The 2016 Pre-Feasibility Study for the Bayovar 12 Phosphate Project describes a two-train phosphate beneficiation plant using seawater throughout the process to produce a combined 1,000,000 dry mtpy of reactive phosphate rock concentrate.
Report context
The Bayovar 12 Phosphate Project Pre-Feasibility Study (Form 43-101F1) was completed on 08 February 2016 (project number M3-PN140103). The report presents the design basis for two phosphate beneficiation plants that will process ore mined from 13 phosphate-rich layers, or capas, to produce Reactive Phosphate Rock (RPR) concentrate. The study relies on testwork performed by Jacobs Engineering to establish the design parameters and mass balances.
Processing route
Plant Configuration
The project comprises two process plants. Plant 1 will process 1,320,370 dry mtpy of ore from capas 1, 2, 5, 7, 8, and 9 to produce 500,000 dry mtpy of concentrate at a target grade of 24 percent P₂O₅. Plant 2 will process 1,585,868 dry mtpy of ore from capas 3, 4, 6, 10, 11, 12, and 13 to produce 500,000 dry mtpy of concentrate at a target grade of 28 percent P₂O₅. Plants 1 and 2 are identical except for the particle size cut point required to make the higher grade concentrate.
ROM Ore Handling
Haul trucks deliver ore from the open pit mine to stockpiles with 14 days of storage capacity. The Plant 1 stockpile holds 50,644 tons of dry ore and the Plant 2 stockpile holds 60,828 tons. Front end loaders transfer ore at rates of 177.3 dry mtph for Plant 1 and 213 dry mtph for Plant 2. The ore travels from the dump pocket to a belt feeder and conveyor that delivers to the drum washer.
Each plant is fed at the rate shown below. A metallurgical sampler located at the drum washer feed conveyor collects wet, salt-bearing material entering the plant, and a belt scale determines the feed weight.
Drum Washing, Size Classification and Cyclone Classification
The drum washer mixes ROM ore with process water to form a slurry containing 35 percent solids. Testwork established a required drum washer retention time of 3 minutes. The scalping screen removes particles larger than 12,500 microns that contain only 8 percent P₂O₅; this oversize is considered reject and is disposed of at the waste rock storage facility. Screen undersize flows to the Primary Cyclone Feed Pumps.
The primary cyclones use centrifugal force to separate solids by particle size and density. The cyclone cut size is 53 microns (-270 mesh) for both plants. Cyclone overflow contains very fine diatomite particles and flows to the tailing tank. Cyclone underflow, containing approximately 55 percent solids, is the product stream and flows to the Primary Attrition Scrubber.
Primary Attrition Scrubbing
The primary attrition scrubbers disaggregate waste material from product by intense scrubbing at a slurry density of 55 percent solids. Testwork showed a required retention time of 12 minutes.
Secondary Attrition Scrubbing, Size Classification, Cyclone Classification, and Hydraulic Sizing
The secondary attrition scrubbers receive slurry from the primary circuit and further disaggregate waste from product at 55 percent solids. The attrition screen removes material larger than 600 microns for additional upgrading. The secondary cyclone feed tank combines the attrition screen underflow, secondary attrition screen discharge and process water to a slurry density of approximately 20 percent solids.
The secondary cyclones split the incoming stream by size and density. Cyclone overflow containing fine diatomite particles flows to the tailing tank. The cyclone underflow is the product stream, containing approximately 55 percent solids, and flows to the hydrosizer.
The hydrosizer uses an upward flow of water to fluidize small, low-density particles into the overflow stream. In Plant 1, the overflow stream normally contains particles smaller than 53 microns (-270 mesh); a coarser cutpoint can be achieved if required. At Plant 2, the overflow stream normally contains particles smaller than 106 microns (-150 mesh); a coarser cutpoint can also be achieved if required. Hydrosizer overflow flows to the tailing tank, while the underflow containing 65 to 70 percent solids is the product stream.
Belt Filtering
The hydrosizer underflow discharges into a distribution box above the concentrate filter, where an auger spreads the slurry across the width of the belt filter. The filter dewaters the concentrate from 65 percent to 85 percent solids. Testwork indicated that rinsing the filter cake with seawater did not reduce cadmium content, so the filter was sized for dewatering without rinsing. The filtrate is returned to the process at the secondary cyclone feed tank. The filter cake discharges to a bucket elevator that carries it to the concentrate dryer feed bin.
Concentrate Drying and Product Storage
The dewatered filter cake is stored in the concentrate dryer feed bin and metered by screw feeder into a fluid bed concentrate dryer. The dryer heats the concentrate from 25 degrees Celsius to 90 degrees Celsius, reducing moisture from 15 percent to approximately 4 percent. The dryer is fueled by liquefied natural gas; the burner supplies 7,380 kW with a burner blower delivering 55,200 kg/h of air. The dried concentrate is conveyed to one of two product silos per plant, each with a 7-hour retention time and volume of approximately 438 cubic meters. Dryer off-gas passes through a dust collector, and the baghouse dust is returned to the process at the silo bucket elevator.
