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close this bookBlending of New and Traditional Technologies - Case Studies (ILO - WEP, 1984, 312 p.)
close this folderPART 2: CASE STUDIES
View the documentChapter 3. Application of microcomputers to Portugal’s agricultural management*
View the documentChapter 4. Off-line uses of microcomputers in selected developing countries*
View the documentChapter 5. The use of personal computers in Italian biogas plants*
View the documentChapter 6. Microelectronics in textile production: A family firm (United Kingdom) and cottage industry with AVL looms (United States)
View the documentChapter 7. Microelectronics in small/medium enterprises in the United Kingdom*
View the documentChapter 8. Integration of old and new technologies in the Italian (Prato) textile industry*
View the documentChapter 9. The use of numerically controlled machines on traditional lathes: The Brazilian capital goods industry*
View the documentChapter 10. Electronic load-controlled mini-hydroelectric projects: Experiences from Colombia, Sri Lanka and Thailand*
View the documentChapter 11. The application of biotechnology to metal extraction: The case of the Andean countries*
View the documentChapter 12. Cloning of Palm Oil Trees in Malaysia*
View the documentChapter 13. Technological Change in Palm Oil in Costa Rica*
View the documentChapter 14. Biotechnology applications to some African fermented foods*
View the documentChapter 15. Use of satellite remote-sensing techniques in West Africa*
View the documentChapter 16. India’s rural educational television broadcasting via satellites*
View the documentChapter 17. New construction materials for developing countries*
View the documentChapter 18. Photovoltaic solar-powered pump irrigation in Pakistan*
View the documentChapter 19. Photovoltaic power supply to a village in Upper Volta*

Chapter 11. The application of biotechnology to metal extraction: The case of the Andean countries*

* Prepared by Ms. A. Warhurst. Science Policy Research Unit. Sussex University. Brighton, on behalf of ILO and UNIDO. This chapter is largely based on the report by the author for UNIDO which is entitled The application of biotechnology in developing countries: the case of mineral leaching with particular reference to the Andean Pact copper project. This more extensive treatment of the subject is currently in the process of publication by UNIDO.

RESERVE DEPLETION, A decline in grade of mineable ore, stricter pollution regulations, rising energy and investment costs and low and unstable metal prices, are the emerging factors governing the development of new mines and the viability of existing operations.

With the depletion of easily accessible high grade mineral concentrations many of the ore deposits planned to be developed are large low-grade complex (i.e. multi-mineral) bodies. These are mainly located in the developing countries - such as those which typify the Andean mountain chain running from Colombia and Ecuador through Peru and Bolivia to Argentina and Chile. These were previously mined for one mineral, e.g. copper or tin, but now it is becoming increasingly necessary to recover associated by-products such as gold, silver, zinc, nickel, cobalt, lead and to extract pollutant elements like sulphur, arsenic and bismuth. There are also pressures to stretch further existing mine capacity through recovering values previously not exploited in ancient waste dumps and the marginal ore overlying open-pit mines in the process of development. The exploitation of these deposits in the present economic climate poses a unique set of metallurgical problems which inevitably stimulate technical change in the mining and mineral-processing industry.

Microorganisms can be profitably utilised by mineral producers in developing countries. However, the geological and geographical peculiarities of each mine determines the nature of the techniques that are available to extract and treat the contained metals. Microorganisms can be employed in two ways: in leaching processes for extracting metals from low-grade ore and concentrates, and in resolving certain metallurgical problems; and for recovering accumulated dissolved metals through absorption processes. This chapter focuses on the first, and probably most important, group of biotechnology applications - the bacterial leaching of metals. It reports findings of both general and case-study research carried out during 1982-83 in Bolivia, Chile, Colombia and Peru as well as the United Kingdom and the United States. The objectives are to analyse the factors which determine the potential of biotechnology applications to metal extraction in developing countries and to point out some policy implications based on an evaluation of a technology development project undertaken by the Andean Pact countries of Bolivia and Peru during the 1970s.1


Bacterial leaching is a naturally occurring chemical-biological process. Certain microorganisms, notably Theobacillus Ferrooxidans, enable the conversion of normally insoluble sulphide minerals - containing, for example, copper, zinc, nickel and lead - into water soluble forms thus freeing the associated metal ions for recovery. These bacteria are ubiquitous in acid environments like the mine waters of sulphide ore deposits, waste dumps and hot sulphur springs. Functioning as oxidising agents they obtain energy for growth through the oxidation of inorganic compounds of iron and sulphur. Powerful leach solutions of ferric sulphate and sulphuric acid are generated by these reactions which occur, if optimal conditions for bacterial growth exist, at rates of up to a million times faster than in the presence of air alone. Recent research has demonstrated that the bacteria also act directly on the oxidisable parts of sulphide minerals.

Since these bacteria are living organisms, they require a series of special conditions for optimal growth which will in turn ensure optimal oxidation and mineral leaching rates. In general, they require abundant oxygen, a highly acid pH medium and specific nutrients. Certain dissolved metals like uranium and cadmium are toxic to them. However, each strain will have adapted through time to the specific conditions of its mine habitat such as the mine water pH, high concentrations of certain metals, the local ecosystem, and periodic acid dilution during the rainy season, etc. The leach system, its mineralogy, particle size, porosity, air updraught, temperature profile, etc. will also affect the efficiency of the biological reactions and thus the amount of, and rate at which, the contained metals can be freed.

It is this complex and extensive range of requirements and conditions which provide a scope for designing parameters to optimise the natural bacterial leaching process for economic gain. Bacterial leaching can be applied to waste dumps, heaps from open-pit mines, treatment of concentrates and a range of complex metallurgical problems. Each is discussed below.

