Managing poor-quality water from mine wastes is one of the biggest challenges facing mining companies globally. Management tools can be classified along a spectrum. At one extreme, strategies attempt to shut down leaching processes, often leading to the incorrect assumption that the site can be completely abandoned. Examples of these strategies include subaqueous disposal using impoundments and the placement of liners. At the other extreme, there can be reliance on water treatment, which requires conveyance and storage of contaminated water and management of treatment residuals.
Between these extremes are tools that reduce source leaching but ensure a continued site presence to allow for long-term monitoring and maintenance. An example of such a tool is co-disposal (blending) of waste rock classified as potentially acid generating (PAG) and non-PAG so that the resulting mixture behaves as non-PAG. When properly executed by scheduling placement to achieve intermingling, acidification of the PAG components can be prevented in perpetuity, thereby eliminating the high concentrations of metals associated with acid rock drainage. There is no reason these conditions cannot be sustained indefinitely.
Weathering processes will continue at low rates, but leaching may occur at levels low enough that either drainage treatment to achieve acceptable concentrations for discharge is never required, or semi-passive water treatment technologies can be used. These management measures may require a limited ongoing site presence but, importantly, conveyance and storage of highly contaminated acidic water can be avoided.
SRK has been working with several clients to implement co-disposal of PAG and non-PAG waste rock, with a focus on the mining approaches required to achieve effective intermixing.
The scale at which mixing needs to occur is based on theory¹ and has been demonstrated to prevent acidification at small scales, which is the ultimate objective².
(1) https://doi. org/10.1144/geochem2021-066
(2) https:// bc-mlard.ca/files/presentations/2023- 19-DAY-DONKERVOORT-waste-rock-geochemical-management-practices-teck.pdf
