This section covering sources of potash comprises these pages:
Introduction
Potash mining
Potassium chloride (Muriate of Potash, MOP)
Potassium sulphate – (SOP)
Other forms of potash fertilisers
Introduction
The term “potash” originally only referred to crude potassium carbonate, which was recovered by the leaching of near-seacoast wood ashes in large pots. The ashes of inland plants were generally higher in sodium carbonate, which gave rise to the Arabic word for soda ash, alkali. The term was then carried over after potassium was discovered to form the Latin word for it, “kalium”. The recovery of potash from ashes became a thriving small cottage industry throughout the world’s coastal areas, and people of developing economies, such as the early settlers in the United States, were able to generate much-needed income from its recovery and sale.
This industry was rapidly phased out with the advent of the LeBlanc process for producing soda ash in 1792, and the discovery about the same time of the massive sodium-potassium nitrate deposits in the Atacama Desert of Chile. During the 1800s many “officinas” were established throughout the deposit to produce crude potassium nitrate, which became the world’s source of potash for industrial, agricultural, and, most of all, gun powder needs. This remained the case until the large buried carnallite (KCl • MgCl2 • 6H2O) deposits were found by drilling in the Stassfurt, Germany, area. Afterward, buried deposits and brines from saturated lakes became the world’s dominant potash sources. All commercial potash deposits come originally from evaporite deposits and are often buried deep below the earth’s surface. Potash ores are typically rich in potassium chloride (KCl), sodium chloride (NaCl) and other salts and clays, and are typically obtained by conventional shaft mining with the extracted ore coarsely ground underground (to prevent blockages in the hoppers), and then finely ground into a powder once on the surface.
Other methods include dissolution mining and evaporation methods from brines.
In the evaporation method, hot water is injected into the buried potash-rich deposit. The potash is dissolved and then pumped to the surface where it is concentrated by solar induced evaporation. Amine reagents are then added to either the mined or evaporated solutions. The amine coats the KCl but not the NaCl, due to the characteristics of the particular amine used. Air bubbles cling to the amine + KCl and float it to the surface while the NaCl and clay sink to the bottom. The surface is skimmed for the amine + KCl which is then dried and packaged for use as a K rich fertilizer—KCl dissolves readily in water and is available quickly for plant nutrition.
Potash deposits can be found all over the world. At present, deposits are being mined in Canada, Russia, China, Belarus, Israel, Germany, Chile, the United States, Jordan, Spain, Laos, the United Kingdom, Uzbekistan and Brazil, with the most significant deposits present in Saskatchewan, Canada.
With the rapidly expanding world population and subsequently more intensive farming, the need for potash has rapidly increased, and an ever-increasing number of potash deposits have been discovered and exploited, which gives rise to the very large industry that exists today. Potash has become one of the world’s largest tonnage chemicals (2021 production is around 90 million tons).
Potash in agriculture
By far most of the world’s potash production is used in agriculture. Over 95%-97% of it is sold to improve the world’s food, fibre, and other farm output. Potassium is one of the three major plant nutrients and as such must be added to all intensive farming soils as it becomes depleted. Some potassium-containing minerals such as polyhalite, clay, feldspar, and mica are found naturally in soils, and the potassium slowly becomes available with weathering. It then goes into solution or is in an ion exchangeable form, both of which are available to the plants. The potassium from fertilizers may also become ion exchanged with clays or organic matter near the surface (Table 1) and thus not be very mobile; therefore, the placement is important in many soils. Finally, the function of potassium in plant metabolism is different from that of the other major nutrients. The other nutrients become part of the plant structure, but potassium largely remains as an ion in the cells and sap. The function of potassium is to help control the plant’s water intake and metabolism.
Some of the specific effects of potash are to increase root growth; improve drought resistance by reducing water loss, wilting and respiration (maintaining “turgor“); and lower the plant’s energy losses. Potash helps form cellulose and reduce lodging (‘lodging’ refers to the permanent displacement of crop stems from their vertical position as a result of stem buckling and/or root displacement. It is most likely to occur 2-3 months before harvest and is associated with a reduction in yield and grain quality, as well as increased susceptibility of grain to mycotoxin-producing fungi.), enhances many enzyme actions, aids in photosynthesis and food formation, helps in the translocation of sugars and starch, helps increase the starch and/or protein content of plants, and helps retard crop diseases. It is sometimes called the “quality” nutrient because of these many beneficial functions. To attain maximum effectiveness, primary nutrients must be supplied to crops in essentially the same proportions as they exist in most plant life, where the ratio of nitrogen to potassium is about 2: 1.