Tailing Impoundment
Overflow from the primary cyclone cluster, secondary cyclone cluster and hydrosizer is collected in a vessel and pumped to the tailing pond. The tailing slurry contains approximately 9 to 10 percent solids. Due to the very slow settling rate, reclaiming water in a thickener is impractical. Plant 1 tailings are pumped to the tailings impoundment facility; Plant 2 tailings are pumped to the Plant 1 sump where they are commingled with Plant 1 tailings. Each process line is sampled separately.
Water Systems
Seawater is used throughout the beneficiation process at Plants 1 and 2. Two vertical turbine pumps, each with an 895 kW motor, deliver a total of 891 m³/h to Plant 1 and 944 m³/h to Plant 2. Seawater is stored in two ponds (Pond 1 at 71 by 71 by 9 meters; Pond 2 at 62 by 62 by 9 meters), each sized for 24 hours of plant water plus a firewater system reserve. Each plant includes a reverse osmosis desalination plant producing 1.4 m³/h of potable water for laboratory and personnel use. Seawater is used at the drum washer, scalping and attrition screens, cyclone feed tanks, hydrosizer, and for cleaning the concentrate filter cloth. Salt is not removed by freshwater rinsing, and the process water is not recycled from the tailings pond.
Key reported parameters
| Parameter | Plant 1 | Plant 2 | Basis |
|---|---|---|---|
| Ore feed rate | 1,320,370 dry mtpy | 1,585,868 dry mtpy | Design |
| Ore feed grade | 11.5% P₂O₅ | 14.1% P₂O₅ | Design |
| Ore moisture | 30% | 30% | Design |
| Water soluble salts in feed | 6.45% | 2.94% | Design |
| Concentrate production | 500,000 dry mtpy | 500,000 dry mtpy | Design |
| Concentrate grade | 24% P₂O₅ | 28% P₂O₅ | Target |
| P₂O₅ recovery | 81.1% | 72.4% | Testwork |
| Concentrate (mass balance) | 505,051 t/y at 24.14% P₂O₅ | 505,051 t/y at 28.83% P₂O₅ | Testwork |
| Shipped concentrate | 500,000 t/y at 24.14% P₂O₅ | 500,000 t/y at 28.83% P₂O₅ | After shrinkage |
| Primary cyclone cut size | 53 microns | 53 microns | Design |
| Hydrosizer overflow cut size | 53 microns (-270 mesh) | 106 microns (-150 mesh) | Design |
| Attrition scrubber slurry density | 55% solids | 55% solids | Design |
| Attrition scrubber retention time | 12 minutes | 12 minutes | Testwork |
| Slurry density to secondary cyclones | 20% solids | 20% solids | Design |
| Cyclone underflow solids | 55% | 55% | Design |
| Filter feed solids | 65% | 65% | Design |
| Filter discharge solids | 85% | 85% | Design |
| Product moisture after drying | 4% | 4% | Design |
| Seawater requirement | 891 m³/h | 944 m³/h | Design |
| Potable water production | 1.4 m³/h | 1.4 m³/h | Design |
| Operating availability | 85% | 85% | Design |
| Annual operating hours | 7,446 h/y | 7,446 h/y | Design |
Technical qualifications
The following limitations are stated in the report:
- The Plant 2 mass balance is based on 28.83% P₂O₅ concentrate with a recovery of 72.3 percent, whereas testwork showed the hydrosizer cutpoint can be adjusted to achieve a coarser cut if required.
- Salt content in the final product was calculated by Metsim simulation at 0.6 percent; this was not verified by pilot plant testing of the complete drying circuit.
- The report states that the scalping screen removes particles larger than 12,500 microns; the screen is equipped with wash sprays.
- Testwork showed that drum washer retention time of 3 minutes and attrition scrubber retention time of 12 minutes are required.
- Due to the very slow settling rate of fine particles, thickening of tailings is impractical, and water is not reclaimed from the tailings pond.
- The concentrate filter was sized without a rinsing step because testwork showed that seawater rinsing of the filter cake did not reduce cadmium content.
- The report notes that the cyclone cut size for both plants is 53 microns, but the hydrosizer cutpoint differs: the Plant 1 overflow stream normally contains particles smaller than 53 microns, while the Plant 2 overflow stream normally contains particles smaller than 106 microns. The difference in cut size is the basis for the different concentrate grades and recoveries.
Source: Bayovar 12 Phosphate Project, Form 43-101F1 Pre-Feasibility Study, M3-PN140103, 08 February 2016, Sections 17.1 through 17.3 and 17.4.
