This section provides an overview of the properties and applications of some compounds containing potassium, which can also be seen in Table 1.
Table 1
Properties and applications of some potassium-based compounds
Potassium-containing compounds | Relative molecular mass | Morphological features | Applications | References |
KCl | 74.551 | Potassium chloride is a colorless, odorless, crystalline solid, also known as mineral salt, with orthogonal crystal system at room temperature. | Inhibitory effect on plant diseases;Improving the resistance of plants and microorganisms to stress; As a substitute for NaCl; Increase crop yield | (Zhang et al. 1998, 2020; Zhao et al. 2022; Zou et al. 2023) |
K2SO4 | 174.259 | Potassium sulfate is a colorless, odorless crystal with an equiaxed crystal system at room temperature. | Improve crop yield and quality; Improves crop salinity resistance; Promote nutrient uptake by crops | (Kausar et al. 2016; Barut 2019) |
K2SiO3 | 154.28 | Potassium silicate is a colorless, odorless, white crystal with a trigonal crystal system at room temperature. | Improving salt tolerance in crops; As a catalyst for production use; Promotion of photosynthetic protein expression | (Wu et al. 2014; Park et al. 2018; Oraee and Tehranifar 2023) |
K2O | 94.196 | Potassium oxide is a white solid with a cubic crystal system at room temperature. | Synthetic ceramics instead of sodium oxide; Used to prepare various potassium salts; As a catalyst for diesel production from vegetable oils | (da Costa Evangelista et al. 2016; Zia et al. 2018; Peng et al. 2019) |
KNO3 | 101.10 | Potassium nitrate is a colorless crystalline solid with a rhombohedral crystal system at room temperature. | Production of explosives; Commonly used heat transfer media in solar energy; Improves plant resistance to flooding and salt | (Lei et al. 2013; Mahajan et al. 2020; Ahmad et al. 2022) |
KMnO4 | 158.034 | Potassium permanganate is a purple-black crystal, usually made into a purple solid, with an orthogonal crystal system at room temperature. | As precursors for the synthesis of manganese nanomaterials; As a modifier; As lithium battery cathode material | (Ahmed 2016; Ding et al. 2017; Wang et al.) |
KH2PO4 | 136.086 | Potassium dihydrogen phosphate is a colorless, transparent crystal with a monoclinic crystal system at room temperature. | One of the important raw materials for the production of potash; Removal effect on heavy metals | (Wang et al. 2020; Borges et al. 2021) |
2.1 Potassium chloride
Potassium chloride is a very widely used inorganic compound with the chemical formula KCl. The chemical formula of potassium chloride is KCl, an inorganic compound. It appears similar to table salt, is odorless and has a salty taste. It is commonly used as a low-sodium salt substitute, a diuretic in the pharmaceutical industry, and a potassium fertilizer in agriculture. When applied directly to farmland, it can improve soil moisture in lower layers and has drought resistance effects. KCl has a taste similar to sodium chloride (bitter), and is also used as an additive in low-sodium salt or mineral water.
KCl can also be used as a substitute for table salt (NaCl). High salt (NaCl) intake can negatively do harm to human body, while potassium is particularly used in meat production. Compared to using only NaCl, using KCl as a partial replacement can increase protein digestion rates also improve antioxidant capacity and prevent oxidation damage. Using potassium chloride to partially replace sodium chloride can significantly affects protein and peptide spectrum digestion rates in meat. Samples with added KCl showed better water retention and texture characteristics compared to samples with reduced NaCl (1.95% NaCl) (Zhang et al. 2020; Zou et al. 2023).
KCl is widely used in agriculture. Research by Mingchu Zhang et al. found that using KCl to coat small-seeded crops promotes early-stage growth. For example, coating barley seeds promotes both seed germination and seedling growth, with rapeseed showing more significant effects than barley or wheat. In addition, KCl can be used as an effective component for preventing and treating plant diseases. Juan Zhao et al. found that KCl may inhibit the occurrence of citrus fruit rot disease through the TOR signaling pathway, it could be an effective treatment option for fruit rot (Zhao et al. 2022).
Research by Yingchao Xu et al. showed that adding KCl can improve the long-term culture tolerance of yeast cells in high concentration sucrose. Therefore, adding KCl is an effective strategy for enhancing yeast physiological activity in industrial fermentation processes(Xu et al. 2020). In the study by P M Bhujbal and S J Dhoble, thermoluminescence was investigated as a possible dose measurement material for developing high-dose ionizing radiation dose measurement.
2.2 Potassium sulfate
Potassium sulfate is an inorganic salt with the chemical formula K2SO4, and it appears as white crystalline powder. It is a high-quality and commonly used water-soluble potassium fertilizer and is the main ingredient in producing chlorine-free nitrogen, phosphorus, and potassium ternary compound fertilizers. Potassium sulfate is a commonly used potassium fertilizer in agriculture, with a potassium oxide content of 50%.
