Potassium sulfate

Potassium sulfate is manufactured from potassium chloride by reacting sulfuric acid with a mixture of sulfur dioxide, 

Alternatively potassium sulfate is manufactured by metathesis of potassium chloride with the sulfate of another metal, particularly magnesium sulfate. This reaction takes place in two steps  

Potassium. sulfate from potassium chloride and magnesium sulfate  

The double sulfate is separated and reacted with additional potassium chloride  

Worldwide over 1 10 t/a of potassium sulfate (as K2O) is manufactured by this process. 

Potassium sulfate (poe-TAS-ee-yum SUL-fate) is also known as potash of sulfur, sulfuric acid dipotassium salt, arcanum duplicatum, and sal polychrestum. It is a colorless or white granular, crystalline, or powdery solid with a hitter, salty taste. It occurs in nature as the mineral arcanite and in the mineral langheinite (K2Mg2(S04)3). The compound was known to alchemists as early as the fourteenth century, and was analyzed hy a number of early chemists, including Johann Glauber (1604-1670), Robert Boyle (1627-1691), and Otto Tachenius (c. 1620-1690). 

A variety of methods for preparing potassium sulfate is available. In one process, the compound is extracted from the mineral langeinite by crushing and washing the mineral and then separating out the double salt, K2Mg2(S04)3. The product is then treated with an aqueous solution of potassium 

Potassium sulfate. Red atoms are oxygen yellow atom is sulfur and turquoise atoms are potassium, publishers 

In a variation of this procedure, potassium chloride is treated with the raw materials from which sulfuric acid is made, rather than the acid itself 4KCI + 2S02 + 2H20 + 02 — 2K2S04 + 4HCI. 

Over 90 percent of the potassium sulfate produced in the United States is used as a fertilizer. It provides plants with two essential elements potassium and sulfur. It finds its greatest use on crops that are sensitive to the chloride ion (C1-) present in most conventional agricultural fertilizers. Those crops include coffee, tea, tobacco, citrus fruits, grapes, and potatoes. However, its use is somewhat limited because it is twice as expensive as fertilizers that contain potassium chloride. 

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Note 2. Potassium hydroxide should not be used, since potassium sulfate is much... 

Examples 3CdS04 8H2O, cadmium sulfate—water (3/8) Al2(S04)3 K2SO4 24H2O, aluminum sulfate—potassium sulfate—water (1/1/24) AICI3 4C2H5OH, aluminum chloride—ethanol (1/4). 

Sodium chloride is relatively inexpensive and is provided either free or incorporated directly into animal feed to prevent sodium and chloride deficiencies. Potassium is usually not deficient because most forages have adequate quantities. Therefore, it should be supplemented only when animals consume poor quaHty roughages or a high concentrate diet, or when they are under stress, dehydrated, or suffering from diarrhea (5). Potassium deficiency usually is alleviated by changing the diet or by supplementing with potassium sulfate. 

Potassium Sulfate. Potassium sulfate is a preferred form of potash for crops that have a low tolerance for chloride. Tobacco and potatoes ate two such crops. K2SO4 is produced most often from langbeinite by metathetical reaction in aqueous solution ... 

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

Other sources of by-product HCl include allyl chloride, chlorobenzenes, chlorinated paraffins, linear alkylbenzene, siHcone fluids and elastomers, magnesium, fluoropolymers, chlorotoluenes, benzyl chloride, potassium sulfate, and agricultural chemicals. 

The potassium combines with the sulfur to form potassium sulfate, which condenses as a soHd primarily in the electrostatic precipitator (ESP) or baghouse. The recovered potassium sulfate is then deUvered to a seed regeneration unit where the ash and sulfur are removed, and the potassium, in a sulfur-free form such as formate or carbonate, is recycled to the MHD combustor. It is necessary also to remove anions such as Cf and E which reduce the electrical conductivity of the generator gas flow. These are present in the coal ash in very small and therefore relatively harmless concentrations. As the seed is recycled, however, the concentrations, particularly of CF, tend to build up and to become a serious contaminant unless removed. 

A diagram for one implementation of this process (61,62) is shown in Eigure 11. Recovered potassium sulfate is converted to potassium formate [590-29 ] by reaction with calcium formate [544-17-2] which is made by reacting hydrated lime, Ca(OH)2, and carbon monoxide. The potassium formate (mp 167°C), in hquid form, is recycled to the combustor at about 170°C. Sulfur is removed as soHd calcium sulfate by filtration and then disposed of (see... 

The oxidant preheater, positioned in the convective section and designed to preheat the oxygen-enriched air for the MHD combustor to 922 K, is located after the finishing superheat and reheat sections. Seed is removed from the stack gas by electrostatic precipitation before the gas is emitted to the atmosphere. The recovered seed is recycled by use of the formate process. Alkali carbonates ate separated from potassium sulfate before conversion of potassium sulfate to potassium formate. Sodium carbonate and potassium carbonate are further separated to avoid buildup of sodium in the system by recycling of seed. The slag and fly-ash removed from the HRSR system is assumed to contain 15—17% of potassium as K2O, dissolved in ash and not recoverable. 

