Notes for Reprocessing of Historical Tailings

The recovery of valuable components from mine waste and tailings is not a new concept and in theory all that is needed is the right technology and an adequate amount of material to make the exercise economically justifiable.

However, the author’s recent experience with several gold recovery projects indicates that, as with most if not all mining projects, reality is much more complicated and involves consideration of many factors. Successful metal recovery depends on grade, tonnage and processing technology but the determination of those factors depends on adequate and appropriate sample collection and a range of laboratory tests.

Sampling of tailings is necessary to assess variations in tailings thickness and grade as these may follow significant trends that reflect not only the original composition of the ore but also variations in historical recovery rates and disposal patterns within the tailings storage area. As well, tonnage and grade estimates are necessary for economic evaluation of the project and therefore a rigorous and systematic drill program is a necessary early component of any tailings recovery study.

Laboratory tests are necessary to check the state of oxidation of the materials, to determine variations in grain size and liberation in order to establish suitable processing and recovery methods. The collection of all available historical processing data is another very important way at this stage that can help to choose the proper test procedures.

Once the process at a lab scale has been confirmed, a process design can be started that will include metallurgy and engineering components. Materials handling can be a challenge as reprocessing is not simply a matter of dumping new tailings into the old tailings storage area; a new or transitional storage area may be necessary, and when chemicals are involved, this may require a specific environmental impact study.

An environmental impact study as well as a full permitting process are also integral components of any tailings recovery study. These components can be complicated and challenging, particularly when the tailings in question are old and the tailings storage area or the tailings themselves have been reclaimed or adapted for other uses.

In addition to technical considerations, all projects must be subject to economic analysis and a practical cutoff grade must be established based on project economics. Although most tailings materials are very fine, regrinding may liberate significant quantities of contained metal that can be recovered using modern technologies. However, for a standalone tailings reprocessing project, the cost of regrinding can easily make the process uneconomic so careful economic analysis is critical.

In conclusion, simple ideas are sometimes complicated. The reprocessing of tailings can be an easy route to mineral production and short-term cash-flow. However, like any mining project, careful technical and financial analysis are required first and caution is required at every step.

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