Other Potassium Fertilizers

Potassium sulfate is the second largest tonnage potassium compound, and it is also used primarily as a fertilizer. The sulfate or other nonchloride forms of potassium are preferred for certain crops that do not tolerate the chloride ion well, e.g., tobacco and some fruits and vegetables. Nonchloride potash sources are also needed in areas where chloride accumulation in the soil is a problem. This is important in arid areas where chloride salts from irrigation water accumulate or in areas of very intensive agriculture, e.g., in the Netherlands. Potassium sulfate may be preferred because of its sulfur content where soils are deficient in both potassium and sulfur. 

2 Potassium Sulfate Production 15.5.2.1 Mannheim Process - Historically potassium sulfate has been made primarily from KCl and sulfuric acid (and a small amount from KCl and SO2) when the byproduct HQ was the dominant product. However, over the years the HCI market has had more competition, and natural K2SO4 with lower capital and operating costs has begun to dominate its production in some countries with natural complex salts. 

The Mannheim process was originally developed from sodium sulfate production by reacting NaCl wTth suffuric acid. Replacing NaCl wth KCl produces potassium sulfate. The reaction is two-stage  

The HQ gas is cooled in a graphite heat exchanger and absorbed in water in two stages to produce 33% hydrochloric acid as a byproduct. The process gives an excellent quality that contains over 50% K 0 and less 

2 Recovery of Potassium Sulfate From Natural Complex Salts - The chief natural complex salts that are the source of the potassium sulfate are  

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KCl —NaCl —MgS04) and in many brines. Separated by fractional crystallization, soluble water and lower alcohols. Used in fertilizer production and to produce other potassium salts. 

Economic Aspects and Uses. Total world production of potassium products is 29,000,000 tons per year (65). Potassium chloride is removed from brine at Moab, and Wendover, Utah, and at Seades Lake, California. Potassium sulfate is made from Great Salt Lake brine by Great Salt Lake Minerals Corp., which is the largest producer of solar potassium sulfate in the wodd. Combined, these U.S. faciUties stiU produce a relatively small percentage of potash fertilizers in the wodd. Production from the Dead Sea, for example, is 10 times greater than production of potassium from brines in the United States. More than 95% of all the potassium produced is used in fertilizer blends. The remainder is converted to other potassium chemicals for industdal use (see Potassium compounds). 

Agriculture therefore depends on there being a sufficient supply of inorganic nutrients to plants. Cereals, vegetables, fruit-bearing trees or plants, and animal fodder require bioavailable nutrients, that is, nutrients in forms that they can use. Since intensive agriculture depletes many natural nutrients, synthetic nutrients (fertilizers) must be supplied.1-7 In particular, we need to fix the inert N2 of the atmosphere as soluble, reactive compounds such as nitrates, ammonia, and ammonium salts. Other major fertilizer components are sulfate, potassium, and phosphate ions. It may also be necessary to provide trace nutrients, such as cobalt compounds, or to remove excess soil acidity by treatment with lime (CaO). World fertilizer demand in the year 2001 is expected to be about 1.5 x 10s metric tons N, 7.6 x 107 metric tons P2O5, and 6.7 x 107 metric tons K2O these projections represent an... 

Potassium hydroxide is used for the production of potassium carbonate, tetrapotassium pyrophosphate and other potassium phosphates, liquid fertilizers, and soaps. 

Many other potassium compounds are commercially important, although no use begins to compare with the amount of potash used for fertilizers. Some examples of other important potassium compounds are ... 

Prevention and Control Soil tests can alert you to deficiency problems before they become serious. Regular applications of compost or other organic fertilizers will help to maintain an even potassium supply. Sources of potassium include kelp meal, granite dust, greensand, and wood ashes. Use wood ashes sparingly, as they can raise the soil pH. 

The largest application of potassium chloride is in the production of fertilizers. More than ninety percent of the potassium chloride produced in the United States is used for that purpose. The compound provides the potassium plants need to stay healthy and grow normally. It is one of three macronutrients—substances needed in relatively large amounts—for normal growth. The other two macronutrients are phosphorus and nitrogen. Smaller amounts of potassium chloride are used in the production of other potassium compounds, in photography, and in chemical research applications. 

Millions of tons of ammonia are used worldwide each year to supply crops with nitrogen. Ammonia is either added to irrigation water or injected directly into the ground. Many other nitrogen fertilizers are synthesized from ammonia. Phosphorus in fertilizers originates from phosphate (P04 ) in rock deposits. Potassium in fertilizers comes from evaporated ancient seabeds in the form of potassium oxide (K2O). 

