| HS Code | 909257 |
| Chemical Formula | Na2SeO3·5H2O |
| Cas Number | 26970-82-1 |
| Molecular Weight | 263.01 g/mol |
| Appearance | White or colorless crystalline powder |
| Density | 2.16 g/cm3 at 20°C |
| Melting Point | Decomposes and loses water at approximately 40°C |
| Solubility In Water | Soluble; approximately 85 g/100 mL at 20°C |
| Ph 1 Aqueous Solution | Approximately 8.5 to 9.5 (alkaline) |
| Purity Typical | ≥98% |
| Storage Conditions | Store in a tightly closed container in a cool, dry, well-ventilated area |
| Hazard Classification | Toxic if swallowed; causes skin and eye irritation; dangerous for the environment |
As an accredited Sodium Selenite Pentahydrate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Sodium Selenite Pentahydrate, 25 kg net, supplied as white crystalline powder in double polyethylene-lined fiber drums, sealed for moisture protection. |
| Container Loading (20′ FCL) | 20' FCL: Sodium Selenite Pentahydrate packed in drums/pails, palletized, secured, with hazard labels and ventilation. |
| Shipping | Ship sodium selenite pentahydrate as UN 2630, Class 6.1 (toxic) in tightly sealed, corrosion-resistant containers. Label clearly, avoid moisture, acids, and incompatible materials. Use spill-containment packaging and secure upright handling. Comply with international dangerous goods regulations, include proper documentation, and ensure emergency response information accompanies all shipments. |
| Storage | Store Sodium Selenite Pentahydrate in a tightly sealed, clearly labeled container in a cool, dry, well-ventilated area. Keep away from incompatible substances, strong acids, reducing agents, and food/feed materials. Protect from moisture and direct sunlight. Access should be restricted to trained personnel, and proper PPE must be used when handling. |
| Shelf Life | Sodium selenite pentahydrate has a typical shelf life of 3–5 years when stored tightly sealed in a cool, dry place. |
In continuous container-glass furnaces operating at 1,480–1,520 °C, iron oxide present in silica sand and cullet shifts the transmitted spectrum toward green-to-yellow wavelengths. Sodium selenite pentahydrate (Na2SeO3·5H2O) is metered into the batch as a chemical decolorizer, providing 30.0 wt% Se and therefore requiring a multiplication factor of 3.33 to convert from elemental selenium to pentahydrate mass. For flint container ware, the normal production addition range is 0.001–0.01 wt% Se equivalent on batch mass, and the set point is reoptimized when mixed cullet exceeds 20% or Fe2O3 exceeds 0.06 wt%. In the furnace, Se4+ is partly reduced to elemental selenium, shifting the glass from green to a neutral grey-flint; overdosing pushes the colour into a pink blush, while carbon batch reductants alter the selenium redox balance and require furnace crown temperature and excess-oxygen adjustment. Batch house lines use sealed bag dump stations, loss-in-weight screw feeders, and batch mixers; selenium species can partition to flue-gas dust, so baghouse residue and stack monitoring are part of batch-to-batch traceability. Compliance for finished hollow glass includes ISO 9050:2003 for light transmittance, ASTM E308-18 for CIE colour coordinates, and EU Regulation (EC) No 1935/2004 where food-contact packaging is qualified. Workplace exposure to selenium-bearing dust is maintained below the ACGIH TLV-TWA of 0.2 mg/m³ as Se. Terminal finished product types include flint bottles, jars, tableware, and pharmaceutical glass containers.
A multistep dilution sequence becomes necessary because the target selenium concentration in complete feed is three to six orders of magnitude below the 30.0 wt% Se content of the pentahydrate. In the European Union, sodium selenite is authorized as nutritional feed additive E8 with a maximum total selenium content in complete feed of 0.5 mg/kg at 12% moisture; in the United States, 21 CFR 573.920 limits selenium from sodium selenite to 0.3 mg Se/kg complete feed for chickens, turkeys, swine, sheep, beef cattle, and dairy cattle. For a 0.3 mg Se/kg finished feed, the sodium selenite pentahydrate addition is 1.0 mg/kg; for a 0.5 mg Se/kg finished feed, the addition is 1.67 mg/kg. A typical premix line first dilutes the crystalline pentahydrate at 1:10 in calcium carbonate or ground rice hulls using a horizontal double-ribbon mixer filled to 60–70% of working volume and operated at 12–18 rpm. The intermediate is then diluted again into the final premix; segregation is monitored by collecting samples according to ISO 6497:2002 and determining selenium by EN 17053:2018 after microwave digestion. Acidic carriers or molasses-based liquid blends below pH 4.0 are avoided because Se4+ can reduce to elemental selenium and settle in storage tanks, producing sub-therapeutic finished feed. Terminal products include vitamin-mineral premixes, complete poultry feeds, swine rations, and dairy/beef cattle concentrates.