Dump Leaching

Sulphide values can be leached from waste dumps of old mining operations by spraying acid solutions containing leaching bacteria over their surfaces. The solutions percolate through the dumps dissolving the minerals and when metal concentrations are high enough (that is, two grams per litre) they are recovered from the effluent by precipitation on scrap iron or through more efficient solvent extraction and electro-winning techniques. Similarly, residual metal values in disused underground or open-pit mines can be recovered by bacterial leaching. The ore is usually blasted to expose as much surface area as possible and bacterial solutions are then circulated through the mine. After the leaching process, the solutions are pumped back to the surface from the lowest collection point.

Investment and operating costs for dump leaching operations are generally low. Optimisation of the bacterial leaching process is limited since the dumps have already been built. There are therefore no costs involved in system design, micro-biological research and development (R and D) or dump construction, nor for that matter in mining, transportation and dumping. Additional costs are mainly for acid resistant pipes, pumps and collecting tanks which may range between US$1 million and US$2.5 million depending upon dump dimensions and topography.2 Although the process is very flexible, given that ore grades are low, (e.g. generally less than 0.5 per cent copper) and recovery rates are unpredictable and sub-optimal (less than 40 per cent of the contained metal) economies of scale can be important. These would have to be calculated for each mine operation but generally bacterial leaching can be used to extract metals from small dumps of less than 25 metric tonnes to huge dumps of thousands of millions of metric tonnes of material producing up to 23 metric tonnes of copper per day. Operating costs are minimal since, if the process works efficiently, acid is self-generated and no purchased energy is required.

The environmental impact of this process is positive. Indeed, the metal ions and sulphuric acid produced by natural, that is, uncontrolled bacterial leaching, is a dangerous pollutant if it is allowed to enter water supplies. When the process is harnessed for economic gain and metal ions are recovered, chemical changes render the solutions non-pollutant. Also the barren solution is recycled over the dump and is thus subject to further oxidation by the bacterial activity.

As yet there exists no viable alternative to bacterial leaching for the processing of such low-grade material and, since the technique is applied to previously unexploited resources, the employment effects are necessarily positive. Working conditions are also much safer than those in the interior of a mine. The labour force would range between 10 to 30 depending on the size of dumps and plant and the extent of ongoing research and analysis. The skill composition, reflecting the limited scope for optimisation, would probably be two-thirds unskilled and one-third skilled in the areas of metallurgy, chemical engineering and mining engineering. It is unlikely that microbiologists or geologists would be employed, although this is not necessarily an advisable policy.

The implications of this technique for developing countries are enormous. Many of them have a long history of mining. In mines where cut-off grades3 have been lowered over time, or where only one mineral was mined, there will probably exist dumps containing currently economically viable ore. For example, in Bolivia, ancient dumps from tin mining contain higher percentages of copper, silver, nickel and zinc, as well as tin than the grade presently mined.

Heap Leaching

Perhaps the most promising application of biotechnology to metal extraction is the leaching of marginal ore during on-going operations, and of overburden from newly developed open pit mines, that is, arranged in heaps designed to be constructed and operated according to parameters for optimal bacterial activity at that mine. The three main routes to optimise bacterial leaching are through system design, improved bacterial activity and solution management. Metal recovery rates are more predictable and may range from 40 to 80 per cent depending on the geological characteristics of the system, the environmental context and the extent to which optimisation procedures are followed. For example, optimal heap dimensions could be determined to fulfil particular aeration and temperature requirements of specific species of bacteria; strain selection, nutrient addition and ecosystem design and control may be undertaken to stimulate bacterial activity. The chemical composition of mine water solutions may be changed and controlled to accelerate oxidation and inhibit precipitate formation within the heap.

The investment and operating costs of an optimised heap leaching system are more variable than those for a dump system since they will depend on the extent to which a technology search and R and D programme are carried out. Other important variables would have to be considered: the rock type and its natural particle size after blasting will determine the necessity for expensive preliminary crushing, the addition of extra acid or the design of long, shallow and narrow “finger heap” systems; the hydrogeology and soil types will determine the need for costly ground-base preparation; the availability and characteristics of local acidified mine water and a vibrant bacterial population will ultimately determine the efficiency of bacterial leaching for a given mine site. Investment costs for heap operations could therefore range between US$5 and 50 million. However, this should be placed in the context of current mine investment costs which are upwards of US$1,000 million.

Employment would again be generated, perhaps by up to 50 people since bacterial leaching is a unique process for treating previously unexploited marginal ore. The skill composition of this labour force would reflect the nature of the optimisation programme followed and may be expected to encompass microbiology, geology, metallurgy, and chemical and mining engineering.

The potential of heap leaching becomes evident when one considers that many developing countries, including Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Indonesia, Papua New Guinea and Peru are embarking on process route selection for new mineral projects. Heap bacterial leaching could be applicable in most of these, principally for copper minerals.

Concentrate Leaching

Energy-intensive and pollutant-smelting operations are currently facing problems.

Partly for this reason, it is believed that confined bacterial leaching systems may become an alternative for the treatment of copper and zinc concentrates in the future.4 This is made more relevant by the fact that the majority of unexplored mineralised zones are in developing countries and these, as well as recently discovered mineral deposits, will not be developed for another 10 to 30 years.5 Developing-country producers usually export their minerals in concentrate form to Europe, Japan and the United States. Through bacterial leaching developing countries could obtain more value - added for their minerals, since both leaching and metal recovery (by solvent extraction and electro-winning to produce a cathode copper which is approximately 99.9 per cent pure) takes place at the mine site.

