Mineral Extraction in the Amazon and the Environment - ACS

Chapter 22

Mineral Extraction in the Amazon and the Environment

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The Mercury Problem Roberto C. Villas Bôas Centra de Tecnologia Mineral, Rua 4, Quadra D, Cidade Universitária, Ilha do Fundão, CEP 21941-590 Rio de Janeiro, RJ, Brazil

Materials play a fundamental role in developing a nation. How significant such a role will be depends the overall economy, as expressed by its own domestic industrial production and innovation capacity, its consumer demands, and, last but not least, its worldwide bargaining power. In Brazil, particularly in the Amazon region, which accounts for the larger part of its territory, natural resources are an asset for providing the material bases for development. However, what are the environmental problems posed in developing mineral resources, specifically gold, and what is known of these ? This paper presents a summary of some of these problems, with emphasis on mercury pollution.

There are several the stages in a product life cycle and the way in which it interacts with the environment. From the extraction stage, the materials are processed, manufactured, utilized and wasted, being, in a greater or lesser fashion, reused, manufactured and recycled. Such an interaction with the environment is inherent to the production processes due to the very fact that they require inputsfromthe surroundings (energy, ores, fuel, etc.) as well as, like the Maxwell demon, their very presence interferes with the surroundings (7). In this work attention is given to the mining stage, identified as extraction, as it relates to the Amazonian region. The main ore products extracted and commercialized in the Brazilian Amazon are iron ore, bauxite, alluvial gold, tin, kaolin and, to a lesser degree, manganese. Large kaolin project expansions are underway in the Rio Capim area (2). The mineral potential in the Amazon region, however, seems to be much larger and has been reported in the literature (5-5). Figure 1 shows the mineral resources of the Brazilian Amazon.

0097-6156/95/0588-0295$12.00/0 © 1995 American Chemical Society In Chemistry of the Amazon; Seidl, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

In Chemistry of the Amazon; Seidl, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

Figure 1. Mineral Resources of the Brazilian Amazon.


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Environmental Impacts A comprehensive study, under the Mining and Environmental Research Network, coordinated by the SPRU group at the University of Sussex, in England, and involving several organizations in Europe, United States, Africa, Asia and South America, dealing with the Brazilian aspects of mining/metallurgy and the environment was recently published (6). Of the interest to the Amazonie aspects of the discussion are the remarks on the Albras/Alunorte projects that resulted from an association of the Companhia Vale do Rio Doce (CVRD), a large mining concern that belongs to the Federal Government, with the Japanese, and the Alumar project of Alcoa in association with Shell/Billiton, dealing with the environmental concerns that were incorporated into the process design of the production stages. In this same study, coordinated in Brazil by the ΝΑΜΑ group at the University of the São Paulo, a review of the environmental aspects of tin extraction, largely represented by the Paranapanema group is given, as well as that of gold extraction in "garimpos" and mining companies. The iron ore project of CVRD, located in Carajãs has been, subjected to an overall analysis of its environmental sustainability as well. Very interesting experiences were registered (7). A summary of some of the aspects linked to the production of the aforementioned commodities and the effects on the environment, is given in Table I.

Table L Major Environmental Impacts of Selected Commodities of Interest to the Brazilian Amazon. Au Al Fe Sn Waste water; solid Red mud, HF, C 0 ; Waste water; solid Waste waters; Tar pitch; volatiles; wastes; heavy heavy metals; C 0 ; wastes; cyanide; mercury; spent pot linings; metals; C 0 ; earth rivers and earth particulate matter; cyanide; earth moving; moving; rivers & earth movements; reclamation; reclamation; reclamation; particulate matter. moving; dusts. reclamation. dusts. 2

2

2

Sustainable exploitation methods are being sought, in a effort to introduce agrobusiness into the Amazonian rainforest area. However, timber productivity is low, 2-3 m per year (8). The reasons for such a low productivity are the heavy leaching of nutrientsfromthe soil and the fast decay of organic matter that follows. The soils of the Amazon are very poor in nutrients and lime is absent, showing a very low cation exchange capacity and high aluminium toxicity, so agriculture does not seem very appropriate. Mining is a prospect for the sustainable development of the Amazon notwithstanding. Hoppe (9) has compared the total area of the Brazilian Amazon 3



