The 2014 technical report for Xtierra Inc. describes a proposed 2,000 tpd mineral processing plant designed to treat silver-lead-zinc sulphide ore through crushing, grinding, flotation, regrind, and dewatering circuits to produce lead-silver and zinc concentrates.
Report context
The report, dated April 28, 2014, was prepared for Xtierra Inc. and documents the process design for a mineral processing plant intended to treat silver-lead-zinc sulphide ore at a design throughput rate of 2,000 tonnes per day. The plant was designed to produce lead-silver and zinc concentrates for off-site transport. The report includes principal process parameters, a general site layout, and a simplified process flow diagram for the 2,000 tpd processing rate.
Processing route
Primary Crushing
Run-of-mine (ROM) ore was designed to be delivered by haul trucks and dumped directly into the dump pocket of the primary crusher. The dump hopper capacity is 125 tonnes, corresponding to three truckloads. A heavy-duty hydraulic rock-breaker, controlled remotely by the crusher operator, was specified to break oversize boulders. ROM ore discharges from the dump hopper onto a grizzly feeder and is fed into a jaw crusher capable of crushing ore up to 600 mm in diameter.
The primary jaw crusher was designed to operate at a nominal closed side setting of 70 mm, producing a product with a P80 of approximately 95 mm at an average throughput rate of 105 t/h. Crushed ore is transported by conveyor to a crushed ore stockpile with a live capacity of 24 hours. Four vibrating pan feeders withdraw crushed ore from the stockpile to feed the semi-autogenous grinding (SAG) mill circuit.
SAG Milling
Crushed ore is fed into the SAG mill to produce a product with a P80 of approximately 3.1 mm at an average throughput rate of 91 t/h. Process water is added to achieve a SAG mill discharge of 70% solids. The SAG mill product is sent to the ball milling circuit. A trommel screen with an aperture size of 9.5 mm captures oversize material, which is conveyed to undergo secondary (pebble) crushing.
Secondary Crushing
Oversize from the SAG mill trommel screen is conveyed to a secondary crusher surge bin with a capacity of approximately 25 tonnes, from which a pan feeder supplies a cone crusher. The conveyor is equipped with a metal detector. The cone crusher was designed to operate at a nominal closed side setting of 9 mm, producing a product with a P80 of approximately 10 mm at an average throughput rate of approximately 24 t/h. The secondary crushed ore is discharged onto a conveyor that feeds material back to the SAG mill.
Ball Milling
A ball mill is operated in closed circuit with a cluster of cyclones. Cyclone overflow becomes lead rougher flotation feed, and underflow returns by gravity to the ball mill. Mill discharge passes through a trommel to remove tramp metal. Ball mill discharge, SAG mill discharge, lime, NaCN, ZnSO4, and process water are collected in a common pumpbox, from which slurry is pumped to the cyclone cluster.
Ball mill discharge is targeted for a P80 of approximately 100 microns. Lime is added to control the pH of the flotation feed to 7.7, and process water is added to achieve a ball mill discharge of 70% solids. The ball mill trommel has an opening size of 9.5 mm. The cyclone cluster is fed by a slurry pump equipped with a variable speed drive. Cyclone overflow (P80 of 100 microns, 35% solids) flows by gravity to the lead rougher conditioner tank.
Lead Rougher Flotation
Lead rougher flotation feed conditioning is carried out in the lead rougher feed conditioner, where cyclone overflow, lime, MIBC, and 3418A are agitated for 2.5 minutes at a pH of 8.0. Slurry overflows to the first cell of the lead rougher bank, with flotation cells stepped for gravity flow. Lead rougher concentrate froths are collected and flow by gravity into pipe launders leading to the lead rougher concentrate pumpbox, from which they are pumped to the lead regrind circuit. Lead rougher tails are pumped to the zinc recovery circuit. MIBC and A211 are added to the lead rougher flotation cell bank, and process water is used for froth control and dilution.
