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Gold losses and mercury recovery in artisanal gold mining on the Madeira River, Brazil
Journal of Cleaner Production 102 (2015) 370e377
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Gold losses and mercury recovery in artisanal gold mining on the Madeira River, Brazil Michela Balzino a, b, Jacopo Seccatore b, c, *, Tatiane Marin b, d, Giorgio De Tomi b, d, Marcello M. Veiga e a
Department of Environment, Landscape and Infrastructure Engineering, Politecnico di Torino, Italy ~o Paulo, Brazil Research Center for Responsible Mining, University of Sa ~o Paulo, Brazil Instituto of Geoci^ encas, Universidade de Sa d ~o Paulo, Brazil Department of Mining and Petroleum Engineering, University of Sa e Norman B. Keevil Institute of Mining Engineering, University of British Columbia, Canada b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 March 2015 Received in revised form 28 April 2015 Accepted 4 May 2015 Available online 12 May 2015
For the last 40 years artisanal mining has been playing a key role in the economy of the Madeira River, ^ nia, in the Brazilian Amazon. The main process through which artisanal miners in the State of Rondo region recover gold is by river dredging. The dredges are floating platforms that excavate the bottom of the river and, after a sorting phase, separate the gold (Au) from the sediment by means of mercury (Hg) amalgamation. The objectives of this paper are to map the process, demonstrate the inability to completely recover the Au from the excavated sediments, and reveal the actual impact of Hg. Several dredges were visited and all the unit operations involved in the mining and processing circuit were analyzed. Significant losses of Au are associated with inefficient sorting techniques. The Au grade of the sediments rejected during the sorting phase ranges from 0.1 to 7.8 ppm, reaching values higher than the world average Au grade of the producing mines. Analyzing the amalgamation process, it was possible to quantify the Hg released into and recovered from the environment. The results show that, contrary to common belief, Hg is recovered from the bottom of the river instead of being released into it. The total Hg-mass balance is actually closed with a positive recovery and with an emission factor (Hg:Au ratio) lower than the average (0.1e0.2). Despite this result, Hg continues to be volatilized into the atmosphere in the form of vapors. In the region of the Madeira River a campaign must be developed to encourage the use of more efficient and Hg-free technologies for Au recovery. Responsible and Hg-free AGM operations can contribute effectively to rehabilitate the entire area. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Artisanal mining Mercury Gold Amazon Madeira River
1. Introduction Artisanal gold mining (AGM) is an important source of income in a developing, low-income region (Hentschel et al., 2003) such as the Brazilian Amazon due to the high Au concentration in the sediments of the river bottom (3e30 g/m3)and in the layer of al^ (up to35 g/m3) luvial over-consolidated deposit called mocororo (Bastos, 2004). This activity has played and currently plays an important economic role in the country, attracting a large number of miners (Veiga, 1997a,b) with an estimated Au production of 21 t/
* Corresponding author. Research Center for Responsible Mining, University of S~ ao Paulo, Brazil. E-mail address: [email protected] (J. Seccatore). http://dx.doi.org/10.1016/j.jclepro.2015.05.012 0959-6526/© 2015 Elsevier Ltd. All rights reserved.
a (Seccatore et al., 2014). Even though the artisanal Au mining, locally called garimpagem, has long roots in the history of this territory since the 1950s (Cremers et al., 2013), the sector truly began to grow as a viable livelihood alternative in the 1970s (UNDP, 2011; Cremers et al., 2013) and in the early 1980s when the Au price reached US$ 850/oz (Mylchreest, 2007). In particular, the area of Madeira River has been one of the most productive Au regions of Brazil in the last decades, starting as an individual and informal manual activity with floating sluice boxes in the riverside during the dry season and quickly transformed into a mechanized activity (Bastos and Lacerda, 2004). Garimpagem was regulated in 1979 (Almeida et al., 2009), when the Brazilian government established an Artisanal Mining Reserve (Reserva Garimpeira, Ministry Decree. 1345/79 and 1034/80) in the area between Porto Velho and Vila de ~ (Linhares et al., 2009). Nowadays, Au mining in Madeira Abuna
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River is performed mainly aboard dredges (dragas, see Fig. 1), which are floating platforms (from the smallest observed 8 m 14 m, to the largest 10 m 30 m). Dredges excavate the bottom of the river with a rotating drum, and pump the disaggregated material aboard, where the sorting and processing phases take place (Bastos, 2004). Amalgamation is used on board to separate the Au from the concentrated sediments. The recovery process is usually not well planned and the techniques and devices employed are rudimentary, unsafe and outdated. The methods of extraction and separation are often not efficient, resulting in high losses of profit. Furthermore, the Hg involved in the amalgamation is as much inefficient as dangerous due to the Hg vapors emitted to the atmosphere and around the burning sites. The Hg level can be alarmingly high, reaching the WHO (World Health Organization) limit for public exposure of 1.0 mg/m3 (EHP, 2014). For this reason, over the past twenty years the artisanal mining activities have been constantly denounced in the local and international media (Hacon et al., 2008). Despite the much higher awareness among the artisanal Au miners about Hg issues and the actual improvement of their techniques (Hester and Harrison, 1994), the area continues to be affected by the impact of past mining activities that have been the cause of 3000 t of Hg released in the middle of the Amazon environment from 1975 to 2002 (Bastos et al., 2008; Diaz and Elmer, 2000). For a comparison, “annual emissions from ASGM are estimated at 727 tonnes, making this the largest sector accounting for more than 35% of total anthropogenic emissions” (UNEP, 2013). Nowadays, the impact of the AGM in the area has drastically decreased (Bastos et al., 2006) but the lack of support from governments, poor technical management and a high interest in immediate profits mean that Hg releases and emission remain a problem in the region (Veiga and Hinton, 2002). Improvement of the current situation requires deeper knowledge of the operating methods, and participation of the miners in the transformations and the decision-making process is paramount to convert them into small, responsible entrepreneurs (Seccatore et al., 2013; Hinton et al., 2003). The present study is part of such an effort.
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2. Mining, concentration and amalgamation The gold recovery process is organized into three main phases: mining, concentration, and amalgamation of the concentrated ore. Fig. 2 shows the flowchart of the whole process. Fig. 3 shows the flow of the ore aboard a dredge, from excavation to waste disposal. Fig. 4 shows pictures of the equipment and materials involved in the process. A cutting drum (locally called abacaxi, pineapple in Portuguese) excavates the river bottom, at depths from 15 to 20 m, breaking up rocks and consolidated materials. The cutting drum is coupled to an arm (which ranges from 10 to 40 m in length), whose structure is composed of a pipe connected to a suction pump that sucks the mixture (water, gravel and sand) on board at the same time. The arm is controlled through cables and winches by an operator aboard the dredge, and no diver is employed (Fig. 4A). The pumped material is sorted by grain size in grids that act as sieves. The grids are made of iron bars with an average opening of 2.9 cm, where larger stones and other impurities are retained. The oversize is rejected and dumped into the river (Waste1, Figs. 2 and 3). The selected material flows over sluice boxes covered with carpets (Carpets1, Figs. 2 and 3). The sluice boxes are slightly inclined (about 20 ). Finer Au is trapped in the carpet fibers by sedimentation, together with sands and other impurities (Fig. 4B). The engine is stopped for 1 h every 20, when the carpets are quickly removed, rolled and replaced with dry ones. The carpets from the sluice boxes are then washed intensely in a tank with running water, so that the fine particles detach from the carpet fibers and flow into a tank. After this phase, fine particles flow onto another smaller sluice box, covered with new carpets (Carpets2, Figs. 2 and 3) which concentrate the heavier fraction and reduce the amount of sand (Fig. 4C, Figs. 2 and 3). The washing operation is repeated with Carpets2 and the obtained concentrate is collected for the amalgamation process. The coarser material is rejected and dumped into the river (Waste2, Figs. 2 and 3). Amalgamation of Au from the gravity concentrates employs metallic Hg which is introduced into a cement mixer for no longer than 60 min (Fig. 4D). The amount of Hgin introduced in
Fig. 1. One of the dredges observed during the research.
