Chem Connections


Copper Mine

Cpper Mine Image


opper mine

Prerequisites (from Tool Kit):
chemical reactions (balancing, stoichiometry, common types), atomic structure, chemical bonding and molecular structure
Interdisciplinary aspects:
biology - aerobic bacterial leaching from sulfide ores
engineering - mixing effects in leaching, process materials balance, batch vs. continuous process models, energy and efficiency assessment
Classroom, laboratory, or both: Both
Number of one-hour class periods: 15
Number of 3-4 hour lab periods: 3 minimum (4 is better)

Mary Walczak (Chemistry Department, St. Olaf College, Northfield, MN)
Doug Williams (Chemistry Department, Kalamazoo College, Kalamazoo, MI)

Description

Copper - from where does it come and what does it cost? Does it matter how we produce it? What are the environmental consequences? Students will explore the science (especially the chemistry) behind these questions and develop informed answers. The module uses a variety of pedagogical techniques including case teaching, collaborative laboratory work, and classroom group problems to teach the tradtional chemistry topics of redox reactions and acid/base, solubility, and electrochemical equilibria. In lab, students work in "assessment teams" on the analysis and hydrometallurgical processing of an ore sample. Based upon their own ore analyses, student teams will design and perform a study of suggested processing options which include chemical and bacterial ore oxidation methods. A mini-poster session to report these preliminary results and plans is followed by a 1-2 week leaching study. In the final lab, copper is recovered by solvent extraction/electrowinning (SX/EW) from "recycled" production streams and accumulated wastes are treated for safe disposal. The classroom portion of the module integrates technical, environmental, and economic issues with the traditional chemistry concepts so that effective decisions can be made. The module is completed with a report of mining feasibility from each team and a mock review panel for the entire class.

Tool Kit (2 or 3 primary tools):
Chemical Principles: redox reactions, general principles of equilibrium, solution phase equilibrium, electrochemical cells and potentials

Thinking Like a Scientist: Sampling, data analysis (system modeling), team work, analysis of social impact

Audience: general chem (first year, 2nd term)

Materials to be developed

  • Draft of instructions for students and teachers (including reference lists)
  • Video tapes (pro-mining and pro-environment perspectives)
  • Readings on technical aspects of mining (to be developed)

Class Plan

Outcome objectives of the module

The major goal of student work in this module is to gather enough information to ascertain the value of a proposed mining development project in the context of natural resource and market factors. Accomplishment of this objective requires understanding of the chemical aspects of copper extraction. The suggested background materials for the module will describe major pyrometallurgical and hydrometallurgical methods but students may seek less conventional approaches if desired. The laboratory exercises focus on hydrometallurgical processing of a supplied copper ore. Additional exploration and discussion of engineering, environmental, and socioeconomic aspects of mining are encouraged insofar as the class schedule allows.

The relative value of copper and byproducts vs. material[1], energy[2], and environmental [3] costs is a difficult issue to address within the time constraints of a 3 or 4 week module. However, a semi-quanitative list of such factors should be easily generated by all students by the end of the module. Students should also be able to describe and argue for or against various copper production methods on the basis of their suitability for a given type of ore and by their relative environmental impact.

Chemical principles to be taught in the module (from the Tool Kit):

  • stoichiometry (electrodeposition, coulometric equivalence)
  • electromagnetic radiation and absorption (Beer's Law, spectroscopic analysis)
  • ionic/covalent/metallic bonding (physical properties of ore and copper, especially thermal/pyrometallurgical, strong and weak electrolytes)
  • oxidation states (redox titration, ore roasting/smelting, electrodeposition, bacterial Fe(III)/Fe(II) cycle)
  • free energy (E, electrodeposition, ore roasting/smelting)
  • Le Chatelier's principle (solvent extraction)
  • solubility and distribution equilibria (oxidic vs. sulfidic ore, copper complexation in spectroscopic analysis and solvent extraction)
  • acids and bases (acid consumption titration, leachate pH control, solvent extraction exchange)
  • redox reactions (redox titration, oxidative leaching, electrodeposition, cementation of copper with scrap iron)
  • catalysis (aerobic bioleaching)


