SODIUM HEXAMETAPHOSPHATE

SODIUM HEXAMETAPHOSPHATE

Sodium hexametaphosphate (SHMP) is a salt of composition Na6[(PO3)6]. Sodium hexametaphosphate of commerce is typically a mixture of metaphosphates (empirical formula: NaPO3), of which the hexamer is one, and is usually the compound referred to by this name. Such a mixture is more correctly termed sodium polymetaphosphate. They are white solids that dissolve in water.

CAS No. : 68915-31-1
EC No. : 233-343-1

Synonyms:
sodium cyclo-hexaphosphate; Calgon S; Glassy sodium; Graham's salt; Hexasodium metaphosphate; Metaphosphoric acid, hexasodium salt; SHMP; Calgon; Phosphate glass; sodyum hekzametafosfat; sodyum heksametafosfat; sodyum hegzametafosfat; sodyum hegsametafosfat; sodium hexa-meta-phosphate; sodıum hexa meta phosphate; water soluble; Polyphosphate sodium salt; SHMP; Sodium polyphosphate; Sodium metaphosphate; Maddrell's salt; Kurrol's salt; Sporix; Metaphosphoric acid, sodium salt; 10361-03-2; Sodium Hexametaphosphate; shmp; SODIUM HEXAMETAPHOSPHATE; Sodium Kurrol's salt; Metaphosphoric acid (HPO3), sodium salt; Poly(sodium metaphosphate); UNII-532IUT7IRV; Sodium phosphate (NaPO3); Polymeric sodium metaphosphate; Sodium metaphosphate (NaPO3); Insoluble metaphosphate; HSDB 5055; EINECS 233-782-9; 532IUT7IRV; Insoluble sodium metaphosphate; Sodium metaphosphate, insoluble; Metaphosphoric acid (HPO3), sodium salt, homopolymer; 14550-21-1; sodium phosphenate; EINECS 238-595-6; Metaphosphoric acid (HPO3), sodium salt (1:1); 50813-16-6; LS-89897; HYPOPHOSPHORIC ACID,SODIUM SALT (1:4); Q4291659; SODIUM HEXAMETAPHOSPHATE 98+% FOR ANALYTICAL PURPOSE

Sodium Hexametaphosphate

Uses of Sodium hexametaphosphate
Sodium hexametaphosphate is used as a sequestrant and has applications within a wide variety of industries, including as a food additive in which Sodium hexametaphosphate is used under the E number E452i. Sodium carbonate is sometimes added to SHMP to raise the pH to 8.0–8.6, which produces a number of Sodium hexametaphosphate products used for water softening and detergents.

A significant use for sodium hexametaphosphate is as a deflocculant in the production of clay-based ceramic particles. Sodium hexametaphosphate is also used as a dispersing agent to break down clay and other soil types for soil texture assessment.

Sodium hexametaphosphate is used as an active ingredient in toothpastes as an anti-staining and tartar prevention ingredient.

The energy drink NOS contains sodium hexametaphosphate.

Food additive
As a food additive, Sodium hexametaphosphate is used as an emulsifier. Artificial maple syrup, canned milk, cheese powders and dips, imitation cheese, whipped topping, packaged egg whites, roast beef, fish fillets, fruit jelly, frozen desserts, salad dressing, herring, breakfast cereal, ice cream, beer, and bottled drinks, among other foods, can contain Sodium hexametaphosphate.

Preparation of Sodium hexametaphosphate
Sodium hexametaphosphate is prepared by heating monosodium orthophosphate to generate sodium acid pyrophosphate:

2 NaH2PO4 → Na2H2P2O7 + H2O
Subsequently, the pyrophosphate is heated to give the corresponding sodium hexametaphosphate:

3 Na2H2P2O7 → (NaPO3)6 + 3 H2O
followed by rapid cooling.

Reactions of Sodium hexametaphosphate
SHMP hydrolyzes in aqueous solution, particularly under acidic conditions, to sodium trimetaphosphate and sodium orthophosphate.

History of Sodium hexametaphosphate
Hexametaphosphoric acid was named (but misidentified) in 1849 by the German chemist Theodor Fleitmann. By 1956, chromatographic analysis of hydrolysates of Graham's salt (sodium polyphosphate) indicated the presence of cyclic anions containing more than four phosphate groups; these findings were confirmed in 1961. In 1963, the German chemists Erich Thilo and Ulrich Schülke succeeded in preparing sodium hexametaphosphate by heating anhydrous sodium trimetaphosphate.