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Fig. 2. Flowchart of the Au recovery process.
the amalgamation barrel (cement mixer) is arbitrarily determined by the worker in charge of the amalgamation process. The worker in charge determines the required quantity according to the suspected Au grade detected by observation when the carpets are washed: the higher the amount of Au observed in the carpets, the higher the amount of Hg added into the mixer. No measurement is performed during this phase. This mixing process eventually
pulverizes the Hg, forming droplets that are lost with tailings that squez-Lo pez et al. (2010) report that the return to the river. Vela amalgamation of concentrates using barrels or mixers loses around 1.4% of the Hg introduced in the process, whereas 30% of Hg is lost when the whole ore is amalgamated in small ball mills. The amalgam is separated from the rest of the heavy minerals by panning in a bucket and the worker removes the ferrous fraction
Fig. 3. Scheme of the flow of the ore aboard a dredge, from excavation to waste.
M. Balzino et al. / Journal of Cleaner Production 102 (2015) 370e377
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Fig. 4. A e Arm and cutting drum, B e Grid and Carpets1, C e Open tank and Carpets2, D e Cement mixer, E e Retort, F e Final Au.
with a magnet. After squeezing off the excess Hg, the amalgam, usually containing 60% Au and 40% Hg, is decomposed by burning in a furnace with a retort which retains up to 95% of the evaporated Hg (Fig. 4E). This process has been described in detail in dedicated works (Veiga et al., 2013; UNEP, 2008). The impure Au, called dor e, is melted in open air with a propane torch, obtaining Au with a residual 4% of Hg and other impurities (Fig. 4F), according to the cooperative COOGARIMA (Cooperativa de Garimpeiros do Rio Madeira, cooperative of artisanal miners of the Rio Madeira, located ^ nia). in Porto Velho, Rondo
made it impossible to determine precisely the first Au-mass balance parameters. It was possible, however, to sample and determine the Au grade of Waste 1 and 2. Samples of the rejected material were collected, separated from the liquid component, homogenized and quartered up to obtain the sample to analyze by fire assay. The sampling procedure was accomplished on six dredges for eight recovery processes. 4. Methodology to assess the role of Hg 4.1. System boundaries and Hg-balance equation
3. Methodology to assess the Au losses 3.1. System boundaries and Au-balance equation In order to analyze the Au recovery process, an Au-mass balance was developed to assess the amount of Au that enters and exits the system, from the excavation phase to the final produced Au. The mass balance equation of the process is as follows:
Auin Aulost1 Aulost2 ¼ Auproduced
(1)
where: Auin is the Au introduced in the system, Aulost1 is the Au lost in grids from Waste1, Aulost2 is the Au lost in the rejected material from Waste2, Auproduced is the final Au produced. To assess the parameters of the Au-mass balance, a preliminary analysis was required to quantify the solid fraction of the jets entering the system and leaving it in Waste 1 and 2. This is done with Equation (2).
Auin ¼ F*t*GAu
(2)
where: F is the flow of the solid fraction [t/h], t is the time of the process [t] and GAu is the Au grade[g/t]. 3.2. Sampling conditions Difficulties in assessing the flow rate of the solid fraction (due to the lack of safe conditions during sampling from the main pipe)
The Hg-mass balance was performed to determine the losses of Hg in the Au recovery process. This balance assesses the Hg introduced into the amalgamation system and the portion recovered at the end of the process. Based on the analysis of the incoming and outgoing masses, the mass balance equation of the amalgamation process was developed (3).
Hgin ¼ Hgriver þ Hgevaporated þ Hgrecovered þ Hggold
(3)
where: Hgin is the Hg introduced in the system, Hgriver is the Hg in transference with the river (either recovered or introduced), Hgevaporated is the Hg evaporated in the whole process, Hgrecovered is the Hg recovered during the process, Hggold is Hg trapped with Au in the produced impure gold. The sign of Hgriver determines whether the Hg is recovered from or introduced into the river: if Hgriver > 0 then Hgriver ¼ Hglost, that is Hg released to the river; if Hgriver < 0 then Hgriver ¼ Hggained that is Hg recovered from the river. The variable Hgevaporated can be broken down to its components: it is the sum of the Hg evaporated due to the losses in the furnace (Hgev1), and the Hg evaporated during the burning with a blowtorch (Hgev2). Also the variable Hgrecovered can be broken down to its components: it is the sum of the surplus of Hg squeezed from the piece of fabric (Hgsqueezed) and the Hg recovered from the retort (Hgretort).
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M. Balzino et al. / Journal of Cleaner Production 102 (2015) 370e377 Table 1 Methods for measuring Hg emissions. Evaluation
Procedure
Hg entering the system (Hgin) Hg squeezed off from the amalgam (Hgsqueezed) Weight of the amalgam (Wamalgam) Hg recovered with the retort (Hgretort) Weight of the gold (WAu)
Hg was weighed before being introduced into the amalgamation process. Hg was weighed after squeezing the amalgam. Amalgam was weighed before burning to eliminate the Hg. Hg was collected in the retort and weighed after burning. Au was weighed after burning with propane torch.
Table 2 Formulas for measuring Hg emissions. Evaluation
Procedure
Hg evaporated during the burning phases (Hgevaporated) Hgevaporated ¼ Wamalgam ½g Hgretort ½g WAu ½g
(4)
Hgrecovered ½g ¼ HgSqueezed ½g þ Hgretort ½g
(5)
Hgriver < 0/Hgriver ¼ Hggained
(6)
4% of Wgold
(7)
Recovery of Hg ¼ Hgrecovered=Hgin
(8)
Hg recovered during the amalgamation process (Hgrecovered)
Hg recovered from the river (Hggained) a
Hg impurities in the gold (Hggold)
Percentage of Hg recovered with respect to that introduced (Recovery of Hg)
a
From interviews with the members of the COOGARIMA cooperative.
4.2. Materials and methods The approach used to quantify the involved Hg wasted was to weigh it with precision balances before and after each unit operation involved in the amalgamation process. The procedure was followed at six dredges during eight amalgamation processes by weighing the Hg introduced into the system (Hgin), the Hg squeezed (Hgsqueezed), the amalgam before and after the furnace, the Hg recovered by the retort (Hgretort) and the Au produced. The procedure is described in Table 1. It was integrated based on interviews with the miners and the operators of COOGARIMA for the correct interpretation of the process phases. Inverse equations were obtained to calculate the missing parameters based on the Hg-mass balance equation. These equations are shown in Table 2. 5. Results and discussion
According to The Global Au Mine & Deposit ranking (Natural Resource Holdings, 2013), the average grade of all producing mines in the world was 1.01 g/t in 2013. This means that the garimpeiros are rejecting material with an Au grade comparable to that of industrial Au mines around the world. This consideration highlights the inefficiency of the Au recovery process aboard these dredges. 5.2. More Hg recovered than released into the environment In reference to previous studies, it was expected to get high levels of Hg released into the environment (Shandro et al., 2009; Spiegel and Veiga, 2010; Veiga, 1997a,b, 2009; Veiga et al., 2006; squez-Lo pez et al., 2010). Negative values of Hgriver represent Vela Hg recovered from the river (Hggained) and not released into it, resulting in a recovery of Hg greater than 100%. These results prove that, during each Au recovery process, a considerable amount of Hg is recovered from the environment as well (27.8%). Even if some Hg
5.1. Au losses The average Au grades of the rejected material, Waste1 and 2, are shown in Table 3. The highest Au concentrations occurred in Waste1due to a probable lack of liberation of Au particles trapped in coarser sediments. The carpets technique shows better efficiency on the finer material, resulting in lower losses of Au.