Preferred prerequisite chemical principles for the module:
  • Students should already be familiar with the particulate nature of matter (atoms, molecules, mole, reaction stoichiometry, balancing chemical equations). It is also helpful if they are at least briefly familiar with the definitions of acid and base and with common types of chemical reactions (acid/base, precipitation, redox). Definition and conversion of various concentration units is particularly important for accurate preparation of standards and the calculation of analytical results.
  • A working knowledge of periodic properties, common oxidation states, the octet rule, and Lewis dot structures will be helpful in making sense of reactivities observed in the module.
  • An understanding of bond polarity will be helpful in discussion of complexation and acid/base phenomena.
  • An understanding of the general properties of various phases (gases, liquids, solids, solutions) is useful in distinguishing important stages in pyro- and hydrometallurgical methods.


Classroom Schedule

This schedule provides a template of topics and resources for 15 hours of class. Ideally, there will be time for 3-4 class periods before the first scheduled lab.

Class 1
Topics
Presentation of the problem and objectives of the module. Information will include perspectives on the scope, location, general methods, and environmental impacts of copper production. Market uses of copper and the impact of copper recycling should also be mentioned.
In-class activities
*10 min lecture introduction to objectives of the module and the video
*video, shown in-class to give visual impression of the scale and impact of mining operations
*brief group discussion to produce an outline (for a grade) of the environmental and scientific issues in designing a copper production facility
*assign lab teams and have them meet outside of class to delegate their tasks for the first lab period
Readings/resources
*video (Morenci Operations, 1995, 24 min)
*Ideally, a reading of 10-20 pp. should be prepared to summarize the following sources and support the perspective given in the video. Alternatively, the following could be assigned as readings directly.
*The best overview may be in the Kirk-Othmer Encyclopedia of Science and Technology, 4th ed. (consider excepts from the unit on Copper in vol 7,pp. 381-428).
*Chapter 1 (Synopsis) in Extractive Metallurgy of Copper (Biswas and Davenport) is suitable for an overview of copper production technology but does not deal with environmental aspects per se. Chapter 2 on Production Statistics should be used for instructor reference and lecture preparation, but not assigned.
*Chapter 1 (Mineral Extraction) in Environmental Effects of Mining (Ripley, Redman, Crowder) is a longer but more comprehensive reading in that it organizes the environmental factors around the production of a wide variety of materials.
*Recommend that students check one or more of the following web sites:
· US Geological Survey : http://www.usgs.gov/
· Minenet: http://www.microserve.net:80/~doug/
· Info-Mine: http://www.info-mine.com/main.html
· EcoNet Resources for Mining Activists: http://www.igc.apc.org/mining/
(includes e-mail subscription info for EarthWINS Daily, the mining-exchange newsletter - edited by Alice McCombs)

An exercise with internet-accessible information is conceivable but has not be developed yet in the module.

Class 2
Topics
Copper ore characteristics: predominant mineral forms (oxidic vs. sulfidic), their relative value (quality) and geological location (depth and associated minerals), the relative solubility (magnitude of Ksp) and acid-base characteristics of these minerals. Review of oxidation states, balancing simple redox reactions (as necessary in preparation for methods in classes 3 and 4).
In-class activities
*lecture and handout on on the application of equilibrium constants (Ksp) in solubility systems and the qualitative influence of acids and bases
*lecture table demonstration of the solubility of CaO and/or CaCO3 in neutral or acidic water
*example problems for students to work on balancing redox reaction problems specifically as related to the reactions of this module
*assemble in groups to work several illustrative quiz problems (submit for grading)
Readings/resources
*course text book selections on solubility rules, definition of Ksp
*assign problems to illustrate the qualitative consequences of acid-base activity on salt solubility.
*a good overview of copper mineral deposits and mining methods is in Copper: It's Ores, Mining and Extraction (Copper Development Association: Radlett, Herts, UK, no. 46, 1951, pp. 2-15.)
*Useful tables of copper minerals and locations are Tables 1 and 2 in the Copper unit in the Kirk-Othmer Encyclopedia of Science and Technology, 4th ed. (vol 7,pp. 381-428) and Table 2.6 in Extractive Metallurgy of Copper 3rd ed. (Biswas and Davenport, p. 34).