K2SO4 is an excellent water-soluble potassium fertilizer, with low hygroscopicity, good physical properties, and convenient application as it does not easily form lumps. In a study by Barut, H., it was found that spraying wheat with K2SO4 and urea before and after flowering significantly affects the development of wheat. In a study by Kausar, A. et al., two wheat genotypes were used, and when K2SO4 fertilizer was applied in a saline-alkali environment, will increase the accumulation and absorption of nutrients.(Kausar et al. 2016). Therefore, applying K2SO4 in saline soil can weaken the adverse effects of salinity and increase the crop yield.
2.3 Potassium Silicate
Potassium silicate is a colorless or slightly yellowish, semi-transparent to transparent glassy substance with hygroscopic properties and strong alkaline reactions. It decomposes in acid and precipitates silica. It is slow to dissolve in cold water or nearly insoluble in water (depending on its composition), and insoluble in ethanol. Potassium silicate is commonly used in the manufacture of welding rods, welding electrodes, reducing dyes, and fire retardants. It is also used as a fluorescent screen coating and soap filler. In a stable state, it is a transparent, viscous liquid with a blue-green color. It is soluble in water and acid, and precipitates as gel-like silica, with higher potassium content leading to higher solubility.
K2SiO3 is a good source of silicon and a supplement in the process of plant growth.. It can also be applied during crop harvesting to maintain the quality of crops. In A. Manivannan's study, the application of K2SiO3 significantly increased axillary shoot proliferation and tissue silicon content compared to CaSiO3. Yoo Gyeong Park's research showed that silicon played an crucial role in promoting plant growth and increasing photosynthetic rates in two strawberry plant varieties. The results showed that regardless of the application method, providing 35 or 70 mg L− 1 Si in the form of K2SiO3 maximally promoted photosynthetic protein expression in both varieties.
In the experiment conducted by Adel M.R.A. ABDELAZIZ et al., grape vines were sprayed with K2SiO3, SA, and CaCl2 before harvesting, during harvesting, and after harvesting. The conclusion was that applying K2SiO3 at both concentrations was effective treatment for maintaining the quality of grapes (Abdelaziz et al. 2022). Atiyeh Oraee and Ali Tehranifar's research showed that under salt stress, the activity of peroxidase, ascorbate peroxidase, hydrogen peroxide, and superoxide dismutase increased with the application of K2SiO3. Therefore, their results suggest that the use of K2SiO3 can be considered a common strategy for maintaining plant growth under salt stress.
Furthermore, Haitang Wu's research found that K2SiO3 can be loaded onto mesoporous molecular sieves to produce biodiesel as an ester exchange catalyst (Wu et al. 2014).
2.4 Potassium oxide
Potassium oxide (K2O) is a compound with a chemical formula of K2O and is a gray cubic crystal. It has a molecular weight of 94.196 and a density of 2.3g/cm³. It decomposes at 350℃ and is hygroscopic. It is soluble in water and reacts with water to form potassium hydroxide.
K2O is mainly used in the inorganic industry as a basic material for manufacturing various potassium salts.
K2O can be used as a catalyst in reactions and is commonly used in the production of new glass and ceramics in the inorganic industry.
From an economic perspective, K2O is a good solid base catalyst. Al-loaded K2O is a promising catalyst and various potassium compounds containing Al2O3 have been prepared using impregnation (da Costa Evangelista et al. 2016). Peng et al. synthesized Na2O-xK2O-40Nb2O5-20SiO2 microcrystalline glass using traditional melt methods. As the K2O content increased, the glass network structure became more relaxed and more types of phases were formed. The strength of samples increased first and then decreased with the increase of K2O content, reaching a maximum value(Peng et al. 2019). Rehana Zia et al. replaced Na2O with K2O in the solid-phase preparation of Na2O-CaO-P2O5-SiO2 ceramics, which increased the biological activity of the samples. The addition of K2O enhanced the formation of hydroxyapatite, making them suitable for defects and fractures in bones (Zia et al. 2017, 2018).
2.5 Potassium nitrate
Potassium nitrate is an inorganic compound commonly known as saltpeter or nitre. Its chemical formula is KNO3, and it is a potassium salt of nitric acid. It exists as colorless, transparent monoclinic or rhombic crystals or as a white powder with a salty and cool taste but no odor or toxicity. It has slight hygroscopicity in the air, is not prone to caking, and is soluble in water.