Table 3 Au grade in the rejected material.
P1 P2 P3 P4 P5 P6
Au grade Waste1 [ppm]
Au grade Waste2 [ppm]
0.15 0.27 7.83 0.88 2.68 1.68
0.49 0.08 0.10 1.17 0.41 0.07
Fig. 5. Hggained and Hgevaporated.
M. Balzino et al. / Journal of Cleaner Production 102 (2015) 370e377 Table 4 Average Hg distribution in amalgamation processes.
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Table 5 Percentage of Hg dispersed in the atmosphere.
Hg distribution
Material
Estimation method
Hgin [g] Hgsqueezed [g] Wamalgam [g] Hgretort[g] WAu [g] Hggold [g] Hgevaporated Hgrecovered[g] Hgriver[g] Hggained[g] Recovery Hg
382.6 ± 187.1 322.6 ± 140.6 249.6 ± 113.0 150.8 ± 68.8 101.3 ± 44.3 4.8 ± 1.8 52.9 ± 5.7 540.1 ± 153.5 118 ± 71.4 118.8 ± 71.4 120%
Weighing Weighing Weighing Weighing Weighing Eq. (7) Eq. (4) Eq. (5) Eq. (3) Eq. (6) Eq. (8)
Amalgamation process
% Hgevaporated compared with the initial Hg
A1 A2 A3 A4 A5 A6 A7 A8
2.3 2.8 1.8 27.3 3.1 1.3 1.6 1.8
Note: Arithmetic mean ± standard deviation, n ¼ 7.
result from 1988 shows that the emissions of Hg have dramatically decreased in the last 26 years.
is released during the process in the form of vapors (Hgevaporated ¼ 1.9e3.6%), the total balance shows that the operation is actually capturing more Hg that is already present in the river. This result is contrary to the common perception of a polluting AGM. Looking at the recovery processes as a whole, it “cleans up” more than it pollutes, and AGM should be seen as a potential stakeholder in the process of rehabilitation of the area by reclaiming the bottom of the river. Comparing the values of Hggained and Hgevaporated (Fig. 5), it is shown that sometimes the proportion between them can be ten times as high. The results obtained are reported in Table 4. The relation between Hgin and Hgrecovered (Fig. 6) was analyzed in order to confirm these results. The amount of Hg recovered during the amalgamation process is systematically higher than the amount introduced at the beginning. The excess in recovery is indeed Hg coming from the bottom of the river.
5.4. Hg losses
5.3. HgeAu ratio The relationship between the Hg and Au produced was calculated in order to compare the proportion of Hg released into the environment (that in this study is equivalent to Hgevaporated) in relation to the amount of Au produced during the whole amalgamation process (Lacerda, 2003a,b). This value is called the emission factor (EF) or Hg:Au ratio and is quite variable, depending on the site, techniques and devices used (Lacerda and Pfeiffer, 1992). EF usually ranges from 1 to 5, and in particular in between 1 and 1.5 in the Amazon (Lacerda, 2003a,b). Pfeiffer and Lacerda (1988) found a mean EF of 1.3 in mining sites located in the Madeira River. The average EF measured during this study ranges from 0.1 to 0.2. The reduction of 78.5% with respect to the previous
Despite these results, the analyzed Au recovery processes are really far from the concept of a clean production. It still exists a release of Hg in the environment in the form of vapors that are dangerous for the workers. This source of pollution is represented by the Hgevaporated as the sum of Hg losses from the furnace and the Hg dispersed during the burning phase in open air with the propane torch. The second constituent is often the main cause, but in some processes the employment of handmade and overused retorts can cause a high level of Hg to be released from the furnace with the retort. This problem is more evident in some cases where the level of Hg evaporated is higher than the average. This is the case of amalgamation process 4, which is excluded from the statistical analysis because it is an outlier (A4 in Table 5) caused by process deviations. During the field work it was noticed that the furnace employed was outdated, dilapidated and in its proximity there was a strong odor. The retorting efficiency depends on the type of connections or clamps used (UNEP, 2008) and in that case were of a low quality. Well-made retorts, like the majority of the analyzed cases, if properly used, can collect and recycle a high amount of Hg used during the process (Maponga and Ngorima, 2003; Jønsson et al., 2013). This occurrence suggests that inappropriate devices result in reduced recovery efficiency and therefore higher losses. 5.5. The Hg in the river Madeira River is one of the rivers most contaminated by Hg in the Amazon basin (Silveira et al., 1998). The amount of Hg is linked mainly to the mining activities and reached its highest values during the years of the maximum Au production (the 1980s, Bastos and Lacerda, 2004). High levels of Hg, according to Lechler et al. (2000), can also be attributed to natural sources. However, determining the origin of Hg in the river goes beyond the aim of this paper. The scope of this work was to evaluate the exchange of Hg that mining activities have with the environment. The values of Hggained could then be correlated with thigh deposited at the bottom of Madeira River that it is dredged during the excavation phase and enters the Au recovery process. Hg has a high specific weight and during the sorting phase is captured by the carpets until reaching the amalgamation process. Indeed, observing the sediments coming from the bottom of the river, the presence of Hg was always visible to the naked eye (Fig. 7). 6. Conclusions
Fig. 6. Hgin and Hgrecovered.
In this paper it is shown that AGM is still an important source of income in the Madeira River. An inefficient Au recovery method
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Brazil), FAPESP (Foundation for Support to the Research of the State ~o Paulo, Brazil) and CNPq (National Council for Technological of Sa and Scientific Development, Brazil) for their support of the research effort. References
Fig. 7. Hg in a sample collected from the bottom of the river.