Safety of Sodium hexametaphosphate
Sodium phosphates are recognized to have low acute oral toxicity. Sodium hexametaphosphate concentrations not exceeding 10,000mg/l or mg/kg are considered protective levels by the EFSA and USFDA. Extreme concentrations of this salt may cause acute side effects from excessive blood serum concentrations of sodium, such as: “irregular pulse, bradycardia, and hypocalcemia."

Properties of Sodium hexametaphosphate
Chemical formula Na6P6O18
Molar mass 611.7704 g mol−1
Appearance White crystals
Odor odorless
Density 2.484 g/cm3
Melting point 628 °C (1,162 °F; 901 K)
Boiling point 1,500 °C (2,730 °F; 1,770 K)
Solubility in water soluble
Solubility insoluble in organic solvents
Refractive index (nD) 1.482

General description of Sodium hexametaphosphate
Sodium hexametaphosphate is an inorganic polyphosphate salt commonly used as a corrosion inhibitor, emulsifying agent and as a tooth whitening agent in dentifrice formulations.

Application of Sodium hexametaphosphate
Sodium hexametaphosphate has been used as a deflocculant to prepare clay suspensions.

Final report on the safety assessment of Sodium Metaphosphate, Sodium Trimetaphosphate, and Sodium Hexametaphosphate
These inorganic polyphosphate salts all function as chelating agents in cosmetic formulations. In addition, Sodium Metaphosphate functions as an oral care agent, Sodium Trimetaphosphate as a buffering agent, and Sodium Hexametaphosphate as a corrosion inhibitor. Only Sodium Hexametaphosphate is currently reported to be used. Although the typical concentrations historically have been less than 1%, higher concentrations have been used in products such as bath oils, which are diluted during normal use. Sodium Metaphosphate is the general term for any polyphosphate salt with four or more phosphate units. The four-phosphate unit version is cyclic, others are straight chains. The hexametaphosphate is the specific six-chain length form. The trimetaphosphate structure is cyclic. Rats fed 10% Sodium Trimetaphosphate for a month exhibited transient tubular necrosis; rats given 10% Sodium Metaphosphate had retarded growth and those fed 10% Sodium Hexametaphosphate had pale and swollen kidneys. In chronic studies using animals, growth inhibition, increased kidney weights (with calcium deposition and desquamation), bone decalcification, parathyroid hypertrophy and hyperplasia, inorganic phosphaturia, hepatic focal necrosis, and muscle fiber size alterations. Sodium Hexametaphosphate was a severe skin irritant in rabbits, whereas a 0.2% solution was only mildly irritating. A similar pattern was seen with ocular toxicity. These ingredients were not genotoxic in bacterial systems nor were they carcinogenic in rats. No reproductive or developmental toxicity was seen in studies using rats exposed to Sodium Hexametaphosphate or Sodium Trimetaphosphate. In clinical testing, irritation is seen as a function of concentration; concentrations as high as 1% produced no irritation in contact allergy patients. Because of the corrosive nature of Sodium Hexametaphosphate, it was concluded that these ingredients could be used safely if each formulation was prepared to avoid skin irritation; for example, low concentration in a leave-on product or dilution of a higher concentration as part of product usage.

Uses of Sodium hexametaphosphate
Salt mixture of metaphosphates
Great for combining with sodium citrate for making cheese sauces
Commonly used as a pH buffer and sequestrant
Cold/hot soluble, free flowing powder

DESCRIPTION of Sodium hexametaphosphate (SHMP)
100% Pure Food Grade Sodium Hexametaphosphate SHMP (e452i) for use in molecular gastronomy. SHMP is a sequestrant, which allows gelling agents to be hydrated at much lower temperatures. It is the highest performing sequestrant available. And unlike sodium citrate, it has no taste at the concentrations used for gel hydration.

