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Remining Old Tailings Dams

Remining Old Tailings Dams. John A. Meech and Jessica Xing Ye Wang The University of British Columbia The Norman B. Keevil Institute of Mining Engineering Vancouver, British Columbia . Outline. Background Tailings Retreatment Tailings Retreatment Model Design and Economic Module

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Remining Old Tailings Dams

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  1. Remining Old Tailings Dams John A. Meech and Jessica Xing Ye Wang The University of British Columbia The Norman B. Keevil Institute of Mining Engineering Vancouver, British Columbia 2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITIONSHECHTMAN INTERNATIONAL SYMPOSIUM

  2. Outline Background Tailings Retreatment Tailings Retreatment Model • Design and Economic Module • Disposal and Reclamation Module • Risk Assessment Module • Decision-Making Module Validation and Verification Conclusions and Recommendations 2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITIONSHECHTMAN INTERNATIONAL SYMPOSIUM

  3. Issues with Old Tailings Dams Stability (slopes, erosion, chemicals) Aquatic Emissions (acid, metals) Atmospheric Emissions (toxic gases, mercury) Dust releases Dam failures High-grades of values Revegetation and reclamation 2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITIONSHECHTMAN INTERNATIONAL SYMPOSIUM

  4. Environmental & Social Concerns • Physical Stability • Failure • Dust Issues • Chemical Stability • Acid Rock Drainage • Metal Pollution • Social Concerns: • Poor reputation of mining • Close monitoring by public/aboriginals/ NGOs • Political pressure (local/global) • Regulation requirements • ARD • Britannia Mine, BC • Dust - Colomac Mine • Yellowknife, NWT • Dam Failure - 1994 • MerriespruitMine, South Africa Sources: http://www.tailings.info/merriespruit.htmhttp://www.aadnc-aandc.gc.ca/eng/1100100026732/1100100026841

  5. Tailings Retreatment Processes Simplified Flowchart of Retreatment Method

  6. Tailings Retreatment Investment opportunity Revenue from metal extraction Offset of rehabilitation costs Dam Failure prevention Elimination of pollution remediation costs Long-term liability reduction 2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITIONSHECHTMAN INTERNATIONAL SYMPOSIUM

  7. Tailings Retreatment Model A Model to Assist Decision-making on Retreatment of Copper Tailings Dams • Model addresses two issues: • Economic benefits • Improvements in long-term liability “Should you reprocess the tailings?” • How does it work? • Input via a set of questionnaires • Data processed by model • Generates a report Framework of the Tailings Retreatment Model

  8. Tailings Retreatment Model An Excel spreadsheet model including: Mathematical calculations Fuzzy Logic Rule-based System 2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITIONSHECHTMAN INTERNATIONAL SYMPOSIUM

  9. Tailings Retreatment Model • Fuzzy Sets • Rule Base • Fuzzy Associative Memories Weighted-Inference Method • Defuzzification Method DoB = Degree of Belief (0-100) and Sup = Supremum

  10. Design and Economic Module Economic Criteria Procedure for Flowsheet Selection and Economic Analysis

  11. Flowsheet Alternatives • - Excavation or Monitor Mining • - Grinding coarse or bulk • Flotation (bulk) • Regrinding (coarse) + Flotation (bulk) • Flotation (bulk) + heapleaching flotation tailings • Flotation (bulk) + tankleachingof concentrate • Flotation (bulk) + heap leaching of concentrate pile • Heap leaching (bulk) • Heap leaching (coarse) • Agglomeration/heap leaching (bulk) • Tank leaching (bulk) • Tank leaching + Flotation of leach residue • Regrinding (coarse) + Tank leaching (bulk) Complete Retreatment Flowsheet– over 1,000 combos