| Target selenium in complete feed | Na2SeO3·5H2O addition | Se content in final 1% inclusion premix |
|---|---|---|
| 0.1 mg/kg | 0.333 mg/kg | 10 mg/kg |
| 0.3 mg/kg | 1.0 mg/kg | 30 mg/kg |
| 0.5 mg/kg | 1.67 mg/kg | 50 mg/kg |
Unlike container glass decolorizing, tinted architectural glass uses sodium selenite pentahydrate to generate a bronze-to-grey transmission spectrum through co-melting with iron and cobalt oxides. Bronze float-glass formulation windows generally operate at 0.005–0.05 wt% Se equivalent, with Fe2O3 at 0.20–0.70 wt% and CoO at 0.001–0.005 wt%; a selenium deviation of ±0.002 wt% creates a red-colour drift measurable at 6 mm thickness. In a float-glass furnace operating at 1,580–1,620 °C, the selenium redox balance is controlled by the sulfate-to-carbon batch ratio; strongly reducing conditions drive selenium toward elemental retention, while over-oxidizing conditions increase selenium volatilisation as SeO2. Downstream processing uses a cross-fired regenerative melter, a nitrogen-hydrogen tin bath at 600–700 °C, an annealing lehr, and automatic cutting; selenium carry-over in flue-gas baghouse dust is monitored to avoid cross-contamination between tinted and clear campaigns. Compliance includes EN 410:2011 for light transmittance and solar factor, ISO 9050:2003 for glazing photometric performance, and ECE R43 where the glass is qualified as automotive safety glazing. Terminal finished product types include architectural spandrel panels, solar-control glazing, and privacy automotive side lights.
Solution stability in fertigation tanks is constrained by pH and reducing agents because selenite (Se4+) is less mobile than selenate (Se6+) and can precipitate as elemental selenium if the tank pH falls below 4.0 or dissolved iron(II) is present. Published field data for sodium selenite in winter wheat biofortification commonly evaluate foliar rates between 10 g Se/ha and 40 g Se/ha; soil-applied rates in selenium-poor soils are commonly assessed at 20–60 g Se/ha. In a liquid fertilizer line, the pentahydrate is dissolved separately in water at 20–25 °C, then injected into the mother tank at a target concentration of 5–20 mg Se/L; the batch is passed through a 50-mesh screen before entering drip tape or a foliar boom. The downstream process includes pH adjustment to 5.5–6.5, blending with NPK stock solutions, field injection, and harvesting of treated grain with destination-market selenium monitoring. Compliance for the finished crop is governed by national food tolerance limits for selenium and by destination-market registration for selenium-bearing fertilisers; the EU Fertilising Products Regulation (EU) 2019/1009 does not list selenium among the mandatory micronutrients in Annex II, so registration is managed under national rules where permitted. Terminal products include selenium-biofortified wheat grain and flour, rice, and horticultural crops. Published data for this specific formulation under multi-crop commercial fertigation is limited; batch-scale trials remain the validation route before shipment-scale design.
Gravimetric preparation of a single-element selenium standard from the pentahydrate requires correction for water of crystallization. To prepare 1 L of 1,000 mg/L Se stock solution, 3.330 g of Na2SeO3·5H2O is dissolved in high-purity water acidified to 1–5% HNO3, and the resulting solution is verified against NIST SRM 3149 under ISO/IEC 17025:2017 calibration requirements. Downstream synthesis of selenious acid and sodium selenate uses controlled oxidation with hydrogen peroxide under alkaline conditions, with reactor cooling to maintain the exotherm below 60 °C; the oxidation step is carried out in glass-lined vessels with pH-controlled dosing and final filtration through 0.45 µm membranes for reagent-grade solutions. Compliance for industrial chemical intermediates is governed by REACH registration for CAS 10102-18-8—the pentahydrate is CAS 26970-82-1—and by local hazardous chemical inventories. Terminal products include certified single-element ICP-MS selenium standards, laboratory QC concentrates, and raw material for manufacturing sodium selenate and selenious acid.