seems to be the cause of Au losses during the sorting phases. The high Au grade in Waste1 (2.3 ppm) demonstrates that the coarser material contains fine unliberated particles of Au. Moreover, the Au grade of average industrial mines in the world is comparable to that rejected during the recovery process. The profits of the operation as a whole, and therefore its economical sustainability, are strongly compromised by its lack of efficiency. Focusing on the amalgamation process, it was observed that the current AGM activity in the Madeira River, albeit continuing to employ Hg for amalgam, shows signs of awareness, as retorts appear to be widespread and commonly employed, helping to mitigate the environmental emissions. The rate of Hg released is far lower than the amount involved in the past (with a decrease of 78.5%) (Pfeiffer and Lacerda, 1988). The mass balance allowed to demonstrate that each process recovers a large amount of Hg from the river. In the eight processes analyzed, a total 3.6 kg of Hg were introduced during the amalgamation and 4.7 kg of Hg were collected at the end of the processes and only 0.4 kg were lost into the atmosphere as vapors, with an emission factor (Hg:Au ratio) from 0.1 to 0.2. These results show that, for the analyzed cases, 131% of Hg was recovered with respect to the amount introduced. This is a positive environmental role played by the AGM operation, and at the same time shows that a large amount of Hg is deposited on the river bottom. Despite this improvement, the activity of garimpeiros cannot be defined as clean production as it continues to use Hg and is dangerous for the environment and humans. Measures to eliminate the practice of whole ore amalgamation should be encouraged through the introduction of more efficient and Hg-free technologies, as described in Veiga (2009), and implement local training programs, as described in Sousa and Veiga (2009) and Veiga et al. (2015). At the same time, a reclamation plan of the bottom of Madeira River should be integrated with this program, in order take advantage of the ongoing AGM operations to help rehabilitate the entire area. Acknowledgments Many thanks go to the COOGARIMA for their help during field ~o (Research work. A special acknowledgment goes to NAP.Mineraça ~o Paulo, Center for Responsible Mining of the University of Sa
~es nas concenAlmeida, M., Lacerda, L.D., Saldanha, G., Bastos, W., 2009. Variaço ~es de mercúrio em solos da reserva garimpeira do alto Rio Madeira. traço Geochim. Bras. 23 (1), 139e150. ^ncia ambiental do mercúrio e sua presenca em populaco ~ es Bastos, W., 2004. Ocorre ^nia. ribeirinhas do baixo Rio Madeira- Amazo Bastos, W.R., Gomes, J.P.O., Oliveira, R.C., Almeida, R., Nascimento, E.L., Bernardi, Lacerda, L.D., Silveirs, E.G., Pfeiffer, W.C., 2006. Mercury in the environment and riverside population in the Madeira River basin, Amazon, Brazil. Sci. Total Environ. 334e351. Bastos, W., Lacerda, L., 2004. A contaminacao por mercurio na bacia do Rio Madeira: uma breve revicao. Bastos, W., Rebelo, M., Fonseca, M., Almeida, R., Olaf Malm, O., 2008. A description of mercury in fishes from the Madeira River basin, Amazon, Brazil. Acta Amaz. 38 (3). Cremers, L., Kolen, J., De Theije, M., 2013. Small-scale Gold Mining in the Amazon the Cases of Bolivia, Brazil, Colombia, Peru and Suriname. CEDLA, Amsterdam. Diaz, Elmer, 2000. Mercury pollution at gold mining sites in the Amazon environment. Principles of Environment Toxicology. EHP, 2014. Mercury exposure and health impacts among individuals in the artisanal and small-scale gold mining community: a comprehensive review. Environ. Health Perspect. Hacon, S., Barrocas, P.R., Vasconcellos, A.C.S.D., Barcellos, C., Wasserman, J.C., Campos, R.C., Ribeiro, C., Azevedo-Carloni, F.B., Jul. 2008. An overview of mercury contamination research in the Amazon basin with an emphasis on Brazil. Cad. Saúde Pública 24 (7). Rio de Janeiro. http://www.scielosp.org/scielo.php? pid¼S0102-311X2008000700003&script¼sci_arttext. Hentschel, Hruschka, Priester, 2003. Artisanal and Small-scale Mining: Challenges and Opportunities. IIED, WBCSD. Hester, R., Harrison, R., 1994. Mining and its Environmental Impact. Royal Society of Chemistry. Hinton, J., Veiga, M., Veiga, A., 2003. Clean artisanal gold mining: a utopian approach? J. Clean. Prod. 11 (2), 99e115. Holdings, N. R, 2013. Global Gold Mine and Deposit Ranking. Jønsson, J., Charles, E., Kalvig, P., 2013. Toxic mercury versus appropriate technology: artisanal gold miners. Resour. Policy 60e67. Lacerda, L.D., 2003a. Updating global Hg emissions from small-scale gold mining and assessing its environmental impacts. Environ. Geol. 3, 308e314. Lacerda, L., 2003b. Updating global Hg emissions from small-scale gold mining and assessing its environmental impacts. Environ. Geol. 308e314. Lacerda, L., Pfeiffer, W., 1992. Mercury from gold mining in the amazon environment-An overview. Quìmica nova 15 (2), 155e160. Lechler, Mille, Lacerda, Vinson, Bonz, 2000. Elevated mercury concentrations in soils, sediments, water, and fish of the Madeira River basin, Brazilian Amazon: a function of natural enrichments? Sci. Total Environ. Linhares, D., da Silva, J., Lima, T. d., Almeida, R., B, W.R., 2009. Mercúrio em differ^ nia ocidental. entes tipos de solos marginais do baixo Rio Madeira-Amazo Geochim. Bras. 117e130. Maponga, O., Ngorima, C.F., 2003. Overcoming environmental problems in the gold panning sector. J. Clean. Prod. 147e157. Mylchreest, P., 2007. Gold War. Pfeiffer, W., Lacerda, L., 1988. Mercury inputs into the Amazon region. Brazil. Environ. Technol. Lett. 9, 325e330. Seccatore, J., M, T., De Tomi, G., Veiga, M., 2013. A practical approach for the management of resources and reserve in small-scale mining. J. Clean. Prod. 1e6. Seccatore, J., Veiga, M., Origliasso, C., Marin, T., De Tomi, G., 2014. An estimation of the artisanal small-scale production of gold in the world. Sci. Total Environ. Shandro, J., Veiga, M., Chouinard, R., 2009. Reducing mercury pollution from artisanal gold mining in Munhena, Mozambique. J. Clean. Prod. 17 (5), 525e532. Silveira, E.G., Salvioni Gali, P.A., Barbosa, R.V., Braga, I.C., 1998. O mercúrio nos garimpos de ouro do Rio Madeira/RO. Rev. Educ. Cult. meio ambiente. Sousa, R.N., Veiga, M.M., 2009. Using performance indicators to evaluate an environmental education program in artisanal gold mining communities in the brazilian amazon. AMBIO: A J. Hum. Environ. 38 (1), 40e46. Spiegel, S., Veiga, M., 2010. International guidelines on mercury management in small-scale gold mining. J. Clean. Prod. 18 (4), 375e385. UNDP, United Nations Development, 2011. Small-scale gold mining in the transboundary areas of Brazil, Suriname and French Guiana. Social and Environmental Issues. UNEP, 2008. Module 3 Mercury Use in Artisanal and Small Scale Gold Mining. UNEP, 2013. Global Mercury Assessment 2013. Available at: http://www.unep.org/ PDF/PressReleases/GlobalMercuryAssessment2013.pdf. Last visit on 27/04/ 2015. Veiga, M.M., 1997a. Introducing New Technologies for Abatement of Global Mercury Pollution in Latin America. UNIDO/UBC/CETEM/CNP. Veiga, M.M., Hinton, J.J., 2002. Abandoned artisanal gold mines in the brazilian amazon: a legacy of mercury pollution. Nat. Resour. Forum 13e24.
M. Balzino et al. / Journal of Cleaner Production 102 (2015) 370e377 Veiga, M., 1997b. Mercury in Artisanal Gold Mining in Latin America: Facts, Fantasies and Solutions. UNIDO. Veiga, M.N., 2009. Mill leaching: a viable substitute for mercury amalgamation in the artisanal gold mining sector? J. Clean. Prod. 17 (15), 13. Veiga, M.M., Angeloci, G., Niquen, W., Seccatore, J., 2015. Reducing mercury pollution by training Peruvian artisanal gold miners. J. Clean. Prod. 94, 268e277.
377
Veiga, M., A, G., Hitch, M., Velasquez-Lopez, P., 2013. Processing centres in artisanal gold mining. J. Clean. Prod. 1e10. Veiga, M., Maxson, P.A., H, L.D., 2006. Origin and consumption of mercury in smallscale gold mining. J. Clean. Prod. 14 (3e4), 436e447. squez-Lo pez, P.C., Veiga, M., Hall, K., 2010. Mercury balance in amalgamation in Vela artisanal and small-scale gold mining: identifying strategies for reducing environmental pollution in Portovelo-Zaruma, Ecuador. J. Clean. Prod. 226e232.