Since more controls can be imposed on confined systems, genetic engineering of the leaching bacteria may provide a breakthrough. Related research has focused on selective mineral leaching, speeding up oxidation functions, reducing toxicity effects, bacterial adaptability to saline waters and the self-generation of nitrogenous nutrients. However, it is felt that not enough is known about the physiology and metabolism of the leaching bacteria. Furthermore, even if the genetic code is cracked it is predicted that problems will remain in controlling the production of the bacteria in actual mining situations.

Bacterial Leaching and Complex Metallurgy

Bacterial leaching can be applied to a range of emerging metallurgical problems associated with the development of complex ore bodies in the developing countries. Most important is its potential to liberate gold from the crystal matrice of iron pyrites, a form in which gold occurs in many developing countries such as Colombia, Bolivia and Peru. Bacterial leaching can also be employed to extract arsenic from copper concentrates, extract sulphur from coal, separate “difficult” lead-zinc concentrates and indirectly leach uranium.6

Potential for Developing Countries

Despite the potential of bacterial leaching for Third World countries, there apparently exist only three industrial scale applications within their boundaries: a dump operation at Bourgainville in Papua New Guinea, a combined dump and underground leaching operation at Cerro de Pasco in Peru and an optimised “heap leaching” operation at Cananea in Mexico. However, projects to develop bacterial leaching technology are at various stages of development throughout the Andean Region. In Chile CODELCO has given a high priority to bacterial leaching technology.7 Projects are being developed for dump, heap and concentrate leaching at Chuquicamata and plants on a semi-industrial scale are giving excellent recovery rates and grades of copper. One project has involved working directly with a team from a local research institute and the University of Chile in the area of genetic engineering. There are also plans to control and optimise natural bacterial leaching occurring in a disused section of the El Teniente mine. A worker group extracting copper from tailings dumped from the concentrator at Salvador mine has asked the University of Valpariso to advise it in the optimisation of an artisanal technique which, in effect, is a method of bacterially leaching copper concentrates. In Bolivia, heap leaching projects are planned for sulphide minerals at Tasna, Bolivar, Siglo XX and Carguaicollo and for zinc concentrates at Colquiri. In Colombia, it is planned to bacterially leach copper and molybdenum values from marginal overburden at the Mocoa mine, while in Peru, bacteria heap leaching is planned for marginal ore at Toromocho, Cerro Verde and Pativilka.

However, virtually all the commercial applications of this process are confined to old waste dumps in the advanced industrialised countries. In the United States, for example, more than 10 per cent of total copper produced in 1982 came from this source8 and the proportion probably increased during 1983. In a recent survey undertaken by us in Arizona and New Mexico, states which produce more than 60 per cent of the United States bacterially leached copper, it was found that many mines there had closed down their conventional mining, concentrating and smelting operations. The only production process considered to be profitable in the climate of low prices and soaring operating costs was the bacterial leaching of waste material and metal recovery by solvent extraction. Bacterial leaching accounts for 100 per cent of copper production in several mines, e.g. Miami Copper and Pinto Valley.

These figures become even more significant when it is realised that these dumps have surprisingly low recovery rates because the microbiological component of sulphide leaching was not realised at the time of the dumps’ construction. Indeed, even now it is difficult to convince mine managers that the dissolution of minerals in their dumps is due to biological and not solely chemical factors, and thus can be controlled and optimised. The complex requirements of the leaching bacteria explain the low metal recovery rates (from five to 40 per cent of the contained metal in periods lasting from five to 20 years). For example, since waste is usually placed in large mounds in valleys for dumping convenience, dump interiors may be inhospitable due to a dearth of air and high temperatures. Since some dumps are both very old and large, “fines” may form through weathering and pressure. This prevents percolation and therefore, solution and bacteria - substrate contact; oxidation reactions are slowed down and pH consequently rises making the environment unsuitable for bacteria. In addition, this promotes the formation of precipitates which coat mineral surfaces permanently and prohibits further leaching.

The main implication of all this, (which in itself helps to explain why bacterial leaching has not been introduced on a larger scale in the developing countries, and practically why it has been difficult to persuade managers of the technology’s potential) is that there exists no precedent in the advanced industrialised countries of optimised bacterial leaching operations. High transport and dumping costs, environmental restrictions and the lack of new mine sites reduce the possibilities of changing this situation in the future. Therefore, there are no general models upon which the developing countries can base their leaching projects.

Thus, as a source of technology transfer the potential of the advanced industrialised countries, although important, is limited. Since they are restricted to optimisation through only solution management the majority of their industrial experts are chemical engineers who have little idea of the biological factors that affect the efficiency of leaching. At the same time, most of the microbiological research is carried out in universities by scientists who have little idea of the engineering principles involved in applying laboratory results to larger-scale applications. Technology transfer from the advanced industrialised countries to the developing countries clearly requires a planned approach because, unlike typical mining and mineral-processing techniques, we are basically considering the assimilation of disembodied technology from diverse sources and its on-site integration with locally-derived technology.

While the potential for optimised bacterial leaching operations is much higher in the developing countries - dumps can be reconstructed, heaps built at new mine sites and future projects may benefit from concentrate leaching - they also pose a huge challenge. This is largely because mining companies are very rigidly structured and bacterial leaching technology development requires a multidisciplinary team which must work in close cooperation with the production right from the very beginning. Under these circumstances, the advantages of a planned approach to investment in the technological capabilities needed for developing such projects are clear. Furthermore, given the complex, extensive and multidisciplinary requirements involved, it is evident that these investments are best spread across firms and institutes or even across countries. Indeed, this is precisely what Chile is doing at a national level and the Andean Pact countries at a sub-regional level.