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Sodium selenite pentahydrate, CAS 26970-82-1, is the crystalline five-water adduct of disodium selenite with the formula Na2SeO3·5H2O and a molecular weight of 263.01 g/mol. The theoretical selenium content is 30.02 wt% on the hydrated basis, while the anhydrous equivalent factor is 0.657. This hydrated salt is supplied as a white crystalline solid; the water of crystallization accounts for 34.25 wt% of the molecular weight. In commercial assay practice, the product is specified against the pentahydrate formula rather than against the anhydrous salt. A formulation that requires 1.00 kg of anhydrous sodium selenite must use 1.52 kg of the pentahydrate to maintain constant selenium input, because the conversion factor is 0.657. Supplier product codes are not harmonized across manufacturers; model designations typically encode the hydration state as Na2SeO3·5H2O and the purity tier, but the chemical identity is governed by CAS 26970-82-1 rather than by a manufacturer model number. The main differentiation from sodium selenate lies in oxidation state: selenite contains Se(IV), whereas selenate contains Se(VI).
Feed-grade sodium selenite pentahydrate is controlled under selenium supplementation regulations; in the United States the applicable citation is 21 CFR 573.920, which defines the additive source and species restrictions. The compound is incorporated into premixes at controlled selenium concentrations and then diluted into complete feed; formulators must verify the current maximum supplemental selenium level for the target species rather than relying on historical 0.1–0.3 mg/kg complete-feed values. Reagent-grade material is typically specified by assay, insoluble matter, chloride, sulfate, iron, and heavy metals. Table 1 lists representative acceptance criteria derived from combined supplier certificates of analysis and applicable pharmacopoeial monographs for sodium selenite where available; the purchaser should confirm the lot-specific method because monographs vary between jurisdictions.
| Parameter | Typical value or range | Test technique |
|---|---|---|
| Assay as Na2SeO3·5H2O | 98.0–101.0% | Iodometric titration |
| Selenium content | 29.8–30.2% | ICP-OES per ISO 11885:2007 |
| Chloride | ≤0.005% | Ion chromatography |
| Sulfate | ≤0.01% | Turbidimetric or ion chromatography |
| Iron | ≤0.001% | ICP-MS per ISO 17294-2:2016 |
| Heavy metals as Pb | ≤5 mg/kg | ICP-MS |
| Insoluble matter | ≤0.005% | Filtration gravimetric |
The choice between feed-grade and reagent-grade material is driven by the target analytical burden; feed premix operations prioritize selenium concentration and trace heavy-metal consistency, whereas laboratory synthesis uses the higher assay limit to avoid chloride or sulfate interference in downstream precipitation.
In soda-lime container glass production, sodium selenite pentahydrate is introduced as a batch component to control color by shifting the redox equilibrium of iron impurities. The melt addition level is typically expressed as elemental selenium equivalent in the range of 0.01–0.50 wt% of the batch, although the actual amount is furnace-specific and depends on iron content, cullet ratio, and melting atmosphere. The salt decomposes at glass-melting temperatures of 1350–1450°C, releasing selenium species into the melt; the resulting reddish-brown ferric selenite color center is balanced against the blue-green iron(II) absorption. Overdosing produces amber or pink cast, and underdosing fails to mask the iron green. Because selenium volatility is high at melt temperature, retention efficiency is lower than that of iron oxide colorants; batch compacting or cullet pre-wetting can reduce carry-out and volatilization losses. A cross-fired regenerative furnace with 100–300 t/day pull may show color drift if sulfur and selenium redox batch inputs are not held to within ±5% of the set point. Published data for specific furnace configurations is limited; therefore, glass manufacturers ordinarily derive selenium demand from a plant-scale color calibration curve rather than from laboratory-only predictions.
Conversion between hydrated and anhydrous sodium selenite is not cosmetic; the 0.657 anhydrous-equivalent factor corresponds to a required mass multiplier of 1.52 for replacement of anhydrous salt with the pentahydrate. This factor changes the concentration of selenium in a premix: 1.000 g of sodium selenite anhydrous contributes 0.4565 g selenium, while 1.000 g of the pentahydrate contributes 0.3002 g selenium. When selenium concentration is fixed by regulation, a formulation error of 34.25% arises if the hydration state is ignored. The same arithmetic applies to analytical standard preparation: a stock solution labeled as containing 1.000 g/L sodium selenite anhydrous cannot be prepared from 1.000 g of the pentahydrate without mathematical correction. In automated batching, the weigh-out should be tied to the certificate of assay and the hydration state; if the material has partially effloresced during storage, the actual water content may be below theoretical, and the assay-backed selenium value is the only reliable basis for adjustment.