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to that necessary to develop 350 mineral ore bodies and shown that they would require less than 0,1% of the total area! Recently, Stigliani (70) advanced the concept of a "chemical time bomb", i.e., a waste deposit that does not offer any immediate danger, but which can eventually have disastrous environmental effects as geochemical conditions change. The effects of these time bombs are non-linear and delayed (e.g., toxic metals can "break through" once the specific buffering capacity of a sediment or soil system has been surpassed (7)). Consequently, these sites require "proactive assessment and management", as in the words of Fôrstner (77). Salomons and Lacerda applied this concept to the Amazon (72). The "Index of the Relative Pollution Potential", as defined by Fôrstner and Muller (73), or "Technophility Index", as proposed by Nikiforova and Smirnova (14), may be used since the ratio of the annual mining activity to the mean concentration in the earth's crust, suggests that the highest degree of changes of the geochemical budget by man's activities, has occurred for metals such as Cd, Pb, and Hg (values in 5 χ 10 ) 7

Mn = Fe < Ni < Cr < Zn < Cu = Ag < Hg = Pb < Au < Cd 1 1 2 4 10 20 20 30 30 60 140 This index does not imply in a constante value, changing in time reflecting the "societal demand" for that particular metal, or group of metals. In this respect, for instance, up to the end of the century, according to Nikiforova and Smirnova (14), the TP of mercury will increase 3 times, while that of lead by 4.5 times. What About Mercury ? In gold processing of alluvial ores in rainforest areas (15-19) mercury is widely utilized as a gold amalgam. Its utilization is not just a question of legislation, law enforcement and social pressures exerted upon the utilizers (20); it is a question of survival for the "garimpeiros"! On the other hand, the environmental problems that may originatefromthe presence of mercury in the environment, being it through liquid, ionic form or vapor, are all well documented in the literature (21-23). However no alternative route to Hg amalgamation is in effect, and processes like cyanidization (a problem in itself), oil or wax agglomeration, halide extraction, etc. neither compete economically nor are suitable for the kind of operation usually employed in such tropical areas (24). Fergusson (25) listed some of the alkyl derivatives of the heavy metals relevant to the environmental chemistry. Environmental interest in the compounds lies in their toxicity and the fact that methylation occurs for many of the heavy metal elements. Methylation represents the transfer of a methyl group from one compound to another, the process occurring biologically or abiotically. Bacteria and fungi so


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far reported to methylate Hg, As, Se, Te, Pb, Cd, TI and In, are usually aerobic (except Clostridium sp and methanobacterium which are anaerobic). There is good evidence for the biomethylation of mercury, arsenic, selenium and tellurium; however there are doubts regarding that of the other heavy metals. The evidence of human poisoning led to the disclosure of environmental methylation: arsenic (nineteenth century); mercury (in the fifties: Minamata). In the sixties it was revealed that the main form of mercury in Minamata Bayfisheswas CH Hg +

3

3

In 1964 the cobalt complex ion [CH Co(CN)5] ' (model for vitamin B ) was shown to methylate mercury. In 1968 Wood suggested that the methylating agent associated with methane-producing bacteria was methylcobalamin, i.e. the methyl derivative of vitamin B where the CN" group is replaced by CH " (26). Methylation by non-enzymatic MeCoB may be treated as abiotic, except that the reagent itself is produced biotically and may be re-methylated biotically. The two main abiotic methylation processes are transmethylation, and to a lesser extent photochemical. Several features of the chemistry of mercury facilitate its existence in organo-species. Both Hg " * and C H H g are soft acids and bond well to soft bases such as S " and SH". The cation is large and polarizable, and because of the dipositive charge, is itself a good polarizing cation and tends to form covalent bonds. The Hg-C bond (around 60-120 kJ/mole), though not that thermodynamically strong, is stronger than Hg-0 bonds, therefore persisting in the environment. It is also non-polar. Turning to the bacteria associated with methylation of mercury, they are located in the bottom sediments ofrivers,estuaries and the oceans, in intestines and feces, in soils and yeast. Several factors influence the formation of CH Hg , including temperature, mercury and bacteria concentrations, pH, type of soil, type of sediment, the sulphide concentration, and, of course, redox conditions. Seasonal variations in methylation in estuarine sediments, relate to bacterial activity, which may also apply to organic sediments, compared to sandy sediments. Methylation of Hg occurs in both aerobic and anaerobic conditions, though the latter are the best; maximum methylation occurring in the Eh range +0,1 to -0,2V; the pH has a very significant effect as C H H g is more stable in neutral to acid conditions and (CH ) Hg in basic. The binuclear species (CH Hg) OH seems to be of minor importance. The influence of sulphide ion depends on the redox conditions: if anaerobic HgS (low solubility) will remove much of the Hg avoiding it from being methylated; if aerobic, the S " ion may be oxidized to SO4" thusfreeingHg ion for methylation. The rate of production of C H H g depends on the exposed conditions and the reaction matrix, being generally greater in saline than fresh water.


