Credit: INAP Covers Report – Illustrator Derrill Shuttleworth
Over the years, INAP has instigated and funded a number of key Acid and Metalliferous Drainage (AMD) research projects to fill knowledge gaps. Cutting-edge technologies are studied, AMD measures at specific sites are examined, and literature reviews are undertaken to summarise AMD state-of-the-art.
Current and Ongoing INAP Projects
Updates to Global Acid Rock Drainage Guide (GARD Guide)
The GARD Guide is intended as a state-of-practice summary of the leading practices and technology to assist mine operators and regulators to address issues related to sulphide mineral oxidation. The GARD Guide is a living document and requires periodic updates and this was started in 2017. The first step was a detailed review of the existing chapters by global experts to identify gaps and to prioritize the chapters requiring updating. Chapter 7, Treatment, was the first of the chapters to be selected and this work, a collaboration between Klohn Crippen Berger and Golder, will be completed in early 2021.
One of the gaps that was identified was the integration of recent developments in mine closure and sustainability to the GARD Guide. It was agreed that a dedicated chapter on “Mine Closure / Sustainability” would be added to the GARD Guide. Golder was awarded the contract in early 2021 and this dedicated chapter will significantly raise the profile of this area and provide a more focussed and holistic view for stakeholders and users of the Guide.
The next chapter to be updated will be Chapter 6 – Prevention and Mitigation. Plans are to have the work started in 2021. Please consult the GARD Guide web page for complete project details.
INAP has launched a webinar series that aims to provide a mechanism for INAP member companies to share new technical knowledge on a more frequent basis. In addition, it would provide access to an expanded audience who do not typically attend AMD/ARD management related conferences or presentations and would introduce INAP to non-member companies with the goal to increase membership by demonstrating value. Mine Waste Management (MWM) of Perth, Australia was hired to coordinate and host the webinars. The webinars are presented in two different time slots, which allows participants to select the session that best suits their time zone.
INAP, via MWM, hosted two webinars in 2020 and more are planned for 2021. Some of the webinars are for member companies only and others are open to other organizations. Some will feature projects funded by INAP but others will be of general interest to members. The two held in 2020 were on “Building Mine Rock Stockpiles to Enhance Operational and Closure Performance” and the “Update to Chapter 7 of the GARD Guide”. Videos of the presentations are posted on the INAP website for future viewing. The response to the webinar series has been excellent and information on future webinars can be found on the INAP home page and on the INAP LinkedIn page.
Geochemical Degradation of Tailings and Fills (Collaborative project with MEND)
INAP, in partnership with MEND, are funding a literature review and gap analysis by Klohn Crippen Berger on the effects of geotechnical implications of geochemical reactions in tailings dam materials. The literature review will outline key processes related to degradation of structural fill, including the chemical weathering of fill materials resulting in a change in material strength or permeability, the formation and accumulation of secondary minerals from seepage resulting in pore space reduction and a change of material physical properties, and the mineral alteration and grain size reduction of tailings and other fill materials. How these processes lead to change to material compressibility, consolidation, cohesion, porosity and permeability will also be discussed. A synthesis report indicating how these processes ultimately alter the materials such that original design intent is compromised, potentially resulting in a global stability of the tailings storage facility will be the final outcome of this study.
Completed Research Projects
- Rock Placement Strategies to Enhance Operational and Closure Performance of Mine Rock Stockpiles – Phase 1
- Global Cover System Design – Technical Guidance Document
- Store and Release Covers – The Role of Vegetation (Stage 2)
- Evaluation of the Long Term Performance of Dry Covers
- Waste Rock Dump Characterization
- Treatment of Sulfate in Mine Effluents
- Rum Jungle Waste Rock Cover
- Diffusive Gradients in Thin-films
- Co-Mixed Tailings Waste Rock and Slag
More information, including project reports and presentations, can be made available by contacting the Technical Manager, Gilles Tremblay.
Rock Placement Strategies to Enhance Operational and Closure Performance of Mine Rock Stockpiles – Phase 1 (Earth Systems and O’Kane)
The mining sector worldwide is experiencing significant increases in closure costs and is accumulating a growing number of stranded liabilities due to poor closure outcomes. Direct and indirect measurement of acidity loads from various mine site domains at more than 40 sites over the past 25 years has revealed that disposed mine rock materials are responsible for the majority of AMD/ARD pollution (60-80%) at most mine sites.
Conventional mine rock stockpile (MRS) construction typically involves disposal of well sorted, relatively dry rock materials from the back of tip-trucks down angle-of-repose slopes of previously disposed material with wide particle size distributions. This method minimises costs associated with loading, hauling and placing rock, while maintaining geotechnical stability of the MRS. However, it also optimises sulfide oxidation and minimises acid neutralisation; the approach is therefore largely responsible for long-lived water quality impacts post-closure.