Potash production, consumption, and price
The main production areas for potash products are Canada, Russia, Belarus, Laos, China, Germany, USA, and Chile. Consumption of the annual 75 million tons of potash in fertilisers takes place all over the world, but relatively more in countries with more sophisticated agriculture (Europe, USA, Brazil, Russia). In 2021 prices fluctuated, dependent on supply and demand, within a range of $200-$500/ ton KCl.
Forms of potash
Potash is used in fertilisers in different forms, for example:
KCl or MOP (Muriate of Potash), 60% K2O.
K2SO4 or SOP (Sulphate of Potash), 50% K2O. Low chloride, 17% S content.
KNO3 or NOP (Nitrate of Potash), 46% K2O (+ 13 % N). Low chloride content.
KH2PO4 or MKP (mono potassium phosphate), 34% K2O (+52% P2O5). Low chloride content.
MgKPO4.6H2O or K-struvite, product from recycling, varying compositions.
Various K-Mg mix crystals/mixtures: Kornkali (0-0-40+6MgO), Patentkali (0-0-20+10MgO; low chloride, high S), KMag/Trio (0-0-22+10 MgO; low chloride, 21% S), Polyhalite (0-0-14+6MgO; low chloride, 19% S).
Environmental impact of potash production
Potash production has some environmental issues that need to be managed carefully in order for this to become a more sustainable industry:
- Mining in general leaves underground workings with excavated roadways that will subside slowly and could cause damage to buildings on the surface. In potash mining there are roadways in salt (which will close very slowly) as well as in potash (closing quickly). A sustainable operation will take care that once an area is left, these roadways will be filled. This can be done with “overburden”, gangue or with waste product that is solidified with an MgCl2 brine (backfill).
- Beneficiation plants for potash have liquid effluent that must be disposed of, either on the surface or underground. In addition to various salts this effluent can contain chemicals from floatation operations.
- Beneficiation plants also have a substantial output of by-product NaCl, that can be sold as de-icing material or can be refined to a food quality via re-crystallisation and purification. Another option, used frequently in the past, is building waste piles of salt. However this is less attractive from an environmental point of view.
- Beneficiation plants require substantial amounts of energy to turn a wet product (potash after flotation) into a dry product. The type of fuel used will determine the carbon footprint of this operation. Heat-Power combinations, as well as renewable energy sources, could reduce this footprint.
- In general wastes from potash production and use lead to some spillage of salts, which can cause damage to the environment (salinity increase).
Potash is not a limited resource. Global reserves of potash are abundant, many deposits are known and can be brought into production at today’s market prices. Further deposits can become reserves if market prices increase. In general, future projected growth of potash consumption can be easily met.
References
Munson, R. D. 1980. “Potassium Availability and Uptake,” Potassium in Agriculture, Potash and Phosphate Institute, pp. 67-108.
Searls, J. P. 1991. “Potash,” Mineral Industry Surveys, Bureau of Mines, U.S. Department of Interior, Washington, D.C, U.S.A.
Links to related IFS Proceedings
22, (1953), Potash Mining and Production, P L Garès
193, (1980), Potash Deposits Outside of North America, G Rüping
297, (1999), Tailoring Potash to the Needs of the Fertiliser Industry, H. Rug, K. Kahle
328, (1992), Environmental Aspects of Potash Needs, Use and Production, H Beringer
608, (2007), Beneficial Effects of Potassium on Human Health, F J He, G A MacGregor
613, (2007), Potassium and Soil Fertility: Long Term Experimental Evidence, A E Johnston
617, (2007), Use of Potassium Fertilisers: Global Trends and Balances, B Bain, L Smith
Useful Contacts
APEP -European Potash Producers
IPI – International Potash Institute
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