The Andean Pact Copper Project particularly warrants analysis in this respect since it is one of the few examples of the development and application of bacterial leaching technology within the Third World. A specific strategy of technology capability development was designed to achieve this. Essentially, it involved the utilisation and development of local resources and skills in the area of bacterial leaching augmented by the international acquisition of technology from both the advanced industrialised nations and among developing countries of the sub-region.

The project was designed to solve the problem of recovering copper from low grade ore and waste dumps. It was a collaborative project involving only Bolivia and Peru;9 COMIBOL and the IIMM participated in the former country and CENTROMIN, MINEROPERU and INGEMMET in the latter.10 The Copper Project was one of the four technology development projects undertaken by the Andean Pact as part of a general programme for the planning of the local generation of technology; the others being the Tropical Woods Project, the Food Project and the Rural Project.11 These were conceived of as projects aimed at copying, adapting, and creating technology through joint efforts to achieve specific economic and social objectives within the framework of regional integration.


The Copper Project was originally designed to achieve the following two objectives12:

(i) To form teams capable of managing efficiently copper leaching technology from the laboratory level up to the design, construction and operation of industrial plants;

(ii) To create in Bolivia and Peru (and Chile) laboratory facilities for analysing, evaluating and developing research on copper mineral leaching.

No alternative technique was considered during project selection since currently no other method is feasible for treating previously unexploited ore. However, account was taken of the process of copper production itself and sub-projects were undertaken involving copper oxide leaching through chemical means, solvent extraction and electro-winning, that might complement bacterial leaching. Since Decision 87 of the Board of Cartagena Agreement emphasised bacterial leaching as the core of the Andean Pact Copper Project, this is the focus of the present analysis.

An 18-month planning period funded by unconditional assistance from the IDRC13 to the Andean Pact’s Technology Policy Group proved to be crucial to the project’s success. The funding permitted the Project Coordinator who was a trained metallurgist, to visit technology suppliers in Canada and the Federal Republic of Germany, as well as industrial bacterial operations in the United States. A preliminary survey was made of both the technical possibilities of applying bacterial leaching in the region and the political willingness and existing capabilities of firms and institutes which could participate.

Delays in the signing of the aid contract and the transfer of finance had serious repercussions particularly for Bolivia. Consequently, the Copper Project did not begin until February 1976. The programme of technology development included intensive seminar courses, on-site training undertaken by foreign experts, and visits to industrial dump leaching operations in the United States. Attendance at international conferences on bacterial leaching was possible as well. It is concluded that the objectives of the Copper Project have largely been achieved in Peru and, to a lesser extent, in Bolivia.


The main achievements of the Copper Project are outlined below.

(i) In the case of CENTROMIN (Peru) a semi-industrial bacterial leaching pilot plant was installed at the Toromocho mine to extract copper from low-grade overburden employing cementation on scrap iron as the recovery method. The multidisciplinary team based at the Division of Special Projects in metallurgy at CENTROMIN’s smelter-refinery complex in nearby La Oroya provided an important input to a prefeasibility study for the Toromocho industrial project. The team is involved in a new pilot project employing a Krupp solvent extraction pilot plant presented by the Federal Republic of Germany in order to obtain parameters for scale-up for optimal bacterial heap leaching. In addition, natural bacterial leaching processes at Cerro de Pasco are being optimised and copper from the effluent solutions recovered electrolytically. Experiments are also in progress that involve recovery of silver from the solutions.

(ii) INGEMMET has now built up a strong research capability in bacterial leaching evidenced by its anticipative R and D work on ore from MINEROPERU’s mine at Cerro Verde.14 Since the oxide zone at that mine is virtually depleted, the intention is to bacterially leach the remaining sulphide values from copper oxide heaps leached with the sulphuric acid and marginal ore from the underlying sulphide zone. The installed capacity of its solvent extraction plant could be adapted to recover the copper from solution. Since MINEROPERU alone lacks the capabilities it is planning to contract experts from INGEMMET to work with its own personnel at the mine site. This is perhaps one of the closest links that has been forged between research centres of the mining companies in the Andean subregion. In addition, INGEMMET has recently been contracted to assess the leachability of various ores by small government-owned mining companies. Carrying out R and D on the extraction of arsenic by bacterial leaching from smelter feeds is another of its activities. Personnel, including a microbiologist, have undergone further training, which built upon their experience in the Andean Pact Copper Project. As one of the most advanced teams of its kind in the region, it is engaged in the organisation of national and international workshops on bacterial leaching. Finally, because of its close proximity to Peru’s principal engineering university the team has taught and supervised over 15 theses on bacterial leaching.

(iii) The R and D department, the Division of Special Projects in Metallurgy, was initiated within COMIBOL as part of the Copper Project. Applied research was carried out by a trained team on the bacterial leaching of copper ore from Tasna, and a pilot plant programme for leaching copper at Palaviri was planned though, for reasons to be discussed, not implemented. In addition, some more innovative research was carried out on bacterially leaching marmatite (zinc) concentrates from Colquiri. Although the results were positive the technology has still not been developed, nor has mine management been informed of its potential as an alternative for recuperating marmatite from flotation tailings.15 There has been a considerable diffusion of technology and related ideas to other mine sites and firms stimulated by turnovers of personnel during the Copper Project and the employment in other companies and institutions throughout the Andean Region. For example, the former director of the project at CENTROMIN is now developing bacterial leaching for a private company in Peru, while the projects’s coordinator is helping to promote an ambitious bacterial leaching project in Chile from his new position in another international organisation. Most important, however, are the plans of the Andean Pact itself. A second phase is being designed which will involve: a) the transfer of bacterial leaching technology from Bolivia and Peru to the other member countries (Colombia, Ecuador and Venezuela) where mines suitable for such applications have been identified; b) the further development of the technology to solve other shared problems such as the extraction of gold from iron pyrites, the bacterial leaching of other metals like zinc, nickel, arsenic and lead, and other materials like copper and zinc concentrates; and (c) the development of joint strategies to improve the negotiating capabilities of the member countries in the transfer of mining and mineral-processing technology.

