This technical report presents a proposed processing flowsheet for the Buena Vista iron project in Nevada, based on feasibility studies and in-house development through 2013.
Report context
The Buena Vista Iron Project technical report, dated October 2013, describes a proposed magnetite ore beneficiation operation located in Nevada, USA. The processing flowsheet presented in this report is the result of successive development stages: an initial GR Engineering (GRES) feasibility study at 4.8 Mtpa using conventional three-stage crushing and rod-ball grinding; a subsequent update by Samuel Engineering in late 2011 for 6 Mtpa using SAG-ball mill grinding; and in-house studies that led to the proposed 10.44 Mtpa design incorporating dry pre-concentration by low-intensity magnetic separation (LIMS) ahead of ball milling.
Processing route
Primary Crushing and Stockpile
Run-of-mine ore of nominal 100 tonne truck capacity will be delivered either direct to the primary crusher tipping point or to a 30,000 tonne ROM ore storage facility. The ROM stockpile will allow blending of low, intermediate, and high-grade mineralization. A low-grade ore stockpile will be maintained adjacent to the waste dump. Blended ROM ore will be reclaimed by front-end loader for plant feed. A 54-inch by 74-inch HD primary gyratory crusher will reduce ore to nominal 6-inch product, discharged to a coarse ore product bin for controlled feeding to the conveying system.
Fine Crushing and Dry Magnetic Pre-Concentration
Coarse ore will be withdrawn from the coarse ore bin and fed to a secondary crusher screen for by-pass of fines at nominal 30 mm. Oversize will pass to an MP1000 secondary standard crusher (open circuit, 30 mm closed side setting) for reduction to nominally minus 50 mm. Combined by-pass fines and crusher product will be conveyed to the tertiary circuit for screening and separation of fine ore product at nominally 10 mm. Oversize from this screen passes to MP1000 tertiary shorthead crushers set at nominally 10 mm closed side setting. Tertiary crusher discharge will combine with secondary product for recycle to the tertiary screen.
Product from the crushing circuit at nominally minus 10 mm will pass to parallel holding bins ahead of dry magnetic separators (DFA units) described as highly efficient drum units with axial pole magnets. Dry waste from this pre-concentrating stage will be conveyed to waste dumps. The magnetic concentrate will pass as fine ore to fine ore bins ahead of the grinding circuit. The crushing circuit is designed to operate approximately 6,000 hours per annum at an average rate of 1,740 tonnes per hour.
Fine Ore Storage and Primary Ball Milling
The wet milling and wet LIMS circuit will operate 8,000 hours per annum. Assuming 40% waste rejection in pre-concentration, this equates to an average throughput rate of 783 dry tonnes per hour. A fine ore storage facility of 20,000 tonnes live capacity will be provided between crushing and milling. Ore will be reclaimed by two rows of feeders onto the primary ball mill feed conveyor. A single stage primary ball mill, 5 m diameter by 10 m effective grinding length (EGL) with a 4000 kW drive motor, will reduce particle size from nominal 10 mm to nominal 80% passing 500 µm.
Primary Wet Low-Intensity Magnetic Separation
Primary grinding product will be distributed to primary LIMS consisting of six double drum units, each 1.2 m diameter by 3 m long, with space for one additional unit if required. Tailing rejects will pass to a sands spiral rake classifier system for recovery of the coarse sand fraction, which will be conveyed to a sands storage facility for dry disposal. Fines from the classifier will be pumped to the tailings thickener. Concentrate from primary LIMS will be pumped to the secondary grinding circuit.
Secondary Grinding and LIMS Circuit
Primary LIMS concentrate will be cycloned to densify the product for secondary milling in one grinding mill, 5.5 m diameter by 10 m EGL with a 5.5 MW drive. Cyclone fines will combine with secondary mill discharge as feed to secondary LIMS. Secondary LIMS will comprise two modules, each of four triple 1.2 m diameter by 3 m long drum units, with space allowed for two additional triple drum units per module. Secondary LIMS tailings will combine with primary LIMS fine tailings for the tailings thickener. Magnetic concentrate from secondary LIMS will be pumped to two Derrick stack-sizer screens (75 to 90 µm cloths) for rejection of coarse middlings. Stack-sizer overflow will return to secondary mill feed; screen underflow will be final concentrate.
