The Aripuanã Zinc Project is designed to treat 2.214 Mtpa of underground-mined ore through a conventional sulphide flotation flowsheet to produce separate copper, lead, and zinc concentrates.
Report context
This technical report, dated February 9, 2021, was prepared for Nexa Resources S.A. for the Aripuanã Zinc Project, project number 3252. The processing description and key design criteria are based on metallurgical test work and conventional technology selection. At the time of reporting, the plant design was planned for 2.214 Mtpa of run of mine (ROM) ore from the Arex, Link, and Ambrex underground mines.
Processing route
Overview
The Aripuanã flowsheet has been developed through metallurgical test work and the use of conventional technologies for the treatment and recovery of copper, lead, and zinc as separate concentrates. Two main ore types are present: stratabound and stringer, which have different hardnesses and therefore different throughput rates. Stratabound material will make up approximately 89% of the ore to be processed, with the feed blend expected to peak at 21% stringer material during Year 5.
Estimated processing rates for the two ore types individually, based on hardness, are approximately 5,000 tpd (dry basis) for stringer material and 6,300 tpd (dry basis) for stratabound material. Throughput for the blended ore is estimated as a weighted average of the throughputs of the two ore types.
Key elements of the process flowsheet include primary crushing, a SAG mill followed by a ball milling and pebble crushing (SABC) circuit, talc pre-flotation, and sequential flotation of copper, lead, and zinc for stratabound mineralization, and copper flotation for stringer mineralization.
Crushing and grinding
ROM material will be trucked from the underground mine to ROM stockpiles near the primary crushing area. Material will be directly discharged into an 80 t capacity primary crusher dump hopper or held temporarily in four stockpiles based on mineralization type and grade (approximately 7,000 t each, one stringer stockpile and three mixed stockpiles of different grades) and recovered later by front end loader.
A static grizzly on top of the dump hopper with 600 mm by 600 mm openings will prevent oversize material from reaching the discharge of the hopper. Discharge will be via apron feeder to a vibrating grizzly with an aperture of 130 mm. Oversize material will feed the primary jaw crusher while undersize will bypass the crusher. The crusher product, with a top size of 140 mm, will be collected on a conveyor belt together with fines from the apron feeder and grizzly undersize. A metal detector will remove scrap metal from the crushed ore.
The conveyor will feed a crushed ore bin with a capacity of 2,500 t, with the provision for two additional crushed ore bins that would bring combined capacity to 9,100 t. Two variable speed apron feeders per bin will withdraw crushed product and deliver it to the grinding circuit via conveyor belt. A belt scale will control the speed of the apron feeders and therefore the feed rate to the grinding circuit.
The grinding circuit will consist of a conventional SAG mill, ball mill, and pebble crusher in SABC configuration. Both grinding mills will have variable speed drives to allow for process optimization over a range of ore competencies and hardnesses. A double-deck vibrating screen at the SAG mill discharge will separate oversize (scats and pebbles) from undersize. Scats will be separated from pebbles by belt magnets, with pebbles recycled to the SAG mill feed conveyor via the pebble crusher, or directly to the SAG mill feed conveyor when the pebble crusher is under maintenance.
SAG mill discharge screen undersize and ball mill discharge will be pumped to hydrocyclones. Hydrocyclone underflow will return to the ball mill while overflow with P80 of 150 µm will be transferred to the flotation feed pump box. An online particle size analyzer will provide periodic measurement of the hydrocyclone overflow stream.
Talc flotation
Hydrocyclone overflow slurry will be conditioned prior to the talc flotation circuit, which consists of three column flotation stages: rougher, cleaner, and reverse copper flotation. Reagents added for talc flotation include MIBC as a frother and SMBS as a depressant of iron sulphides. The talc rougher concentrate will be cleaned in the second column, with the cleaned concentrate reporting to the reverse copper flotation column where talc will be depressed with CMC while copper in the talc concentrate is recovered and reports to downstream sulphide flotation. The final talc concentrate will be combined with sulphide flotation tailings for disposal.
Due to the high content of light minerals in stratabound mineralization, these minerals must be removed prior to sulphide flotation. Stringer ore contains only minor amounts of these minerals, so processing of stringer ore only would generally by-pass the talc flotation step, as the minor talc content can be depressed with carboxymethyl cellulose (CMC).
Copper flotation
Prior to copper rougher flotation, talc flotation tailings will be conditioned in two tanks in series where reagents will be added, including A3894 (dialkyl thionocarbamate copper collector), zinc sulphate (sphalerite depressant), SMBS (iron sulphide depressant), MIBC (frother), CMC (talc depressant), and lime (pH control).