Evaluation and Some Policy Issues

It is difficult to evaluate the cost-effectiveness of the Andean Pact Copper Project, in part because it was a subregional technology development project as opposed to the simple introduction of a new technique at the level of the firm and partly because of the nature of the technology itself. The extent of diffusion of the technology has already been mentioned and this, along with the long-term possible benefits of having established research and development divisions with trained multidisciplinary teams in the participant companies cannot be assessed through a simple cost-benefit analysis of the project. It is also difficult to carry out a conventional cost-effectiveness evaluation since the technology is being applied to reserves previously unexploited and for which no alternative process exists. Therefore, the relevant question is whether the returns to investment are considered sufficient to warrant the application of the technology. The investment may be determined more by local geological, geographical and bibliogical factors than by the costs of pipes and pumps. Nevertheless, something can be said about CENTROMIN’s Toromocho project which was the most advanced of those undertaken in the Copper Project.

Seven heaps were constructed between October 1977 and mid 1979 after an extensive research programme to determine the parameters for optimal pilot plant design.16 Their sizes varied between 3,600 and 9,800 metric tonnes, their height between 4.6 and 9.2 metres and their copper content averaged around 0.55 per cent. Two rock types from Toromocho were used - “skarn” and intrusives. The fine-grained “skarn” degraded easily and produced only a 40 to 50 per cent extraction level since the related rapid fine formation reduced bacterial activity and caused iron hydroxide precipitation. The intrusive rock type leached well, being harder and also more permeable, and extraction levels reached between 75 to 85 per cent. Of course, a range of non-geographical factors are involved in explaining the different results obtained. For example, throughout the heaps’ operation conditions were changed - solution application rates were varied, nutrients added and the heaps were innoculated with specially cultivated bacteria. Ongoing experimental work, although very limited, tested stability of the heaps, maximum rest periods (that is lulls in solution application), and the effects of changes in pH. The investment costs for the heap and pilot plant at Toromocho are summarised below:17


General accounts


Preparation of base of heaps


Linking channel with collecting pond


Preparation of heaps


Construction of iron precipitation pilot plant



Between 1978 and 1980 total operating costs were estimated to be US$376,631 and total value added, US$60,698.18 However, there are several problems with this evaluation. For example, there would be economies of scale involved in the preparation and construction of the system; a solvent extraction-electrowinning plant would produce a higher grade of copper more cheaply; the evaluation was based on the average rate of extraction achieved, yet the industrial plant would obviously use the type of rock most suitable for leaching and build the heaps and operate them according to the optimal conditions. Presumably, 80 per cent recovery rates from the whole system would be the goal. Some rough calculations were done to get an idea of the feasibility of an industrial scale project. Apparently, there are 530 million metric tonnes of leachable ore with an average content of 0.39 per cent copper. An 80 per cent (70 per cent, 60 per cent, 50 per cent, 40 per cent) recovery of that copper would be worth about US$226,047,000 (US$197,791,000; US$169,535,000; US$141,279,000; US$113,023,000, respectively) at current metal prices.19 Even with investment costs of around US$30 to 40 million and estimated operating costs for leaching/solvent extraction-electrowinning at US$600-650 per metric tonne produced - which is an average based on data from industrial scale leaching operations - it is clear that a significant return on investment can be expected.


Technical change and innovation in bacterial leaching processes are highly complex since they function as part of a system which involves geology, hydrogeology, soil science, geography, microbiology, chemical and metallurgical engineering as well as management. Furthermore, there are different social and environmental contexts within which the technology must be applied. Neither is innovation in bacterial leaching simply research-initiated. From the outset, a collectively-trained multidisciplinary team needs to work in close cooperation with the production sector to ensure optimal metal leaching. Initial fieldwork inputs are required from geologists, hydro-geologists, geographers and microbiologists. These results must then be interpreted during process design by chemical and metallurgical engineers who themselves need to work alongside miners and mining engineers since the latter will ultimately be responsible for the extraction and dumping of material according to the parameters established. However, COMIBOL and CENTROMIN have demonstrated that appropriate project choice, relevant research and even R and D undertaken by the firm are not sufficient to ensure the industrial application of the optimised technology. The mining divisions work towards short-term economic objectives which are different from those of the researchers. Bacterial leaching projects require the crossing of this traditional division between miners and metallurgists which characterises virtually all mining companies. COMIBOL’s experience illustrated the necessity to improve communication links between the research and administrative centres and between the research and production site - often hundreds of miles away in remote mountain regions. Some mine managers were unaware that their minerals were being researched while others had never heard of bacterial leaching. This is particularly significant since production divisions in the mining industry traditionally have considerable freedom to make decisions. This represents a challenge which demands the commitment of management to the development of the technology in order to obtain the “structural” changes required to set up multidisciplinary teams and release research and production personnel for training and group meetings. Furthermore, each procedure to optimise the bacterial leaching process will have its own specific cost attached to it and will require individual consideration for its approval. It is interesting to note that during early stages of operation each bacterial leaching project evaluated in Bolivia, Chile, Colombia and Peru, crucially involved the enthusiastic commitment of one member of management amidst considerable opposition.