Dewatering and Product Disposal
Tailings from primary and secondary LIMS circuits will be fed to a 25 m diameter high-rate thickener, with flocculent and coagulant addition for clear overflow to process water storage. Underflow at 64% to 65% solids by weight will be pumped via a stock tank to four pressure filters. Filter cake at about 22% moisture will be conveyed to dry stacking. Secondary LIMS concentrate will be pumped to an 18 m diameter high-rate thickener. Thickened underflow at nominal 75% solids by weight will report via a stock tank to pressure filtration. Filter cake moisture of 7.0% to 7.5% will be conveyed to a 20,000 tonne truck load-out storage facility.
The report states that Nevada Iron proposes initially to truck concentrates to the rail-head at either Huxley or Colado. The alternative is a dedicated pipeline. The economic analysis in the report allows for trucking for the first three years, with hydraulic transport by pipeline assumed from Year 4 onward.
Process Utilities
Total installed power is estimated at about 15 MW, with the processing facility at approximately 14 MW. Annual power draw is expected to be about 114,250 MWh, equal to 10.94 kWh/tonne of primary crusher feed. At $0.065/kWh this equals $0.71/tonne crushed.
Based on dry stacking of tailings and a process throughput of 10.44 Mtpa at 19% Fe feed grade, total make-up water for the plant is about 1 million US gallons per day. Combined with mining requirements (400,000 US gpd), potable and other uses (140,000 US gpd), and a 10% contingency, daily requirement was estimated at 1.71 million US gpd, equivalent to 2,157,450 m³ per year. An application for water rights of 1,750 Acre Feet Annually (2,159,000 m³ per year) was approved in 2011 by the Nevada Department of Conservation and Natural Resources, Division of Water.
Key reported parameters
| Parameter | Value | Unit | Basis |
|---|---|---|---|
| Design throughput (proposed plant) | 10.44 | Mtpa | Proposed design |
| Crushing circuit operating hours | 6,000 | hours/annum | Proposed design |
| Crushing circuit average rate | 1,740 | t/h | Proposed design |
| Milling/LIMS circuit operating hours | 8,000 | hours/annum | Proposed design |
| Milling circuit average rate (post pre-concentration) | 783 | dry t/h | Proposed design (assuming 40% rejection) |
| Primary ball mill dimensions | 5 m dia. x 10 m EGL | metres | Proposed design |
| Primary ball mill drive power | 4,000 | kW | Proposed design |
| Primary ball mill product size | 80% passing 500 | µm | Proposed design |
| Secondary ball mill dimensions | 5.5 m dia. x 10 m EGL | metres | Proposed design |
| Secondary ball mill drive power | 5.5 | MW | Proposed design |
| Secondary ball mill product size | approx. P80 63 | µm | Proposed design |
| Total installed power | ~15 | MW | Proposed design |
| Annual power draw | 114,250 | MWh | Proposed design |
| Specific power consumption | 10.94 | kWh/t crusher feed | Proposed design |
| Power cost | $0.71 | $/tonne crushed | Estimated at $0.065/kWh |
| Process make-up water (at 19% Fe feed) | ~1,000,000 | US gpd | Proposed design |
| Total daily water requirement (with contingency) | 1,710,000 | US gpd | Proposed design |
| Annual water demand | 2,157,450 | m³/yr | Proposed design |
| Approved water rights | 1,750 | Acre Feet Annually | Approved, 2011 |
| Tailings thickener diameter | 25 | m | Proposed design |
| Tailings filter cake moisture | ~22 | % | Proposed design |
| Concentrate thickener diameter | 18 | m | Proposed design |
| Concentrate filter cake moisture | 7.0 to 7.5 | % | Proposed design |
| Fine ore storage live capacity | 20,000 | tonnes | Proposed design |
| Truck load-out storage capacity | 20,000 | tonnes | Proposed design |
| Groundwater salinity | 10,000 to 20,000 | mg/L TDS | Measured (historical) |
Project website: https://www.nevadairon.com/site/buena-vista-nevada-mine
Technical qualifications
The processing description in this report is entirely based on proposed design parameters. No historical operating data from the Buena Vista site are presented in the processing sections. No testwork results are cited in the processing description. The report notes that the economic analysis allowing for initial trucking of concentrates is to provide time for additional economic analysis, environmental studies, and permit applications. No information is provided on achieved metallurgical recoveries, final concentrate grade specifications, or actual plant construction or operation.
Source: Buena Vista Iron Project, Nevada, USA , Technical Report, October 2013, Section 17: Recovery Methods.
