Field Assessment of Sulphide Oxidation Rates in Cold Environment: Case Study of Raglan Mine

In this field study conducted on Raglan Mine's tailings storage facility (TSF), tailings oxidation rates were characterized with the oxygen consumption (OC) method. Surface tailings unfrozen volumetric water content and temperature were also measured simultaneously with OC tests. Oxygen fluxes between 30 and 550 mol·m⁻²·yr⁻¹ were observed during summers 2011 and 2012 when tailings temperature and unfrozen volumetric water content varied between -0.1 and 12.8°C and 0.09 and 0.23 respectively. These oxygen fluxes are non-negligible, but lower than those measured in the lab for the same tailings, which varied between 390 and 1070 mol·m⁻²·yr⁻¹ at 21°C. Oxygen flux drops in October 2011 to values below 10 mol·m⁻²·yr⁻¹ with unfrozen volumetric water contents less than 0.09 and temperatures of around -4°C. Results of this study show that, as expected for dry stack tailings, the degree of saturation at Raglan Mine's TSF (generally between 40% and 60%) is not sufficiently high to control oxidation reactions. Oxygen fluxes decrease with temperature and they are greatly reduced when tailings temperature reaches a value of -6°C, conditions observed for a period of 168 days of the year. This study also showed that be used to approximate the effect of temperature on oxygen fluxes for activation
energy values between 60 kJ/mol to 124 kJ/mol.