Preparing for growth – phosphate mining

Materials World magazine
,
1 Jul 2009

Fertilisers are required to boost crop production. Michael Forrest reports on the Chilisai phosphate rock deposit in Kazakhstan.

According to the UN Food and Agriculture Organisation, developing countries will need an extra 120 million hectares for crops in the next 30 years, an overall increase of 12.5%. This extra farmland is available, but the need to preserve forest cover and support infrastructure will constrain agricultural development. The UN forecasts a rise in global population of 200 million over the next three years, with the total population reaching nine billion by 2050.

To provide food for an expanding population and meet industrial demand for agricultural products, farmland will have to be more productive, thus requiring fertilisers. One of the most important fertilisers is phosphate, which is normally produced in a combined form with nitrogen to create diammonia phosphate (DAP) and monoammonia phosphate. It is also used to produce NPK (nitrogen, phosphate and potassium) fertilisers.

Phosphate is derived from phosphate rock found in most continents where shallow seas in geological times, often isolated by tectonic movements causing repetitive sedimentation, gave rise to organic-rich sediments. Often phosphoric horizons have been reworked during and after deposition. Such is the case of the Chilisai deposit in the Aktyubinsk Phosphorite Basin of northwest Kazakhstan. Of Cretaceous age, the phosphates were deposited on a near-marine shoreline that developed sands associated with the transgression of the palaeo-Caspian sea.

Zones and plates

Chilisai is one of the largest deposits in the former Soviet Union and was estimated by Soviet geologists to contain over one billion tonnes of phosphate rock grading around 10% P2O5. Three distinct lithologies occur in the phosphate bearing zone – a basal pebble zone, followed by a nodule zone and capped by a weakly cemented plate.

The plate is not always present but contains up to 18% phosphate and consists of phosphate nodules and pebbles cemented by a sandy phosphate with an average thickness of 0.2m. The nodule layer comprises concretions of fine sandy nodules, often cemented together, that are one to five centimetres in size.

The pebble zone contains oval shaped fragments, one to three centimetres in size, that in some cases are well flattened. Both the nodule and pebble beds are set in a matrix of glauconite-quartz sands with silica being 50% of the total gangue minerals. Overall the grain size of the deposit falls within the 0.8-25mm range. Simple mine site screening upgrades the material to 17% P2O5, a concentration that allows direct acid digestion and obviates the need for flotation.

The large scale of the deposit and its location near transport links to Russian and Chinese markets attracted UK-registered company Sunkar Resources. Serikjan Utegan, Chief Executive Officer, says, ‘The large reserves indicated by the Soviet geologists provide a long-term mine life upon which an integrated fertiliser industry can be based’. Sunkar has begun mining phosphate rock using earth moving machinery of the type used in civil construction.

Commercial outlook

'The unconsolidated overburden [which averages only three metres over the company’s contract area, which exceeds 800km2] and relatively soft sediments can be removed and ripped by bulldozers and loaders and, by simple screening, a saleable product can be obtained. Mining can take place for 10 months of the year and it is only in the depth of winter [when temperatures can be as low as –30ºC] that frozen ground halts operations,’ Utegan adds.

The saleable product is ground phosphate rock containing around 17% P2O5. This is also soluble, enabling direct application. Utegen says, ‘In the past there has been a ready market for this type of fertiliser in the region. Sunkar has been mining the deposit since September 2008 with a view to finding sales to provide a steady cash flow. In addition, the phosphate concentrate can be sold to Russian fertiliser producers to boost phosphate levels in their operations’.

Although a plant for the production of direct application phosphate rock was developed by the Russians in the 1970s a lack of investment, followed by the collapse of the Soviet system in the early 1990s, resulted in closure. In 1975, Russian geologists estimated the tonnage and grade occurring within the Sunkar licence area. These resources were classified under the Russian system (A to C), equivalent to measured, indicated and inferred levels of western codes and sufficient to support a mine for many years.

The initial mine plan is to produce five million tonnes per year, and 10Mt/y by year five of operation. The mining takes place in three stages – removal and stockpiling of topsoil, removal and disposition of overburden, and mining and transport of ore to the beneficiation plant. Stripping ratio is favourable at 1.69m3 overburden to one tonne phosphate rock. A pre-feasibility study has determined that mining equipment costs are US$39.8m with operational costs of US$3/t.

Full integration

Sunkar intends to develop a fully integrated fertiliser plant at Chilisai. Attempts in the Soviet era failed when fatty acid flotation was used to upgrade the ore in preparation for making phosphoric acid and then DAP. As mineralisation does not occur in discrete monomineralic particles, only a 20% concentrate was achieved, marginally better than screening alone.

Sunkar’s scoping study suggests the conceptual integrated plant should consist of three units – a sulphuric acid plant, phosphoric acid plant, and a DAP production and granulation facility. The production of DAP requires the dissolution of mined concentrate in sulphuric acid to produce phosphoric acid and phosphogypsum, which is filtered and discarded. The phosphoric acid is then brought into contact with liquid ammonia, resulting in a wet DAP. At full capacity the conceptual plant will produce 1.76Mt of DAP from 0.83Mt of phosphoric acid at 400,000t of liquid anhydrous ammonia per year. The wet DAP is dried and granulated for dispatch.

‘Raw materials and transport are critical in bulk fertiliser production,’ says Utegen. ‘The Chilisai operation has a number of advantages that will increase profitability. The first is location, only a “last mile” from power lines and rail transport to major markets in central Asia, Russia and China. Freight rates to the Black Sea are US$35/t and US$20/t to western China. The second is the stranded sulphur production from the petrochemical plants of the Caspian region.

‘With no local market for by-product sulphur, the integrated plant offers a price opportunity for Sunkar and no-penalty disposal for the oil industry. The other essential raw material, ammonia, is also a waste product of the industry. All planned mining and downstream projects require offtake, it is an essential part of planning.’

He adds, ‘Our market advisors, British Sulphur Consultants, forecast a 4.3% compound annual growth rate for phosphate fertiliser to 2016 in the former Soviet Union, compared with 1.3% for the rest of the world. Kazakhstan is a major grain exporter. Full-scale production of 1.76Mt of DAP is planned for that date and estimated cash costs are in the bottom quartile for global DAP production. The major savings are in cheap near-surface mining and low acid costs’.

Further information: Sunkar Resources plc