Potash

World Resources and Production

Potash is the common name given to a group of potassium-bearing minerals such as potassium carbonate and various mined and manufactured salts containing the element potassium. The term potash arose from the traditional practice of producing potassium carbonate, needed for making soap, by the leaching of wood ashes in large iron pots. The ash-like crystalline residue remaining in the large iron pots was called ‘‘pot ash’’. While there are a number of such minerals, only those that are water-soluble are of significant commercial interest. The most common commercial product is potassium chloride (‘‘KCl’’), also known as muriate of potash (‘‘MoP’’) or sylvite, a naturally occurring pink, salty mineral of which Canada, Russia and Belarus are the leading producers and exporters accounting for more than 56% of global production in 2009.

Since the amount of potassium contained in potash varies, the industry has established a common standard of measurement by defining a product’s potassium content in terms of equivalent percentages of potassium oxide (K2O). For example, sylvite contains approximately 63% K2O equivalent and carnallite typically contains approximately 17% K2O equivalent.

According to the IFA, in 2010, approximately 90% of the world’s potash production was used as agricultural fertilizer. Plants deficient in potassium are less resistant to pests and disease, and have poor size, shape, colour, taste and shelf life. Most virgin soils contain adequate potassium to allow farmers to produce average crops. The agricultural cycle of growing and harvesting crops depletes the soil of potassium, nitrogen and phosphate, which need to be replenished in consistent ratios if the soil is to remain fertile. This explains the historical agricultural practice of leaving land fallow for a number of years in order to replenish itself, however, this practise is becoming less possible in today’s world given higher population levels and thus larger crop demands from similar acreage as before. 26

Fertilizers replace the nutrients that crops remove from the soil, thereby sustaining or enhancing the yield of crops. Farmers determine the types, quantities and proportions of fertilizer to apply depending on the crop, soil quality, weather conditions, regional farming practices and fertilizer and crop prices. The functions potassium performs cannot be carried out by other nutrients and potash has no commercially viable substitute as a potassium fertilizer source. Besides agriculture, the remainder of potash consumption consists of the manufacture of potassium bearing chemicals, detergents, ceramics, pharmaceuticals, water conditioner and de-icing salt.

Mining Methods

Mining techniques for potash deposits can be divided into two common extraction techniques: underground and solution mining, although open pit or solar evaporation may occasionally be employed. The selection of the most appropriate technique is predominantly dependent on depth, geometry and mineralogy of the deposit. Solution mining typically requires slightly lower upfront capital expenditure compared to conventional underground mining techniques which require significant mine development prior to production. Conversely, operating costs for underground mining techniques are generally lower compared to solution mining techniques which can be energy intensive.

Underground Mining

Deeply buried marine evaporite deposits, such as those typically found in Canada and Russia, typically range from 400 m to greater than 1,000 m below the surface. Most potash is sourced from buried deposits using conventional mechanized underground mining methods, typically utilizing the room and pillar method. At great depths, conventional room-and-pillar mining for potash faces technical challenges and costs can be prohibitive due to the significant costs associated with sinking deep shafts and the increasing likelihood of water infiltration. Most potash deposits are found in sedimentary sequences with significant aquifers which pose constant threats to underground mining operations. The land area affected is typically confined to the immediate area of the shaft, plant, and waste disposal, but may be up to several km2.

Room-and-Pillar

Pillar
Haulage
Continuous
Mining Machine
Conveyor Belt
Continuous Mining

Solution Mining

Solution mining methods are also employed for the buried marine evaporite deposits. Solution mining employs the injection of a brine solution into underground potash bearing seams. The solution dissolves the potash bearing minerals from the seam and the pregnant potash bearing solution is then recovered to the surface for processing.

Processing of Potash Ores

There are three primary types of processing of Potash ore which are summarised as:

Flotation:

Flotation can only be used for Sylvinite ores, Sylvite (KCl) is hydrophobic and will therefore attach itself to air bubbles in a flotation plant from which it can be separated from the gangue material. The flotation process has advantages over hot leaching and crystallisation as it is not as energy intensive and has a lower capital cost.

Thermal Dissolution-crystallisation (Hot Leaching):

This process is based on the fact that potassium chloride (KCl) has a higher crystallisation temperature than sodium chloride (NaCl). The ground and scrubbed ore is heated to dissolve the KCl and some of the NaCl it is then cooled to a temperature where the KCl crystallises thus separating itself from the NaCl which remains in solution in the brine. The KCl is then separated from the brine and the brine returned to the milling circuit. (note if Solution Mining is used, the need for dissolving the Sylvinite is negated)

Electrostatic Separation:

Electrostatic separation is possible because potash minerals are not naturally conductive and can only be used where gangue minerals are conductive