Class 3
Topics
The chemistry of the analytical methods scheduled in the lab
In-class activities
*Lab teams convene for internal discussion of the lab analyses; students will assume the role of specialists for each method and are responsible to describe the chemical interactions, reactions, and mathematical formulas that are pertinent for their assigned method. Each specialist should bring to class copies of a one-page handout which describes these aspects of their method. Answers to pertinent pre-lab questions must be included in the handout. A single copy of all the handouts generated by each team is to be collected, stapled, and submitted for grading.
Readings/resources
*Assign course text book readings as appropriate for each method (below)
· Methods A/B & C (spectroscopic analysis): Beer's Law, use of a standard calibration curve and regression analysis, the chemical basis of light absorption, electronic energetics of atomic metals and molecular complexes, reading on the atomization process is needed if method A is used
· Method D (redox titration): review of oxidation states, spontaneity of redox reactions, electrochemical series, titration stoichiometry and quantification
· Method E (acid/base titration): definition of pH, description of a titration curve, pH at equivalence, choice of indicators, titration stoichiometry and quantification
· Method F (heavy metal tests): solubility of metal ion species, acid/base dependence of solubility, general solubility rules

Class 4
Continuation of class 3 presentations.

Class 5
Topics
Organized summary of equilibrium concepts, definition and use of acid-base, complexation, solubility equilibrium constants (Ka, Kb, Kw, Ksp, and Kf).
In-class activities
*Lecture presentation of how to use these constants to calculate equilibrium concentrations of components in simple systems which are dominated by a single equilibrium, i.e. calculate the solubility, calculate the pH, etc.
*A good lecture table demonstration to illustrate the interplay between solubility and complexation equilibria is the sequential precipitation and complexation of Ag(I) (see Shakhashiri, B. Chemical Demonstrations, vol. 1, Univ. of Wisconsin Press: Madison, WI, 1983, pp. 307-313). This demo also ties in nicely to the analytical lab method for detection of Ag(I) in the ore samples.
Readings/resources
*Assign readings as appropriate for determination of equilibrium conditions in aqueous systems.
*Assign for next class appropriate practice problems, including some which are related to copper or metal extraction technology.

Class 6
Topics
Hydrometallurgical processing options for copper extraction. Presentation and references should provide and compare typical production parameters and results (i.e., concentrations, volumes, leaching rates). Should describe the major options which will be available for lab teams to use in the leaching study, i.e., bioleaching or chemical oxidation (Fe(III))
In-class activities
*If available, a guest lecturer on hydrometallurgy would be excellent because students could ask a presumed expert about the consequences of specific characteristics of their ore (as determined during the analysis lab).
*An alternative option would be to run short concurrent info sharing sessions on different processing options. Each lab team would send a representative to each session. Lab teams would reconvene (jigsaw model) to debrief and decide how to best conduct their leaching study.
Readings/resources
*Chapter 18 (Hydrometallurgical Copper Extraction) in Extractive Metallurgy of Copper (Biswas and Davenport) would be an excellent reference for students to read for conventional approaches.
*The best overall reference for bioleaching is the review "Bacterial Leaching" (Brierley, C.L. Crit. Rev. Microbiology, 6, 207-242 (1978)) but it is too long to assign in it's entirety. Good excerpts include (p. 207-212) Introduction, Leaching Methods, The Chemistry of Leaching (Copper), Bacterial Leaching, Commercial Leaching Operations Using Bacteria (Copper), and (pp. 241-250) Factors Affecting Bacterial Leaching.
*Short text book descriptions include:
*"Iron-Oxidizing Bacteria," "Biogeochemical Cycles: Iron," "Microbial Leaching" (in Brock, T.D.; Madigan, M.T.; Martinko, J.M.; Parker, J. The Biology of Microorganisms, 7th ed., Prentice Hall: Englewood Cliffs, NJ, 1994, pp. 592-595, 660-665).
*"Bioleaching of Metals" (in Atlas, R.M. Microbiology: Fundamentals and Applications, 2nd ed., Macmillion: New York, 1988, pp. 523-527).
*For leaching with chlorine/bleach, see: Cho, E.H. J. Metals, 1987, vol. 39, pp. 18-20.
*For leaching with ammonia, see: p. 378 in Extractive Metallurgy of Copper (Biswas and Davenport).