Finally, many mining companies in developing countries do not have medical facilities which can be adapted to carry out microbiological research (as CENTROMIN did to ameliorate the effect of aid delays during the beginning of the Copper Project). And a genetic research programme is beyond the scope of all but the large multinationals. Therefore, both local research institutes and universities need to play important supporting roles during the technology development. Particularly so because the bacterial activity can best be optimised in their indigenous environment (as opposed to a research centre in the Northern hemisphere), the characteristics of local mine water change with transport (which in any case is impractical and expensive) and due to the large input of local knowledge which is required during project development. One of the most striking features of the Copper Project and the ensuing technology development in bacterial leaching, was a unique example of (for those countries) linking between universities and research centres and mining companies at the national level.20


The sub-optimal dump leaching operations in advanced industrialised countries, already noted above, naturally limited the contribution of technology transfer to the Copper Project.

The majority of experts in developed countries are chemical engineers since optimisation of dump leaching systems is limited to solution management. Research on microbiological and physio-chemical reaction is exclusively carried out in the universities by scientists with little idea about engineering and industrial production. Virtually no mining companies have microbiologists since microbiological optimisation of dumps is so limited. Experts in bacterial leaching are rarely geologists since most dump and tailing reserves in the developed countries, unlike in developing countries, have been subject to geological evaluation and thus such skills are not required. Also their mineral content can be more readily estimated since stricter controls were enforced and more detailed analyses undertaken at the time of mining and dumping. Similarly, few mining engineers are involved in bacterial leaching projects in the developed countries since the dumps are “faits accomplis” and their cooperation is not needed to implement the optimised parameters for heap design.

This situation was reflected in the Andean Pact Copper Project. The teams trained were largely composed of metallurgists and chemical engineers. Microbiologists were included for a short time: there were no geologists or mining engineers although the Bolivian team was forced to bring in the geological division of the firm to check the mineral content of a proposed dump operation. The analysis clearly showed that the application of the technology was not viable. However, much time, money and reputation would not have been lost if the evaluation had been carried out in the beginning. There are a few specialised experts in the exclusive area of bacterial leaching and their role has been mainly to assess the leachability of ores on the basis of a short-term contract for the large mining companies. Their involvement in technology transfer programmes would thus tend to be biased in favour of the research, albeit applied research, stages of bacterial leaching technology development rather than industrial aspects. Again these factors were reflected in the training programme and in the choice of experts who ran them: a chemical engineer from an institute that carries out contract research for industry and a research scientist working on micro-reactions at the crystal-solution interface.21 This structure of technological capabilities in the developed countries helps to explain why much of the technology is disembodied and why sufficiently optimised bacterial leaching systems and wide-ranging industrial applications have yet to be achieved in the Andean Region. Technology transfers in this area clearly require a planned and technically informed approach since we are concerned with different types of disembodied technology from diverse sources which must be searched out and acquired - no easy task when the technology is embodied in people and their experience and work and has to be assimilated and integrated with diverse local technology inputs.

The Andean Pact Copper Project demonstrated the advantages of technical cooperation among developing countries through the spreading of investment in building capacity across firms, institutes, and national boundaries. This was done through joint seminar programmes, regional visits by foreign experts, literature searches, compilation and distribution programmes, and through the creation of a more stimulating learning environment - essential to the attainment of some disembodied technology. It is probable that technical cooperation among developing countries is more effective at a regional level since neighbouring countries, particularly those sharing mineralised mountain ranges, will inevitably face common metallurgical problems. After all, metalogenic zones do not respect political boundaries.

Difficulties in technical cooperation endeavours cannot be over-emphasised due to each country’s different state of economic and political development and the role that mining plays in national policy. However, it is believed that technical cooperation, unlike marketing cooperative endeavours, is more flexible, requiring less and limited commitment by the participants and having few and less controversial implications. Thus they may be more effective instruments of regional integration.


The leaching bacteria themselves are not known to be toxic to humans. However, the environment in which they flourish and which they create - highly acid mine water - is highly pollutant if permitted to enter drainage waters. It has already been indicated that these acidic waters are generated naturally in the mine environment where the leaching bacteria are ubiquitous. Therefore, one important advantage of the controlled application of bacterial leaching technology is the prevention of this pollution through the recovery of the dissolved metals - returning the ferric ions back to their less pollutant dissolved metals state and recycling the solutions within a closed system. Indeed, in some cases it may be feasible to recover the metals solely to prevent pollution rather than for their intrinsic value. However, this also implies that solution losses from the leach circuit are extremely dangerous. Ground surfaces, based on knowledge of underlying soils and hydrogeology should be well prepared. Workers too should avoid contact with solutions and released toxic gases.

It is difficult to estimate the savings bacterial leaching could offer through the prevention of pollution, especially since few developing countries have implemented environmental regulations in the mining regions. However, the governments of Chile and Peru spend thousands of dollars every day adding chemicals to water for their major cities due in large part to acidic and metal-rich effluents entering the main servicing rivers from natural bacterial leaching processes in the dumps and tailings left in the valleys of the Andean mountains above.22

With regard to the social context of the Andean Pact Copper Project, insufficient consideration was given to existing patterns of resource use (that is, dumps and mine water which are essential inputs for some applications of bacterial leaching) and the possible detrimental implications of the project’s implementation. This was particularly relevant in the case of Bolivia where the technology applications were considered mainly for extracting metals from old mining dumps. COMIBOL has not opened a new mine since it was established over 30 years ago; most of its plant and equipment is also over 30 years old and therefore obsolete. Only a little over 50 per cent of the tin mined is recovered at the processing stage. The rest is “lost” in dumps and tailings and significant amounts of tin are carried away in mine water emanating from the mine or from the processing plants. Various labour processes have been established by distinct groups of workers. They are dependent on the company which often rents out work sites and establishes compulsory selling contracts with them - but not being official employees, they do not receive stable wages or any social benefits. For example, women whose husbands have died of mine accidents or diseases lose the family social benefits (to which the employees are entitled) and are not paid compensation. Instead, the company allows them to mine tin from the dumps by hand. In July 1982 at the mine of Tasna - one of the sites chosen for the application of bacterial leaching for the extraction of copper - women miners were receiving the equivalent of 30 US cents daily in contrast to the daily dollar rate received by the male miners.23 The Tasna bacterial leaching project was never applied at the industrial scale in part because of its distance from the research centre and in part because the expert contracted by the Andean Pact recommended that the project be transferred to another mine with apparently greater potential.

