Abstract:
The water quality of mine drainage predicted by hydro-chemical modelling is sensitive to the approach implemented when going from the chemical characterization of representative samples to prediction models.
To estimate the reactivity of mining solid samples, kinetic tests must be used. For this, several methods exist, but the international standard in the last 3 decades has been the Humidity Test Cells (HTC) as described in the ASTM D5744-18. Nevertheless, this method does not intend to reproduce actual leachate from the field nor simulate site-specific conditions.
This work compares two approaches to predicting the quality of leachates produced by a 30 m high Waste Rock Dump (WRD). The first method corresponds to the direct HCT leaching rate scale-up, the most common method used in the mining industry for water quality prediction. The second method corresponds to the calibration of the abundance and reactive surface of the mineral assemblage responsible for the observed HCT leaching rates considering a 1D reactive transport column implemented in PhreeqC.
This work concludes that short—and long-term water quality predictions using the direct HCT leaching rate scaling method do not reproduce the physico-chemical characteristics of WRD seepages. This conclusion is extensive to any other mine facility, as the stable leaching rates methodology does not consider the physico-chemical processes that are expected to occur within a WRD (nor in any other facility)
On the contrary, water quality predictions using the calibrated abundance and specific surfaces of the mineral assemblage tested in the HCTs reproduce the physicochemical characteristics observed in the seepages correctly. To do so, these calibrated parameters must be used as an input in reactive-transport simulators (e.g., Hydrus-HP1, Phast) where more accurate water quality prediction can be performed by coupling the water, gas and heat transport phenomena, and the water-rock-gas interaction process.
Authors:
Oscar Benavente | SRK US
Ignacio Villalón | SRK Chile
