| Discharges to Air and Associated Mitigation Methods | Waihi North Project Air Discharge Assessment - Waihi Surface Facilities | 4396626-1331619777-99 | 16/06/2022 | 25 The metal discharge rates and stack discharge concentrations for all the metals included in the 2021 emission testing programme are summarised in Appendix D. The stack emission parameters (e.g. stack diameter, discharge velocity and temperature) are also summarised in this appendix. An assessment of the emitted metals from the smelting processes is provided in Appendix F. Table 3-2. Selected metal emission rates (g/h) and stack discharge concentrations (µg/m3) discharged from the Electrowinning Stack and Gold Room Furnace Stack - 2021 emission test programme Metal Electrowinning Stack Gold Room Furnace Stack Discharge concentration (µg/m3) Discharge rate (g/h) Discharge concentration (µg/m3) Discharge rate (g/h) Arsenic 0.33 0.0009 0.16 0.002 Cadmium BDL* (<0.002) BDL* (<.00005) 7.84 0.0979 Chromium 0.75 0.0019 0.61 0.0078 Copper 6.18 0.016 4.97 0.063 Mercury 1.15 0.003 72.56 0.926 Manganese 1.37 0.0036 0.37 0.0046 Nickle 4.91 0.013 0.06 0.0008 Lead 0.97 0.0025 9.88 0.124 Selenium 0.36 0.0009 39.19 0.494 *BDL = below detection limit 3.6.2 Mercury discharges Mercury emissions from the Process Plant will vary over the project period in response to the quantity and type of ore which is processed. 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. Approximately 96% of emitted mercury is attributed to the period when GOP ore is being processed. Table 3-3 shows the Processing Plant’s estimated maximum annual mercury emission rate. The emission estimate is based on an annual ore processing rate of 2.25 MPTA, assuming 0.611 MTPA of GOP ore is being processed. Table 3-3. Estimated mercury emission rate for the proposed ore processing rate of 2.25 MPTA, assuming 0.611 MPTA of the processed ore is from the GOP (assuming the retort oven is installed). Source Mercury emission rate – with retort oven installed (kg/year) Electrowinning 5.38 Oven/Furnace 3.90 Carbon Regen 122.12 Total 131.39 An assessment of the emitted mercury from the Processing Plant is provided in Appendix F.
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