Sodium hexametaphosphate（SHMP chemical) of commerce is typically a mixture of polymeric metaphosphates, of which the hexamer is one. It is more correctly termed sodium polymetaphosphate, which is prepared by melting monosodium orthophosphate and cooling it rapidly then. SHMP can hydrolyze into sodium trimetaphosphate and sodium orthophosphate in aqueous solution, especially under acidic conditions.
Appearance: Colorless and transparent glass flake or white granular crystals.
Solubility: Soluble in water, Insoluble in organic solvents, strong hygroscopicity, soluble complexes can be formed with metal ions such as, calcium and magnesium.
Toxicity: Accident consumption of sodium hexametaphosphate can cause severe poisoning and even death. The most common symptoms of poisoning include shock, arrhythmia, and slow heartbeat. Once poisoned, you should go to the hospital for treatment as soon as possible.
Environmental impact: It is usually slightly harmful to water bodies. Don’t expose undiluted or large amounts of SHMP chemical to ground water, water channels or sewage systems. Don’t discharge materials into the surrounding environment without government permission.
Total phosphate, as P2O5 % ≥
Inactive phosphate, as P2O5 % ≤
Iron, as Fe % ≤
Ph value (1% solution) % ≤
Water insoluble % ≤
Heavy metals, as Pb % ≤
Arsenic, as As % ≤
Fluoride as F % ≤
SHMP Chemical Uses
1.Application in detergents and water treatment. It can prevent the iron and manganese dissolved in the water from redening and blackening due to oxidation. And prevent the precipitation of calcium and magnesium ions to form scale and reduce the heat transfer efficiency at the same time.
2.Used in food.
- It can improve water holding capacity, increase caking and prevent fat oxidation when used in meat products, fish sausage, ham, etc…
- Used for bean paste and soy sauce to prevent discoloration, increase viscosity, shorten the vinegar period and adjust the taste.
- It can increase the juice yield and viscosity to inhibit the decomposition of vitamin C when used in fruit drinks and refreshing drinks.
- For ice cream, it can increase the expansion capacity, the volume, enhance the emulsification, prevent the destruction of the paste, improve the taste and color at the same time.
- Prevent gelation in dairy products and beverages, clear beer liquid, prevent turbidity, stabilize pigments, maintain food color. Spraying on cured meat can improve antiseptic properties.
3.Application in mineral processing and oil field industry. Sodium hexametaphosphate is a commonly used inhibitor in flotation, which is mainly used to inhibit quartz and silicate minerals, as well as calcite, limestone and other carbonate minerals. In the oil field industry, as a drilling mud additive, SHMP chemical can avoid the precipitation of multivalent metal ions, improve the salt resistance of mud and reduce mud water loss. In addition, dissolving a certain amount of sodium hexametaphosphate and injecting it into the water pipe can form a thin film on the pipe wall to prevent corrosion of the pipe.
4.Application in metallurgy and meta anticorrosion. Adding some additives to sodium hexametaphosphate to repair the steel-making converter at a certain temperature and pressure can greatly extend the life of the converter. The integration of SHMP and divalent metal ions in solution can form a positively charged polyelectrolyte, which forms a dense, continuous films when it is adsorbed on the metal surface. The film can completely cover the corrosion micro-battery, reduce or prevent the corrosion current from passing to play a role of corrosion protection.
5.The role in color film processing. Sodium hexametaphosphate is an excellent soft water agent. It must be added in the configuration of color developer in order to reduce the hardness of water, prevent the formation of calcareous texture, ensure clear and bright color. Meanwhile, it have no effect on the oxidation and reduction of the developer.
6.Applications in the fiber industry. It can suppress the formation of metal soap in the refining process, make the colloid in the raw cotton easy to remove and improve the refining efficiency. In the bleaching process, it can prevent the decomposition of hydrogen peroxide, reduce the loss of bleach and improve the bleaching efficiency. In the dyeing, it can prevent the color of the dyed substance from changing, maintain the original color of the dye, prevent the occurrence of dyeing stains, poor feel, white cloth yellowing and fiber strength reduction.
7.Used in paper-making industry. The mixture of SHMP chemical and sulfonated benzaldehyde can be used as a dispersant for steel paper coatings to disperse lead carbonate pigments.
Production Method of SHMP Chemical
It can be mainly divided into two-step method and one-step method.
