Serrote Project — Feasibility Study

The Feasibility Study process comprises crushing, grinding, flotation, tailings disposal, and copper concentrate dewatering to produce a flotation copper concentrate containing gold credits.

Report context

The process plant design for the Serrote Project Feasibility Study was completed by SNC and reviewed by Ken Major of KWM. The report sections describe a processing facility with a nominal name-plate capacity of 7.0 Mt/y (19,178 t/d), based on testwork and engineering design. A significant amount of testwork has been completed on the mineralization to recover a magnetite product, but this magnetite recovery process has not been included as part of the project development at this stage and has been identified as a future opportunity with additional analysis following commissioning of the copper plant.

Processing route

Primary Crushing

Run of mine (ROM) ore, with a top size of 1.2 m, will be transported by 90 t capacity off-highway trucks to the primary crusher dump pocket. Ore will be reclaimed from the dump pocket by a vibrating grizzly feeder, with the oversize discharging to a model C160 jaw crusher set to generate a product top size of 300 mm. The product from the jaw crusher will be combined with the grizzly fines and conveyed to a 10,000 t live capacity coarse ore stockpile. This stockpile decouples the open pit ore haulage and primary crusher from the secondary and tertiary crushing and screening facility.

Coarse Ore Stockpile and Reclaim

Ore is reclaimed from the coarse ore stockpile using two variable speed apron feeders. Reclaimed ore will be conveyed to the secondary HP800 cone crusher circuit.

Secondary and Tertiary Crushing

Coarse ore reclaimed from the stockpile will be conveyed to a double deck, 3.0 m x 7.3 m banana screen. Oversize from the two decks will discharge to a standard configuration HP800 cone crusher. The discharge from the crusher will be conveyed to the tertiary crushing circuit. Fine product from the banana screen will discharge to the screens undersize conveyor feeding the fine ore stockpile.

For tertiary crushing, product from the secondary crusher and the tertiary crushers will be combined and conveyed to the tertiary screen feed system consisting of a feed surge bin and three independent belt feeders to feed three parallel, 3.0 m x 3.7 m double deck banana screens. Coarse oversize from each screen will be discharged into a dedicated HP800 shorthead configured tertiary cone crusher, with crusher product recycled to the screen. Fine screen product will be collected and conveyed to a 10,000 t live capacity fine ore stockpile.

Ball Mill Grinding

Reclaimed material from the fine ore stockpile will be conveyed to a single stage 7.6 m diameter x 12.8 m long, 15 MW dual pinion drive ball mill (25 ft diameter x 43 ft long). The ball mill will also be fed from the cyclone underflow and will operate in closed circuit with a cyclone bank composed of twelve 660 mm cyclones (nine operating and three stand-by). The ball mill circulating load has been estimated to be 300%. Cyclone distributor will be fed from the cyclone feed pump box by two centrifugal slurry pumps (one operating and one stand-by). The target cyclone overflow is P80 = 100 µm, and the cyclone overflow slurry will be piped directly to the copper rougher flotation circuit.

Copper Flotation and Regrinding

Cyclone overflow from the ball mill circuit will be piped to the rougher flotation bank consisting of a single bank of six 160 m³ tank cells. Rougher flotation tailing will be pumped to the tailing thickener. Rougher concentrate will feed the concentrate regrind circuit prior to cleaner flotation.

Rougher concentrate will be reground in one 1,119 kW (1,500 HP) vertical mill operating in closed circuit with cyclones. The cyclone cluster will have nine 15-inch diameter cyclones (seven operating and two stand-by). Cyclone underflow will be delivered to the regrind mill, and cyclone overflow will feed the first cleaner flotation feed distributor. The target cyclone overflow size, based on testwork, is P80 = 38 µm.

First cleaner flotation will be processed in two parallel 4 m diameter x 10 m tall column flotation cells. First cleaner flotation tailing will be fed to the cleaner scavenger flotation circuit consisting of a single row of five 40 m³ tank cells operated in series. Cleaner scavenger concentrate will be recycled to the regrind mill circuit, and cleaner scavenger tailing will be piped to the final flotation tailing pump box where it will be combined with the rougher flotation tailing.

First cleaner concentrate will be pumped to the second cleaner flotation consisting of one 4 m diameter x 10 m tall flotation column. Second cleaner concentrate will be pumped to the copper concentrate thickener. Second cleaner tailing will be recycled to the first cleaner feed.

Copper Concentrate Thickening and Filtering

Copper final concentrate will feed a 10 m diameter elevated conventional thickener with steel tank. Thickening will require the use of a flocculant polymer. Solution overflow from the thickener will be recycled to the plant as process water. Thickener underflow at 68% solids will be pumped to the agitated filter feed tank.

Concentrate filtration will use a 1,500 mm x 1,500 mm plate and frame pressure filter with 50 plates installed. Filtration will reduce moisture content to approximately 10%. Copper concentrate cake from the filter will discharge by gravity to the concrete floor of the filtration area to form a stockpile, then be loaded by front-end loader into covered concentrate trucks for onward transport to the port of Maceió. Filtrate from the pressure filter will be circulated to the concentrate thickener.

Tailing Thickening

Tailing from the copper flotation plant will be received in the tailing pump box and then pumped to the feed of a 27 m diameter high rate type tailing thickener with elevated steel tank. Thickening and water clarification will be aided by the use of a flocculant polymer. Thickener overflow will be recycled to the plant as process water. Tailing thickener underflow at 65% solids will be pumped to the tailing dam, with the starting point for deposition located about 1 km from the thickener.

Reagent Mixing and Distribution

Reagents and procedures are described as typical for copper flotation projects worldwide. Reagent quantities are stated to be small and practically negligible in relation to the ore slurry flows, so that resulting pulps are considered inert. The reagents have been determined by metallurgical testwork.

Key reported parameters

Technical qualifications

The magnetite recovery process has not been included as part of the project development at this stage. The report identifies magnetite recovery as a future opportunity with additional analysis following commissioning of the copper plant. The simplified process flowsheet is referenced as Figure 17.1 in the original report. The reagent quantities and types were determined by metallurgical testwork, and the regrind cyclone overflow target size of P80 = 38 µm is explicitly stated as being based on testwork.

Source: Serrote Project , Feasibility Study, Section 17.0 Recovery Methods and Section 17.1 Process Description.