Global potash deposits

Potash is a general term referring to any potassium fertilisers used in agriculture. Potassium is a naturally occurring element which cannot be manufactured synthetically. As one of the most important plant nutrients (besides nitrogen and phosphate), it is indispensable for productive and healthy plant growth. Potassium fertilisers therefore make a decisive contribution to better providing the growing world population with food, in terms of both quantity and quality. A number of intermediate products are also produced from potassium. These are used in the production of industrial and pharmaceutical goods which would be inconceivable without potash.

Potassium is the seventh most common element occurring in the Earth’s crust, accounting for 2.4% of its mass. Potash deposits, i.e. natural concentrations of raw potash, consist of potassium salt rock, predominantly made up of the potassium minerals sylvite (KCl), carnallite (KMgCl3*6 H2O), kainite (KMg[Cl|SO4]*2.75 H2O) and langbeinite (K2Mg2(SO4)3), or potassium-bearing salt solutions either underground or in salt lakes.

How potash deposits are formed

All the major solid potash deposits are of marine origin and were formed due to the evaporation of sea water in almost all geological systems in the Earth’s history since the Cambrian period approximately 550 million years ago.

The formation of the potash deposits („Barrier theory“)

 

According to Ochsenius’ “bar theory” (1877), in the geological past large inland seas existed for a time, which were separated from the oceans by straits and ridges (“bars”). These bars hindered or completely halted the influx of salt-bearing sea water. Because an arid climate frequently prevailed over large parts of the Earth in different periods of the Earth’s history, often with powerful sunlight, the salt-bearing sea water in the inland seas evaporated as if in a gigantic evaporation pan. As a result, the salt concentration of the water increased and the dissolved salts crystallised, which were then deposited in the order of their solubility – first rock salt and later potassium and magnesium salts.

This process was repeated over millions of years and resulted in layers of rock salt with a thickness of several hundred metres and potash seams several metres in thickness being formed on top of each other. Later in the Earth’s history, water-impervious clay strata settled on the salt deposits (they were often blown over the dried-out salt pan by the wind), thus preventing the salts from being dissolved again.

The birth of potash mining

The first potash deposits in the world were discovered in 1856, when potash-bearing strata were found during sinking work aimed at opening up a rock salt deposit in Staßfurt, near Magdeburg in Saxony-Anhalt. The commencement of raw potash salt extraction in Staßfurt five years later marked the birth of potash mining. The nutrient potassium, which until then could only be obtained from wood ashes (the origin of the word “potash”), was now available in large quantities for use in agriculture.

Until the beginning of the 20th century, potash mining was only practised in Germany. However, numerous deposits were also opened up for mining in other European countries and overseas, especially after 1930.

Today, natural potash deposits all over the world are still predominantly extracted in solid form by conventional underground mining. The crude salt is dislodged using explosive charges or by cutting several hundred metres below the ground and is then brought to the surface via vertical shafts and processed in aboveground plants.

 

The first potash plant of the world at Staßfurt

Another type of potash mining, solution mining, was introduced a few decades ago. This method allows potash deposits to be mined which cannot be accessed by conventional means. It involves dissolving the easily soluble potash salts in the deposits with fresh water via deep boreholes and bringing the solution to the surface in large containers. The warm solution then cools off causing the potassium chloride to crystallise. There are only a few large solution mining plants due to the technical difficulty of the process.

The largest potash deposits in the world

The potash deposists worldwide
Quelle: K+S Käding/Beer

 

Total worldwide geological potash deposits (known) amount to an estimated 210 billion tonnes of K2O (potassium oxide is a measure for potassium content). According to current estimates, up to 16 billion tonnes of K2O are recoverable using current technology.

The largest recoverable potash reserves are concentrated in the northern hemisphere. Canada alone has almost 10 billion tonnes of recoverable K2O deposits (in the province of Saskatchewan), which account for approximately 60% of global potash reserves. The deposits were discovered during the Second World War, and mining operations began in the 1960s. Today, a number of potash mines are operated in the area, by PotashCorp, Mosaic and Agrium.