Potassium nitrate is used as a raw material for manufacturing black powder, such as mining explosives, fuses, and firecrackers, and as a salt bath for quenching during mechanical heat treatment. It is also used in the ceramic industry to produce glazes and pigments and as a glass clarifying agent. It is used to make automotive lamp covers, optical glass cathode ray tubes, and as a compound fertilizer for crops and flowers.
Sodium nitrate and potassium nitrate can often be used as heat transfer media in solar energy according to Qingguo Zhao et al.'s research (Zhao et al. 2017). Ju Hee Oh et al. modified the TiO2 photoelectrode surface with KNO3 and found that the modified photoelectrode could improve of the function of material sensitization, indicating that KNO3 can serve as an effective flame retardant (Oh et al. 2015).
KNO3 also has extensive applications in agriculture. Lei BIAN et al. studied the effect of KNO3 pretreatment on the habitat condition of Acanthopanax. They found that seeds treated with KNO3 had significantly higher germination rates and growth than untreated seeds, which also applies to C. japonicum seeds stored in cold storage after treatment. Therefore, this pretreatment method can be used in the planting process of C. japonicum trees (Lei et al. 2013). In addition, the application of KNO3 can enhance plant tolerance to salt and flooding stress (Ahmad et al. 2016; Mahajan et al. 2020).
2.6 Potassium permanganate
Potassium permanganate, also known as KMnO4, is a strong oxidizing agent that appears as black-purple crystals with a blue metallic sheen. It is odorless and soluble in water and alkaline solutions, but only slightly soluble in methanol, acetone, and sulfuric acid. When in contact with certain organic or oxidizable substances, it can easily cause explosions. Widely used as an oxidant in chemical production, it is used in the production of saccharin, vitamin C, isoniazid, and benzoic acid. It is also used as a preservative, disinfectant, deodorant, and detoxifier in the medical industry, as well as a water treatment agent for purifying water and treating wastewater. Additionally, it is used as a bleaching agent, adsorbent, coloring agent, and disinfectant. KMnO4 has a range of applications in conditioning agents, in the preparation of new materials, and in the battery manufacturing industry. In this review, we have consulted many literatures on the application of KMnO4.
Shun Zhang investigated the effect of the amount of KMnO4 and pH changes on the dewatering performance and substance conversion of anaerobic digestion sludge in the ADS conditioning process. The study found that with the increase of KMnO4 dosage, the particle size and capillary suction time of the sludge gradually decreased, and the water content significantly decreased, indicating that KMnO4 can be used as a conditioning agent (Zhang et al. 2022). Keqiang Ding's team reported the discovery that KMnO4 can be directly used as a negative electrode material for the first time (Ding et al. 2017). KMnO4 can also be used to modify corn stalks. In Hanxi Wang's study, 0.1 mol/L of KMnO4 was found to have the most significant improvement in the surface properties of modified biochar (Wang et al.). In addition, KMnO4 can be used as a precursor for the preparation of nano-manganese oxide materials. Khalid Abdelazez Mohamed Ahmed used Crystal Maker Demo software to estimate the anisotropic transformation of KMnO4 into manganese oxide nanoparticles (Ahmed 2016).
2.7 Potassium dihydrogen phosphate
Potassium dihydrogen phosphate, also known as KH2PO4, is an inorganic compound that is hygroscopic in nature. When heated to 400℃, it melts into a transparent liquid, which solidifies into an opaque glassy form of potassium dihydrogen phosphate upon cooling. Industrially, it is used as a buffering agent, a culture medium, a flavoring agent in the synthesis of sake, and as a highly efficient phosphorus-potassium compound fertilizer in agriculture.
In the research conducted by Ranran Zhao et al., KH2PO4 was found to contribute to the removal of arsenic from soils in southern China. Under optimal conditions (0.1 mol/L KH2PO4 concentration), the removal rates of As in aggregates greater than 2 mm and less than 0.053 mm were 48.56% and 42.88%, respectively. In aggregates with particle sizes smaller than 0.25 mm, the extraction rate of As was 62.82% (Zhao et al. 2016). Xiankai Wang et al. studied the preservation of nitrogen and sulfur, as well as passivation of heavy metals using KH2PO4 and FeSO4. The results showed that compared to the control group, the loss rate of N during composting was reduced by 27.5% and the loss rate of S increased by 32.1% after the addition of the materials. X-ray absorption spectroscopy indicated that S was transformed into a higher oxidation state during the composting process with the addition of KH2PO4. After the addition of KH2PO4, the migration coefficients of Cu, Zn, and Pb were reduced. Therefore, KH2PO4 can increase the preservation of N and S during composting and reduce the migration of heavy metals (Wang et al. 2020).
In agriculture, Roger Borges' team used a solvent-free mechanized chemical process between discarded eggshells and potassium phosphate to produce a soil conditioning substance (KH2PO4) for soil adjustment (Borges et al. 2021).