A pilot plant was planned for this new mine site which required the diversion of the mine water over a dump with the objective of recovering the assumed copper content and leaving the tin free from corroding mineral salts for later reprocessing. Again the social impact of the project was ignored. Hundreds of family operators work in the valley below the dump and mine recovering tin from the mine water. When they heard of the project during its later stages they went on strike; their protest was largely responsible for the closure of the project. These complex areas clearly require more study before any policy suggestions can be made. However, they illustrate how deeply inter-woven these activities are with the mining economy of that country and their important implication for technical change. These groups of people, who are all organised in trade unions, need to be included in the decision-making processes relating to the application of this technology. Indeed, they should receive priority for the employment generated. In turn, this implies their formal incorporation into the work force of the company.

Employment and Skills Generation

Finally, the employment generation and skill formation achieved through the Andean Pact Copper Project need to be mentioned. In Bolivia, 23 technicians and engineers were trained in bacterial leaching and related processes. At least nine of these were originally at the IIMM and were contracted by COMIBOL to work in the Copper Project. No employment was generated directly in production since there was no industrial application of the technology. In Peru 35 technicians and engineers received training. Of these about ten were directly employed in the Toromocho pilot project and unskilled labour for heap construction and maintenance of about four persons was arranged through shifting workers from other duties.

Personnel turnover in the project was a problem. However, on the positive side, it accounted for much of the diffusion of the technology to other production sites and companies particularly in the case of Bolivia. In contrast, in Peru capabilities were consolidated through the joint writing of technical reports, the compilation of research procedure manuals and the communication of information among trainees. This meant that more retraining was necessary for the Bolivian team; it also created some imbalances in the joint seminar courses. Although interest is still maintained within the participant institutions through ongoing research and project development, work in bacterial leaching, with the exception of INGEMMET, has been reduced since the Copper Project finished in 1981. For this reason, a follow-up project is being planned - a rare occurrence in technology development programmes. The consolidation of the technological capabilities of Bolivia and Peru in bacterial leaching forms the basis for the second phase which is intended to provide the dynamics for the diffusion of the technology and its widespread and efficient application in the Andean Region.


Bacterial leaching could provide major benefits to Third World mineral producers. First, it enables the recovery of extra metal values, the solution of some metallurgical problems and the prevention of natural environmental contamination. Second, bacterial leaching may provide many mineral producers in developing countries with a low-cost technique for diversifying their mining sectors. After all, most of the reserves that can benefit from the process have either been mined already or will be mined in the future irrespective of leaching. Third, the development of this technology has led to increased local participation in associated technical change. As has been explained above, the efficient exploitation of bacterial leaching on an industrial scale demands the development of local technological capability. (This follows from the requirement of site-specific adjustment of the technology and the impracticality of testing environmentally sensitive bacteria too far from the location of the material to be leached.) The result has been a strengthening of interactions between research institutes and the production sector.

Given the nature of bacterial leaching technology there is a clear need for a national or regional policy approach for the application of biotechnology to mining. The lessons and insights gained from the Andean Pact Copper Project have provided many of the basic building blocks for formulating such an approach. Geological realities, among other factors, dictate that the policy must perforce emphasise the indigenous technological capabilities of the developing countries.


1. Fieldwork carried out in the Andean Region was supported by the Technology Programme of UNIDO. I would especially like to thank Louis Soto Krebs, UNIDO Senior Industrial Development Field Advisor in Brasilia. During this period, I was based at the offices of the Technology Policy Group of the Andean Pact without whose generous help and support this work could never have been carried out. Particular thanks are due to Gustavo Flores. the then Acting Head of the Group and to Carlos Aguirre, the present Head as well as Janette Ivazetta and Waldo Neves. The assistance of Kurt Hoffman and Geoff Oldham of the Science Policy Research Unit (SPRU) at the University of Sussex is also gratefully acknowledged.

2. A solvent extraction and electro-winning recovery plant, with a 22,250 litres per minute capacity producing over 9.09 metric tonnes of copper per day may cost around US$10 million.

3. Cut-off grade refers to the minimal metal content for a particular ore that is economically viable at a given time.

4. Research programmes are already well advanced in this area. Breakthroughs at a Canadian Research Centre - in fact the technology supplier to the Andean Pact Copper Project - indicate that at current energy costs the leaching of copper concentrates can be carried out at the commercial scale for 60 to 70 per cent of the costs of the corresponding smelting operation. Gold and silver, as well as a dilute sulphuric acid can also be recovered. See for example, R.O. McEllroy and A. Bruynesteyn: “Continuous Biological Leaching of Chalcopyrite Concentrates: Demonstration and Economic Analysis” in L.W. Murr A.E. Torma, and J.A. Brierley: Metallurgical applications of bacterial leaching and related micro-biological phenomena. Academic Press, New York, 1978, pp. 441-462. The Canadian Government is contributing to the funding of the development work on this process through its recently launched biotechnology for Mining Programme which is to receive an annual budget of US$10 million. Another project for the bacterial leaching of copper concentrates in situ is being planned by Mountain States Research in Arizona, United States.