3

12

1 2

3

12

2 1

+

3

2

+

3

+

3

3

2

3

2

+

3


2

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Methylmercury accounts for circa 0,1 to 1,5% of the total mercury in sediments, and around 2% of the total in sea water, but infishit accounts for over 80% of total mercury. It is not clear, however, if the C H H g is taken in by the fish from sea water or formed within the fish. Evidence suggests the former, though in rotting fish (CH ) Hg is formed. The changing chemistry of mercury, as pointed out by Renuka (27) is always a point of concern among those who study mercury. Recently, the electroxidation method for removal of mercury was utilized to remove itfrom"garimpo tailings, the chemistry of the process being: +

3

3

2


H

+

2

2NaOCl + Hg° + 4HC1 -» 2Na + HgCl" + 2 H 0 + C l 2

2

the mercury being precipitated as stable tetrachloride (28). And the Particulates ? Besides mercury, the release of particulate material coming from earth-moving operations also contributes to the deleterious effects on the biota. Physical impacts on the environment coming from mining activities are related to the release of particulates intorivers,lakes, oceans and the air. For the purpose of this article, particulate emissions in the region are related to dusts corning from the mining of bauxite, iron ore, manganese, and sediments coming from gold and tin extraction. These interact with the environment and may alter the biota. Little is known for the Brazilian Amazon in this regard, and not much research has been published, particularly for mercury (29). From the little that is known, mercury seems to be associated to thefinesof the sediments, the "sands" being poorer in mercury than the "fines", due to the presence of iron-aluminate-hydroxides. The partitioning of the contaminants may be determined via partition coefficients (Kd's) between the several compartments of interest, i.e. water, sediment, particulate matter and biota. As shown by Duursma (30) such partition coefficients might furnish useful empirical data in determining the percent distribution between dissolved and particulate matter, accumulation in organism, etc. A very interesting, and intriguing fact, along with the chemical-time bomb idea, is that a newly contaminated tropical estuary might be a sink for a long period, afterwards becoming a source as equilibrium is attained faster than in temperature climates, as discussed by Duursma (30). A very extensive program, called CAMGA-TAPAJOS, monitoring the garimpo activities at the Rio Tapajos area, is being conducted by the Government of the State of Para (37). Table Π, extracted from a report on this program, gives the relationship between the extraction and concentration techniques employed in the area and the impacts caused on the environment.



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Table Π. Environmental Impacts Derived from Extraction and Concentration Techniques for Gold Recovery in Rio Tapajos, as Related to Particulate Matter Physical Causes and/or Biological Anthropic Chemical damaging fishing erosion/increasing Ε C Χ Ο suspended load activities changes in color, changes in Τ Ν turbidity and ecological R C A E other organoleptic habitats C N water properties increase in water T T treatment costs I R silting-out and changes in river losses of natural O A Ν T courses resources water pollution changes in I O (soaps and oils) ecological endemic diseases N habitats losses of natural resources

Literature Cited 1. 2. 3.

4. 5.

6.

7.

8.

Eyring,G. Miner. Today; U.S.B.M., Apr. 1993; pp 24-30. Luz, A. B.; Damasceno,E. C. Caulim: um Mineral Importante; Série Tecnologia Mineral, no. 65; CETEM: Rio de Janeiro, RJ, 1993; 32 pp. Fernandes, F. R. C.; Portela, I. C. Recursos Minerais da Amazónia -Alguns Dados Sobre Situação e Perspectivas; Série Estudos e Documentos, no. 14; CETEM: Rio de Janeiro, RJ, 1991; pp 1-44. Costa,M. L. Potencial Metalogenético dos Minérios da Amazônia; Monografia UFPA, 1991; 44 pp. Amaral Jr.,A.; Capocchi, R. In: Iron & Steel International Conference Proceedings; A.B.M., Brazilian Metals and Material Association, S. Paulo, SP, 1990; pp 551-580. Rattner, H.; Acero, L.; Rodrigues, T.; Hanai, M.; Barreto, M.L.; Coelho Neto, J.S. Impactos Ambientais: Mineração e Metalurgia; MERN/SPRU/NAMA/USP/CETEM, 1993; 281 pp. Dall'Orto, Jr., V. C. Abstract ofPapers, 1 International Symposium on Chemistry of the Amazon, Manaus, AM, Associação Brasileira de Quimica, 1993; 91 pp. Hoppe, A. Annaherung, Naturforsch. Ges 1990, pp 1-264. st


