Main forms of phosphates

outline: In agriculture, phosphates are one of the three primary macronutrients for plants and constitute a major component of fertilizers. Phosphate rock is mined from phosphate-bearing strata in sedimentary rocks. In the past, it could be used directly after extraction without further processing; however, today unprocessed phosphate is typically reserved for organic farming. More commonly, it undergoes chemical processing to produce superphosphate, triple superphosphate, or ammonium dihydrogen phosphate—products that have higher nutrient concentrations and greater water solubility, enabling plants to absorb them more rapidly.

　　 Chemical Fertilizer Industry

　　Phosphates are commonly used in detergents as water softeners; however, because the ebb and flow of algal blooms can influence phosphate discharge in watersheds, phosphate-containing detergents are subject to regulation in certain regions.

　　In agriculture, phosphates are one of the three primary macronutrients for plants and constitute a major component of fertilizers. Phosphate rock is mined from phosphate-bearing sedimentary strata. Historically, it could be used directly after extraction without further processing; however, today unprocessed phosphate is typically reserved for organic farming. More commonly, it undergoes chemical processing to produce superphosphate, triple superphosphate, or ammonium dihydrogen phosphate—products that have higher nutrient concentrations and greater water solubility, enabling plants to absorb them more rapidly.

　　Fertilizer grades are typically expressed as three numbers: the first indicates the nitrogen content, the second the phosphate content, and the third the potash content. Thus, a 10-10-10 fertilizer contains 10% of each nutrient, with the remainder consisting of inert fillers.

　　Phosphates carried by runoff from over-fertilized agricultural land can trigger eutrophication, red tides, and subsequent hypoxia. Similar to phosphate-based detergents, these phosphates can cause oxygen depletion in fish and other aquatic organisms.

　 　Refractory materials

　　Phosphates are used as binders in refractory materials. Phosphate binders are refractory binders whose main constituents are acidic orthophosphates or polyphosphates and which exhibit cementitious properties. The bonding mechanism of phosphate binders is either chemical reaction bonding or polymerization bonding. Binders prepared by the reaction of phosphoric acid with alkali metal or alkaline earth metal oxides and their hydroxides are mostly air-setting binders, meaning that they can set and harden at ambient temperature without the need for heating. In contrast, binders formed by the reaction of phosphoric acid with amphoteric oxides and hydroxides or with acidic oxides are predominantly heat-setting binders, requiring heating to a specific temperature to initiate the reaction and thereby achieve setting and hardening. As binders for refractories, phosphates exhibit high bonding strength in the medium- and low-temperature range prior to the formation of ceramic bonds; hence they are widely employed as binders for unshaped and unfired refractories.

　　Phosphorus is an essential mineral element required by the human body, with the primary dietary sources being natural foods and food-grade phosphate additives; phosphates are naturally present in nearly all foods. Due to their ability to enhance or impart a range of desirable functional properties to food, phosphates have been used in food processing for more than a century, with widespread adoption beginning in the 1970s. Phosphates are among the most widely used and heavily applied categories of food additives, serving as critical ingredients and functional additives in the processing of meat products, poultry products, seafood, fruits, vegetables, dairy products, baked goods, beverages, potato products, seasonings, and convenience foods. The phosphates employed in food processing typically include sodium, calcium, and potassium salts, as well as iron and zinc salts used as nutritional fortifiers. More than thirty varieties of food-grade phosphates are commonly utilized, with sodium phosphates being the predominant type consumed in China. Concurrently, with advances in food-processing technology, the consumption of potassium phosphates has also been increasing year by year.

　　To fully exploit the synergistic effects among various phosphates and between phosphates and other additives, and to meet the evolving demands of food-processing technologies, compound phosphate formulations are frequently used in practice as food ingredients and functional additives. Consequently, the research and development of compound phosphates has increasingly emerged as the primary direction for the innovation and application of phosphate-based food additives.

　　 Food Industry

　　According to the United States Pharmacopeia–Food Chemicals Codex (FCC), the functions of phosphates in the food industry can be classified into 15 categories:

　　1. Acidulant: Phosphoric acid

　　2. Anti-caking agent: Calcium phosphate

　　3. Antioxidant: Calcium hypophosphite

　　4. Buffering agents: diammonium hydrogen phosphate, ammonium dihydrogen phosphate, calcium hydrogen phosphate, calcium phosphate, calcium pyrophosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium acid pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, and sodium pyrophosphate.

　　5. Dough improvers: diammonium phosphate, ammonium dihydrogen phosphate, calcium dihydrogen phosphate, and calcium hydrogen phosphate.

　　6. Emulsifiers: potassium phosphate, potassium polyphosphate, potassium pyrophosphate, sodium aluminum phosphate (alkaline), sodium metaphosphate (insoluble), sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium polyphosphate (glassy form), sodium pyrophosphate

　　7. Hardening agent: Calcium dihydrogen phosphate

　　8. Humectant: Potassium Polyphosphate

　　9. Fermentation agents: diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium acid pyrophosphate, and sodium aluminum phosphate (acidic).

　　10. Nutritional supplements: calcium dihydrogen phosphate, calcium hydrogen phosphate, calcium phosphate, calcium pyrophosphate, ferric phosphate, ferrous pyrophosphate, magnesium hydrogen phosphate, magnesium phosphate, manganese hypophosphite, sodium ferrous pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, and sodium pyrophosphate.

　　11. Preservative: Sodium hypophosphite

　　12. Chelating agents: calcium dihydrogen phosphate, phosphoric acid, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium acid pyrophosphate, sodium metaphosphate (insoluble), and sodium polyphosphate (glassy).

　　13. Modified starch additives: tripolyphosphate, potassium dihydrogen phosphate

　　14. Soil conditioners: potassium pyrophosphate, potassium tripolyphosphate, sodium metaphosphate (insoluble), disodium hydrogen phosphate (glassy), sodium tripolyphosphate

　　15. Fermented foods: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, calcium dihydrogen phosphate, calcium dihydrogen phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate.

　　As shown above, phosphates serve two primary functions in food processing: as quality-improving agents and as nutritional fortifiers.