521 2.2 Pyrolysis Test Methodology In a Lindberg tube electric furnace equipped with a 4inches diameter steel tube and dust-collecting filters, pyrolysis tests were performed on the Enargite concentrate (EC1) to remove and capture arsenic as As₂S₃, leaving an arsenic-depleted calcine. Schematic representation of the complete set-up is shown in Figure 1. Figure 1 – Pyrolysis work installation with Lindberg furnace and dust-collectors Tests were conducted under SO2 atmosphere on 40g sub-samples at a peak temperature of 650– 675°C for 80min, starting when the thermocouple read 600°C. An on-line gas analyzer was linked to the circuit after the furnace to determine oxygen levels post-pyrolysis, indicative of the airtightness of the setup (<1% for a functioning system). The As₂S₃ by-product collected in the cooling zone and dust filters was oxidated to As2O3, using a similar set-up using a glass tube under air and vacuum. 2.3 Iron-based Arsenic Co-Precipitation Methodology Iron-based co-precipitation was conducted on the scrubber blowdown sample (AS1) to precipitate arsenic as iron-arsenic oxyhydroxide, suitable for vitrification. Tests were performed on sub-samples of 500mL, in a 1L beaker with magnetic stirrer (360 RPM) at room temperature and ambient pressure under a fume hood. A fixed quantity of FeCl3, based on a ratio of iron to arsenic of 1, was added to AS1 until complete dissolution. MgO was then added to the beaker until reaching pH 6, before stirring the mixture for 6 hours. Afterwards, the mixture was filtered using a Büchner funnel assembly under vacuum and Whatman #3 filter paper. FLUIDIZING AIR OFF GAS FLUIDIZED BED PYROLYSIS POST-COMBUSTION CHAMBER AIR SO2 (g) As2O3 (s) As2S2 (g) ARSENIC-FREE CONCENTRATE COOLING SCREW As2O3 (s) O/F U/F 2 3 TO MARKET / LEACHING PROCESS 5.3 % As CONCENTRATE CYCLONE ARSENIC BAG HOUSE 1 TO VITRIFICATION PLANT COOLING WATER 4 TO ATMOSPHERE GYPSUM TO LANDFILL LIME SLURRY TANK LIME SILO OFFLOAD TRUCK SO2 SCRUBBER GYPSUM RETENTION TANK TO EFFLUENTS PROCESS WATER WATER WASTE HEAT BOILER OFF GAS OFF GAS CYCLONE CYCLONE QUENCH TO BAGHOUSE WATER GAS SPRAY COOLER As2O3 (s) STEAM SO2 (g) As2O3 (g) SO2 (g) As2O3 (g) Dust Trap Dust Trap
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