Lead Concentrate Regrind
The lead concentrate regrind circuit consists of a cyclone cluster ahead of a regrind ball mill operating in closed circuit. Cyclone overflow becomes lead cleaner flotation feed, while underflow returns by gravity to the regrind mill. Lead rougher concentrate, process water, and recycle streams from the lead cleaner-scavenger concentrate and second lead cleaner tails are collected in a pumpbox and pumped to the cyclone cluster. Lime, NaCN, ZnSO4, and A3894 are added directly into the regrind mill.
Regrind mill cyclone overflow is targeted for a P80 of approximately 43 microns. Lime is added to control pH to 8.4, and process water is added to achieve a regrind mill discharge of 53% solids. The regrind mill trommel has an opening size of 9.5 mm. Cyclone overflow (P80 of 43 microns, 32% solids) flows by gravity to the first lead cleaner.
Lead Cleaner and Cleaner-Scavenger Flotation
Lead regrind cyclone overflow is pumped to the first lead cleaner, comprising two stages. Lime and 3418A are added only to the first stage, and MIBC is added to both stages, with pH controlled between 8.7 and 9.0. First lead cleaner concentrate is pumped to the second lead cleaner. First lead cleaner tails gravity flow to the lead cleaner-scavenger.
The second lead cleaner flotation is performed in three stages. Lime is added only to the first stage and MIBC to the first and last stages, with pH controlled between 9.5 and 10.5. Second lead cleaner concentrate is pumped to the third lead cleaner. Second lead cleaner tails are recycled back to the lead regrind circuit.
The third lead cleaner flotation is done in three stages. Lime is added only to the first stage and MIBC to the second and third stages, with pH controlled between 9.0 and 10.0. The third lead cleaner concentrate is the final lead concentrate product, collected in a pumpbox and pumped to the dewatering circuit. Third lead cleaner tails flow by gravity to the second cleaner flotation.
The lead cleaner-scavenger flotation is done in a single stage to which MIBC, A211, and 3418A are added. Lead cleaner-scavenger concentrate is pumped back to the lead regrind circuit. Lead cleaner-scavenger tails flow by gravity to a pumpbox and are pumped to the zinc recovery circuit.
Zinc Rougher Flotation
Zinc rougher flotation feed conditioning is carried out in two stages. Lime is added to the first tank to target a pH of 10.5, and CuSO4 is added to the second tank. Slurry overflows to the first cell of the zinc rougher bank, with cells stepped for gravity flow and levels automatically controlled by dart valves.
Zinc rougher concentrate froths flow by gravity to the zinc rougher concentrate pumpbox and are pumped to the zinc regrind circuit. Zinc rougher tails are pumped to the tailings thickener. Lime, A211, and U250 are added to the zinc rougher flotation cell bank, and process water is piped along the cells for spray water and dilution.
Zinc Concentrate Regrind
The zinc concentrate regrind circuit consists of a cyclone cluster ahead of a regrind ball mill operating in closed circuit. Cyclone overflow becomes zinc cleaner flotation feed, while underflow returns by gravity to the regrind mill. Zinc rougher concentrate, process water, and recycle streams from the zinc cleaner-scavenger concentrate and second zinc cleaner tails are collected in a pumpbox and pumped to the cyclone cluster. Lime is added directly into the regrind mill to target a pH of 10.1.
Regrind mill cyclone overflow is targeted for a P80 of approximately 37 microns. Process water is added to achieve a regrind mill discharge of 53% solids. The regrind mill trommel has an opening size of 9.5 mm. Cyclone overflow (P80 of 37 microns, 35% solids) flows by gravity to an agitated tank where CuSO4 is added before it continues by gravity flow to the first zinc cleaner.
Zinc Cleaner and Cleaner-Scavenger Flotation
Zinc regrind cyclone overflow is gravity fed to the first zinc cleaner, comprising two stages. Lime and A211 are added only to the first stage, and U250 is added to both stages, with pH controlled to 10.5. First zinc cleaner concentrate is pumped to the second zinc cleaner. First zinc cleaner tails gravity flow to the zinc cleaner-scavenger.
