| Processing Plant Emissions | WNP Processing Plant Air Discharge Assessment | 4397169-66885702-113 | 16/06/2022 | 4 Sensitivity: General lower and therefore, a higher proportion of the mercury content of the ore is expected to be emitted to the atmosphere. As a consequence, unmitigated mercury emissions from the Processing Plant would be expected to increase when the WNP is commissioned. Peak emission rates would occur when GOP ore is being processed. A summary of the ore properties is shown in Table 2-1. Table 2-1. Summary of ore properties MUG Ore WUG ore GOP Ore Mercury content 0.30ppm 0.60ppm 3.3ppm Percentage mercury retained in tailings 99.3% 90% 70% OGNZL has undertaken mass balance assessments of the mercury discharged from the Processing Plant when processing existing MUG ore and for the WUG and GOP ores. The mass balance analysis was informed by results of emission testing undertaken in 2021 (when MUG ore was being processed), and laboratory testing of the material process streams. Table 2-2 summarises the predicted mercury emission rate per tonne of ore processed (i.e. mg/tonne). A summary of the OGNZL derived monthly mercury mass balance when WUG and GOP ore is being processed is shown in Appendix B. A summary of the mercury emission testing is shown in Table 2-3. Table 2-2. OGNZL estimated emission rate of mercury per tonne of ore processed (mg/tonne) – uncontrolled emissions Emission Source MUG Ore (mg/tonne) WUG ore (mg/tonne) GOP Ore (mg/tonne) Electrowinning 0.00244 0.48 7.9 Oven 0.116 8.81 145.8 Furnace 0.188 14.33 237.1 Carbon Regen 0.141 10.87 179.7 Total 0.447 34.49 570.5 Table 2-3. Mercury emission rates (g/h) and stack discharge concentrations (µg/m3) discharged from the Electrowinning Stack and Gold Room Furnace Stack - 2021 emission test programme results Metal Electrowinning Stack Oven/Furnace Stack Discharge concentration (µg/Nm3) Discharge rate (g/h) Discharge concentration (µg/Nm3) Discharge rate (g/h) Mercury 1.15 0.003 72.56 0.926 2.3 Annual Average Mercury Emission Emissions Mercury emissions from the Processing Plant will vary over the project period in response to the quantity and type of ore which is processed. The estimated annual mercury emission rate (kg/year) for each project year is shown in Table 2-4 and annual ore production rate over the project year is shown in Table 2-52. Peak annual mercury emissions are expected to occur in Year 5 of the project when the projected GOP ore processing rate peaks at 0.611 MTPA. The maximum ore which is expected to be processed during any year is 1.76 MPTA. 2 For New Zealand consenting purposes only. Forward looking information must not be relied on for investment purposes
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