Chile has important mineral wealth, where copper stands among the most important. Back in its history, the Spanish conquerers realized the potential of Chile as a mining territory, although at that time they were mostly focused on the recovery of gold and silver. During the 17th and 18th centuries, copper exploitation was a small industry that became important at the beginning of the 19th century after the independence of the country. However, at the end of that century, copper production sharply decreased especially because minerals with high copper content became scarce, and the investment of the mining sector focused on nitrate salt production as a natural fertilizer. At the beginning of the 20th century, this situation changed mainly because foreign companies having the adequate technology to recover the metal present at lower concentrations made investments and initiated its exploitation. Two of the most emblematic mines in Chile were established at that time: El Teniente, owned by the Braden Copper Company in 1904, later controlled by the Kennecott Corporation, and Chuquicamata, built by the Chile Exploration Company in 1910, later sold to the Anaconda Copper Company.
Two important steps given by the country were the “Chilenization” of the copper industry in 1966, meaning that the state of Chile made the necessary investments in order to become the owner of 51% of each one of the most important mines in the country. Later in 1971, the state of Chile took complete control of the mines partially owned at that time by foreign investors. Any further exploitation of new mines based on private investors had to be authorized by state law. As a consequence, in 1976, the Corporación Nacional del Cobre de Chile (CODELCO) was created as a state enterprise gathering the principal mines in one huge corporation.
In terms of copper production, during the period of colonization, the amount of copper produced is estimated to be between 1500 and 2000 tonnes per year. Most of that copper remained in Chile, destined to make decorative objects, different utensils and tools, coins, pieces of artillery, etc. Only approximately one third was exported annually.
The situation changed in an ostensible manner in the 19th century, when the copper was demanded by a great variety of technological applications derived from the European industrial revolution. It is estimated that, between 1820 and 1900, Chile produced 2 million tonnes of copper, being, for a time, the number one producer and exporter of the world. The peak production occurred in 1876 at 52,308 tonnes of copper, 30% of the world‘s production. Toward the end of the century, this position fell down to 9.7% in 1890 and to just 5.5% in 1900 [1
The definitive takeoff of copper mining in Chile started at the beginning of the 20th century, along with the exploitation of new, large mineral sites. Since then, the annual production of copper has increased to occupy the primary producer of copper in the world, with a volume equivalent to approximately one third of the world‘s production, as is depicted in Table 1
. The highest participation of Chile in world copper production so far was in 2004 at 36.9%.
The principal mines operating nowadays in Chile and their copper production in 2014 are listed in Table 2
and Table 3
, corresponding to those owned by CODELCO and private investors, respectively.
The copper production in Chile is based mostly on the exploitation of ores containing copper sulfides, with chalcopyrite (CuFeS2
), chalcocite (Cu2
S), covellite (CuS), bornite (Cu3
), enargite (Cu3
), and tennantite (Cu3
) being the most important. Through the years of exploitation of the copper in Chile, the ore mineralogical composition has changed. In the past, the oxides, easy to produce, were abundant, and the copper content was over 5%. Nowadays, the copper oxides have become scarce; practically speaking, the only sources of copper are sulfides, and its content has diminished down to approximately 1%. In accordance with this change, the reserves of copper in Chile consist mainly of chalcopyrite, which in 2012 was estimated to be in 190 millions of tonnes of copper, representing approximately 30% of the world‘s copper reserves [7
3. Historical Development of Bioleaching in Chile
3.1. Early Research Efforts
In the late sixties and early seventies, the first registered studies on Acidithiobacillus ferrooxidans, formerly known as Thiobacillus ferrooxidans, were done by Manuel Rodriguez at the Faculty of Biological Sciences of the Pontificia Universidad Católica de Chile and Claudio González at the Faculty of Chemistry and Pharmacy at the Universidad de Chile. These investigations were centered mostly on the basic microbiology of this bacterium rather than in its potential application to biomining.