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Gold losses and mercury recovery in artisanal gold mining on the Madeira River, Brazil Michela Balzino a, b, Jacopo Seccatore b, c, *, Tatiane Marin b, d, Giorgio De Tomi b, d, Marcello M. Veiga e a
Department of Environment, Landscape and Infrastructure Engineering, Politecnico di Torino, Italy ~o Paulo, Brazil Research Center for Responsible Mining, University of Sa ~o Paulo, Brazil Instituto of Geoci^ encas, Universidade de Sa d ~o Paulo, Brazil Department of Mining and Petroleum Engineering, University of Sa e Norman B. Keevil Institute of Mining Engineering, University of British Columbia, Canada b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 March 2015 Received in revised form 28 April 2015 Accepted 4 May 2015 Available online 12 May 2015
For the last 40 years artisanal mining has been playing a key role in the economy of the Madeira River, ^ nia, in the Brazilian Amazon. The main process through which artisanal miners in the State of Rondo region recover gold is by river dredging. The dredges are floating platforms that excavate the bottom of the river and, after a sorting phase, separate the gold (Au) from the sediment by means of mercury (Hg) amalgamation. The objectives of this paper are to map the process, demonstrate the inability to completely recover the Au from the excavated sediments, and reveal the actual impact of Hg. Several dredges were visited and all the unit operations involved in the mining and processing circuit were analyzed. Significant losses of Au are associated with inefficient sorting techniques. The Au grade of the sediments rejected during the sorting phase ranges from 0.1 to 7.8 ppm, reaching values higher than the world average Au grade of the producing mines. Analyzing the amalgamation process, it was possible to quantify the Hg released into and recovered from the environment. The results show that, contrary to common belief, Hg is recovered from the bottom of the river instead of being released into it. The total Hg-mass balance is actually closed with a positive recovery and with an emission factor (Hg:Au ratio) lower than the average (0.1e0.2). Despite this result, Hg continues to be volatilized into the atmosphere in the form of vapors. In the region of the Madeira River a campaign must be developed to encourage the use of more efficient and Hg-free technologies for Au recovery. Responsible and Hg-free AGM operations can contribute effectively to rehabilitate the entire area. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Artisanal mining Mercury Gold Amazon Madeira River
1. Introduction Artisanal gold mining (AGM) is an important source of income in a developing, low-income region (Hentschel et al., 2003) such as the Brazilian Amazon due to the high Au concentration in the sediments of the river bottom (3e30 g/m3)and in the layer of al^ (up to35 g/m3) luvial over-consolidated deposit called mocororo (Bastos, 2004). This activity has played and currently plays an important economic role in the country, attracting a large number of miners (Veiga, 1997a,b) with an estimated Au production of 21 t/
* Corresponding author. Research Center for Responsible Mining, University of S~ ao Paulo, Brazil. E-mail address: [email protected] (J. Seccatore). http://dx.doi.org/10.1016/j.jclepro.2015.05.012 0959-6526/© 2015 Elsevier Ltd. All rights reserved.
a (Seccatore et al., 2014). Even though the artisanal Au mining, locally called garimpagem, has long roots in the history of this territory since the 1950s (Cremers et al., 2013), the sector truly began to grow as a viable livelihood alternative in the 1970s (UNDP, 2011; Cremers et al., 2013) and in the early 1980s when the Au price reached US$ 850/oz (Mylchreest, 2007). In particular, the area of Madeira River has been one of the most productive Au regions of Brazil in the last decades, starting as an individual and informal manual activity with floating sluice boxes in the riverside during the dry season and quickly transformed into a mechanized activity (Bastos and Lacerda, 2004). Garimpagem was regulated in 1979 (Almeida et al., 2009), when the Brazilian government established an Artisanal Mining Reserve (Reserva Garimpeira, Ministry Decree. 1345/79 and 1034/80) in the area between Porto Velho and Vila de ~ (Linhares et al., 2009). Nowadays, Au mining in Madeira Abuna
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River is performed mainly aboard dredges (dragas, see Fig. 1), which are floating platforms (from the smallest observed 8 m 14 m, to the largest 10 m 30 m). Dredges excavate the bottom of the river with a rotating drum, and pump the disaggregated material aboard, where the sorting and processing phases take place (Bastos, 2004). Amalgamation is used on board to separate the Au from the concentrated sediments. The recovery process is usually not well planned and the techniques and devices employed are rudimentary, unsafe and outdated. The methods of extraction and separation are often not efficient, resulting in high losses of profit. Furthermore, the Hg involved in the amalgamation is as much inefficient as dangerous due to the Hg vapors emitted to the atmosphere and around the burning sites. The Hg level can be alarmingly high, reaching the WHO (World Health Organization) limit for public exposure of 1.0 mg/m3 (EHP, 2014). For this reason, over the past twenty years the artisanal mining activities have been constantly denounced in the local and international media (Hacon et al., 2008). Despite the much higher awareness among the artisanal Au miners about Hg issues and the actual improvement of their techniques (Hester and Harrison, 1994), the area continues to be affected by the impact of past mining activities that have been the cause of 3000 t of Hg released in the middle of the Amazon environment from 1975 to 2002 (Bastos et al., 2008; Diaz and Elmer, 2000). For a comparison, “annual emissions from ASGM are estimated at 727 tonnes, making this the largest sector accounting for more than 35% of total anthropogenic emissions” (UNEP, 2013). Nowadays, the impact of the AGM in the area has drastically decreased (Bastos et al., 2006) but the lack of support from governments, poor technical management and a high interest in immediate profits mean that Hg releases and emission remain a problem in the region (Veiga and Hinton, 2002). Improvement of the current situation requires deeper knowledge of the operating methods, and participation of the miners in the transformations and the decision-making process is paramount to convert them into small, responsible entrepreneurs (Seccatore et al., 2013; Hinton et al., 2003). The present study is part of such an effort.
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2. Mining, concentration and amalgamation The gold recovery process is organized into three main phases: mining, concentration, and amalgamation of the concentrated ore. Fig. 2 shows the flowchart of the whole process. Fig. 3 shows the flow of the ore aboard a dredge, from excavation to waste disposal. Fig. 4 shows pictures of the equipment and materials involved in the process. A cutting drum (locally called abacaxi, pineapple in Portuguese) excavates the river bottom, at depths from 15 to 20 m, breaking up rocks and consolidated materials. The cutting drum is coupled to an arm (which ranges from 10 to 40 m in length), whose structure is composed of a pipe connected to a suction pump that sucks the mixture (water, gravel and sand) on board at the same time. The arm is controlled through cables and winches by an operator aboard the dredge, and no diver is employed (Fig. 4A). The pumped material is sorted by grain size in grids that act as sieves. The grids are made of iron bars with an average opening of 2.9 cm, where larger stones and other impurities are retained. The oversize is rejected and dumped into the river (Waste1, Figs. 2 and 3). The selected material flows over sluice boxes covered with carpets (Carpets1, Figs. 2 and 3). The sluice boxes are slightly inclined (about 20 ). Finer Au is trapped in the carpet fibers by sedimentation, together with sands and other impurities (Fig. 4B). The engine is stopped for 1 h every 20, when the carpets are quickly removed, rolled and replaced with dry ones. The carpets from the sluice boxes are then washed intensely in a tank with running water, so that the fine particles detach from the carpet fibers and flow into a tank. After this phase, fine particles flow onto another smaller sluice box, covered with new carpets (Carpets2, Figs. 2 and 3) which concentrate the heavier fraction and reduce the amount of sand (Fig. 4C, Figs. 2 and 3). The washing operation is repeated with Carpets2 and the obtained concentrate is collected for the amalgamation process. The coarser material is rejected and dumped into the river (Waste2, Figs. 2 and 3). Amalgamation of Au from the gravity concentrates employs metallic Hg which is introduced into a cement mixer for no longer than 60 min (Fig. 4D). The amount of Hgin introduced in
Fig. 1. One of the dredges observed during the research.