With minor exceptions, the commercial fertilizer, products are triple superphosphate (TSP), ammonium phosphates, and other compound fertilizers (some of the minor exceptions are potassium phosphates and magnesium ammonium phosphate [MgNH4P04]). Use of phosphoric acid in compound fertilizers will be described-under subject headings Compound Fertilizers" (Chapter 16), Liquid Fertilizers and Mtrogen Solutions" (Qiap-ter 10), and Nitrophosphate Fertilizers (Chapter 13). The present chapter wSi deal mainly wrath TSP and solid ammonium phosphates. 

Inorganic fertilizer is often synthesized using the Haber-Boseh proeess, whieh produees ammonia as the end produet. This ammonia is used as a feedstoek for other nitrogen fertilizers, sueh as anhydrous ammonium nitrate and urea. These eoneentrated produets may be diluted with water to form a eoneentrated liquid fertilizer. Ammonia ean be eombined with roek phosphate and potassium fertilizer in the Odda Process to produee eompound fertilizer. 

Many studies have focused on the influence of different levels of nitrogen and potassium fertilization. The removal of these minerals by the harvest is relatively low, compared with other crops. Since the roots exploit a large volume of soil, vine mineral needs are relatively low. 

MgO. Only about 5% of total fertilizer potash is furnished as potassium sulfate and other nonchlotide forms including potassium nitrate. 

Resources for Potash Fertilizers. Potassium is the seventh most abundant element in the earth s cmst. The raw materials from which postash fertilizer is derived are principally bedded marine evaporite deposits, but other sources include surface and subsurface brines. Both underground and solution mining are used to recover evaporite deposits, and fractional crystallization (qv) is used for the brines. The potassium salts of marine evaporite deposits occur in beds in intervals of haUte [14762-51-7] NaCl, which also contains bedded anhydrite [7778-18-9], CaSO, and clay or shale. The K O content of such deposits varies widely (see Potassium compounds). 

Principal uses of KOH include chemicals, particularly the production of potassium carbonate and potassium permanganate, pesticides (qv), fertilizers (qv), and other agricultural products soaps and detergents scmbbing and cleaning operations, eg, industrial gases dyes and colorants and mbber chemicals (qv) (10,34). 

Potassium is analyzed in chemicals that are used in the fertilizer industry and in finished fertilizers by flame photometric methods (44) or volumetric sodium tertraphenylboron methods (45) as approved by the AO AC. Gravimetric deterrnination of potassium as K2PtClg, known as the Lindo-Gladding method (46), and the wet-digestion deterrnination of potassium (47) have been declared surplus methods by the AO AC. Other methods used for control purposes and special analyses include atomic absorption spectrophotometry, inductively coupled plasma (icp) emission spectrophotometry, and a radiometric method based on measuring the radioactivity of the minute amount of the isotope present in all potassium compounds (48). 

However, the fertilizing effect of nitrates (and sulfates) may be counterbalanced by the leaching of potassium, magnesium, calcium, and other nutrients from forest soils. There is little evidence that agricultural crops are being injured by exposures to nitrates in precipitation. The amount of nitrates in rainwater is almost always... 

Nitrophosphate fertilizer is made by digesting phosphate rock with nitric acid. This is the nitrophosphate route leading to NPK fertilizers as in the mixed-acid route, potassium and other salts are added during the process. The resulting solution is cooled to precipitate calcium nitrate, which is removed by filtration methods. The filtrate is neutralized with ammonia, and the solution is evaporated to reduce the water content. The process of prilling may follow. The calcium nitrate filter cake can be further treated to produce a calcium nitrate fertilizer, pure calcium nitrate, or ammonium nitrate and calcium carbonate. 

Nitrogen makes up 78 % of the atmosphere, hence, it is readily available. Ammonia is produced by fixing of atmospheric nitrogen with hydrogen. Mineral sources of phosphorus and potassium are converted to a suitable form for fertilizer. These three elements have other use than fertilizer they are used and interact with other facets of the chemical industry, making a highly complex picture. A schematic of the interactions is presented in Figure 7.2-1. 

The seventh element in order of abundance in the Earth s crust is potassium - about the same as sfjdium with similar properties. While sodium is readily available from the ocean, potassium is found and extracted from many mineral formations. About 90 percent of the potassium that is extracted goes to the production of fertilizers. Other purposes for it are ceramics and fire extinguishers for which potassium bicarbonate is better than sodium bicarbonate. 

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