Innovative tailings solutions – high density thickened tailings (paste), dry stacking
Exploring innovative tailings storage solutions is one way to potentially reduce operation costs – and significantly.
Commodity prices are still low and the need to reduce operation costs is still high. The opportunity to utilise innovative techniques to improve mining project outcomes is now favourably viewed when conducting feasibility studies.
Options available include the use of high density (HD) thickened tailings or filtered tailings. Selection of the tailings system for the project will determine the tailings’ geotechnical characteristics within the storage facility, i.e. tailings density and strength. These will have a number of design implications, including the storage capacity required, water management and closure capping construction.
The potential benefits can be significant and include:
- reducing ‘whole of life’ costs
- improving water management and the associated costs for the project, including water conservation
- better closure outcomes, i.e. closing and restoration is easier and cheaper
- simplifying regulatory approvals
Coffey recently conducted a value engineering study for a large copper mine in Chile South America. One of our client’s main project drivers was water – in terms of cost and conservation.
They were looking to improve their tailings design which comprised large thickened tailings storage, and they also wanted a third party review undertaken.
Our tailings team conducted a design optimisation study which involved looking at multiple strategies to moderate seepage and tailings deposition. We also reviewed alternative methods including central thickened discharge and dry stacking.
As part of the study, design concepts were developed for the above options, and detailed modelling was also conducted, which included:
- tailings beach modelling, for design of containment embankments and discharge
- water balance modelling to estimate water savings
The cost analysis for the design optimisation indicated that the benefit of adopting underdrainage and a lining system was a marginal water cost saving – the main reason for adoption would be to reduce environmental risk.
It was assessed that the existing design would potentially expose the client to significant business risk if the design criteria on tailings beach slope were not realised in practice. Analyses of a facility using central thickened discharge techniques indicated that the costs would be similar to a down valley discharge design, but overall business risks could be reduced.
Water costs in Chile are high at around US$2.50/m3 - making water conservation a high priority aspect for these projects.
A financial model for the dry stacking project was developed presenting the cash flow for the project life. The value of the dry stacking project was assessed in terms of capital costs, operating costs and water savings in relation to the adoption of dry stacking rather than thickened tailings to provide an estimate a net capital and operating cost.
The financial assessment indicated that the dry stacking project resulted in a positive cash flow, or Net Present Value, when water savings were taken into account. This provided the client with clarity on this aspect of their assessment as they progressed with broader design and production considerations.
How we can help
Conducting value engineering or options studies is a good way of exploring the cost benefit of various alternate solutions, and ultimately to identify the optimum solution for a particular project.
The value engineering studies should include:
- civil / geotechnical engineering aspects
- process engineering aspects, including piping, pumping, thickeners, filters etc
- environmental aspects
- risk and reliability management
- cost estimation
- SWOT analysis
- option ranking
If you have any questions about how this might help you with your project, please contact Chris Hogg, Principal Tailings Engineer on +61 427 665 262 or via email at firstname.lastname@example.org