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Fig. 2. Flowchart of the Au recovery process.
the amalgamation barrel (cement mixer) is arbitrarily determined by the worker in charge of the amalgamation process. The worker in charge determines the required quantity according to the suspected Au grade detected by observation when the carpets are washed: the higher the amount of Au observed in the carpets, the higher the amount of Hg added into the mixer. No measurement is performed during this phase. This mixing process eventually
pulverizes the Hg, forming droplets that are lost with tailings that squez-Lo pez et al. (2010) report that the return to the river. Vela amalgamation of concentrates using barrels or mixers loses around 1.4% of the Hg introduced in the process, whereas 30% of Hg is lost when the whole ore is amalgamated in small ball mills. The amalgam is separated from the rest of the heavy minerals by panning in a bucket and the worker removes the ferrous fraction
Fig. 3. Scheme of the flow of the ore aboard a dredge, from excavation to waste.
M. Balzino et al. / Journal of Cleaner Production 102 (2015) 370e377
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Fig. 4. A e Arm and cutting drum, B e Grid and Carpets1, C e Open tank and Carpets2, D e Cement mixer, E e Retort, F e Final Au.
with a magnet. After squeezing off the excess Hg, the amalgam, usually containing 60% Au and 40% Hg, is decomposed by burning in a furnace with a retort which retains up to 95% of the evaporated Hg (Fig. 4E). This process has been described in detail in dedicated works (Veiga et al., 2013; UNEP, 2008). The impure Au, called dor e, is melted in open air with a propane torch, obtaining Au with a residual 4% of Hg and other impurities (Fig. 4F), according to the cooperative COOGARIMA (Cooperativa de Garimpeiros do Rio Madeira, cooperative of artisanal miners of the Rio Madeira, located ^ nia). in Porto Velho, Rondo
made it impossible to determine precisely the first Au-mass balance parameters. It was possible, however, to sample and determine the Au grade of Waste 1 and 2. Samples of the rejected material were collected, separated from the liquid component, homogenized and quartered up to obtain the sample to analyze by fire assay. The sampling procedure was accomplished on six dredges for eight recovery processes. 4. Methodology to assess the role of Hg 4.1. System boundaries and Hg-balance equation
3. Methodology to assess the Au losses 3.1. System boundaries and Au-balance equation In order to analyze the Au recovery process, an Au-mass balance was developed to assess the amount of Au that enters and exits the system, from the excavation phase to the final produced Au. The mass balance equation of the process is as follows:
Auin Aulost1 Aulost2 ¼ Auproduced
(1)
where: Auin is the Au introduced in the system, Aulost1 is the Au lost in grids from Waste1, Aulost2 is the Au lost in the rejected material from Waste2, Auproduced is the final Au produced. To assess the parameters of the Au-mass balance, a preliminary analysis was required to quantify the solid fraction of the jets entering the system and leaving it in Waste 1 and 2. This is done with Equation (2).
Auin ¼ F*t*GAu
(2)
where: F is the flow of the solid fraction [t/h], t is the time of the process [t] and GAu is the Au grade[g/t]. 3.2. Sampling conditions Difficulties in assessing the flow rate of the solid fraction (due to the lack of safe conditions during sampling from the main pipe)
The Hg-mass balance was performed to determine the losses of Hg in the Au recovery process. This balance assesses the Hg introduced into the amalgamation system and the portion recovered at the end of the process. Based on the analysis of the incoming and outgoing masses, the mass balance equation of the amalgamation process was developed (3).
Hgin ¼ Hgriver þ Hgevaporated þ Hgrecovered þ Hggold
(3)
where: Hgin is the Hg introduced in the system, Hgriver is the Hg in transference with the river (either recovered or introduced), Hgevaporated is the Hg evaporated in the whole process, Hgrecovered is the Hg recovered during the process, Hggold is Hg trapped with Au in the produced impure gold. The sign of Hgriver determines whether the Hg is recovered from or introduced into the river: if Hgriver > 0 then Hgriver ¼ Hglost, that is Hg released to the river; if Hgriver < 0 then Hgriver ¼ Hggained that is Hg recovered from the river. The variable Hgevaporated can be broken down to its components: it is the sum of the Hg evaporated due to the losses in the furnace (Hgev1), and the Hg evaporated during the burning with a blowtorch (Hgev2). Also the variable Hgrecovered can be broken down to its components: it is the sum of the surplus of Hg squeezed from the piece of fabric (Hgsqueezed) and the Hg recovered from the retort (Hgretort).
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M. Balzino et al. / Journal of Cleaner Production 102 (2015) 370e377 Table 1 Methods for measuring Hg emissions. Evaluation
Procedure
Hg entering the system (Hgin) Hg squeezed off from the amalgam (Hgsqueezed) Weight of the amalgam (Wamalgam) Hg recovered with the retort (Hgretort) Weight of the gold (WAu)
Hg was weighed before being introduced into the amalgamation process. Hg was weighed after squeezing the amalgam. Amalgam was weighed before burning to eliminate the Hg. Hg was collected in the retort and weighed after burning. Au was weighed after burning with propane torch.
Table 2 Formulas for measuring Hg emissions. Evaluation
Procedure
Hg evaporated during the burning phases (Hgevaporated) Hgevaporated ¼ Wamalgam ½g Hgretort ½g WAu ½g
(4)
Hgrecovered ½g ¼ HgSqueezed ½g þ Hgretort ½g
(5)
Hgriver < 0/Hgriver ¼ Hggained
(6)
4% of Wgold
(7)
Recovery of Hg ¼ Hgrecovered=Hgin
(8)
Hg recovered during the amalgamation process (Hgrecovered)
Hg recovered from the river (Hggained) a
Hg impurities in the gold (Hggold)
Percentage of Hg recovered with respect to that introduced (Recovery of Hg)
a
From interviews with the members of the COOGARIMA cooperative.
4.2. Materials and methods The approach used to quantify the involved Hg wasted was to weigh it with precision balances before and after each unit operation involved in the amalgamation process. The procedure was followed at six dredges during eight amalgamation processes by weighing the Hg introduced into the system (Hgin), the Hg squeezed (Hgsqueezed), the amalgam before and after the furnace, the Hg recovered by the retort (Hgretort) and the Au produced. The procedure is described in Table 1. It was integrated based on interviews with the miners and the operators of COOGARIMA for the correct interpretation of the process phases. Inverse equations were obtained to calculate the missing parameters based on the Hg-mass balance equation. These equations are shown in Table 2. 5. Results and discussion
According to The Global Au Mine & Deposit ranking (Natural Resource Holdings, 2013), the average grade of all producing mines in the world was 1.01 g/t in 2013. This means that the garimpeiros are rejecting material with an Au grade comparable to that of industrial Au mines around the world. This consideration highlights the inefficiency of the Au recovery process aboard these dredges. 5.2. More Hg recovered than released into the environment In reference to previous studies, it was expected to get high levels of Hg released into the environment (Shandro et al., 2009; Spiegel and Veiga, 2010; Veiga, 1997a,b, 2009; Veiga et al., 2006; squez-Lo pez et al., 2010). Negative values of Hgriver represent Vela Hg recovered from the river (Hggained) and not released into it, resulting in a recovery of Hg greater than 100%. These results prove that, during each Au recovery process, a considerable amount of Hg is recovered from the environment as well (27.8%). Even if some Hg
5.1. Au losses The average Au grades of the rejected material, Waste1 and 2, are shown in Table 3. The highest Au concentrations occurred in Waste1due to a probable lack of liberation of Au particles trapped in coarser sediments. The carpets technique shows better efficiency on the finer material, resulting in lower losses of Au.