Copper rougher flotation concentrate will be reground in a vertical stirred mill to a P80 of 45 µm to increase sulphide liberation and promote cleaner stage recovery. Two stages of cleaning in column cells will produce the final copper concentrate. Copper rougher-scavenger concentrate will be recycled to the rougher flotation feed. When processing stringer ore, rougher-scavenger flotation tailings can be pumped directly to tailings dewatering. Cleaner circuit tailings are recycled to the copper rougher feed.
Lead flotation
Copper rougher-scavenger flotation tailings will be thickened prior to being pumped to the lead flotation circuit. Lead flotation is only necessary for stratabound mineralization, as stringer ore contains only very low concentrations of lead and zinc minerals. The lead circuit consists of rougher flotation, rougher concentrate regrinding to P80 75 µm, rougher-scavenger flotation, and two-stage cleaner flotation. The product from the lead cleaner flotation circuit will be the final lead concentrate.
Reagents used for lead flotation include Aerophine 3418A (dialkyl dithiophosphinate collector for lead), zinc sulphate (sphalerite depressant), SMBS (iron sulphide depressant), lime (pH control), CMC (talc depressant), and MIBC (frother). Prior to lead rougher flotation, feed slurry will be conditioned with these reagents in two tanks in series.
Zinc flotation
The zinc flotation circuit is similar to the copper and lead flotation circuits, though the quantity of flotation cells and some reagents used are different. Lead rougher-scavenger flotation tailings will be thickened prior to being pumped to the zinc flotation circuit. Reagents used for zinc flotation include AERO 208 or A208 (dialkyl dithiophosphate collector for zinc), copper sulphate (sphalerite activator), lime (pH regulator), and MIBC (frother).
Prior to zinc rougher flotation, feed slurry will be conditioned in two tanks in series. The zinc circuit consists of rougher flotation, rougher concentrate regrinding to P80 75 µm, rougher-scavenger flotation, and two-stage cleaner flotation. The product from the zinc cleaner flotation circuit will be the final zinc concentrate. Zinc rougher-scavenger flotation tailings will be pumped to tailings dewatering for disposal.
Concentrate handling and tailings
Three concentrates (copper, lead, and zinc) will be produced, with each thickened and filtered separately. Concentrate slurries will be pumped to storage tanks feeding pressure filters dedicated to each concentrate, reducing moisture to approximately 10%. Filtered copper and zinc concentrates will fall by gravity onto belt conveyors delivering material to segregated covered storage areas, then reclaimed by front end loader and loaded into trucks for shipping. Lead concentrate will be bagged in lined supersacs and loaded into containers for shipping.
Filtrates will be recovered for re-use in their respective flotation circuits. Excess filtrate and concentrate thickener overflow will be discharged to an engineered wetland treatment system and can be recycled to the processing plant as make-up water as required or discharged.
Sulphide flotation tailings will be thickened and filtered in three pressure filters and combined with filtered talc concentrate prior to disposal. The sulphide flotation tailings thickener underflow will be filtered to produce a filter cake with approximately 10% moisture, suitable for dry stacking in two stockpiles with capacity of approximately 5,200 t each.
Backfill
The backfill plant will serve the Arex, Link, and Ambrex mines. Talc concentrate will be combined with flotation tailings and mixed with cement to produce a paste backfill with approximately 76% solids by mass. Backfill will be provided to the underground mines as required.
Water systems
The water system is designed to maximize water recovery and recirculation. Water from tailings thickener overflow and tailings filtration will be pumped to a recovered water pond with a two-day retention capacity. After treatment with hydrogen peroxide, the water is pumped to a 600 m³ recovered water tank, which will receive make-up water as required.
Make-up water will be collected from a storage pond close to the processing facilities and pumped to a 400 m³ make-up water tank. This water will be used for specific uses including feed for the water treatment station, pump seal water, fire suppression, vacuum pump seal water, reagent preparation, potable water, and feed to various points in the plant circuit.
Reagent preparation
AERO 3894 will be supplied as a liquid product at 100% concentration in sealed 200 L drums. The solution will be transferred to a storage tank and distributed without dilution in copper flotation. AEROPHINE 3418A and AERO 208 will also be supplied as liquid products at 100% concentration in sealed 200 L drums, with solutions mixed with water at desired concentrations and pumped at required dosages to various flotation stages.
SMBS will be supplied in one metric tonne bags and delivered to a storage hopper, then transferred by screw feeder to an agitated mix tank where it will be dissolved in water to reach a concentration of 5% w/w. Copper sulphate will be supplied similarly and dissolved to a concentration of 5% w/w, with solution pumped to zinc flotation. Zinc sulphate will be supplied in one metric tonne bags and dissolved to a concentration of 10% w/w, with the solution transferred to a storage tank and pumped at required dosages to copper and lead flotation.
MIBC will be supplied in liquid form at 100% concentration in sealed 200 L drums, with the frother pumped to storage and distribution tanks and added in separate lines to various flotation stages.
