The release of nitrates (NO3−) and ammonia (NH3) from explosives during mining are usually attributed to spillage or incomplete detonation and subsequent dissolution of ammonium nitrate (NH4NO3). Field Kinetic Cells
(FKT) monitored over three years were used to determine the rate of release of the nitrates from pre-blast, freshly blasted (<10 days old) waste rock and kimberlite (KMB), and fresh tailings. The field conditions were -15˚C and 10˚C (extreme winter), 23˚C maximum average temperatures, 750 mm mean annual rainfall, and frequent snowfall.
The study indicated that >75% of the nitrates are flushed by recharging water during the displacement of the first stored water volumes. Leaching occurred during summer. No leaching occurred in winter due to frozen conditions and lack of rainwater to mobilise nitrates. The leaching rates were established to be as follows in decreasing order in mg/kg/day:
Blasted KMB (0.0002−0.024) > Blasted Waste Rock (BWR) (0.0001−0.019) >
Tailings (0.0002−0.008) > Unblasted Waste Rock (UBWR) (0.0001−0.0024)
The study followed the recommended procedure for predicting nitrates export by Ferguson and Leask (1988) . The FKT leaching rates were scaled to field rates using particle size (density) scaling factors. The results indicated that it will take 12−17, 2.6−3.5, and 2.2–2.9 years for nitrates to be leached from WRD1, WRD2, and TSF respectively. The apportionment of the nitrates’ loads to the site components will affect the predicted times and can be refined based on the number and sizes of the waste facilities over time.