The second zinc cleaner flotation comprises three stages. Lime is added only to the first stage, and A211 and U250 are added only to the last stage, with pH controlled to 11.3. Second zinc cleaner concentrate is pumped to the third zinc cleaner. Second zinc cleaner tails are recycled back to the zinc regrind circuit.
The third zinc cleaner has a two-stage configuration. Lime is added only to the first stage and U250 to the second stage, with pH controlled to 12.0. The third zinc cleaner concentrate is the final zinc concentrate product, collected in a pumpbox and pumped to the dewatering circuit. Third zinc cleaner tails flow by gravity to the second cleaner flotation.
The zinc cleaner-scavenger flotation is done in one stage to which A211 and U250 are added. Zinc cleaner-scavenger concentrate is pumped back to the zinc regrind circuit. Zinc cleaner-scavenger tails flow by gravity to a pumpbox and are pumped to the tailings.
Lead Dewatering and Filtration
The final lead concentrate from lead cleaner flotation is pumped to the lead concentrate thickener to produce a concentrate of 76% solids. The thickener is of high-rate design with flocculant addition. Thickener overflow flows by gravity to the process water tank, and underflow is pumped to the lead concentrate thickener underflow tank, providing surge capacity between the lead flotation and dewatering circuits.
The thickened lead concentrate is pumped to a pressure filter to produce a final lead concentrate filter cake with 7% moisture. The filter cake is discharged onto a stockpile and transported to the lead loadout area by front-end loader. Filtrate is recycled to the lead concentrate thickener.
Zinc Dewatering and Filtration
The final zinc concentrate from zinc cleaner flotation is pumped to the zinc concentrate thickener to produce a zinc concentrate of 76% solids. The thickener is of high-rate design with flocculant addition. Thickener overflow flows by gravity to the process water tank, and underflow is pumped to the zinc concentrate thickener underflow tank, providing surge capacity between flotation and dewatering.
The thickened zinc concentrate is pumped to a pressure filter to produce a final zinc concentrate filter cake with 8% moisture. The filter cake is discharged onto a stockpile and transported to the zinc loadout area by front-end loader.
Tailings Dewatering
Tailings from the zinc flotation circuit are pumped to the tailings thickener to produce a thickened tailings with 65% solids. The thickener is of conventional design with flocculant addition. Thickener overflow flows by gravity to the process water tank, and underflow is pumped to the tailings treatment facility.
Key reported parameters
| Parameter | Unit of Measure | Rate |
|---|---|---|
| Daily throughput | tonnes/day | 2,000 |
| Ore grade, silver | grams/tonne ore | 63.96 |
| Ore grade, zinc | percent | 2.10 |
| Crush size | microns (80% passing) | 95,000 |
| Zinc regrind size | microns (80% passing) | 37 |
| Flocculant consumption | kilogram/tonne ore | 0.051 |
| Lead concentrate grade, silver | percent | 73.4 |
| Lead concentrate grade, lead | percent | 90.6 |
| Lead concentrate grade, zinc | percent | 5.7 |
| Zinc concentrate grade, silver | percent | 6.7 |
| Zinc concentrate grade, lead | percent | 0.8 |
| Zinc concentrate grade, zinc | percent | 76.7 |
| Zinc concentrate, silver | grams/tonne concentrate | 1,335.00 |
| Zinc concentrate, lead | percent | 54.00 |
| Contained zinc | pounds/year | 25,563,714 |
Technical qualifications
The report is based on a proposed design for the mineral processing plant and does not include historical operating data or testwork results in the sections reviewed. Specific limitations identified in the report include:
- The report must be read in its entirety and is subject to third party disclaimer clauses contained in the body of the report.
- The process design parameters represent targeted design values, with some circuits described as "targeted" (e.g., regrind mill cyclone overflow, ball mill discharge), indicating these may not be verified operating data.
- The report includes reagent consumptions and concentrate grades that appear to be design targets rather than measured values.
- The source material notes that the report was prepared for Xtierra Inc. and must be read in its entirety, with third party disclaimer clauses applicable.
Source: ADV-TO-00011, April 28, 2014, Recovery Methods section, pages 167-173.