Table 3 Au grade in the rejected material.
P1 P2 P3 P4 P5 P6
Au grade Waste1 [ppm]
Au grade Waste2 [ppm]
0.15 0.27 7.83 0.88 2.68 1.68
0.49 0.08 0.10 1.17 0.41 0.07
Fig. 5. Hggained and Hgevaporated.
M. Balzino et al. / Journal of Cleaner Production 102 (2015) 370e377 Table 4 Average Hg distribution in amalgamation processes.
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Table 5 Percentage of Hg dispersed in the atmosphere.
Hg distribution
Material
Estimation method
Hgin [g] Hgsqueezed [g] Wamalgam [g] Hgretort[g] WAu [g] Hggold [g] Hgevaporated Hgrecovered[g] Hgriver[g] Hggained[g] Recovery Hg
382.6 ± 187.1 322.6 ± 140.6 249.6 ± 113.0 150.8 ± 68.8 101.3 ± 44.3 4.8 ± 1.8 52.9 ± 5.7 540.1 ± 153.5 118 ± 71.4 118.8 ± 71.4 120%
Weighing Weighing Weighing Weighing Weighing Eq. (7) Eq. (4) Eq. (5) Eq. (3) Eq. (6) Eq. (8)
Amalgamation process
% Hgevaporated compared with the initial Hg
A1 A2 A3 A4 A5 A6 A7 A8
2.3 2.8 1.8 27.3 3.1 1.3 1.6 1.8
Note: Arithmetic mean ± standard deviation, n ¼ 7.
result from 1988 shows that the emissions of Hg have dramatically decreased in the last 26 years.
is released during the process in the form of vapors (Hgevaporated ¼ 1.9e3.6%), the total balance shows that the operation is actually capturing more Hg that is already present in the river. This result is contrary to the common perception of a polluting AGM. Looking at the recovery processes as a whole, it “cleans up” more than it pollutes, and AGM should be seen as a potential stakeholder in the process of rehabilitation of the area by reclaiming the bottom of the river. Comparing the values of Hggained and Hgevaporated (Fig. 5), it is shown that sometimes the proportion between them can be ten times as high. The results obtained are reported in Table 4. The relation between Hgin and Hgrecovered (Fig. 6) was analyzed in order to confirm these results. The amount of Hg recovered during the amalgamation process is systematically higher than the amount introduced at the beginning. The excess in recovery is indeed Hg coming from the bottom of the river.
5.4. Hg losses
5.3. HgeAu ratio The relationship between the Hg and Au produced was calculated in order to compare the proportion of Hg released into the environment (that in this study is equivalent to Hgevaporated) in relation to the amount of Au produced during the whole amalgamation process (Lacerda, 2003a,b). This value is called the emission factor (EF) or Hg:Au ratio and is quite variable, depending on the site, techniques and devices used (Lacerda and Pfeiffer, 1992). EF usually ranges from 1 to 5, and in particular in between 1 and 1.5 in the Amazon (Lacerda, 2003a,b). Pfeiffer and Lacerda (1988) found a mean EF of 1.3 in mining sites located in the Madeira River. The average EF measured during this study ranges from 0.1 to 0.2. The reduction of 78.5% with respect to the previous
Despite these results, the analyzed Au recovery processes are really far from the concept of a clean production. It still exists a release of Hg in the environment in the form of vapors that are dangerous for the workers. This source of pollution is represented by the Hgevaporated as the sum of Hg losses from the furnace and the Hg dispersed during the burning phase in open air with the propane torch. The second constituent is often the main cause, but in some processes the employment of handmade and overused retorts can cause a high level of Hg to be released from the furnace with the retort. This problem is more evident in some cases where the level of Hg evaporated is higher than the average. This is the case of amalgamation process 4, which is excluded from the statistical analysis because it is an outlier (A4 in Table 5) caused by process deviations. During the field work it was noticed that the furnace employed was outdated, dilapidated and in its proximity there was a strong odor. The retorting efficiency depends on the type of connections or clamps used (UNEP, 2008) and in that case were of a low quality. Well-made retorts, like the majority of the analyzed cases, if properly used, can collect and recycle a high amount of Hg used during the process (Maponga and Ngorima, 2003; Jønsson et al., 2013). This occurrence suggests that inappropriate devices result in reduced recovery efficiency and therefore higher losses. 5.5. The Hg in the river Madeira River is one of the rivers most contaminated by Hg in the Amazon basin (Silveira et al., 1998). The amount of Hg is linked mainly to the mining activities and reached its highest values during the years of the maximum Au production (the 1980s, Bastos and Lacerda, 2004). High levels of Hg, according to Lechler et al. (2000), can also be attributed to natural sources. However, determining the origin of Hg in the river goes beyond the aim of this paper. The scope of this work was to evaluate the exchange of Hg that mining activities have with the environment. The values of Hggained could then be correlated with thigh deposited at the bottom of Madeira River that it is dredged during the excavation phase and enters the Au recovery process. Hg has a high specific weight and during the sorting phase is captured by the carpets until reaching the amalgamation process. Indeed, observing the sediments coming from the bottom of the river, the presence of Hg was always visible to the naked eye (Fig. 7). 6. Conclusions
Fig. 6. Hgin and Hgrecovered.
In this paper it is shown that AGM is still an important source of income in the Madeira River. An inefficient Au recovery method
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Brazil), FAPESP (Foundation for Support to the Research of the State ~o Paulo, Brazil) and CNPq (National Council for Technological of Sa and Scientific Development, Brazil) for their support of the research effort. References
Fig. 7. Hg in a sample collected from the bottom of the river.