Class 7
Topics
Poster presentations of ore analyses
In-class activities
Team members will take shifts in attending and presenting their results to student evaluators during the session. Evaluators will complete assessment forms (yet to be created) and make constructive suggestions about the presentation or the conclusions of the work.
Readings/resources
Student lab guide should provide instructions for poster content and format.

Class 8
Topics:
Basic steps and chemical reactions in pyrometallurgical processing (smelting and conversion). If the instructor is comfortable with preparation of the students, the free energy of system components may be used to explain process temperatures and reactions. Some perspective on the relative importance of pyrometallurgy vs. hydrometallurgy in copper production should be given. The importance of smelter design and consequences for sulfur trapping (as sulfuric acid) is also important to include.
In-class activities
*Undecided at this time. A lecture would do but a suitable video on the topic would be excellent. Students could give short talks on the various types of smelter/converter arrangements after choosing from various reading resources.
*Alternatively, the instructor could use the case Hommers Mining Dilemma by Lantz and Walczak as the basis for a discussion on the differences between pyro and hydrometallurgy and the other social, political, economic, and environmental impacts of copper mining.
Readings/resources
*video (to be found)
*Review the sections on Chapter 1 (Synopsis) in Extractive Metallurgy of Copper (Biswas and Davenport). Selected portions of Chapters 5-7, 11, 14 and 15 can be excerpted to illustrate the technology of smelter/converter operations and sulfur trapping.
*A good, readable summary of pyrometallurgical terminology and methods is given in the Kirk-Othmer Encyclopedia of Science and Technology, 4th ed. (consider excepts from Copper in vol 7,pp. 381-428).
*For a concise summary of smelting reactions, origin of the term "smelting," and other smelting conditions, see "Conversion Reactions in Inorganic Chemistry" (Habashi, Fathi, J. Chem. Ed. 1994, 71, pp. 130-2). This article has a confusing error in reaction (1), which should look the same as reaction (4) but was accidentally written as a null reaction.
*Chapter 15 (Extractive Metallurgy) of Applied Inorganic Chemistry, (Swaddle, T.W.) has some nice figures of the relative thermodynamic stability of minerals under pyrometallurgical conditions.
*See "Copper-Alloy Metallurgy in Ancient Peru" (Shimada, I.; Merkel, J.F., Scientific American, July, 1991, pp. 80-86.). The reading does not focus on the chemistry of the proposed ancient smelting process but gives a nice technical presentation of the evidence (tools, furnaces, etc.). The authors also describe their modern day demonstration of the technique.

Class 9
Topics:
Quiz for first half of class.
Introduction of some examples of some environmentally damaged mining sites.
In-class activities
*Quiz on chemical aspects of copper ore analysis and extraction.
*Short lecture on the major impacts of copper mining (sulfide ores) and their chemical basis.
Readings/resources
*Chapter 5 (Sulphide Ores) in Environmental Effects of Mining (Ripley, Redman, Crowder) is an appropriate overview of the effects of metal sulphides in general. Sections on Copper, Aquatic Ecosystems, Atmospheric Effects, and Reclamation are recommended. The following case studies of environmental damage in Ontario give some perspective on the scale of damage.
*See bibliography of articles for other examples. Some especially interesting stories include:

The Butte/Clark Fork Superfund Complex (MT)
(a) "Hazardous wastes from large-scale metal extraction" (Moore, Johnnie N.; Luoma, S.N., Environmental Science & Technology, v. 24 (Sept. '90) p. 1278-82+) A detailed and educational description of the environmental damage at the Clark Fork River Basin Superfund site in western Montana. Detailed discussion of atmospheric, ground water, and ecosystem damage. (b) "As the Snake Did Away with the Geese" (Levine, Mark, Outside, vol 21, pp. 74-84, 164 (Sept., 1996)). Feature on the death of 342 migrating snow geese in the defunct Butte, MT copper mining pit. Interviews several local notables, including the representative for ARCO, owner of the pit.