OTHER DETAILS of Sodium hexametaphosphate
Dietary Attributes:
Plant-Based, Gluten-Free, Non-GMO, Kosher (OU), Keto-friendly
Ingredient List:
Sodium Hexametaphosphate
Allergen(s):
None

Effect of sodium hexametaphosphate concentration and cooking time on the physicochemical properties of pasteurized process cheese
Sodium hexametaphosphate (SHMP) is commonly used as an emulsifying salt (ES) in process cheese, although rarely as the sole ES. It appears that no published studies exist on the effect of Sodium hexametaphosphate concentration on the properties of process cheese when pH is kept constant; pH is well known to affect process cheese functionality. The detailed interactions between the added phosphate, casein (CN), and indigenous Ca phosphate are poorly understood. We studied the effect of the concentration of Sodium hexametaphosphate (0.25–2.75%) and holding time (0–20 min) on the textural and rheological properties of pasteurized process Cheddar cheese using a central composite rotatable design. All cheeses were adjusted to pH 5.6. The meltability of process cheese (as indicated by the decrease in loss tangent parameter from small amplitude oscillatory rheology, degree of flow, and melt area from the Schreiber test) decreased with an increase in the concentration of Sodium hexametaphosphate. Holding time also led to a slight reduction in meltability. Hardness of process cheese increased as the concentration of Sodium hexametaphosphate increased. Acid-base titration curves indicated that the buffering peak at pH 4.8, which is attributable to residual colloidal Ca phosphate, was shifted to lower pH values with increasing concentration of Sodium hexametaphosphate. The insoluble Ca and total and insoluble P contents increased as concentration of Sodium hexametaphosphate increased. The proportion of insoluble P as a percentage of total (indigenous and added) P decreased with an increase in ES concentration because of some of the (added) Sodium hexametaphosphate formed soluble salts. The results of this study suggest that Sodium hexametaphosphate chelated the residual colloidal Ca phosphate content and dispersed CN; the newly formed Ca-phosphate complex remained trapped within the process cheese matrix, probably by cross-linking CN. Increasing the concentration of Sodium hexametaphosphate helped to improve fat emulsification and CN dispersion during cooking, both of which probably helped to reinforce the structure of process cheese.

Process cheese is made by grinding natural cheese and then heating the cheese in the presence of one or more Ca chelating salts (phosphate or citrates), often called emulsifying salts (ES). In the United States, the Code of Federal Regulations (Department of Health and Human Services, 2004) identifies 13 types of ES that can be used in process cheese manufacture, either singly or in combination, and allows for the addition of up to 3% (wt/wt; Kapoor and Metzger, 2008). These ES help disperse the insoluble CN in natural cheese curd, and it is these solubilized CN that can then act as emulsifiers around the liquid fat released during the heating and shearing of natural cheese. These ES function as ion exchangers, buffers, and Ca sequestrants and cause CN dispersion and peptization. Several reviews exist on the properties of the ES used for process cheese manufacture (Carić et al., 1985; Berger et al., 1998; Zehren and Nusbaum, 2000; Guinee et al., 2004).

Long-chain polyphosphates are commonly (but incorrectly) called hexametaphosphates. The real hexametaphosphates are ring forming and are not used in process cheese. Sodium hexametaphosphates (SHMP) have a wide range of uses in the food industry, including increasing the water binding properties of proteins in processed meats, protein precipitation for purification purposes, and prevention of protein sedimentation in sterilized milks (Molins, 1991). Sodium hexametaphosphates are often used in process cheese manufacture either singly or more commonly in a blend of several types of ES.

Numerous factors, including pH, affect the melting and textural characteristics of process cheese (Mulsow et al., 2007). Many of these factors, which are not well understood at the molecular level, are interrelated and have a combined effect on meltability and texture. It has been reported that the use of Sodium hexametaphosphate produces hard and poorly meltable process cheese (Thomas, 1973; Gupta et al., 1984; Carić et al., 1985). However, it appears that no studies exist on the effect of Sodium hexametaphosphate on process cheese properties where pH was kept constant (to avoid pH as a confounding factor). Gupta et al. (1984) reported that the use of Sodium hexametaphosphate resulted in process cheese with low pH values, which could have contributed to the poor textural attributes. Lu et al. (2008) reported that increasing the pH resulted in improved meltability for process cheese made with Sodium hexametaphosphate. Cooking time also affects the properties of process cheese (Rayan et al., 1980; Shirashoji et al., 2006). One method by which cooking time affects process cheese is by increasing the extent of shearing of curd and thus improving the emulsification of fat (i.e., by reducing the size of emulsified fat globules; Shimp, 1985; Kapoor and Metzger, 2008).

The objective of this study was to investigate the effects of various concentrations of Sodium hexametaphosphate and cooking times on the rheological and textural properties of process cheese. Because pH is well known to influence the texture of process cheese made with Sodium hexametaphosphate (Lu et al., 2008), all samples were adjusted to a constant pH value (∼5.6).

