Boumadine Polymetallic Project — 2022 Technical Report

This article summarizes the processing design for the Boumadine Polymetallic Project as presented in the 2022 technical report, covering the conventional flotation flowsheet for lead, zinc, and pyrite concentrates, including key design criteria and reported plant consumption figures.

Report context

The processing information in this article is drawn from the 2022 technical report for the Boumadine Polymetallic Project, prepared for Aya Gold & Silver Inc. The report presents a conventional flotation process plant design for recovering lead, zinc, and pyrite concentrates, with design criteria based on testwork and assumptions as detailed in the sections below.

Processing route

Process design overview

The process plant design is based on a conventional flotation flowsheet. Lead, zinc, and pyrite concentrates will be recovered and sold to market. The design criteria were selected to minimize operating costs and maximize the use of proven technology, with equipment selection emphasizing suitability for duty, safety, reliability, and ease of maintenance.

Crushing circuit

The crushing circuit will be fed through a ROM bin by direct tipping of mine trucks or by a front-end loader. The ROM bin will feature a static grizzly with an aperture size of 800×800 mm to prevent oversized rocks from entering the crusher, with oversized rocks broken by a fixed rock breaker. The ROM bin discharges onto an apron feeder that feeds a vibrating grizzly with an aperture size of 90 mm. Grizzly undersize bypasses the primary crusher to reduce wear, while oversize feeds a 160 kW jaw crusher, reducing material from an F80 of 501 mm to a P80 of 156 mm at a rate of 444 dry t/h. The crushed product reports to a stockpile with a live capacity of approximately 8,115 tonnes, providing 24 hours of live storage.

Grinding circuit

Crushed material is reclaimed from the stockpile by two apron feeders onto the SAG mill feed conveyor. Flotation reagents including zinc sulphate, sodium cyanide, and Aero 3418A will be added to the primary mill with process water to precondition the material and achieve a target moisture content of 75% w/w. The SAG mill will be 7.92 m in diameter with an effective grinding length of 4.39 m, a high-speed variable speed drive, and an installed motor power of 6.1 MW. The mill will be charged with forged steel balls up to 125 mm, equipped with a grate discharge and trommel screen; screen oversize reports to a scats bunker or recirculates to the SAG mill, while undersize reports to the cyclone feed pump box.

The secondary mill will be a ball mill with a diameter of 6.10 m, effective grinding length of 9.32 m, and installed motor power of 6.1 MW, charged with high-chromium steel balls up to 50 mm. The combined SAG and ball mill discharge will be pumped to a cyclone cluster targeting an overflow P80 of 58 µm, with twelve installed cyclones (six duty, six standby) operating at 85 kPa(g) and a nominal recirculation rate of 382%.

Lead rougher and regrind flotation circuits

Cyclone overflow gravitates to the lead rougher conditioning tank, where zinc sulphate, sodium cyanide, and Aero 3418A are added during a five-minute conditioning period. The lead rougher circuit consists of a single train of six forced-air mechanical cells, with zinc sulphate, sodium cyanide, Aero 3418A, and MIBC added to maximize lead recovery. Rougher concentrate reports to the lead regrind circuit, while tails feed the zinc rougher flotation circuit.

The lead regrind circuit includes a cyclone cluster of sixteen cyclones (eleven duty, five standby) operating at 64 kPa(g) targeting an overflow d50 of 21 µm. Underflow feeds a lead regrind stirred media mill (SMM) with an installed motor power of 1.6 MW, charged with zirconia toughened alumina ceramic beads, reducing particle size from an F80 of 58 µm to a P80 of 16 µm.

Lead cleaner flotation and concentrate handling

The lead cleaner flotation circuit consists of three cleaning stages and one cleaner-scavenger stage, each with one train of forced-air mechanical cells. Zinc sulphate and sodium cyanide are added to the surge tank for conditioning ahead of flotation, with MIBC added to each stage and Aero 3418A to the second and third cleaners. Concentrate and tails travel counter-currently, with the third cleaner concentrate feeding the lead concentrate thickener.

The lead third cleaner concentrate is thickened in an 11 m diameter high-rate thickener to 55% w/w solids, with flocculant added to the feed well. Underflow is pumped to a filter feed tank sized for 24 hours of feed, then to a pressure filter dewatering concentrate cake to 10% w/w moisture. The filter cake is discharged via belt feeder, bucket elevator, and shuttle conveyor into hoppers feeding automatic bagging systems, with bags transported and stacked by forklift for highway truck shipment.

