Mining division - Phalaborwa
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Founded in 1951, Foskor’s Mining Division in Phalaborwa mines phosphate rock (foskorite and pyroxenite), from which Foskor’s Acid Division in Richards Bay produces phosphoric acid and phosphate-based granular fertilisers for local and international markets. The opencast mine in Phalaborwa, in South Africa’s Limpopo Province, has the capacity to yield 2.6 million tons per annum of phosphate rock concentrate from processing 35 million tons of ore per annum. Once crushed, milled, concentrated and dried, most of the phosphate rock concentrate is railed to Foskor’s processing plant in Richards Bay, 800 km away on the country’s east coast.
Commissioned in 1953, Foskor has traditionally mined foskorite and pyroxenite in a 60:40 ratio. With the body of foskorite ore nearing depletion, Foskor appointed Bateman Africa to undertake a feasibility study for the construction of a new mine to increase its pyroxenite processing, as well as remedial measures to enhance throughput on its Extension 8 processing plant.
The Pyroxenite Expansion Project (PEP) Phase 1
With the most recent extension to the mine’s beneficiation capacity being Extension 8 in 1999, PEP Phase 1 represents the ninth extension to the Foskor mine. Approved by the Foskor Board in September 2007, Phase 1 involves the construction of a new opencast mine for the mining of pyroxenite ore (PEP1a), together with the installation of a new primary gyratory crusher and an overland conveyor system to move the ore from the new mine to the existing processing plant five kilometres away (PEP1b). This new source guarantees ore reserves for at least the next 70 years. Establishing the new mine in the South Pyroxenite area was done to replace depleting foskorite above ground and to process pyroxenite ore being mined, which will enable Foskor to maintain its existing phosphate rock concentrate output. The R542 million project was successfully completed in June 2010, on time and within budget.
PEP Phase 2
Phase 2 focuses on de-bottlenecking the existing Extension 8 plant to improve its throughput rate, in order to meet its original design capacity. The PEP2 was approved by Foskor’s Board in September 2008 and is due for completion in March 2011.
When Extension 8 was conceptualised in the late 1990s, a dry milling process was selected over the wet (ball and rod) milling process used elsewhere at Foskor. The advantage of the dry milling process was that ore could be reduced from greater than 125 mm to less than 0.5 mm in one processing step – with obvious economic and environmental benefits. However, due to a combination of process design and equipment under performance, the Extension 8 plant has never performed at design capacity for any extended period. Various process modifications have been attempted to rectify the performance and reliability shortcomings but none have been totally successful to date.
Foskor has to de-bottleneck the Extension 8 plant by adding a separate, parallel tertiary crushing circuit to crush the ore from 125 mm down to about 16 mm. A wet milling section (as used elsewhere in the Foskor plant) has been added, to reduce the ore particle sizes further, from 16 mm to smaller than 0.5 mm. After wet milling, the ore is reintroduced to the Extension 8 process at the flotation conditioners, together with the dry circuit ore. The combination of the two streams ensures that the flotation plant is fully utilised and that Extension 8 is able to perform at design
Processes Used to Produce Phosphate Rock Concentrate
Mining – extensive drilling and blasting is required to extract ore deposits from the igneous complex. Once the rock has been blasted, either a hydraulic or rope shovel or a front-end loader is used to load the ore onto one of Foskor’s 180-ton haul trucks so that the rocks (up to 1.2 metres in diameter) can be transported to the crushers.
Crushing – Foskor owns and operates two large primary crushers, five secondary crushers and five tertiary crushers, used to grind large rocks of phosphate-bearing ore into smaller pebbles (to about 13 mm). Conveyer belts transport the crushed ore to the mills.
Milling – each one of the three milling circuits, comprising between one and 17 individual mills, is dedicated to a flotation circuit. The mills grind the pebble-sized phosphate ore to sand particles. Slurry, formed by mixing water and sand, is then pumped to the flotation circuits.
Flotation – in the four flotation circuits, reagents (such as fatty acids) are added to the slurry to separate phosphates from the other minerals in the ore (which are removed as tailings). Different flotation processes recover copper from the foskorite ores.
Tailings handling – waste materials or tailings are collected and pumped into either the Southern or the Selati tailings dam. The latter is known to be the largest tailings disposal facility in the southern hemisphere and measures approximately 1,100 hectares at its base.
Thickeners and filtration – phosphate concentrates recovered from the flotation circuits are pumped through thickeners, as excess water is drained.
Drying and dispatch – the thickened rock concentrates (in fine powder form) are conveyed to the coal-fired drying kilns to make a sand-like finished product. Approximately 2 million tons of rock concentrate per annum is railed to customers and about 500,000 tons is pumped in slurry form to a neighbouring buyer.