The 2012 preliminary economic assessment defines a processing route for the Sapucaia aluminous phosphate ore, centered on crushing, calcination, and grinding to produce alumina calcined phosphate (TERMOFOS), with several equipment parameters and testwork results reported.
Report context
The Fosfatar Phosphate Project, located in Pará State, Brazil, is documented in a Preliminary Economic Assessment NI 43-101 Technical Report dated 17 January 2012. The report describes a processing plant to be constructed at the Rio Verde site, designed to treat aluminous phosphate mineralization requiring calcination. The process design draws on a technical meeting held 16 December 2010, in Goiania, among Fosfatar, MK, Tec-Liga, and Tecplan, which assessed the optimal processing route for production of alumina calcined phosphate from Sapucaia phosphate ore.
Processing route
Ore preparation and crushing
The phosphate ore, containing at least 6% P₂O₅, will feed a two-stage crushing circuit comprising primary and secondary stages. Crusher output will be screened in closed circuit with a double deck screen (20mm and 5mm). Jaw-type crushers were selected to minimize the generation of fines. Fine material (<5mm) will be stored and reprocessed by separate campaigns in the calcination kilns. Lump ore (+5mm to <20mm) will be directed to storage yards (regulatory stockpiles), which can also be used for blending.
Each stockpile must have a live capacity of 3 days of production of the calcination kiln (autonomy of 72 hours each stockpile, feeding 21.2 t/h, with three shifts per day operations), equaling around 1,500 tonnes each stockpile (piles of 6 m height). If the crushing system operates on two shifts per day (27.5 t/h), the consumption of the stockpiles must provide for about 55 hours of production.
Calcination
The aluminum phosphate is reclaimed and fed into the calcining process, consisting of a pre-heater, rotary kiln, and cooling. The calcined phosphate, called semi-finished (semi-acabado), will then be stored in prismatic piles, which may also be used for improving product blending. It is recommended that a stack of calcined off-grade be maintained, which will be blended with the rich product to obtain a final product within specifications and warranties for sale. Stockpile capacities should be dimensioned to provide for market seasonality based on scheduled monthly sales.
Rotary kiln characteristics reported include:
- Casing internal diameter: 2,270 mm
- Useful internal diameter: 1,970 mm
- Total length: 22 m
- Insulation and refractory brick layer thickness: 150 mm
- Kiln inclination: 3 degrees
- Kiln rotation: 2 to 4 rpm
- Burner: dual type
- Number of support stations: 2
- Distance between support stations: 12 m
- Support tackles diameter: ~750 mm
- Support tackles width: 270 mm
- Gear width: 280 mm
- Pinion width: 450 mm
- Scrolling trails (rings) diameter: ~2,700 mm
- Scrolling trails tread width: 230 mm
The kiln is being prepared to produce 150,000 tonnes/year calcined phosphate. Considering the inclination of 3 degrees and a weight of 100 tf (kiln and hold up), the efforts on the thrust bearing will range between 5 and 10 tf. The total dynamic load of the equipment in operation can exceed 230 tf, requiring an engineered base foundation. The tilt inclination of 3 degrees and rotation in the range of 2 to 4 rpm will provide a product residence time between 10 and 19 minutes.
Heat recovery
The rotary kiln shall be equipped with heat exchangers for gas-solid contact, in the phosphate feeding and calcine discharge. The first heat exchanger will recover the sensible heat of combustion gases and pre-heats the kiln charge; the second exchanger will pre-heat the combustion air, while cooling the calcined phosphate to temperatures below 100°C. It is expected that the two heat exchangers can provide a reduction of approximately 50% in fuel consumption.
Kiln sealing on the phosphate feeding side requires particular attention, since significant infiltration of false air will prejudice the pre-heating of phosphate load and reduce the rotary kiln's operating efficiency and production capacity.
Considering (i) a gas flow of 32,000 m³/h at the output of the phosphate pre-heater, (ii) a bed with 4.5m thick and (iii) internal diameter of 2.4m, the pressure drop estimated for processing of particles with an average of 12mm diameter reached 700mm CA.
Grinding and product handling
NAC P₂O₅ solubility increases with the fineness of the calcined product. It is recommended that the grinding circuit be dimensioned at 200 mesh (Tyler mesh, MOG). A preliminary grinding capacity of 21 tonnes/hour and 650 scheduled operating hours/month will produce about 13,650 tonnes/month.
Due to its high flowability, the milled product should be transferred to cylindrical silos with sufficient capacity to ensure the rate of expedition of the final product in accordance with demand, especially during peak periods. For bulk product shipment, an intensive mixer should be used to incorporate water to TERMOFOS, increasing its moisture and minimizing the emission and loss of particulate matter during handling and transport.
Particulate control
The grinding circuits, final product storage, and shipment loadout system should be provided with dust control systems. A pneumatic cyclone of 1,600 mm diameter is unlikely to adequately control particulate emissions from calcination within environmental standards. The main changes proposed for cyclone design include:
- Reduction of vortex length (S) from 2,100 to 1,100 mm
- Increase in conic section length (Z), from 2,000 to 3,600 mm
- Increase in apex diameter (B), from 100 to 600 mm
The total length of the cyclone will be reduced from 5,800 to 4,200 mm, and the internal distance between the base and apex of the vortex will increase from 2,100 to 4,700 mm.
The dipleg installation in the cyclone incorporates many uncertainties in its configuration, which increases complexity and difficulty predicting performance. It is important that a collector box (hopper) be installed in the apex of the cyclone, sealed with rotary or double action, to prevent the admission of false air and drag of collected material.