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CHEMISTRY OF THE AMAZON Hoppe, A. Nat. Resour. Forum 1992, 232-234. Stigliani,W. M. Chemical Time Bombs: Definition, Concepts, and Examples;E.R.16, CTB Basic Document;IIASA:Luxembourg, Austria, 1991; pp 1-23. Förstner, U. In Lectureship in AquaticSciences;National Water Research Institute: Canada, 1992; pp 1-42. Lacerda,L. D.; Salomons,W. Mercúrio na Amazónia: uma Bomba Relógio Quimica ? Série Tecnologia Ambiental, no. 3; CETEM: Rio de Janeiro, RJ, 1992; 78 pp. Forstner, U.; Muller, G. Heavy Metal Accumulation in River Sediments: a Response to Environmental Pollution; Geoforum 14; 1973; pp 53-61. Nikiforova,E. M.; Smirnova, R. J. In: Proceedings of the International Conference on Metals in the Environment, Toronto, 1975; pp 94-96. Priester,M.; Hentscher,T. Small-Scale Gold Mining, GATE/GTZ; 1992; pp 1-96. Souza,V. P.; Lins,F. A. F. Recuperação do Ouro por Amalgamação e Cianetação: Problemas Ambientais e Possíveis Altemativas; Série Tecnologia Mineral, no. 44, CETEM: Rio de Janeiro, 1989; 27 pp. Lins, F. A. F.; Cotta, J. C.; Luz, A. B.; Veiga, M. M.; Farid, L. H.; Gonçalves, M. M.; Santos, R. L. C.; Barreto, M. L.; Portela, I.C.M.H.M. Aspectos Diversos da Garimpagem de Ouro; Série Tecnologia Mineral, no. 54; CETEM: Rio de Janeiro, 1992; 97 pp. Veiga, M. M.; Fernandes, F. R. C.; Farid, L. H.; Machado, J. Ε. B.; Silva, A. O.; Lacerda, L. D.; Silva, A. P.; Silva, E. C.; Oliveira, E. F.; Silva, G. D.; Pádua,H. B.; Pedroso,L. R. M.; Ferreira,N. L. S.; Ozaki,S. K.; Marins, R. V.; Imbassahy, J. Α.; Pfeiffer, W. C.; Bastos, W. R.; Souza, V. P. Poconé: um Campo de Estudos do Impacto Ambiental do Garimpo; Série Tecnologia Ambiental, no. 1, CETEM: Rio de Janeiro, RJ, 1991; 113 pp. Farid, L. H.; Machado, J. Ε. B.; Gonzaga, M. P.; Pereira Filho, S. R.; Ferreira, A. E. F. C. N. S; Silva, G. D.; Tobar, C. R.; Cãmara, V.; Hacon, S. S.; Lima,D.; Silva, V.; Pedroso, L. R. M.; Silva, E. C.; Menezes, L. A. Diagnóstico Preliminar dos Impactos Ambientais Gerados por Garimpos de Ouro em Alta Floresta/MT: Estudo de Caso; (versão Português/Inglês), Série Tecnologia Ambiental, no. 2, CETEM: Rio de Janeiro, RJ, 1992; 190 pp. Barreto, M. L. Uma Abordagem Critica da Legislação Garimpeira: 19671989; Série Estudos e Documentos, no. 19, CETEM, Rio de Janeiro, RJ, 1993; 58 pp. D'Itri, F. M.. In: Sediments: Chemistry and Toxicity ofIn-Place Pollutants; Baudo, R.; Giesy, J. P.; Muntao, H., Eds.; Ann Arbor, Lewis, 1990; pp 163-214. Cãmara, V. M. Mercúrio em Areas de Garimpo de Ouro; Série Vigilãncia, no. 12; OPAS/OMS: Mèxico, 1993. Pecora, W. T. Mercury in the Environment; Geological Survey Professional Paper 713; Washington, 1970; pp 1-67.


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Cramer, S.W. Problems Facing the Philippines; Int. Min., July 1990; pp 29-31. Fergusson, J. E. The Heavy Elements: Chemistry, Environmental Impac and Health Effects; Pergamon: Oxford, 1990; 614 pp. Wood, J. M.; Rosen, C. G.; Kennedey, S. F. Nature 1968, 173-174. Rewuka, A. J. Chem. Educ. 1993, 70; 871-872. Souza, V. P. In Poconé:umCampo de Estudos do Impacto Ambiental do Garimpo; Série Tecnologia Ambiental, no. 1, CETEM: Rio de Janeiro, RJ, 1991; pp 95-113. Pessoa, A. Mercúrio em Itaituba; CETEM: Rio de Janeiro, RJ, 1994, (PT 009/94); 144pp. Duursma, Ε. K. The Tropical Estuaries Environmental Sinks or Sources?; Monography, France, 1994; 20 pp. Estudos dos Impactos Ambientais Decorrentes do Extrativismo Minera Poluição Mercurial do Tapajós; Monografia GEPA/SEICOM/PA, 1992; 24 pp.

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Mineral Extraction in the Amazon and the Environment - ACS

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