In the late sixties, the Chilean government established two research institutes: the Centro de Investigaciones Minero Metalúrgicas—CIMM (Mining and Metallurgical Research Center)—and the Instituto de Investigaciones Tecnológicas—INTEC (Technological Research Institute). CIMM was a joint project of the Chilean government and the United Nations Development Program (UNDP). In the early seventies, CIMM started a research project on bacterial leaching in the Potrerillos mine in the Atacama region [34
During its start-up, INTEC received the advice of some distinguished international experts, some of them well acquainted with bioleaching technology. At that time, INTEC initiated a research project on bacterial leaching of copper ores [35
An effort that has been ongoing up to now has been that of the School of Biochemical Engineering of the Pontificia Universidad Católica de Valparaíso that started working on the bacterial leaching of copper ores back in 1974. The first results of this line of research were presented in 1976 in the VIII Jornada Chilena de Química, Santiago de Chile. This line of research has received significant scientific and economic support from several international projects such as Metallurgical Technology-Copper from the Organization of American States (OAS), 1979–1981, Research and Development of Metallurgical Processes-Hydrometallurgy, OAS, 1982–1985, and Biotechnology Applied to Copper Mining, OAS, 1985–1988.
These research efforts have been centered in topics such as growth and oxidation kinetics of Acidithiobacillus ferrooxidans in defined media, inhibition effects of organics on growth and oxidation, bioleaching of model copper sulfides, bioleaching of low grade copper ores, tailings and concentrates, bioleaching of copper ores in column and stirred reactors, biooxidation of refractory gold concentrates, biooxidation in continuous single stage and multistage reactors, adaptation of leaching microorganisms to high pulp densities, bioleaching with Sulfolobus metallicus in flasks and reactors, and factors affecting the synthesis of extracellular polymeric substances.
3.2. The United Nations Development Program (UNDP) Project
The United Nations Industrial Development Organization (UNIDO) expert meetings in May 1982, in Lima, Peru, and Santiago, Chile aimed to explore the possibility of establishing an international center for the development of biotechnology, antibiotics, and other pharmaceuticals products in Latin America. Chilean biotechnologists convened and decided to unite their efforts to attack one important topic relevant to the country economy and development. The chosen issue was the Chilean copper mining and the contribution that biotechnology could make in that field. They felt that, due to the complexity of the problem, the project should be addressed in a multi-disciplinary and multi-institutional fashion and should include researchers from the universities, research institutes, and the mining sector, as shown in Table 4
and Table 5
. The project received financial support from the Chilean government and The United Nations Development Program (UNDP), and consisted in two stages, namely “Development of Biological Processes and their Industrial Application to the Bacterial Leaching of Chilean Minerals—Phase I”, UNDP/CHI/85/002, 1985–1988 and “Development of Biological Processes and their Industrial Application to the Bacterial Leaching of Chilean Minerals—Phase II”, UNDP/CHI/88/003, 1988–1990.
The project was very successful and contributed significantly to the bioleaching knowledge in those days. As a result of this experience, Chile was recognized by the United Nations Industrial Development Organization as a world leader in bacterial leaching research [36
]. Several of its personnel moved to mining companies, especially to the Sociedad Minera Pudahuel (SMP), where they contributed effectively with the knowledge and experience gained in the project.
3.3. The Sociedad Minera Pudahuel (SMP) Project: Commercial Bioleaching Operation
In 1980, the Sociedad Minera Pudahuel built and commissioned the Lo Aguirre copper mine located near Santiago, Chile. This small mine obtained copper from mostly oxide minerals through acid leaching in vats. Its first important achievement was the development of the thin layer (TL) leaching technology consistent of pads three to eight meters height of agglomerated ore, which operated successfully, rendering copper at low cost.
As the oxides approached exhaustion SMP personnel realized that after some weeks soluble copper began to leak from the treated oxides. SMP established a research and development department that came to the conclusion that sulfur was oxidized by the bacterial action. This led to the design and commissioning of a successful heap leaching operation that together with a SX/EW plant produced 14,000 tonnes/year of fine copper until the exhaustion of the deposit in 2002 [15
]. It is important to point out that the Aguirre mine was the first copper mine of the world exploited exclusively by bioleaching technology [17
3.4. Large Scale Operations in Chile
During the 1990s and onward, several large-scale bioleaching operations besides Lo Aguirre were installed in different mines in Chile. The Lince-Michilla mine started its heap leaching operation in 1991 with a total production of 22,000 tonnes/year. Two important mines operating completely via bioleaching technology were commissioned in 1994, Quebrada Blanca and Cerro Colorado, while CODELCO’s El Teniente Division exploited the El Crater deposit via in-place biotechnology. Other early copper heap and dump bioleaching operations in Chile were Andacollo, Ivan-Zar, and Los Bronces [40
Several other bioleaching operations are near start-up or in a planning stage. Such is the case of Carmen de Andacollo, Collahuasi, Dos Amigos, Punta Colorada and Spence. Special mention should be made to La Escondida mine, currently the largest world copper mine [17