Rheological Properties of Sodium hexametaphosphate
The effects of ES concentration on the rheological properties of process cheese made with Sodium hexametaphosphate during heating are shown in Figures 1a and b. The rheological properties of the natural Cheddar cheese are also shown for comparison purposes. The G′ value of all cheeses decreased with temperature from 5 to 70°C. The G′ value of the process cheese made with 1.50 and 2.75% ES, as well as natural cheese, increased again at >70°C, although cheese made with 0.25% ES continued to decrease with increasing temperature throughout the entire heating range. This increase in G′ at high temperature was not observed with any of the process cheeses made with trisodium citrate (TSC) in our previous study (Shirashoji et al., 2006). The LT value of process cheese measured at >50°C decreased with an increase in ES concentration. Process cheese made with 2.75% Sodium hexametaphosphate had LT values that were <1 over the entire heating range. Samples with LT values <1 do not exhibit flow (Lucey et al., 2003).

Several factors could explain the effect of increasing Sodium hexametaphosphate concentration on cheese texture. Increasing the concentration of Sodium hexametaphosphate (SHMP) used in process cheese resulted in an increase in hardness and the G′ value at 70°C and a decrease in the LT value at 50°C  and DOF. These effects were not attributable to any compositional factors because we manufactured the cheeses to a constant composition. We believe that the higher hardness and lower meltability with increasing Sodium hexametaphosphate concentration is attributable to a combination of enhanced CN dispersion, Ca chelation, and ion exchange. One of the key functions of ES, such as Sodium hexametaphosphate, is the ability to disperse (sometimes called peptization) the insoluble CN matrix in natural cheese. Polyphosphates have a greater CN dispersing ability compared with orthophosphates or TSC (Lee et al., 1986; Molins, 1991; Dimitreli et al., 2005; Mizuno and Lucey, 2005). The addition of Sodium hexametaphosphate to milk rapidly causes CN dispersion (Vujicic et al., 1968). The use of Sodium hexametaphosphate in process cheese greatly increases CN dispersion (hydration, peptization, or swelling) compared with TSC or orthophosphates (Lee et al., 1986; Guinee et al., 2004), although in these studies the pH of cheese was not kept constant. Increasing the concentration of polyphosphate used in process cheese resulted in an increase in soluble nitrogen content (indicating greater CN dispersion; Lee and Alais, 1980). Hot process cheese after holding at 80°C for 10 min exhibited very large LT values compared with process cheeses made with low ES concentration. The high LT values in hot process cheese made with high ES concentrations suggest that increasing the concentration of Sodium hexametaphosphate greatly increased CN dispersion.

The ability of Sodium hexametaphosphate to disperse CN is pH-dependent with low ability near pH 5 (Dimitreli et al., 2005). Our cheeses were all at pH 5.6, and at this pH value Sodium hexametaphosphate should still be effective at causing CN dispersion. These highly dispersed CN molecules then reassociate during cooling to form a fine-structured gel network (some CN reassociation may be occurring in the hot product as evidenced by the increase in G′ values during the holding of cheese at 80°C). The greater the degree of CN dispersion, the firmer, more cross-linked, and less meltable is the final process cheese. This agrees with the similar trend reported for process cheese made with increasing concentrations of TSC (Shirashoji et al., 2006). Johnston and Murphy (1992) reported that there was greater CN dispersion in milk with an increase in Sodium hexametaphosphate levels; acid gels made from these Sodium hexametaphosphate-treated milks had improved gel textural properties.

Polyphosphates also have a strong ability to complex Ca, and we can rank phosphates and citrates in the following order: long-chain phosphates > tripolyphosphate > pyrophosphate > citrate > orthophosphate (Van Wazer and Callis, 1958). The strong Ca binding properties of Sodium hexametaphosphate should result in greater dispersion of CN because of the loss of CCP cross-links present in natural cheese.

The highly charged anionic nature of polyphosphates causes them to be attracted to the oppositely charged groups on other long-chain polyelectrolytes, such as proteins (Van Wazer and Callis, 1958). In our process cheeses, association of polyphosphate with CN should increase the charge repulsion between CN molecules. In some circumstances the addition of phosphates to milk can cause gelation (Mizuno and Lucey, 2007). Sodium hexametaphosphate was less effective at gelling CN than tetrasodium pyrophosphate. One factor that inhibits gelation of CN is that polyphosphates introduce more charge repulsion to CN because of their multiple negative charges (i.e., polyelectrolyte nature) compared with tetrasodium pyrophosphate.