This method is also known as liquid phase neutralization, drying crystallization fusion polymerization method. Firstly, the generated sodium dihydrogen phosphate solution should be condensed and crystallized or dried by mildew spray to remove free water to produce anhydrous sodium dihydrogen phosphate and crystalline sodium dihydrogen phosphate. Then send it into a melting furnace for dewatering and melting to make sodium hexametaphosphate. This method can accurately control the molecular ratio of Na2O and P2O5, so it is possible to prepare stable SHMP with a certain chain length. For that it is anhydrous sodium dihydrogen phosphate or crystalline sodium dihydrogen phosphate that enters the smelting furnace, less water enters the furnace, which can greatly reduce the partial pressure of water vapor on the surface of the melt and the moisture in the material, so that the material can be made into the product with higher degree of polymerization in a short time. After the melt is released from the furnace, it is cooled by a continuous double-roller internal cooling quencher, which has good cooling effect and can ensure that the product won’t crystallize but becomes glassy. In addition the production is continuous, the capacity is large and the labor intensity is low. Since the materials are reacted and transported in closed reactors and pipelines, the labor environment and sanitation conditions are good. The specific production can be divided into the following methods.
- Sodium dihydrogen phosphate method. Firstly, use yellow phosphorus as raw materials to prepare thermal phosphoric acid, and then use caustic soda as neutralizing agent to obtain sodium dihydrogen phosphate. The sodium dihydrogen phosphate is spray dried and dehydrated to obtain sodium dihydrogen phosphate dry powder. The powder is heated in a graphite heap for high-temperature polymerization and then taken out with a stainless steel spoon and quenched in a cooling disk to obtain flaky-shaped sodium metaphosphate, which can be crushed to obtain a powdered sodium hexametaphosphate chemical. This method has the advantages of easy control of material ration, continuous production and low labor intensity.
- Ferrophosphorus method. This method takes ferrophosphorus produced by yellow phosphorus in electric furnace as raw material, after crushing and grinding, it is mixed with soda ash for roasting and its products are sintered solid. It contains fusible trisodium phosphate, which is leached in hot water to obtain a trisodium phosphate solution and filtered to remove insoluble impurities. The purified trisodium phosphate solution is neutralized to prepare disodium hydrogen phosphate. The disodium dihydrogen phosphate solution is concentrated in vacuum, crystallized to remove soluble impurities, and then is spray dried to make anhydrous sodium, dehydrated to produce sodium hexametaphosphate. The disadvantages of this method is that there are so many processes, the process is long, the fuel and power consumption is high.
- Phosphoric acid and sodium silicate process. Silicon dioxide is prepared by the neutralization reaction of phosphoric acid and water glass. Then the waste liquid from the production of silicon dioxide is filtered, PH adjusted, expanded and evaporated, polymerized, cooled on the roller, crushed and screened to get the SHMP chemical. This method used phosphoric acid and sodium silicate to prepare both silicon dioxide and SHMP, which can achieve various beneficial effects, such as, waste liquid utilization, lower production cost, protection of ecological environment and so on.
- Phosphoric acid and table salt process. The preparation of shmp chemical by polycondensation reaction of phosphoric acid with table salt can not only save soda ash, but also recover hydrochloric acid produced by by-product. This method can also be used to decompose phosphate ore for other uses.
The one-step process of sodium hexametaphosphate uses liquid yellow phosphorus as the raw material, which is directly combined and polymerized with soda ash at high temperature through oxidation. The prepared molten shmp chemical is directly flowed into the cooling disc and quenched in the hearth to obtain sodium hexametaphosphate. This method is also called solid-phase reaction, crucible fusion polymerization method. After being heated and melted, the yellow phosphorus is sent to an oxidizing combustion furnace. Oxygen in the dry air is used for oxidation combustion reaction to produce the intermediate phosphorus pentoxide. After mixing phosphorus pentoxide with soda ash, the product is polymerized at high temperature and then cooled into flake-shaped sodium hexametaphosphate, then crushed into sodium hexametaphosphate powder. The process has the characteristics of less working procedure, short flow and continuous production. The thermal energy of yellow phosphorus combustion can provide heat source for drying and polymerization of sodium hexametaphosphate in the production process, which can effectively save the energy. However, this process is difficult to control and can’t guarantee the stable quality of SHMP.