The next largest potash reserves are in Russia (up to 2.2 billion tonnes of K2O) and Belarus (up to 1.0 billion tonnes). In Russia, the two existing potash mining companies, Uralkali and Silvinit, concentrate their operations on a large deposit in the Urals, which has been mined since 1931. The Belarusian deposits near Minsk have been mined for potash crude salts by the local company Belaruskali since the beginning of the 1960s.

With recoverable reserves of up to 0.8 billion tonnes of K2O, Germany’s potash deposits are the fourth largest in the world. The opening of the first potash plant in the world in Staßfurt in 1861 marked the beginning of the now almost 150-year history of German potash mining.

Other solid potash reserves are mined in the USA (by Mosaic and Intrepid), England (Cleveland Potash), Spain (Iberpotash) and Brazil (Vale).

K+S KALI GmbH – the leading supplier in Europe

K+S KALI GmbH currently operates six mines in three German potash districts: the Hanover district in Lower Saxony, the Calvörder district in Saxony-Anhalt and the Werra-Fulda district in Hesse and Thuringia. While the potash deposits in the Werra-Fulda district lie flat in seams at a depth of 500 to 1,000 metres, there are faults and folds in the deposits in both of the northern districts in Lower Saxony and Saxony-Anhalt due to deformations in the Earth’s crust. The originally level potash deposits are therefore vertical in places. Due to the steep incline, extraction of crude salts takes place at depths of from 400 to over 1,400 metres. Once the potash rock has been blasted, huge shovel loaders with a shovel capacity of up to 20 tonnes transport the crude salt to the crusher plant. From there the ground salt is carried on conveyor belts to the mine shaft.

The formation of Germany’s potash reserves goes back more than 250 million years to the Upper Permian era, when the so-called Zechstein Sea, which at that time covered a wide area of Central Europe, evaporated due to powerful sunlight. In contrast to the chloride-type potash deposits typically occurring in the rest of the world, the German deposits are of a special sulphate type which is characterised by additional magnesium sulphate and potassium sulphate minerals in the crude salt.

On the basis of this special raw material composition, K+S KALI GmbH offers a product range consisting of standard products and high-value special products for agricultural and industrial applications, which in terms of range and diversity cannot be matched by any other potash producer in the world. K+S KALI GmbH is the fourth largest potash producer in the world and the leading supplier in Europe. With regard to our potash- and magnesium-based special products, we are the world leader.

 

Loader with a scoop capacity of up to 20 tonnes in a potash mine of K+S KALI GmbH

Evaporation of potassium-containing salt solutions

Potassium-containing salt solutions lying underground or in salt lakes represent a special form of natural potash deposits. However, recovering these reserves is highly dependent on the climate, as sunlight is used to evaporate the solutions (solar evaporation). The world’s largest reserve of potash in the form of salt solutions is the Dead Sea (up to 1 billion tonnes of K2O), which has been used for potash production since the beginning of the 1930s. Today DSW operates on the Israeli side and APC on the Jordanian side. Evaporation plants for potash recovery are also operated in China, the USA and Chile. The brine used in China is mainly taken from Qarhan Salt Lake. Both of the US producers, Compass Minerals and Intrepid, use brine from the Great Salt Lake or the Bonneville Flats in the Great Salt Lake Desert, while SQM in Chile uses salt solutions occurring close to the surface under the salt crust of Salar de Atacama.

 

World potash production by producers 2008
Year 2008; incl. sulphate of potash and low grade potash. Sources: IFA, K+S

Projects to open up further potash deposits

Both existing and new potash producers are working on a series of projects aimed at accessing further potash reserves for mining exploitation, for example in Canada, Russia, Brazil, Argentina, Thailand, Congo, Ethiopia, Laos, Uzbekistan, Turkmenistan and also Germany.

However, the construction of a new potash mine (a greenfield mine) requires a considerable capital outlay. Expressed as a lump sum, a potash plant with an annual capacity of 1 million tonnes is likely to require an investment of approximately USD 1 billion. Also, the period preceding the start-up of new projects is usually extremely long. After the mining licence has been obtained and the necessary exploration work carried out, on average another five to seven years elapse from the sinking of the shafts to the completion of the underground and aboveground infrastructure.

Potash projects involving the construction of new solar evaporation plants are currently being pursued in China and Australia.