Another possible factor that could contribute to the increased hardness and reduced meltability of cheese made with high concentration of Sodium hexametaphosphate (SHMP) is the formation of new Ca phosphate linkages within the cheese network (Gupta et al., 1984). Taneya et al. (1980) reported that long protein strands were observed in a process cheese made with sodium polyphosphate, whereas these long strands were not observed in a process cheese made with TSC. Long CN strands in process cheese could have resulted from the formation of new Ca phosphate linkages between CN. The insoluble Ca and insoluble P content (Table 3) of process cheese increased with increasing Sodium hexametaphosphate concentration. The addition of Sodium hexametaphosphate to milk protein concentrate at pH 5.8 increased CN-bound Ca (Mizuno and Lucey, 2005). Polyphosphates bind Ca from the native CCP (which help to disperse the CN micelles), but these new Ca phosphates complexes can associate with the dispersed CN (Odagiri and Nickerson, 1965; Mizuno and Lucey, 2005). Lee and Alais (1980) reported that the use of polyphosphates resulted in a high level of insoluble P in process cheese. Johnston and Murphy (1992) reported that skim milk solutions with polyphosphate contained a high proportion of nonsedimentable (soluble) CN. Apart from the lowest ES concentration, all other process cheese samples exhibited an increase in G′ at temperatures >70°C during heating. Udayarajan et al. (2005) suggested that the increase in G′ value of natural Cheddar cheese at high temperature was attributable to the heat-induced formation of additional Ca phosphate cross-links between CN.

The acid-base buffering profiles of process cheese indicate that the addition of Sodium hexametaphosphate caused a shift in the pH value where the buffering peak occurred during acidification. Lucey et al. (1993) suggested that a change in location or shape of the buffering peak observed during the acidification of milk might be attributable to some shift in the structure, or composition, or both, of the indigenous CCP. The buffering profiles of process cheese suggest that increasing the Sodium hexametaphosphate content altered the type and concentration of Ca phosphate salts present in the cheese network.

A small quantity of Sodium hexametaphosphate (0.25%) was not enough to efficiently disperse the CN network even with the use of long holding times during the cooking step. Consequently, fat was poorly emulsified (results not shown) and the process cheese was relatively soft and had good meltability.

Holding time resulted in a significant decrease in the LT value at 50°C, DOF, and Schreiber melt area and a significant increase in hardness and the G′ value at 70°C. Long holding times have previously been reported to reduce melt and increase hardness of process cheese (Rayan et al., 1980). An increase in the hold time also increases the extent of shear applied to the process cheese; this creates smaller homogenized fat globules that reinforce the matrix formed during cooling. During prolonged holding time at high temperatures, it is likely that some heat-induced CN aggregation occurred. Although increasing the concentration of ES used in process cheese resulted in an increase in the initial measured LT of the hot product (i.e., measured after a holding time of 10 min at 80°C), during (further) prolonged holding there was a substantial decrease in the LT and an increase in G′ values. Panouillé et al. (2003) observed that heat-induced aggregation and gelation of CN micelles could occur in the presence of sodium polyphosphates. Holding time had no significant effect on the insoluble Ca or P content. Because Sodium hexametaphosphate is a very effective Ca chelating agent, the time required to heat the process cheese to 80°C was likely sufficient to allow Sodium hexametaphosphate to chelate Ca from CN (i.e., a holding time at 80°C was not required to facilitate Ca chelation).

In solution, polyphosphates can undergo hydrolysis to orthophosphates, particularly at higher temperatures (>60°C; Maurer-Rothmann and Scheurer, 2005). In practice, Sodium hexametaphosphate (SHMP) is likely that the hydrolytic breakdown is low in most process cheese applications (Maurer-Rothmann and Scheurer, 2005). During holding of process cheese at high temperature some hydrolysis of Sodium hexametaphosphate may have occurred (Lee and Alais, 1980); however, holding time had no significant effect on the concentration of insoluble P in process cheese. It has been claimed (Roesler, 1966) that hydrolysis also occurs in process cheese during storage. Because the process cheese samples were not analyzed until after 7 d of storage, any (possible) hydrolysis should already have occurred before testing of cheese.

Comparing the results reported by Shirashoji et al. (2006) for process cheese made with TSC to those made with Sodium hexametaphosphate in the present study, we observed that cheese made with Sodium hexametaphosphate had lower LT values at 50°C and lower DOF values for all experimental conditions. The experimental work for our previous study (Shirashoji et al., 2006) was actually performed around the same time period as the current study. The hardness values for process cheese made with various concentrations of TSC were much lower (range: 1,572–2,685 g; Shirashoji et al., 2006) compared with cheese made with Sodium hexametaphosphate (range: 1,892–4,490 g).