The surfaces of the cylindrical and conical sections must be free of notching to minimize turbulence in the internal flow. Emissions from calcination are estimated at 7,000 to 8,000 mg/Nm³ of dry gas, still far above environmental standards of 75 to 150 mg/Nm³. A gas treatment system for emissions control from the kiln chimney may be required.
Personnel requirements
Based on the mineral processing route, 60 employees are planned: 52 in four shifts for operations including maintenance, and 8 for production management including the laboratory. The headcount estimate includes plant supervisor, plant panel control, crushing plant, homogenization plant, calcination plant, milling plant, dispatching plant, production assistants, lab technicians, mechanics, electrician/instrument, mechanic assistants, and safety personnel.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant nominal capacity | 100,000 t/year TERMOFOS | Design |
| Annual plant capacity | 150,000 t | Calculated from kiln feed estimate |
| Ore feed grade (minimum) | 6% P₂O₅ | Design |
| Ore feed grade (average) | 20% P₂O₅ (dry basis) | Testwork/design assumption |
| Kiln feed rate | 21.2 t/h | Design estimate |
| Specific ore consumption | 1.314 t/t calcined dry basis | Calculated |
| Kiln production capacity | 15 t/h nominal; 25 t/h maximum | Design |
| Kiln dimensions | 2,270 mm casing ID; 1,970 mm useful ID; 22 m length | Recorded |
| Kiln inclination | 3 degrees | Recorded |
| Kiln rotation | 2–4 rpm | Recorded |
| Residence time | 10–19 minutes | Calculated |
| Diesel consumption (pilot) | 31.5 L/h at 350 kg/h calcined | Pilot testwork |
| Specific energy consumption | 776 kcal/kg calcined | Pilot testwork |
| Diesel consumption (industrial, with air cooler) | 41 kg/t (394 kcal/kg) | Vendor offer |
| Fuel calorific value (diesel) | 8,620 kcal/L (10,141 kcal/kg) | Assumed |
| Gas flow at pre-heater outlet | 32,000 m³/h | Design estimate |
| Pressure drop (bed 4.5 m, ID 2.4 m) | 700 mm CA | Estimated |
| Particulate emissions | 7,000–8,000 mg/Nm³ | Estimated |
| Environmental emission standard | 75–150 mg/Nm³ | Regulatory |
| Grinding capacity | 21 t/h | Preliminary |
| Grinding fineness | 200 mesh (Tyler) | Recommended |
| Grinding scheduled hours | 650 h/month | Preliminary |
| Grinding production | 13,650 t/month | Calculated |
| Peak monthly output (seasonal) | 25% of annual (37,500 t) | Market scenario |
| Crushing operating regime | 2 shifts/day, 27.5 t/h | Design |
| Calcination operating regime | 3 shifts of 8 h, 365 days, 85% utilization (7,446 h/year) | Design assumption |
| Bagging/dispatch operating regime | 2 shifts of 8 h, 365 days, 90% utilization (5,256 h/year) | Preliminary |
| Mining operating regime | 2 shifts of 8 h, 365 days, 90% utilization (5,256 h/year) | Preliminary |
| Thermal energy reduction (heat exchangers) | ~50% | Expected |
| Rotary kiln production increase potential | 18% (up to 25 t/h) | Reported |
| Ore moisture | 7% wet basis | Design assumption |
| Loss on ignition | 20% dry basis | Design assumption |
| Fines generation | 5% calcined basis | Design assumption |
| Personnel | 60 total (52 operations/maintenance, 8 management) | Planned |
Project website: https://ca.finance.yahoo.com/news/rio-verde-minerals-announces-positive-110000087.html
Technical qualifications
The report identifies several data gaps and recommendations for future work:
- Brinell hardness data for scrolling trails, support tackles, and pulley anchor tackles were not recorded, preventing analysis of hertzian tensions. The report notes that considering the kiln origin and good mechanical condition of the trails and tackles, satisfactory performance of the kiln's support and anchor systems would be expected.
- The absence of Brinell hardness data of the scrolling trails and support/prop tackles did not allow the analysis of the hertzian tensions.
- The calcination kiln system will not be installed with high efficiency devices for collection of particulate material during the start-up stage, making cyclone design optimization critical.
- Future studies should evaluate the suitability of thermal insulation application for economic reasons (heat losses) and operational safety.
- Recommended future work includes: consolidation of the process concept of granular material handling (storage yards) in conformity with sales planning; consolidation of calcination process of fine phosphate ores (Ø<5mm) and its gas treatment system; characterization of calcined phosphate by chemical analysis by granulometry, especially phosphorus solubility and presence of micronutrients; thermogravimetric analysis of aluminous phosphate to optimize calcination operating conditions (kinetics, temperature of loss on ignition, changes in crystalline structure, crepitation/fines generation); and physico-chemical characterization of surface water from mining and industrial areas for background reference determination.
- Borehole samples should be preserved for audit purposes for the life of the project.
- The report notes the estimated particulate emissions of 7,000 to 8,000 mg/Nm³ are far above the environmental standard of 75 to 150 mg/Nm³, despite cyclone design optimization, and that a gas treatment system for emissions control from the kiln chimney will likely be required.
- The dipleg installation in the cyclone, while a better alternative to increasing the length of the conic section, incorporates many uncertainties in configuration, increasing complexity and difficulty predicting performance.
- Throughput rates and work schedules contemplated in this study should be considered only as preliminary productive capacity.
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Source: Fosfatar Phosphate Project, Pará State, Brazil – CM-br-131011, Preliminary Economic Assessment NI 43-101 Technical Report – 17 January 2012.