  12. Flowsheet Alternatives • - Excavation or Monitor Mining • - Grinding coarse or bulk • Flotation (bulk) • Regrinding (coarse) + Flotation (bulk) • Flotation (bulk) + heapleaching flotation tailings • Flotation (bulk) + tankleachingof concentrate • Flotation (bulk) + heap leaching of concentrate pile • Heap leaching (bulk) • Heap leaching (coarse) • Agglomeration/heap leaching (bulk) • Tank leaching (bulk) • Tank leaching + Flotation of leach residue • Regrinding (coarse) + Tank leaching (bulk) Complete Retreatment Flowsheet– over 1,000 combos

  13. Flowsheet Alternatives • - Excavation or Monitor Mining • - Grinding coarse or bulk • Flotation (bulk) • Regrinding (coarse) + Flotation (bulk) • Flotation (bulk) + heapleaching flotation tailings • Flotation (bulk) + tankleachingof concentrate • Flotation (bulk) + heap leaching of concentrate pile • Heap leaching (bulk) • Heap leaching (coarse) • Agglomeration/heap leaching (bulk) • Tank leaching (bulk) • Tank leaching + Flotation of leach residue • Regrinding (coarse) + Tank leaching (bulk) Complete Retreatment Flowsheet– over 1,000 combos

  14. Flowsheet Alternatives • - Excavation or Monitor Mining • - Grinding coarse or bulk • Flotation (bulk) • Regrinding (coarse) + Flotation (bulk) • Flotation (bulk) + heapleaching flotation tailings • Flotation (bulk) + tankleachingof concentrate • Flotation (bulk) + heap leaching of concentrate pile • Heap leaching (bulk) • Heap leaching (coarse) • Agglomeration/heap leaching (bulk) • Tank leaching (bulk) • Tank leaching + Flotation of leach residue • Regrinding (coarse) + Tank leaching (bulk) Complete Retreatment Flowsheet– over 1,000 combos

  15. Flowsheet Alternatives • - Excavation or Monitor Mining • - Grinding coarse or bulk • Flotation (bulk) • Regrinding (coarse) + Flotation (bulk) • Flotation (bulk) + heapleaching flotation tailings • Flotation (bulk) + tankleachingof concentrate • Flotation (bulk) + heap leaching of concentrate pile • Heap leaching (bulk) • Heap leaching (coarse) • Agglomeration/heap leaching (bulk) • Tank leaching (bulk) • Tank leaching + Flotation of leach residue • Regrinding (coarse) + Tank leaching (bulk) Complete Retreatment Flowsheet– over 1,000 combos

  16. Design and Economic Module Base Case Economic Analysis - Future Failure Cost 5 year failure probability = 5% Year of certain failure = 50 Weibull Cumulative Failure Probability vs. Time

  17. Disposal &Reclamation Module Tailings Disposal and Reclamation Selection Module

  18. Disposal &Reclamation Module

  19. Risk Assessment Module Exposure Assessment Risk Characterization • What are the consequences if it happens? • What can • happen? • What is the risk of each failure mode? • How likely is it to happen? Identify Potential Failure Modes and Mechanisms Consequence Assessment Hazard Assessment FAM Map for Risk Characteristics

  20. Risk Assessment Module Hierarchy of the Risk Assessment Module

  21. Decision-Making Module • Decision-Making Criteria: Three Pillars of Decision-Making about Tailings Retreatment

  22. Validation and Verification Four hypothetical cases

  23. Validation and Verification

  24. Validation and Verification Project Economic Sensitivity Analysis Percent Change in Input Variable to Yield an NPV @5% = 0.0 * Actually gives an NPV of $100M 2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITIONSHECHTMAN INTERNATIONAL SYMPOSIUM

  25. Conclusions • The model is able to: • Conceptually design a tailings retreatment process • Evaluateeconomic and environmental benefits • Assist in multi-criteria decision-making Conclusions • Further modules or rules for: • Detailed mining method selection • Unit processing operations selection • Additional reclamation technologies • User interface to enter or modify internal parameters • Practical "real" cases of copper tailings to be tested Recommendations 2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITIONSHECHTMAN INTERNATIONAL SYMPOSIUM

  26. THANK YOU FOR LISTENING! Questions? 2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITIONSHECHTMAN INTERNATIONAL SYMPOSIUM

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