Conclusions
The concentration of Sodium hexametaphosphate used as an ES in the manufacture of pasteurized process Cheddar cheese greatly affected the textural and melting properties, even when these cheeses had a similar pH value. The added Sodium hexametaphosphate appeared to convert the original form of CCP to a new type of Ca phosphate salt during cooking. A small quantity of Sodium hexametaphosphate (0.25%) was not enough to efficiently disperse the CN network even with long holding times during cooking; consequently, fat was poorly emulsified and the process cheese was soft and highly meltable. Holding times increased hardness and decreased meltability. High levels of Sodium hexametaphosphate produced firm and poorly meltable cheese because CN were highly dispersed during cooking, Sodium hexametaphosphate resulted in the formation of new Ca phosphate-CN linkages, and a fine-stranded network was formed during cooling. The results of this study will assist process cheese manufacturers in understanding the role of Sodium hexametaphosphate as an ES and demonstrates the effect of ES concentration and holding time on process cheese functionality.

Sodium hexametaphosphate (SHMP) Chemical Properties,Uses,Production
Outline
Sodium hexametaphosphate is a kind of sodium metaphosphate polymers. Sodium hexametaphosphate is also known as "polyvinylidene sodium," "sodium multiple metaphosphate", "sodium metaphosphate vitreous body", and "Graham salt". Sodium hexametaphosphate is a colorless transparent glass-like solid or white powder with greater solubility but low dissolving rate in water. Its aqueous solution exhibits acidic property. Its complex of divalent metal ion is relatively more stable than the complexes of mono-valent metal ion. Sodium hexametaphosphate can easily be hydrolyzed to orthophosphate in warm water, acid or alkali solution. Hexametaphosphate has a relative strong hygroscopicity with being sticky after absorbing moisture. For certain metal ions (e.g., calcium, magnesium, etc.), it has the ability to form soluble complexes, and thus being able to being used for demineralizing water. Sodium hexametaphosphate can also from precipitate with lead and silver ions with precipitate being re-dissolved in excess amount of sodium hexametaphosphate solution to form a complex salt. Its barium salt can also form complexes with the sodium hexametaphosphate. Sodium hexametaphosphate can be used as a kind of highly efficient water softener of power stations, rolling stock boiler water; as detergent additive, as corrosion-controlling or anti-corrosion agents; as cement hardening accelerator; as streptomycin purification agent, and the cleaning agent of textile industry and dyeing industry. Sodium hexametaphosphate can also be used as a kind of sedative drug, preservative, stabilizer, and fruit juice precipitant in food industry. In the oil industry, it is used for control of drilling pipe rust and adjusting the viscosity of oil drilling mud. Sodium hexametaphosphate also has applications in fabric dyeing, tanning, paper, color film, soil analysis, radiation chemistry and analytical chemistry and other departments. Our GB2760-1996 provisions that hexametaphosphate is allowable food additives (water retention agent) for being used for canned food, fruit juice drinks, dairy products, soy products; it can also be used as a dye dispersant, and water treatment agent.

Toxicity of Sodium hexametaphosphate
Adl 0~70 mg/kg (in terms of phosphorus); LD50:4g/kg (rat, oral). According to the provision of the GB2760-86, it is allowed for being applied to canned food, fruit juice drinks, dairy products, soy milk as quality improver; the maximum usage amount is 1.0 g/kg. When being used as composite phosphate, calculated as the total phosphate, the canned meat products shall not exceed 1.0 g/kg; for condensation of milk, it shall not exceed 0.50 g/kg.

Chemical Properties of Sodium hexametaphosphate
Sodium hexametaphosphate is colorless and transparent glass flake or white granular crystals. It is easily soluble in water but insoluble in organic solvents.

Uses of Sodium hexametaphosphate
Sodium hexametaphosphate can be used as a food quality improver in food industry, pH adjusting agent, metal ion chelating agents, dispersants, extenders, etc.
Sodium hexametaphosphate can be used as a kind of common analytical reagents, water softener, and also used for photofinishing and printing.
Sodium hexametaphosphate can be used as a water softener, detergent, preservative, cement hardening accelerator, fiber dyeing and cleaning agents; it can also used for medicine, food, petroleum, printing and dyeing, tanning, and paper industry.
Sodium hexametaphosphate can be used as texturizing agent; emulsifiers; stabilizer; chelating agent. Sodium hexametaphosphate is less frequently for being used alone and is generally used in mixture with pyrophosphate and metaphosphate. The mixture is mainly used for ham, sausage, surimi such as the tissue improver for water retention, tendering and meat softening. It can also be used for prevention of crystallization of canned crab as well as dissolving agent of pectin.