Improved construction methods are available and new approaches are emerging. These are principally focused on improved control of gas transport within MRSs, both during and post construction of the MRS, which can be influenced by transport disruption layers / trafficked layers, encapsulation of high-risk materials, decreasing tip head heights, and paddock dumping in thin compacted layers from the base up. Strategic placement of oxygen consuming and pyrite passivating materials can also lower acidity production. Each of these construction methods perform differently under different physical and chemical conditions (e.g. topography, climate, geochemistry) and can also be combined to lead to improved outcomes. Ideal construction methods are highly likely to be site-specific.
This report, Phase I of a multi-phase project, focused on the geochemical benefits of the various construction methods. Numerical modelling was also conducted to demonstrate how the performance of conventional end-dumped MRSs can be compared with some of the improved MRS construction methods, in terms of a percentage reduction in kilograms of acidity produced per tonne of waste rock placed (kg H2SO4/tonne). A failure modes and effects analysis was conducted to demonstrate that risks associated with MRS construction can be progressively lowered (or adaptively managed) by adopting a combination of the improved construction methods. It also provides the groundwork for additional phases, or ‘next steps’, for building improved MRSs.
→ Click here for the final report (5.4 MB)
→ Click here for the Webinar Presentation by Dr. Jeff Taylor, Earth Systems (June 9, 2020)
→ Click here for the Webinar Presentation by Mike O’Kane, Okane (June 9, 2020)
→ Click here for the Webinar Presentation Slides
Global Cover System Design – Technical Guidance Document (November 2017)
The Global Cover System Guidance Document, like the GARD Guide, is intended as a best practice summary to assist mine operators, designers, and regulators to address issues where cover systems can be employed. This document builds on previous technical guidance documents on cover system design, construction, and performance monitoring. The Global Cover System Guidance Document will be of interest to individuals who are seeking more detailed information than what is outlined in Section 6.6.6 of the GARD Guide - Engineered Barriers.
A holistic framework for management of reactive materials during operations and at closure is the pillar of the document. The framework for cover system design is presented at a high level, suitable for readers with minimal technical background. It is presented at a conceptual level, using a hierarchy of climate, geology and materials, and topography, leading to an understanding of the patterns of water movement on a specific landscape. Ultimately, these elements will govern how cover systems perform, and it is up to designers to manipulate them to achieve desired performance.
This document presents a conceptual model of how cover system designs might affect contaminant and acidity loading. This model attempts to determine when the varying roles of the cover system design (e.g. control of net percolation or oxygen ingress), might influence loadings. Acknowledgment of these unique relationships provides an opportunity to optimize ML/ARD management in a cost-effective manner. Other key concepts discussed within the document are the role cover systems play over the life of the mine from early conceptualization to long-term performance monitoring considerations.
Application of the holistic framework is achieved through the use of a cover system design tool that walks users through relevant climatic factors to optimize cover system design alternative for a desired performance design criteria. This allows users to understand what a realistic objective is when developing cover system design alternatives based on site-specific climate conditions. Additionally, the tool refers to specific elements integral to the design where an in text commentary is provided. The tool helps identify where potential for management exists on the site, leading to the selection of the most appropriate form of prevention.
The information provided within the tool is not a replacement for site-specific classification and engineering required for cover system design. However, the tool is a means of beginning early conceptualization to help focus further investigation at a site level and to begin to form realistic expectations for cover system performance at an early stage of a project.
→ Click here for the final report (12.4 MB)
Designing Effective Store - Release Covers for the Long–Term Containment of Mine Waste - The Role of Vegetation (Stage 2)
The former Australian Centre for Minerals Extension and Research (ACMER) research project, managed by the Centre for Mined Land Rehabilitation at The University of Queensland, addressed the following objectives: (1) to use water balance data for vegetated store-release covers to assess the performance of existing covers, and contribute to recommendations of future covers, (2) provide a workable model that links into existing cover water balance models, and effectively describes annual water use as a function of weather, leaf area index, changes in root zone properties and cover construction technique, and (3) facilitate significant improvement in the capacity of existing water balance models to describe hydrological processes in waste storage facilities. The work included quantifying and modeling the water uptake processes of different soil and vegetation community combinations which were (or are being) used as store-release covers at two established sites with differences in climate, vegetation, geology and soils from western and eastern regions of Australia.
In addition to the project report, a list of publications originating from research within this project is available.
A study to improve our ability to accurately predict the long-term performance of dry covers
Dry cover systems are one of the most common preventative measures used to control acid drainage. Accurately predicting the long-term performance of covers is a vital part of minimising the mining industry’s AD legacy issues. With this objective a study on the long-term stability of dry covers was commissioned to O’Kane Consultants Inc.
- Identified and defined factors that affect long-term performance.
- Evaluated state-of-the-art tools for modelling dry cover systems.
- Provided recommendations for improving and validating existing models.
→ Click here for the final report (1674 KB)
A characterization study of the geo-chemical and hydrological nature of 2 waste rock dumps that were being dismantled by member companies.