Ducktown (TN)
"The death of Ducktown: a hundred years ago mining burned the only desert of the Mississippi into the Tennessee mountains" (Barnhardt, Wilton, Discover, v. 8 (Oct. '87) p. 34-6+). A fascinating historical and modern day review of this environmentally devastated region of TN that was once the nations leading Cu producer. Nice photos.

Class 10
Topics:
The mining dilemma: to build or not to build a mine.
In-class activities
Video presentation of the impact of mining operations. Excerpts from mining industry and a mining opposition group should be viewed. Students should take notes and read the assigned articles to prepare for a debate/discussion on the need for mineral resource management policies (in Class 11).
Readings/resources
*video (to be found)
*Mining the Earth (Young, Worldwatch Institute, 1992) is another good introductory reading that focuses on statistics, resources, and environmental impact but is less concerned with descriptions of mining technology.
*"Give the multinationals a break!" (Prance, Ghillean, New Scientist, v. 123 (Sept. 23 '89) p. 62.) This is an interesting pro-mining piece which suggests that fair-minded negotiation with responsible mining companies would improve efficiency and lessen impact of such ventures. Author is a botanical gardens director from England who visited and describes an operating bauxite mine in the Amazon rain forest. It's a little short and does not attempt to present the same broad perspective as the Worldwatch piece. A better selection could probably be obtained from a mining organization.
*Excerpts from or a summary of Chapter 21 (Recycle of Copper and Copper Alloy Scrap) in Extractive Metallurgy of Copper (Biswas and Davenport) would be helpful in understanding the scale, benefits and challenges of copper recycling.

Class 11
Topics:
Viewpoints on management of mineral resources
In-class activities
*Small group discussion of the mining dilemma. Students should critique the perspectives given on mineral rights and mining issues posed in the readings and video presentations. Groups will prepare a short set of insights into the problem which will be written and submitted for credit. Before the end of the class, a person from each group will present and defend their insights to the larger class.
*After class, each student will write a letter of opinion to a designated government official on some appropriate issue of mineral resource management. These will be collected for grading.
Readings/resources
*See Classes 9 and 10. Students may choose others from a list of recommended readings or from their own searching.
*At this time or before, lab teams should be given a hypothetical environmental scenario within in which they are to evaluate the wisdom of building a mine. Presumably, this scenario will include the "site" from which their laboratory ore sample was taken.

Class 12
Topics:
The chemistry of solvent extraction (SX) processing, including materials and parameters. This will involve presentation of metal chelate complexation reactions, Le Chatelier's principle, partition equilibria, and an isotherm model for partitioning.
In-class activities
*Instructor lecture on topics above as they pertain to the SX process. (Note: In order to obtain productive results in the lab in the module time frame, the lecture/demonstration format is preferred with the "demonstration" part achieved in the final lab period. If more time is available, students could be challenged to experiment with a variety of parameters in the SX process (temp, pH, conc. of copper and extractant, volume of phases) and determine appropriate relationships themselves.)
*After class but prior to the final lab, lab teams should calculate the amount of copper that they expect to be collected from their leachate in the SX exercise (see pre-lab questions).
Readings/resources
*Assign course text book readings as appropriate for each subtopic listed above. Recommend or supply appropriate practice problems that will reinforce the readings and application of principles taught.
*Excerpts from Chapter 19 (Solvent Extraction Transfer) of Extractive Metallurgy of Copper (Biswas and Davenport) should provide excellent summaries of the important practical aspects of solvent extraction.
*An illustration of representative results from the manufacturer of the extractant, such as an adsorption isotherm (see Instructor's Guide to the Lab).