Zinc rougher, regrind, and cleaner flotation circuits

Zinc rougher flotation receives lead rougher tails and lead first cleaner-scavenger tails. Lime is added to the first of two conditioning tanks to achieve a target pH of 11.5, with additional lime and copper sulphate added to the second tank, providing ten minutes total conditioning (five minutes per tank). The zinc rougher circuit consists of a single train of six forced-air mechanical cells, with SIPX, lime, and MIBC added to maximize zinc recovery.

The zinc regrind circuit receives rougher concentrate and first cleaner-scavenger concentrate, using a cyclone cluster of eight cyclones (five duty, three standby) at 81 kPa(g) targeting an overflow d50 of 20 µm. The regrind SMM reduces particle size from F80 of 58 µm to P80 of 15 µm, charged with ceramic beads, with an installed motor power of 700 kW.

The zinc cleaner circuit consists of three cleaning stages and one cleaner-scavenger stage, each with one train of three forced-air mechanical cells. SIPX and lime are added to the surge tank ahead of flotation, with five minutes conditioning. Concentrate and tails travel counter-currently, with MIBC added to each stage, SIPX to the first cleaner-scavenger and third cleaner, and lime to the first through third cleaners. The third cleaner concentrate is thickened in an 11 m diameter high-rate thickener to 55% w/w solids, then pressure filtered to 10% w/w moisture, with the cake stockpiled in a covered shed for truck loadout.

Pyrite rougher flotation and concentrate handling

The pyrite rougher flotation circuit receives tails from the zinc rougher and the zinc first cleaner-scavenger. Sulphuric acid is added to a conditioning tank to lower pH to between 7 and 8.5, with five minutes conditioning. The circuit consists of a single train of six forced-air mechanical cells, with PAX and MIBC added to maximize pyrite recovery. Rougher tails feed the flotation tails thickener.

Pyrite rougher concentrate is thickened in a 32 m diameter high-rate thickener to 65% w/w solids, with flocculant added to promote settling. The filter feed tank holds 24 hours of slurry; pressure filters dewater the concentrate cake to 15% w/w moisture. The concentrate is stockpiled by radial stacker with 7,250 m³ live capacity (approximately 24 hours of production), then loaded into highway haulage trucks by front-end loader.

Tailings disposal and water systems

The pyrite rougher flotation tails are pumped to a high-rate flotation tails thickener (22 m diameter), with flocculant added to the feed well, thickening slurry to 40% w/w solids in the underflow. It is estimated that 129 m³/h of water will be decanted from the tailings management facility back to the process water pond. Thickener overflow reports to the process water pond; underflow is pumped to the flotation tailings management facility.

Raw water will be sourced from city sewage treatment effluent into a Raw Water Basin, with a combined raw and fire water tank in the process plant. Main process water is stored in a pond supplied by thickener overflows, tailings facility decant return, and raw water makeup. Process water tanks for lead and zinc circuits are fed by their respective concentrate thickener overflows for use in the last cleaning and filter stages to avoid contaminating final products. Potable water is sourced from an aquifer and treated onsite.

Key reported parameters

The following table summarizes key process design criteria from the technical report, indicating whether each is based on testwork or an assumption.

Reagent consumptions, reported at supply concentration, are summarized below:

Technical qualifications

The technical report identifies several limitations on the process design data. The SMC Axb of 46.2, Bond Abrasion Index of 0.402, and crushing work index of 10.2 kWh/t are stated as assumptions rather than testwork results. Lead and zinc concentrate thickener and filter design criteria will require further definition upon completion of dewatering testwork. Pyrite concentrate thickener design criteria will likewise be further defined upon completion of dewatering testwork. The flotation tailings thickener underflow solids loading of 0.5 t/h/m² and the pyrite concentrate thickener solids loading of 0.5 t/h/m² are assumptions, as are the lead and zinc concentrate thickener solids loadings of 0.2 t/h/m². Reagent consumption figures are provided at supply concentration.

Source: Boumadine Polymetallic Project, 2022 Technical Report, Section 17.0 Recovery Methods and associated tables (Aya Gold & Silver Inc.).