INTRODUCTION

This large mining/metallurgical industry is advancing to a cleaner production, but the problem is complex, so that, environmental challenges in both technology and management need to be faced.

The main environmental impact to air pollution is associated to copper concentrate smelters, due to SO₂ and volatile As emissions (Castro, 2001). However, the disposal of tailings, leaching residues, and other mine products are also serious problems (Castro, 1998). In the same line, disposal of wastewaters into superficial waters, such as rivers, lakes and coastal areas, may affect some fragile ecosystems, such as, flora and fauna associated to sources of water in the Altiplano at the Andes mountain area, and at the Pacific Ocean marine life.

The aim of this paper is to review the main environmental problems associated to the Chilean mining industry, particularly for copper, showing the main sources of pollution, environmental regulations, abatement technologies, chronology and agenda for SO₂ and As reductions from smelters, established in the Decontamination Plan; and some aspects about the maximum allowable pollutant concentrations in discharge of liquids residues to different kind of waters.

RESULTS AND DISCUSION

Traditionally, minerals products were most commonly produced in deposits near the main consuming regions. Today, relatively cheap transport allows the globalization of much production, except for ores and minerals that have a low value relative to the transport cost. Consequently, mining industry is moving towards countries with best resources and less rigorous environmental legislation. However, developed countries such as Australia and Canada, with large deposits of high grade ores, are still active in mineral production. But there has been a gradual migration of mineral production to many developing countries, largely due to the difficulties and longer lead times in getting environmental permits, and the higher labor costs for projects in the most industrialized countries, and because mineral deposits in these countries have in many cases been mined out (MMSD, 2002).

The cradle-to-grave cycle for minerals/metals typically involves a number of unit operations/activities, namely exploration, mine design and development, mineral separation followed by metal extraction through pyro- or hydro-metallurgical techniques. A wide variety of wastes (solid wastes, liquid effluents, and dust/gas emissions) are inevitably generated during each phase of this cycle. The details of major unit operations involved and the kind of wastes produced are illustrated in Figure 1.

Go to Figure 1 (The Cradle-to-Grave Cycle for Metals and Wastes Generated (see Pradip, 1998)

The Chilean case

It is clear that the most serious problem in the Chilean mining industry is produced by gaseous emissions from smelters. However, a number of other dangerous wastes are produced, such as, flotation tailings, sulfuric acid, acid wastewaters, acid mist, leached solid residues, etc. Figure 2 and Figure 3 show an schematic representation of the processes usually employed in Chile for the treatment of sulfide copper ores, and oxidized copper ores, respectively.

Go to Figure 2 ( Schematic illustration of the flotation-smelting-electrorefining conventional technology for copper sulfide ores in Chile.)

Go to Figure 3 ( Schematic illustration of the heap or vat leaching-solvent extraction-electrowinning technology for copper oxidized ores in Chile).

Table 1 shows the most important wastes and the usual abatement technology applied for these two technical routes in Chile (Castro, 2001).

Table 1. Type of wastes and abatement methods for the two most important technological routes employed in the Chilean Mining Industry.

Copper sulfide ores technology	Copper oxidized ores technology

Waste	Abatement	Waste	Abatement
Sterile and low grade ore	Disposal sites	Sterile ores	Disposal sites
Acid min drainage	SZ-EW plants; lime neutralization	Solid leached residues	Disposal sites
Flotation tailings	Tailing dam	Acid mist	Ventilation and use of surface active reagents
Wastewater from thickening and filtrating	Recycled water for processes	Acid wastewater	Lime neutralization
Smelting slags	Disposal sites	Reaffinate solutions	Recycled; neutralization
Sulfuric acid	Hydrometallurgical use	Lead sulphate sludges	Confinement
SO2 emission from smelters	Sulfuric acid plant	SX clarifier sludges	Disposal
Volatile As emissions from smelters	Electrostatic precipitation
As/Sb sludges	Confinement
Acid Wastewaters	precipitation with lime solar dry

The Environmental Legislation

The copper mining industry in Chile is moving toward cleaner production. Stricter regulations have been introduced forcing mining companies to abate their hazardous effluents. Table 2 and 3 show the norms that rules the sulfur dioxide and arsenic emissions from copper smelters.

Table 3 shows the environmental regulations by regions of the country, and the different copper smelters affected. The legal norms indicates only the capacity of the mining industry in terms of copper concentrate production.

On the other hand, Table 4 shows the norm for dissolved pollutants in wastewaters.

Go to Table 3 and 4

Environmental policy laws and the Decontamination Plan

The most significant legislative initiatives undertaken to date to facilitate environmental improvements in the Chilean mining sector has been the formation of CONAMA (Comisión Nacional del Medio Ambiente) in 1990, and the promulgation of the General Law on the Environment (Nº 19,300) in 1994 (Lagos, 1997). This Law, combined with additional regulatory norms, established certain key control mechanisms, such as the Evaluation of Environmental Impact ; and the Environmental Management Plan . CONAMA, together with the Ministries of Health, Agriculture, and Mining, and the community, have the responsibility of promoting sustainable development in the Chilean mining sector. Two other important legislative initiatives are: the non-definitive Norm 2280/year 1995, which regulates the discharge of liquid residues into superficial and underground water; the Decreto Ley 2867/year 1980, which forced industry to implement technical solutions to pollution problems.