Class 13
Topics:
The chemistry of electrowinning (EW). This should include the layout, terminology (anode, cathode), and material dynamics in an electrochemical cell, the Nernst relationship between potential and concentration, and the application of electrochemical stoichiometry (Faraday constant).
In-class activities
*As in Class 12, the efficiency of the lecture/demonstration model is proposed for the sake of time rather than pedagogy. Issues that should be dealt with include the difference between electrowinning and electrorefining (which is not demonstrated in the module) and how to calculate the electrochemical efficiency of copper electrodeposition (2 x moles Cu/moles electrons).
*After class but prior to the final lab, lab teams should calculate the target cell current and amount of time estimated to complete their copper deposition (see pre-lab questions).
*Classroom demonstration of the Nernst equation using various concentrations of Cu(II) (to be developed).
Readings/resources
*Assign course text book readings as appropriate for each subtopic listed above. Recommend or supply appropriate practice problems that will reinforce the readings and application of principles taught.
*Chapter 20 (Electrowinning) and 17.8-17.9 (Electrolytic Refining) of Extractive Metallurgy of Copper (Biswas and Davenport) will describe the empirical details and limits of electrodeposition.
*A good general description of electrolytic refining and EW methods can be found in the Kirk-Othmer Encyclopedia of Science and Technology, 4th ed. (see the unit on Copper in vol 7,pp. 381-428).

Class 14
Topics:
Costs of mining
In-class activities
*A brief lecture on how the costs of the proposed mining project should be estimated and classified in the final report, i.e., capital or financing costs, operating costs (see readings). A current market value for copper will be useful for estimation of economic viability.
*Remainder of class is used for lab team discussions on the approximate total costs of the mine that they are proposing to build.
Readings/resources
*Chapter 23 (Costs of Extracting Copper) in Extractive Metallurgy of Copper (Biswas and Davenport) is a good general and timely summary of capital and operating costs.
*The following readings, about a proposed mining development in Kakadu National Park, Australia, give an interesting scenario for the discussion of how to place a value on treasured places:

Anderson, Ian, "Gold rush threatens Australia's green dreams," New Scientist, v. 130 (Apr. 27 '91) p. 23-4.

"A price on the priceless: Australian government survey on whether to allow mining near the Kakadu National Park," The Economist, v. 320 (Aug. 17 '91) p. 61.

*An overview of the economics of bioleaching (in Chile) are summarized in the following readings:

"Bioleaching at Andacollo," The Mining Magazine, v. 165 (5), pp. 324-328, (Nov., 1991).

"Bioleaching of minerals - a valid alternative for developing countries," Acevedo, F.; Gentina, J. C.; Bustos, S.; Journal of Biotechnology, v. 31 (1), pp. 115-124 (Oct., 1993).

Class 15
Topics:
Should the mine be built?
In-class activities
A body of students posing as regulatory authorities and/or investor/executives will hear other designated students speak as technical experts on the question of whether the construction of a particular copper mine and refinery should be allowed. The structure is flexible and will depend somewhat on how many different mine site scenarios were given to the various lab teams. Several scenarios could be presented and discussed in a competitive fashion or one scenario could be presented and discussed by several experts with opposing viewpoints. The objective criteria for judging the question (economic, safety, environmental) should be spelled out in advance (preferably by the class). Experts should be elected from each lab team or teams that have a particular scenario. The judging body could be the entire class (democratic system) or a selected panel (bureaucratic system).
Readings/resources
No assigned readings are recommended but one recent book gives a fairly comprehensive review of current mining regulation practice in the US: McElfish, J.M.; Bernstein, T.; Bass, S.P.; Sheldon, E. Hard Rock Mining: State Approaches to Environmental Protection, Environmental Law Institute: Washington, D.C., 1996.

[1] Materials include water, sulfuric acid, solvent extraction components. Must assume some loss even with recycling.

[2] Depends on method of extraction - pyrometallurgy requires more energy. Electricity costs of electrodeposition are considered with all methods.

[3] Should consider (as appropriate) collection and treatment of spent leachate, recovery of heavy metals, acid gas controls, and cost of remediation/decommissioning.


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Last modified: 10/18/00 at 12:06 PM