Compressed air systems
Dedicated compressed air systems will be provided for pressure filters for each type of concentrate, with one or more screw type, air cooled, oil free compressors at 7.0 kg/cm² and a stand-by unit for each filtration system. An exclusive small-size compressor without standby will generate dry, oil free air for the laboratory. Screw compressors with one standby unit will generate dry oil free air for the beneficiation plant and workshop service and instrumentation air. Dedicated blowers with one standby unit will generate low pressure, oil free air at approximately 0.4 kg/cm² for flotation tank cells.
Dust suppression and drainage
The dust suppression system for primary crushing and crushed ore storage silos will consist of a central unit with air extraction and filtration systems, as well as piping and spray nozzles for water suppression of dust at conveyor transfer points.
A drainage system has been devised throughout the operational area to capture and contain process area spillage, industrial spillage, rain, and emergency drainage. Process area spillage will be contained by bunded containment areas, collected in sumps, and returned to the production process. Industrial spillage will be routed to emergency drainage and/or effluent treatment station, with a water, oil, and grease separation system in the workshop and areas with industrial effluents. Rain in areas without contamination risk can be disposed of in the hydrographic network without treatment.
All effluent (process, stockpile drainage, and precipitation) will be directed to engineered wetlands for passive treatment prior to discharging the water to the receiving environment.
Key reported parameters
| Parameter | Units | Design Value |
|---|---|---|
| Throughput (operating schedule) | d/a | 365 |
| Annual throughput | Mt | 2.26 |
| Daily throughput – stratabound ore | t | 6,300 |
| Daily throughput – stringer ore | t | 5,000 |
| Utilization – primary crusher | % | 75 |
| Utilization – grinding and flotation | % | 91 |
| Head grade – stratabound | % Cu | 0.18 |
| Head grade – stratabound | % Pb | 1.96 |
| Head grade – stratabound | % Zn | 2.13 |
| Head grade – stringer | % Cu | 0.91 |
| Head grade – stringer | % Pb | 0.10 |
| Head grade – stringer | % Zn | 0.31 |
| CWi (stringer) | kWh/t | 9.32 |
| SMC Axb (stringer) | – | 30.9 |
| BWi (stringer) | kWh/t | 12.4 |
| Ai (stratabound) | g | 1.5 |
| Crusher max feed size | mm | 600 |
| Crusher product size (P100) | mm | 140 |
| Crusher product size (P80) | mm | 118 |
| SAG mill ball fill | % | 14 to 18 |
| SAG mill transfer size (T80) | mm | 1.7 to 2.0 |
| Pebbles generated | % | 19 to 28 |
| Pebble crusher | – | Yes |
| Ball mill fill | % | 35 to 40 |
| Ball mill circulating load | % | 250 to 300 |
| Ball mill product size (P80) | µm | 149 |
| Copper recovery – stratabound | % | 67.6 |
| Lead recovery – stratabound | % | 84.8 |
| Zinc recovery – stratabound | % | 89.5 |
| Copper recovery – stringer | % | 86.9 |
| Talc flotation cell type | – | Columns |
| Talc flotation feed density | % solids | 27 |
| Copper flotation cell type | – | Tank cells/columns |
| Copper flotation feed density | % solids | 27 to 30 |
| Copper regrind (P80) | µm | 45 |
| Lead flotation cell type | – | Tank cells/columns |
| Lead flotation feed density | % solids | 45 |
| Lead regrind (P80) | µm | 75 |
| Zinc flotation cell type | – | Tank cells/columns |
| Zinc flotation feed density | % solids | 43 |
| Zinc regrind (P80) | µm | 75 |
| Copper concentrate grade | % Cu | 30 |
| Lead concentrate grade | % Pb | 62 |
| Zinc concentrate grade | % Zn | 58 |
| Concentrate moisture content | % | 10 |
| Tailings disposal type | – | Dry stack |
| Tailings thickener underflow density | % solids | 65 |
| Tailings filter cake moisture content | % | 10 |
| Paste backfill density | % solids | 76 |
| Cement addition | % | 4 to 6 |
Project website: https://www.nexaresources.com/en/about-us/
Technical qualifications
The following limitations and clarifications apply to the processing information in this report:
- The process flowsheet was developed through metallurgical test work, but no actual plant operating data exists for the Aripuanã project as it had not yet been constructed at the time of reporting.
- Throughput estimates of 5,000 tpd for stringer and 6,300 tpd for stratabound ore are estimated processing rates based on hardness, not confirmed operating performance.
- All design criteria, recoveries, and concentrate grades are design values from the SNC-Lavalin 2019 engineering work and are subject to change with additional testwork or detailed engineering.
- The report does not provide historical operating data for the Aripuanã processing plant.
- The recovery values presented are design criteria, not testwork results, and no supporting metallurgical testwork data is included in the processing sections of this report.
Source: Technical Report NI 43-101 – February 9, 2021, Section 17 Recovery Methods.