It should be noted, however, that Chilean environmental legislation does not differentiate between large, medium and small-scale mining, although certain groups of regulations are only suitable for certain segments. For example, the regulation of SO2 and As emissions ( Decreto Supremo 185/year 1991) is clearly oriented toward the copper smelters of the large- and medium-scale mining sector. However, the norms for the contamination of superficial waters and a series of other environmental regulations are applicable to all sectors.

An agreement between the copper smelters and the environmental authority for abatement of SO₂ and As was denominated the decontamination plan, whose goal was the achievement of regulations for 1999 (Muñoz, 1996, Sanhueza, 1999). However, a re-formulation was needed, and new challenges were recently established for the period 2000 to 2003 and maximum levels of SO₂, arsenic and particulate matter were established in the full decontamination plan, for the five most important copper smelters in Chile (Castro, 2001).

Effluents, pollutants and abatement technologies.

The major environmental impacts for the different mining activities and the wastes associated directly to the mining extractive processes in Chile, were shown in Figures 1 and 4. Table 5 shows an effluent classification, type of pollutants and usual abatement technologies employed in the country (Castro, 1999). It is possibly to see that important efforts have been made in order to achieve results. However, it is necessary to introduce new technologies in order to ensure sustainability of this sector.

Go to Table 5

The most hazardous impurity is arsenic. Usually it occurs in copper deposits as enargite (Cu₃AsS₅). Volatile As in smelter gases emissions reaches the sulfuric acid plant. Hence, arsenical wastewater are produced in gas washing steps. Oxidation of arsenite ions to As(V) ions, and further precipitation with Fe(III) to form As-ferrhidrite is employed. Alternatively, precipitation of As(III) with lime to produce a calcium arsenite precipitate, which is oxidized by roasting around 700ºC to obtain calcium arsenate for disposal purposes, under environmentally stable conditions, is also applied.

On the other hand, arsenical powders are captured from smelter gases and frequently subjected to acid leaching for copper recovering. An arsenical residue is produced, which also contains Pb and Cd. Inertization is possible by co-precipitation with phosphate and lime to form a type of arsenic-phospho apatite. However, Pb exhibits stability problems under long time disposal conditions.

The most important abatement plants are the sulfuric acid plants, which treat gases from copper smelters. In 2000 the total sulfuric acid production in Chile reached to 3,600,000 metric tons (Bulletin of the Comisión Chilena del Cobre, 1999). This large amount of acid is currently used in hydrometallurgical projects. Estimations indicate than later on 2003 an excess of sulfuric acid could be produced.

CONCLUSIONS

Decontamination measurements have been implemented by all copper smelters, to treat gases originated from smelting-conversion operations, in order to accomplish the decontamination plan contemplated in the government s environmental policy. Specific norms to control SO₂ and volatile arsenic emissions have been applied. As a result, around 3.6 million metric tons of sulfuric acid have been produced from SO₂ abatement during year 2000. In the same line, the discharge of industrial wastewater into superficial water, i.e., rivers, lakes or coastal areas, is being controlled rigorously. However, a clean and efficient copper production requires new commitments and periodical update within a framework of sustainable development.

ACKNOWLEDGEMENTS

REFERENCES

CHILEAN MINING COMPENDIUM (Compendio de la Mineria Chilena), 2001, EDITEC Ltda., Santiago, Chile.

CASTRO, S.H., SÁNCHEZ, M. An Environmental View to the Chilean Copper Industry. New development in Mineral processing (G. Onal et al., Eds.) (IX Balkan Mineral Processing Congress. Istambul, 2001), pp.559-564,2001.

CASTRO, S.H., SÁNCHEZ, M.A., VERGARA, F., OYANEDER, E. Water and Slurry Wastes Assessment in the Chilean Copper Industry. In: Environment & Innovation in the Mining and Mineral Technology (M.A. Sánchez, F. Vergara, and S.H. Castro, Eds.), University of Concepción-Chile, pp.1005-1016, (1998).

MMSD - Mining, Minerals and Sustainable Development Project Draft Report, edited by the International Institute for Environment and Development, Chapter 1, March, 2002.

PRADIP, E. FORSSBERG, Stabilization and Utilization of solid Mining Waste in Effluent Treatment in the Mining Industry (S. Castro, F. Vergara, M. Sanchez, Eds), University of Concepcion, 1998.CONAMA (www.conama.cl), 2001.

LAGOS, G. Impactos Ambientales de la Minería en Chile. Minería Chilena- Ambiente y Desarrollo, pp.13-20, 1997.

MUÑOZ, G. Codelco-Chile´s Corporate Decontamination Plan for its Smelters. Clean Technology for the Mining Industry. (M.A. Sánchez, F. Vergara, and S.H. Castro, Eds.), University of Concepción-Chile, pp.53-64, (1996).

SANHUESA, J.A., ROJAS, O.C, BALOCCHI, A.E. Hernán Videla Lira Copper Smelter Fulfillment of Environmental Regulations. Proc. Fourth International Conference-Copper 99, Vol.II (B.A. Hancock and M.R.L. Pon, Eds.), Phoenix, Arizona, USA, pp.307-319, (1999).

CASTRO, S.H., SÁNCHEZ, M.A., VERGARA, F. Environmental Problems and Effluent Treatment in the Chilean Copper Industry. Proc. Fourth International Conference-Copper 99, Vol.II (B.A. Hancock and M.R.L. Pon, Eds.), Phoenix, Arizona, USA, pp.297-305, (1999).

BULLETIN OF THE COMISIÓN CHILENA DEL COBRE. Balance del Acido Sulfúrico en Chile proyectado al año 2006 , 1999.