A discussion on emerging issues and opportunities from the workshop

Alan Robertson (Earth Systems), Jeff Taylor (RGS Environmental), Tania Laurencont (Department of Primary Industry and Resources, NT), David Jones (DR Jones Environmental Excellence), Gilles Tremblay (INAP), Mansour Edraki (SMI/UQ), David Williams (UQ), Richard Martin (BHP)

Chaired by Dr Bruce Kelley

Questions:

• What are the emerging issues and opportunities from the Workshop? What are the AMD issues we face and how can we develop solutions to these?
• Can these translate into R&D or other projects which we can progress, possibly with help from INAP?
• How can we better build and sustain the AMD community in Australia? 
  • Waste rock dump (WRD) structures represent the more significant source of AMD in comparison to tailings storage facilities (TSFs) and final voids. WRD’s are also the major AMD source in old underground mines. A new approach to WRD construction is required. Thin lifts, and base-up construction of waste rock dumps could potentially prevent AMD generation. On the other hand, there has been a strong focus on moisture management in cover systems for mitigating AMD in WRDs. Opportunities also exist to use complementary remediation technologies to build multiple layers of materials to mitigate  AMD by selectively using non-acid forming or acid-consuming materials i.e. oxygen consuming materials, as part of the cover, and/or applying alkalinity producing materials beneath the cover.
  • Above ground TSFs cannot be built in wet climates (in Canada) but in Australia above ground TSFs continue to pose a challenge.  In-pit tailings disposal of tailings provide an opportunity. However, the closure and rehabilitation of those pits, particularly in coal mines, will be problematic due to the entrained (and potentially contaminated) water and low consolidation rates of fine tailings.  
  • Generally “Pit-void” closure is going to be increasingly important. This presents logistical problems during operation and after closure, as water from various sources enter the pit during the life of mine. The Pit lake database can be useful for managing these facilities not only on a site, but on a regional basis.
  • In the last few decades very large scale mining operations have been developed which are now gradually approaching closure. Lab-based risk predictions and management technologies cannot be directly applied to managing large waste storage facilities. The experience of a site like Rum Jungle in Norther Territory (NT) is a good example for the necessity of developing scale up factors from laboratory to field.  With more accurate scale up estimates, closure plans will no longer serve as conceptual models only, but will provide reliable design criteria. 
  • The focus of the AMD workshop has evolved over the years from geochemistry, to geotechnical aspects, and now increasingly includes biological topics. This is a reflection of the need for an interdisciplinary approach to managing AMD. Better integration of those three disciplines will result in a more comprehensive understanding of the complexity of AMD management. There is scope for further work on the role of biological systems.
  •  There are advancements in instrumentation and monitoring, particularly real time monitoring, as well as robust and affordable sensors. Numerical capabilities have also improved, so we can use numerical models with monitoring data to improve our predictive capability for AMD.
  • In the case of surface tailings or in-pit tailings, the optimum conditions for AMD reactions, and similarly for consolidation and  tailings seepage, depends on the intrinsic properties of the tailings, for example clay content and clay mineralogy.  Therefore, an opportunity exists to influence those conditions by “designing” tailings properties produced in a plant. 
  • Case studies are very important as they provide the opportunity to investigate the performance of a technology over time.  
  • Often decisions are based on traditional economic analysis such as NPV calculations. For example, the option of treatment in perpetuity may be driven by NPV analysis rather than considering alternative approaches, for example WRD construction aimed at prevention of AMD.  The nexus between economic analysis and technical analysis needs to be explored more fully to minimize closure and long term treatment costs. It is also likely that decisions on leaving waste above ground and not using voids are based on high level financial analysis. There are examples of highly reactive above ground waste materials that create spontaneous combustion and toxic gases in Australia.
  • To achieve the most cost and environmentally effective outcomes, the business case for AMD prevention and management needs to properly developed and presented to senior management.  An understanding of the company culture is required for more effective business engagement, and that must be done at the right level within the organization.
  • There have been advancements in characterizing AMD source terms, but it is equally important to be able to communicate the AMD risks to a variety of stakeholders, particularly with increasingly stricter regulatory requirements.