Sodium hexametaphosphate can be used as the water softening agent of boiler water and industrial water (including water for the production of dyes, water for the production of titanium dioxide, water for printing and dyeing, and slurry mixing, water for cleaning color copy of the film, as well as chemical industrial water and the water for the medicines, reagents production, etc.) as well as the water treatment agent for the industrial cooling water; it can also be used as a corrosion inhibitor, flotation agent, dispersant agent, high temperature binding agent, dyeing auxiliaries, metal surface treatment, rust inhibitors, detergent additives and also cement hardening accelerator. Coated paper production can use it as pulp dispersants in order to improve the penetration capability. In addition, it can also be apply to the washing utensils and chemical fiber in order to remove iron ions of the pulp. In the oil industry, it can be used for the antirust of the drilling pipe and adjusting the slurry viscosity upon the control of oil drilling.

Sodium hexametaphosphate can be used as the quality improver with various effects of increasing the complex metal ions of food, pH, ionic strength, thereby improving the adhesive capability as well as the water holding ability of food. China provides that it can be applied to the dairy products, poultry products, ice cream, instant noodles and meat with the maximum permitted amount being 5.0 g/kg; the maximal permitted usage amount in canned food, fruit juice (flavored) drinks and vegetable protein drink is 1.0g/kg.

Sodium hexametaphosphate can be used as a food quality improver in food industry and applied to canned food, fruit juice drinks, dairy products, and soy milk. Sodium hexametaphosphate can be used as Ph adjusting agent, metal ion chelate agent, adhesive and bulking agents. When being applied to beans and canned fruits and vegetables, it can be stabilize the natural pigment and protect the food color and lustre; when being used in canned meat, it can be used for preventing the emulsification of the fat and maintaining its uniform texture; when being applied to meat, it can be used to increase the water holding capacity and prevent the deterioration of fat in the meat. Sodium hexametaphosphate can also help to clarify the wine when being supplied to beer and further prevent turbidity.

Chemical Properties of Sodium hexametaphosphate
The sodium polyphosphates class consists of several amorphous, water soluble polyphosphates composed of linear chains of metaphosphate units, (NaPO3)x where x ≥ 2, terminated by Na2PO4- groups. They are usually identified by their Na2O/ P2O5 ratio or their P2O5 content. The Na2O/P2O5 ratios vary from about 1.3 for sodium tetrapolyphosphate, where x = approximately 4; through about 1.1 for Graham’s salt, commonly called sodium hexametaphosphate, where x = 13 to 18; to about 1.0 for the higher molecular weight sodium polyphosphates, where x = 20 to 100 or more. The pH of their solution varies from about 3 to 9. For additional details of description, refer to Burdock (1997).

Uses of Sodium hexametaphosphate
Sodium Hexametaphosphate is a sequestrant and moisture binder that is very soluble in water but dissolves slowly. solutions have a ph of 7.0. Sodium hexametaphosphate permits peanuts to be salted in the shell by making it possible for the salt brine to penetrate the peanuts. in canned peas and lima beans, Sodium hexametaphosphate functions as a tenderizer when added to the water used to soak or scald the vegetables prior to canning. Sodium hexametaphosphate improves whipping properties in whipping proteins. Sodium hexametaphosphate functions as a seques- trant for calcium and magnesium, having the best sequestering power of all the phosphates. it prevents gel formation in sterilized milk. it is also termed sodium metaphosphate and graham’s salt.

Uses
For industrial use, such as oil field, paper-making, textile, dyeing, petrochemical industry,tanning industry, metallurgical industry and building material industry, It is mainly used as a water sortening agent in solution for printing, dyeing ,and boiler; Diffusant in papermersing medium, high temperature agglomerant,detergent and soil analytical chemistry reagent,

Uses
sodium hexametaphosphate is a chelating agent and a corrosion inhibitor. This is an inorganic salt.

Preparation of Sodium hexametaphosphate
Sodium hexametaphosphate is prepared by heating monosodium phosphate (NaH2PO4) rapidly to a clear melt, which occurs slightly above 625°C. Rapid chilling of this melt produces a very soluble glass, which is then crushed or milled.

