficient and results based. It has been noted that miners do not “trouble shoot” problems with retorts, they merely discard them. It may be that one bad experience with a retort is enough to dissuade a miner from using a retort in the future. As was noted in Mozambique, miners openly speak of their experiences using technology. In areas with limited to no formal training opportunities miners may very well dismiss retorts altogether. In areas where educational sessions have occurred, appropriate follow-up is necessary. Educators must return to the site repeatedly to monitor retort usage. Oftentimes this is not financially feasible. The solution may be to construct 70 Evans et al.; Trace Materials in Air, Soil, and Water ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


regional training centers in a centralized location so that miners can continuously have access to educational opportunities from a variety of sources, both local and external (76). In addition, miners trained during pilot projects can use the training center as a base of operations for future classes and follow-up. These training centers may also provide meeting sites to improve relationships between miners and governmental officials, allowing for governmental employees to be trained as instructors for future educational development and monitoring ongoing educational initiatives. In some cases, these initiatives do not require external initiation. The Guyana Geology and Mines Commission (GGMC) and the Guyana Mining School and Training Center (GMSTC) are currently working to develop a training center and curricula to train miners on improving gold yield while minimizing mercury use and pollution. While interventions related to retorts in ASGM communities around the world have been largely ineffective to date, retorts are inexpensive, simple to construct and easy to use. Retorts have the potential to keep miners and mining communities safe from mercury vapor exposure. Seemingly, any disadvantages of using retorts in ASGM pale in comparison to the benefits and yet miners continue to refuse to adopt them. Jønsson and coworkers recently commented that “…while miners’ reluctance may partly have to do with inadequate education and an ignorance stemming from a life with strong adversities, their attitude towards the retort, despite its seemingly numerous advantages, needs to be taken seriously (8).” The education process must reach the miners, processors and community members in their environment, using their language and culture. The United Nations Industrial Development Organization (UNIDO) Global Mercury Project in Zimbabwe addressed the importance of retorts while entertaining 8800 people in mining communities using street theater (77). The play Romeo and Juliet was adapted for the African mining community, highlighting the dangers of mercury and the importance of using retorts. The plot involved the son of a successful gold dealer and the daughter of a farmer whose family farm was overrun by illegal miners. When the two lovers admit their love for one another, the resulting discord between the families results in the young woman moving in with the young man. Over time, they both develop mercury intoxication and debilitating symptoms. Regretting the decisions that drove their children away, the farmer blesses the marriage and the gold dealer adopts technology to provide a safer environment for the community. After the play, retorts and efficient gold recovery sluice carpets were demonstrated for the crowd. Unfortunately, the effectiveness of this approach was not validated due to political instability in Zimbabwe; however, the number of people reached was impressive and future work in this area may lead to an effective and reproducible method of delivering training. In spite of their effectiveness, there is a dearth of reports in the peer-reviewed literature on approaches to training miners on how and why they should use retorts. A coordinated effort must be made to develop a connected community of trainers that can share both positive and negative experiences. Until the trainers work together to develop a strategy to address miners’ reluctance to implement retorts, little progress can be made in addressing this issue.


Acknowledgments


AMK, KD and CSS acknowledge generous funding through the Mercer on Mission program at Mercer University, and the hard work of 34 undergraduate researchers in the collection of data in Mozambique and Ecuador. AMK, KD and MV are thankful for generous financial support from UNIDO (Project No. 100271, Ecuador) and the Inter-American Development Bank (Guyana Project GY-T1106). AMK thanks Ms. Diane McDonald (Head, Mineral Processing Unit, Guyana Geology and Mines Commission) for helpful conversations regarding ASGM activities in Guyana.

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