In 2000, waste rock dumps from the Rio Tinto Kennecott Ridgeway Mine and the Inco Whistle Mine needed to be relocated. The opportunity was seized to study the geochemical and hydrological nature of the waste rock dumps and the extent of oxidation zones within them. The project generated much interest and was jointly funded by INAP, NSERC, and R&D Start Funds. Dr. Ward Wilson from UBC, Maree and Stuart Miller from EGi, and David Williams from the University of Queensland lead the study. The findings from the work link the hydrological and geo-chemical nature of the dumps, which contain complex hydrological pathways that dictate the geo-chemistry of the released drainage. There is an indication that many of the layers within the dumps contain large amounts of stored oxidation products and soluble metals. The layers may not have an adequate degree of saturation to allow water to flow through them, thus reducing final drainage concentrations.
→ Click here for the final report (806 KB)
A review of sulphate treatment practices and a discussion of legislation trends "Treatment of Sulphate in Mine Effluents".
Very little research has been undertaken on the treatment of sulphate in mine effluents. INAP members saw the need to fund a literature review of state-of-the-art sulphate treatment processes including regulations and guidelines from governments and agencies around the world. Lorax Environmental (the consultant) carried out the study, which describes methods for removing sulphate and metals from mine effluents and associated operating costs. Case studies of successful operations are also documented.
→ Click here for the final report (3416 KB).
A case study on the deteriorating performance of the 18 year-old Rum Jungle dry cover system in Northern Territory, Australia.
The 18 year old cover Rum Jungle in Northern Territory, Australia is one of the oldest cover systems for which the design, construction, and continuous monitoring date are well documented. Water infiltration through the covers increased significantly in the last few years and this project was designed to use the data history to understand the reasons for the deterioration performance. The Australian Nuclear Science and Technology Organisation (ANSTO) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) were contracted to undertake the work. The study found that the cover materials no longer met the original design specifications –particularly for permeability which increased by several orders of magnitude. Findings from the study indicated that the increased permeability may be attributed to:
- A shortage of cover material during construction resulting in bare patches;
- A combination of biological and physical process - galleries formed by termites and ants, root growth from
- the pasture grasses and the few volunteer trees, and an extensive system of shrinkage/dessication cracks.
→ Click here for the final report (2224 KB)
A study to use Diffusive Gradient in Thin-films (DGT) technology (or gel samplers), which allows for in situ determinations of free-ion activity of metals in mine water and provides a more accurate representation of biological impacts than measurements of total or dissolved metal concentrations.
Conventional water quality analysis is restricted to measuring total and dissolved metals in discrete water samples. Lorax (the consultant) was commissioned to undertake a study on the use of diffusive gradients in thin-films (DGT) - or gel samplers as this technology can provide a more accurate estimation of metal toxicity in water.
The project findings indicated that the use of DGT provides a measure of metal bioavilability, and hence a more representative measure of metal toxicity in water. This is mainly due to the fact that DGT detect free or weakly complexed metal species without measuring constituents that are not bio-available. The use of DGT also has the advantage of being an in-situ measure and can provide a time-integrated estimation over a deployment interval. This is especially beneficial when dealing with highly variable water quality, as is usually the case when measuring mining effluents discharged into natural watercourses. The use of DGT is, however, limited to a certain pH range (5-9 for most metals, 2-11 for Cu) and is not effective in waters of very low cation concentration. The study concluded that the DGT technique can be applied to various aspects of environmental chemistry, however more work is required to validate the use of DGT in mining-impacted waters.
→ Click here for the final report (1587 KB)
A review of the potential use of co-disposed waste rock and tailings for the construction of covers on mine waste dumps as a practical, low cost AD prevention method.
Following a literature review on the application of co-disposed tailings and waste rock to construct covers, this project was designed to examine the stability and hydraulic conductivity of a number of co-mixtures with varying ratios of tailings, waste rock and slag. Klohn Crippen in association with Dr. Wilson from the University of British Columbia, were commissioned to undertake the study.
The findings of the work can be summarized briefly as follows:
- Well-graded materials provide the best performance for the construction of soil cover systems with high resistance to erosion, frost, and desiccation. The co-mixtures of slag, waste rock and tailings provided a material that showed both excellent geotechnical characteristics and varying degrees of hydraulic conductivity.
- In-situ mixing of tailings and waste rock is feasible for semi-competent rock types and has low costs. However, this method provides poor cover performance on dump slopes. Layering tailings and waste rock results in good covers and involves low costs, but is also difficult to apply on slopes. Mechanically placing engineered mixtures of tailings and rock provides the most flexible cover option for flat and sloping surfaces. Waste rock would optimally be crushed to 50-75 mm minus size to have the right grading, however this method involves double the cost of the other methods.
- When bentonite was added to the co-mix the conductivity decreased, indicating that once the characteristics had been determined it would be possible to blend mixes with varying properties to meet the needs of the cover being designed.
- Estimates of cost indicated that the covers would be potentially expensive and future focus would have to include an examination of means to provide these mixes in a cost effective manner. Bentonite addition particularly added considerable costs to the overall cost per area of co-mix covers.
→ Click here for the final report (202 KB)