seems to be the cause of Au losses during the sorting phases. The high Au grade in Waste1 (2.3 ppm) demonstrates that the coarser material contains fine unliberated particles of Au. Moreover, the Au grade of average industrial mines in the world is comparable to that rejected during the recovery process. The profits of the operation as a whole, and therefore its economical sustainability, are strongly compromised by its lack of efficiency. Focusing on the amalgamation process, it was observed that the current AGM activity in the Madeira River, albeit continuing to employ Hg for amalgam, shows signs of awareness, as retorts appear to be widespread and commonly employed, helping to mitigate the environmental emissions. The rate of Hg released is far lower than the amount involved in the past (with a decrease of 78.5%) (Pfeiffer and Lacerda, 1988). The mass balance allowed to demonstrate that each process recovers a large amount of Hg from the river. In the eight processes analyzed, a total 3.6 kg of Hg were introduced during the amalgamation and 4.7 kg of Hg were collected at the end of the processes and only 0.4 kg were lost into the atmosphere as vapors, with an emission factor (Hg:Au ratio) from 0.1 to 0.2. These results show that, for the analyzed cases, 131% of Hg was recovered with respect to the amount introduced. This is a positive environmental role played by the AGM operation, and at the same time shows that a large amount of Hg is deposited on the river bottom. Despite this improvement, the activity of garimpeiros cannot be defined as clean production as it continues to use Hg and is dangerous for the environment and humans. Measures to eliminate the practice of whole ore amalgamation should be encouraged through the introduction of more efficient and Hg-free technologies, as described in Veiga (2009), and implement local training programs, as described in Sousa and Veiga (2009) and Veiga et al. (2015). At the same time, a reclamation plan of the bottom of Madeira River should be integrated with this program, in order take advantage of the ongoing AGM operations to help rehabilitate the entire area. Acknowledgments Many thanks go to the COOGARIMA for their help during field ~o (Research work. A special acknowledgment goes to NAP.Mineraça ~o Paulo, Center for Responsible Mining of the University of Sa
~es nas concenAlmeida, M., Lacerda, L.D., Saldanha, G., Bastos, W., 2009. Variaço ~es de mercúrio em solos da reserva garimpeira do alto Rio Madeira. traço Geochim. Bras. 23 (1), 139e150. ^ncia ambiental do mercúrio e sua presenca em populaco ~ es Bastos, W., 2004. Ocorre ^nia. ribeirinhas do baixo Rio Madeira- Amazo Bastos, W.R., Gomes, J.P.O., Oliveira, R.C., Almeida, R., Nascimento, E.L., Bernardi, Lacerda, L.D., Silveirs, E.G., Pfeiffer, W.C., 2006. Mercury in the environment and riverside population in the Madeira River basin, Amazon, Brazil. Sci. Total Environ. 334e351. Bastos, W., Lacerda, L., 2004. A contaminacao por mercurio na bacia do Rio Madeira: uma breve revicao. Bastos, W., Rebelo, M., Fonseca, M., Almeida, R., Olaf Malm, O., 2008. A description of mercury in fishes from the Madeira River basin, Amazon, Brazil. Acta Amaz. 38 (3). Cremers, L., Kolen, J., De Theije, M., 2013. Small-scale Gold Mining in the Amazon the Cases of Bolivia, Brazil, Colombia, Peru and Suriname. CEDLA, Amsterdam. Diaz, Elmer, 2000. Mercury pollution at gold mining sites in the Amazon environment. Principles of Environment Toxicology. EHP, 2014. Mercury exposure and health impacts among individuals in the artisanal and small-scale gold mining community: a comprehensive review. Environ. Health Perspect. Hacon, S., Barrocas, P.R., Vasconcellos, A.C.S.D., Barcellos, C., Wasserman, J.C., Campos, R.C., Ribeiro, C., Azevedo-Carloni, F.B., Jul. 2008. An overview of mercury contamination research in the Amazon basin with an emphasis on Brazil. Cad. Saúde Pública 24 (7). Rio de Janeiro. http://www.scielosp.org/scielo.php? pid¼S0102-311X2008000700003&script¼sci_arttext. Hentschel, Hruschka, Priester, 2003. Artisanal and Small-scale Mining: Challenges and Opportunities. IIED, WBCSD. Hester, R., Harrison, R., 1994. Mining and its Environmental Impact. Royal Society of Chemistry. Hinton, J., Veiga, M., Veiga, A., 2003. Clean artisanal gold mining: a utopian approach? J. Clean. Prod. 11 (2), 99e115. Holdings, N. R, 2013. Global Gold Mine and Deposit Ranking. Jønsson, J., Charles, E., Kalvig, P., 2013. Toxic mercury versus appropriate technology: artisanal gold miners. Resour. Policy 60e67. Lacerda, L.D., 2003a. Updating global Hg emissions from small-scale gold mining and assessing its environmental impacts. Environ. Geol. 3, 308e314. Lacerda, L., 2003b. Updating global Hg emissions from small-scale gold mining and assessing its environmental impacts. Environ. Geol. 308e314. Lacerda, L., Pfeiffer, W., 1992. Mercury from gold mining in the amazon environment-An overview. Quìmica nova 15 (2), 155e160. Lechler, Mille, Lacerda, Vinson, Bonz, 2000. Elevated mercury concentrations in soils, sediments, water, and fish of the Madeira River basin, Brazilian Amazon: a function of natural enrichments? Sci. Total Environ. Linhares, D., da Silva, J., Lima, T. d., Almeida, R., B, W.R., 2009. Mercúrio em differ^ nia ocidental. entes tipos de solos marginais do baixo Rio Madeira-Amazo Geochim. Bras. 117e130. Maponga, O., Ngorima, C.F., 2003. Overcoming environmental problems in the gold panning sector. J. Clean. Prod. 147e157. Mylchreest, P., 2007. Gold War. Pfeiffer, W., Lacerda, L., 1988. Mercury inputs into the Amazon region. Brazil. Environ. Technol. Lett. 9, 325e330. Seccatore, J., M, T., De Tomi, G., Veiga, M., 2013. A practical approach for the management of resources and reserve in small-scale mining. J. Clean. Prod. 1e6. Seccatore, J., Veiga, M., Origliasso, C., Marin, T., De Tomi, G., 2014. An estimation of the artisanal small-scale production of gold in the world. Sci. Total Environ. Shandro, J., Veiga, M., Chouinard, R., 2009. Reducing mercury pollution from artisanal gold mining in Munhena, Mozambique. J. Clean. Prod. 17 (5), 525e532. Silveira, E.G., Salvioni Gali, P.A., Barbosa, R.V., Braga, I.C., 1998. O mercúrio nos garimpos de ouro do Rio Madeira/RO. Rev. Educ. Cult. meio ambiente. Sousa, R.N., Veiga, M.M., 2009. Using performance indicators to evaluate an environmental education program in artisanal gold mining communities in the brazilian amazon. AMBIO: A J. Hum. Environ. 38 (1), 40e46. Spiegel, S., Veiga, M., 2010. International guidelines on mercury management in small-scale gold mining. J. Clean. Prod. 18 (4), 375e385. UNDP, United Nations Development, 2011. Small-scale gold mining in the transboundary areas of Brazil, Suriname and French Guiana. Social and Environmental Issues. UNEP, 2008. Module 3 Mercury Use in Artisanal and Small Scale Gold Mining. UNEP, 2013. Global Mercury Assessment 2013. Available at: http://www.unep.org/ PDF/PressReleases/GlobalMercuryAssessment2013.pdf. Last visit on 27/04/ 2015. Veiga, M.M., 1997a. Introducing New Technologies for Abatement of Global Mercury Pollution in Latin America. UNIDO/UBC/CETEM/CNP. Veiga, M.M., Hinton, J.J., 2002. Abandoned artisanal gold mines in the brazilian amazon: a legacy of mercury pollution. Nat. Resour. Forum 13e24.
M. Balzino et al. / Journal of Cleaner Production 102 (2015) 370e377 Veiga, M., 1997b. Mercury in Artisanal Gold Mining in Latin America: Facts, Fantasies and Solutions. UNIDO. Veiga, M.N., 2009. Mill leaching: a viable substitute for mercury amalgamation in the artisanal gold mining sector? J. Clean. Prod. 17 (15), 13. Veiga, M.M., Angeloci, G., Niquen, W., Seccatore, J., 2015. Reducing mercury pollution by training Peruvian artisanal gold miners. J. Clean. Prod. 94, 268e277.
377
Veiga, M., A, G., Hitch, M., Velasquez-Lopez, P., 2013. Processing centres in artisanal gold mining. J. Clean. Prod. 1e10. Veiga, M., Maxson, P.A., H, L.D., 2006. Origin and consumption of mercury in smallscale gold mining. J. Clean. Prod. 14 (3e4), 436e447. squez-Lo pez, P.C., Veiga, M., Hall, K., 2010. Mercury balance in amalgamation in Vela artisanal and small-scale gold mining: identifying strategies for reducing environmental pollution in Portovelo-Zaruma, Ecuador. J. Clean. Prod. 226e232.