Agricultural Uses of Sodium hexametaphosphate
Sodium metaphosphate is the salt of metaphosphoric acid having a molecular formula (NaPO3)n, where n ranges from 3 to 10 (for cyclic molecules) or may be much larger (for polymers).

Cyclic molecules have alternate phosphorus and oxygen atoms in the rings and start with trimetaphosphate (NaPO3)3 to at least decametaphosphate.
Sodium hexametaphosphate may be a polymer where n is between 10 and 20.
Vitreous sodium phosphates have a Na2O:P2O5 ratio near unity and are called Graham's salts. The average number of phosphorus atoms in these vitreous glasses ranges from 25 to infinity.

Industrial uses of Sodium hexametaphosphate
Sodium hexametaphosphate (SHMP) or water glass Na6P6O18 is basically the salt of metaphosphoric acid. Sodium hexametaphosphate is difficult to dissolve. By mixing SHMP for 1-3 h, a solution of 8-10% can be obtained. The pH of this solution is about 5. Because of a weak acid reaction, the Sodium hexametaphosphate reacts with cations of bivalent metals forming Na2MeP6O18 or Na4MeP6O18. In the presence of oxygen, Sodium hexametaphosphate slowly decomposes into pyrophosphate and orthophosphate.

Sodium hexametaphosphate (SHMP) is miscible in water but insoluble in organic solvents. This sequestrant, thickener, emulsifier and texturizer is used in a variety of foods. The phosphorus in the additive helps to prevent mineral corrosion (calcium, iron salts, magnesium, etc.).

Sodium hexametaphosphate is a food additive and a softening agent for water and detergents. Sodium hexametaphosphate can also be found in leathers, clays and pigments, and personal care products such as toothpaste.

ALSO KNOWN AS
SHMP; Calgon; Glassy sodium; Graham's salt; Hexametaphosphate; Hexasodium metaphosphate; Metaphosphoric acid; hexasodium salt

The floatability of scheelite and calcite in the presence of single depressant (SHMP or H3Cit) and mixed depressant (SHMP/H3Cit) was studied by microflotation experiments and artificial mixed mineral experiments. Solution chemical calculation, zeta potential tests, thermodynamic analysis and XPS analysis were used to explain the relevant depressive mechanism. Mixed depressant (SHMP/H3Cit) exhibited excellent selective depressive effect on calcite. The optimal molar ratio of Sodium hexametaphosphate to H3Cit was 1:4. The depressant Sodium hexametaphosphate and H3Cit can be chemically bonded with Ca2+ to form CaHPO4 and Ca3(Cit)2 at pH 8. The CaHPO4 was more easily formed than Ca3(Cit)2 on the mineral surface, which indicated that the depressive effect of SHMP was stronger than H3Cit. The SHMP and H3Cit of the mixed depressant were co-adsorbed on the calcite surface, while the H3Cit of the mixed depressant was weakly adsorbed on the scheelite surface. The mixed depressant can significantly improve the separation efficiency of scheelite from calcite.

Sodium hexametaphosphate (SHMP) is a clean, non-toxic phosphate that is widely used in the food industry and the chemical industry. Sodium hexametaphosphate can be used as a chelating reagent for metal ions, an adhesive, and a swelling reagent. It is also widely used in the mineral processing industry, especially in the floatation. Sodium hexametaphosphate is used as a dispersant and depressant of minerals in flotation. In addition, Sodium hexametaphosphate can be used to depress calcite, but it also has a strong depressive effect on scheelite. Citric acid (H3Cit) is also a clean, non-toxic organic acid and is a tricarboxylic acid compound. Sodium hexametaphosphate is mainly used in the food industry, chemical industry, textile industry, cosmetics and pharmaceutical industries. Citric acid can be used as depressant in flotation. In the dolomite flotation, it can be used to depress apatite. A related study showed that the floatability of rare earth can be inhibited by citric acid. Zeng et al. studied the depression of H3Cit in the process of separating celestite from fluorite and calcite. It is a pity that they did not study the depression of H3Cit in the process of separating scheelite from calcite. At the same time, the effect of the mixed depressant SHMP/H3Cit on the flotation separation of scheelite from calcite had not been systematically studied. The corresponding depressive mechanism of the depressants remain unclear.
In this study, single depressant Sodium hexametaphosphate or H3Cit was studied in the process of separating scheelite from calcite. Sodium oleate (NaOL) was used as a collector during this process. In contrast, mixed depressant SHMP/H3Cit was also studied and eventually the best molar ratio was obtained.