NiSO (NH 2 04-6H20, and nickel potassium sulfate [10294-65-2], NiSO -K2S04-6H20, are prepared by crystallizing the individual salts from a water solution. These have limited use as dye mordants and are used in metal-finishing compositions (59). 

Four minerals are the principal commercial sources of potash (Table 2). In all ores, sodium chloride is the principal soluble contaminant. Extraneous water-iasoluble material, eg, clay and siUca, is a significant contaminant ia some of the evaporates being mined from underground deposits. Some European potassium ores contain relatively large amounts of the mineral kieserite, MgS04-H2 0. It is recovered for captive use to produce potassium sulfate compounds or is marketed ia relatively pure form as a water-soluble magnesium fertilizer. 

Approximately 98% of the potassium recovered ia primary ore and natural brine refining operations is recovered as potassium chloride. The remaining 2% consists of potassium recovered from a variety of sources. Potassium produced from these sources occurs as potassium sulfate combiaed with magnesium sulfate. Prom a practical point of view, the basic raw material for ak of the potassium compounds discussed ia this article, except potassium tartrate, is potassium chloride. Physical properties of selected potassium compounds are Hsted ia Table 3, solubkities ia Table 4. 

Quantities of potassium sulfate produced and consumed as potassium magnesium sulfate [13826-56-7] K2S0-2MgS04, are omitted in the U.S. Department of the Interior reports as classified information. Consumption data for potassium compounds identified as other potassium salts imply that the amount of potassium magnesium sulfate consumed in the United States is about double that of K SO. This gap is expected to widen as soils become more depleted of natural magnesium- and sulfur-containing minerals. 

Several types of chemical processes are used to produce potassium sulfate. The traditional Mannheim process is used in countries that produce KCl but lack a natural source of sulfate salts for converting the KCl to K2SO4. In this process, KCl reacts with sulfuric acid to yield K2SO4 and HCl as a co-product. 

Potassium sulfate is produced in Sicily by controlled decomposition of the natural mineral kainite, KCl-MgS04-2.75H2 0 (26). This salt is first converted to schoenite in an aqueous solution from a potassium sulfate conversion step. A similar process is used in the United States. Kainite is obtained as the potassium feedstock by stage evaporation of Great Salt Lake bitterns (see Chemicals frombrines). 

Water for the kainite conversion comes from the hydrated MgSO. This solution is saturated with K SO. Use of potassium sulfate mother Hquor as a source of water for the reaction lowers the K SO lost in the MgCl2 solution, which is rejected as a waste stream from the process. It also is a solvent for sodium chloride that enters the process as a contaminant in kainite. 

In Canada, ion-exchange (qv) technology has been used to produce potassium sulfate (4). Ion-exchange resins remove sulfate ions from lake water containing sodium sulfate. This is followed by a wash with aqueous solutions prepared from lower grade muriate of potash. High purity potassium sulfate is collected from the crystallizers into which the wash mns. 

In contrast to sodium chloride, langbeinite has an extremely slow rate of solution. Upon control of agitation time, essentially all the sodium chloride dissolves but most of the langbeinite remains as a soHd. Langbeinite is separated from the brine, dried, and then screened into granular, standard, and special-standard particle sizes. These fractions are marketed directiy. In one plant, the unsalable fines are used as the source of sulfate reactant for the production of potassium sulfate. 

Kieserite is not present in U.S. potassium salt deposits in commercial quantities. Langbeinite is the predominant U.S. magnesium sulfate salt. The latter, a raw material for the production of potassium sulfate in New Mexico, reacts directiy with potassium chloride ... 

Potassium sulfate and langbeinite may be screened into three different size ranges to serve all segments of the fertilizer industry. Typical screen analyses of the size products are presented in Table 14. Chemical analyses for the products are shown in Table 15. 

Table 14. Typical Screen Analyses of Potassium Sulfate and Langbeinite ...

Potassium alum is manufactured by treating bauxite with sulfuric acid and then potassium sulfate. Alternatively, aluminum sulfate is reacted with potassium sulfate, or the mineral alum stone, alunite, can be calciaed and leached with sulfuric acid. Alunite is a basic potassium aluminum sulfate... 

Sodium alum occurs naturally as the mineral mendo2ite. Commercially, it is produced by the addition of a sodium sulfate solution to aluminum sulfate. Small amounts of potassium sulfate, sodium siUcate, and soda ash can be added to improve product handling and performance. After adjustment of the ratio of aluminum sulfate to sodium sulfate, water is evaporated to give a hard cake ia the cooling pans. This cake is further heated ia roasters and ground to a fineness of 99% through a 100-mesh (- 150 fiva) sieve. 

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