5. For example, probably less than 10 per cent of the mineralised zone of Colombia has been explored. A recent CEPAL (ECLA) report indicated that only 5 per cent of the mineralised zone of Mexico and 10 per cent of that of Bolivia has been explored. CEPAL: Evoluci perspectivas del sector minero en Amca Latina, Santiago, 1982.

6. Although the latter process has been employed on a commercial scale in the United States, and for a while in Bolivia, it is intrinsically dangerous. Usually, it is applied in underground mines after blasting which presents the threat of radioactive elements being released into drainage systems through fractures. Alternatively, after escaping the material can be blown by strong winds after drying.

7. CODELCO: The National Copper Corporation of Chile.

8. C.L. Brierley: “Microbiological Mining”, in Scientific American, New York, August 1982, pp. 44-53.

9. Originally Chile was to participate in the Copper Project; however with the change of government and accession to power of General Pinochet it left the Andean Pact - and thus the Copper Project - in 1976. Since Chile is the major copper producer in the Andean Region and is more advanced technologically, this inevitably had negative implications for the Copper Project - particularly the technical cooperation aspects.

10. INGEMMET: Institute for Geological, Mining and Metallurgical Research.
MINEROPERU: The Mining Company of Peru (State-owned).
CENTROMIN: The Mining Company of Central Peru (State-owned)
IIMM: The Institute of Mining and Metallurgy Research.
COMIBOL: The Bolivian Mining Corporation.

11. These technology development projects were devised to form part of a strategy to pursue Decision 84 of the Board of the Cartagena Agreement (the official title of the Andean Pact) which aimed at promoting the utilisation and development of local capabilities. Complementary programmes included technology unpackaging, international technology search, classified inventories of technological capabilities and a subregional information system.

12. (Unofficial translation from the Spanish), Junta del Acuerdo de Cartagena: Proyectos Andinos de desarrollo technologica en el area de la hidrometalurgia del cobre, J/GT/12, Lima, September 2, 1974. ibid: Proyectos Andinos de desarrollo tecnologica en el area de la hidrometalugia del cobre, Decisones 86 & 87 de la Comision del Acuerdo de Cartagena, (Lima, June 12, 1975).

13. IDRC: International Development Research Centre, Canada.

14. The OAS (Organisation of American States) supported a follow up programme of research in INGEMMET which was fundamental in the consolidation of the capabilities built up in that institute through the Copper Project. It enabled the bacterial leaching specialist there to go to Belgium for further training and research the leachability of the Cerro Verde ores. A feasibility project was then presented to MINEROPERU and plans call for researchers and production personnel to work together at the mine site to develop and apply bacterial leaching technology.

15. Just as the Peruvian team is still working in the Special Projects Division - although now on other metallurgical problems - so is the Bolivian team. The latter group has recently presented to the Andean Pact for consideration four pre-feasibility studies for the reprocessing of tailing reserves at different mine sites. However, these employ conventional techniques such as flotation rather than bacterial leaching.

16. After basic laboratory research to evaluate the effect on leaching of pH, Ferric ions, sulphuric acid, acid consumption, precipitate formation and particle size, site-specific problems were explored.

These included aeration requirements of the bacteria at altitude (Toromocho is nearly 5,000 metres high) and dilution of pH during the rainy season. These showed that in all cases local bacteria were best adapted to their local conditions and when bacteria presented by the technology suppliers were subjected to the same conditions they were not able to survive. A system for the continuous cultivation of the bacteria was also designed and large colomns of 4.5 metric tonnes capacity were used to establish some of the parameters for scale-up.

17. The cost of the whole Andean Pact Copper Project for Peru - which to some extent is an estimate of the disembodied technology component - was an additional US$ 602,490.

This was to cover training and research programmes as well as laboratory and pilot plant equipment and chemicals, information compilation and distribution, personnel expenses and administration costs.

18. Junta del Acuerdo de Cartagena: “Evaluacion de las actividades realizados por Bolivia en los proyectos Andinos de desarrollo tecnologica en al area del cobre”, Lima, 1981.

19. Current prices for copper are around £925 to 936 per metric tonne cathode copper on the London Metal Exchange. Conversion to United States dollars was made at the rate of US$1.47 per pound sterling (November, 1983).

20. In Chile CODELCO is working on bacterial leaching projects with INTEC (Institute for Technical Change), the University of Chile and the Catholic University of Valpariso while DISPUTADA, a subsidiary of EXXON, has been working with CIMM (Centre for research in Mining and Metallurgy). In Colombia, the University of Bucaramanga in Santander has been researching bacterial leaching of nickel in cooperation with the Cerro Matoso Nickel Corporation. In Peru INGEMMET and MINEROPERU have been working together on the bacterial leaching of copper from Cerro verde.

21. The technology supplier helped to design a four-stage technology transfer programme to include: an introduction to bacterial leaching R and D; an evaluation of the leaching potential of various mines; the design of leach dumps and operation procedures; and the continuous evaluation of the leach process. He wrote that it would take two years to complete. However, eight years later he was still recommending the continuance of his role as consultant. Not only can a different conception of technology generation in bacterial leaching on the part of the technology supplier be detrimental to technology transfer programmes in this area but also their economic constraints may be influential, that is, the need to maintain, and obtain more contracts.

22. DISPUTADA (EXXON) is planning the expansion of a mine above Santiago by the River San Francisco which provides much of the drinking water for that city. It was realised that the dumping of the overburden required to develop the mine would promote natural bacterial leaching processes leading to a large bill from the government for neutralising chemicals. Subsequently, it was calculated that it would be less costly to control this natural bacterial leaching process and recover the dissolved metals thus avoiding contaminating the river and obtaining “extra” copper.

23. During 1983 this dangerous and poorly paid work was on the increase as conditions worsened in the mining centres with the deepening economic crisis facing that country.