The 2012 Preliminary Economic Assessment (PEA) for the Duyker Eiland Project in the Western Cape, South Africa, details a conventional phosphate flotation circuit designed to produce a 33% P2O5 concentrate with an estimated 85% recovery.
The mineral processing design for the Duyker Eiland Project relies on experience from similar operations, published work, and exploratory test work performed at the University of Cape Town Chemical Engineering Department under the supervision of Mr Johansson. The conceptual process flow diagram is based on this limited test work and operational experience. The design targets an optimized de-sliming stage with a finer cut than used in testwork, which is expected to raise overall recovery to 85%. The final concentrate is projected to grade 33% P2O5.
Ore from the mine is tipped by loader into a mill feed hopper and conveyed to a scrubbing mill for light milling and scrubbing to break up lumps and clean surfaces for effective flotation. The mill operates at a water to solids ratio of 0.5 to 1. The scrubbed material is then pumped to de-sliming cyclones. The overflow from the de-sliming cyclone flows to a thickener where overflow water returns to the process water tank and underflow slime reports to the slimes dam. The de-slimed underflow reports to a hydro-separator where it is de-watered to about 70% solids before pumping to the conditioner tank, with excess water overflowing to the process water tank.
Flotation reagents are added in the conditioner. The conditioned slurry reports to a flotation circuit consisting of a scalper, rougher, scavenger, and two cleaner stages. The fastest floating material is scalped off in the first cell and, being quite clean, is pumped directly to the final product hydro-separator. The product from the rougher cell passes through two stages of cleaner cells before being pumped to the final product hydro-separator. Flotation tailings, including from the scavenger, are filtered; the filtered tailings may be mixed with de-watered slime for pit back-filling. The final concentrate is de-watered in a hydro-separator, filtered, and stored for transport to customers.
The mass balance, based on a production rate of 3 million tonnes per annum of ore and 8,000 operating hours per year, specifies a final filtered concentrate rate of 83.5 tonnes per hour at 10% moisture. The de-sliming cyclone underflow feed to flotation contains 427.5 tonnes per hour of solids at 85.0% solids, grading 7.05% P2O5. The final concentrate is filtered to 10% moisture and contains 27.54 tonnes per hour of P2O5, representing 85% recovery.
For transport, the final product could be moved by road in 30 tonne trucks to an approved facility for export, with the conceptual haul route from the mine site to Saldanha Port identified in the report.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Ore throughput | 400 | tph | Design capacity for scrubbing mill |
| Annual ore feed | 3,000,000 | tpa | 8,000 operating hours per year |
| Final concentrate P2O5 grade | 33 | % | Target product grade |
| Overall plant recovery | 85 | % | Expected with optimized de-sliming |
| Final concentrate production | 83.5 | tph | Filtered to 10% moisture |
| Final concentrate P2O5 | 27.54 | tph | At 33% grade and 85% recovery |
| De-sliming cyclone underflow solids | 427.5 | tph | At 85.0% solids |
| De-sliming cyclone underflow grade | 7.05 | % P2O5 | Flotation feed |
| Flotation feed solids | 70.0 | % | After hydro-separator de-watering |
| Feed moisture | 2 | % | Ore received at plant |
| Mill power | 3 to 5 | kWh/t | Power requirement basis |
| Rougher retention time | 5 | minutes | 4 tanks |
| Conditioning time | 3 | minutes | Two mechanically stirred cascading tanks |
| Rougher solids | 20 | % | |
| Rougher residence time | 5 | minutes | |
| Rougher tank size | 10 | m^3 | |
| Rougher power | 30 | kW | |
| Rougher number | 8 | ||
| Slimes thickener design capacity | 25 | tph | 10 m diameter, 5 units |
| Tailings filter design capacity | 350 | tph | 150 kW power, 1 unit |
| Concentrate filter design capacity | 100 | tph | 50 kW power, 1 unit |
| Fatty acid combination | 1000 | g/t | Primary collector, estimated consumption |
| Fuel oil | 300 | g/t | Promoter, estimated consumption |
| Frother | 20 | g/t | Estimated consumption |
| pH regulator | 50 | g/t | Estimated consumption |
| Depressant | 100 | g/t | Estimated consumption |
Overview
The Duyker Eiland Project involves processing phosphate-bearing sand from a mine in the Western Cape, South Africa. The PEA describes a processing route that includes scrubbing, de-sliming, and froth flotation to produce a phosphate rock concentrate for export. The design draws on test work at the University of Cape Town and experience from similar operations. The plant concept was developed to process 3 million tonnes per annum of ore over 8,000 operating hours per year, which corresponds to an average throughput of roughly 375 tph with a design basis of 400 tph for the scrubbing mill.
Key Process Stages
Ore is fed by loader to a hopper and conveyed to a scrubbing mill where light milling and scrubbing breaks up lumps and cleans particle surfaces. The mill discharge is classified in de-sliming cyclones. The de-sliming cyclone underflow is de-watered in a hydro-separator to approximately 70% solids before conditioning. The cyclone overflow reports to a slimes thickener, with the underflow sent to a slimes dam and the overflow water returned to the process water tank.
Flotation feed is conditioned with reagents in two mechanically stirred cascading tanks with a total of 3 minutes residence time. The conditioned slurry reports to a flotation circuit. A scalper cell removes the fastest floating, highest grade material. The rougher concentrate, along with the scalper product, is cleaned in two stages of cleaner flotation. Scavenger flotation recovers additional values from the rougher tailings, with scavenger concentrate returned to the conditioner.
The final concentrate is de-watered in a hydro-separator, filtered, and stored for transport. The tailings thickener underflow and flotation tailings are filtered; the tailings filter operates at a design capacity of 350 tph. De-watered slime may be mixed with flotation tailing for pit back-filling. The filtered concentrate is transported by road in 30 tonne trucks to an export port at Saldanha.
Additional Interesting Data and Summary
The PEA identifies that although a hydroxamic acid type of collector performed better in test work, a fatty acid combination was selected as the primary collector due to the prohibitive cost of hydroxamic acid. The report notes that if hydroxamic acid becomes cheaper, it is a probable choice. Similarly, fuel oil in the form of diesel oil was found to be a good promoter, but future work will aim to limit its use or replace it with biodegradable alternatives, with the reagent suite to be optimised in future test work.
The de-sliming cyclone cut-size is a key design parameter. The report assumes the cyclones run for maximum efficiency at a fine cut-size, an assumption that must be confirmed by test work. The amount of slime is based on test work results, and the rougher concentrate grade was based on a low middlings content assumption.
The major equipment list provides design criteria including a scrubbing mill with a design capacity of 400 tph, flotation cells with a 10 m^3 tank size and 5 minutes retention time for rougher and scavenger stages, and a slimes thickener with a 10 m diameter. The tailings filter and concentrate filter have design capacities of 350 tph and 100 tph respectively.
Key Processes
- Scrubbing and light milling to break up lumps and clean surfaces
- De-sliming with cyclones at a fine cut-size
- De-watering in hydro-separators to about 70% solids
- Conditioning with reagents in two cascading tanks
- Flotation with scalper, rougher, scavenger, and two cleaner stages
- Thickening and filtering of slimes and tailings
- De-watering and filtering of final concentrate
- Road transport of product in 30 tonne trucks
Source: Duyker Eiland Project , 2012 PEA Technical Report, 2012. Project website: Montero Mining and Exploration Limited
Project website: Duyker Eiland Project, 2012 PEA Technical Report