Sodium selenite pentahydrate dissolves to give selenite ion, SeO3²⁻, which undergoes reduction to elemental selenium or selenide depending on reductant strength and pH. In weakly acidic solution, ascorbic acid or sulfur dioxide reduces selenite to amorphous red selenium; the reaction is used in hydrometallurgical selenium recovery and in analytical sample preparation. The product should not be combined with strong acids in closed vessels because selenious acid formation increases volatile selenium release. The aqueous solution is alkaline; pH elevation may be required to maintain the selenite dianion in solution in the presence of polyvalent metal ions. In laboratory synthesis of selenide nanoparticles, the selenite precursor is often reduced at controlled temperature under inert atmosphere; batch-to-batch particle size depends on reducing agent injection rate, which is equipment-specific. Published data for morphologies is available only for defined reagent ratios and stirring geometries; extension to production scale requires pilot testing.
Feed premix manufacturing with sodium selenite pentahydrate is performed by rendering the compound into a carrier such as ground limestone or wheat middlings prior to blending into final feed. The practice is constrained by the legal selenium ceiling in 21 CFR 573.920; because selenium is deficient in many livestock diets, the addition window is narrow. A double-shaft paddle mixer with 5–15 minutes of dry mixing at 30–60 rpm is generally sufficient to obtain a coefficient of variation below 10% for selenium in premix, although this must be confirmed by lot sampling. Pre-drying of the carrier to below 0.5% moisture is recommended when the hydrated selenite is to be stored for long periods in humid environments, because free moisture accelerates agglomeration and local high-selenium spots. Direct addition of the pure salt to feed without a premix is not acceptable; the concentration gradient would exceed the dosing precision of most feed mill microingredient systems.
The table below compares the common inorganic selenium sources. Selenium dioxide, CAS 7446-08-4, carries 71.16% selenium and is water-soluble but has a high vapor pressure and sublimes near 315°C; it is rarely used as a direct feed supplement because of its acute toxicity and handling hazard. Sodium selenate, CAS 13410-01-0 for the anhydrous form, has a higher oxidation state and different redox behavior; reduction to selenite is required before incorporation into selenoprotein pathways in biological systems. Elemental selenium powder provides 100% selenium but is effectively insoluble in water, making its bioavailability dependent on particle size and surface oxide formation. Sodium selenite pentahydrate is therefore selected where water solubility, moderate selenium concentration, and regulatory compliance with 21 CFR 573.920 are required in a single salt.
| Material | Formula | CAS | Molecular weight | Selenium content | Water solubility | Primary technical handling issue |
|---|---|---|---|---|---|---|
| Sodium selenite pentahydrate | Na2SeO3·5H2O | 26970-82-1 | 263.01 g/mol | 30.02% | Highly soluble | Efflorescence in dry air; hydrate water loss |
| Sodium selenite anhydrous | Na2SeO3 | 10102-18-8 | 172.94 g/mol | 45.65% | Highly soluble | Hydration-induced mass gain if exposed to moisture |
| Sodium selenate anhydrous | Na2SeO4 | 13410-01-0 | 188.94 g/mol | 41.78% | Very soluble | Oxidized Se(VI); requires reduction |
| Selenium dioxide | SeO2 | 7446-08-4 | 110.96 g/mol | 71.16% | Soluble as selenious acid | High vapor pressure; sublimes at 315°C |
| Elemental selenium | Se | 7782-49-2 | 78.96 g/mol | 100% | Insoluble | Low aqueous bioavailability; dust hazard |
Analytical and cell-culture use of sodium selenite pentahydrate generally occurs at selenium concentrations in the nanomolar to low micromolar range. In serum-free media, the compound is supplied as a concentrated stock solution, filter-sterilized, and then diluted to working selenium concentrations that are often between 10 and 100 nmol/L; however, published data for specific cell lines varies, and the optimal range is cell-type dependent. The material is also used as a reagent for the preparation of selenious acid solutions and for the controlled synthesis of metal selenide films; the pentahydrate is preferred over selenium dioxide where solid weighing and storage stability are more important than selenium density. In these applications, the water of crystallization is removed or accounted for because it changes the stoichiometric selenium concentration of the reaction medium.
Storage of sodium selenite pentahydrate should be in tightly closed containers in a ventilated area; the product is classified as toxic and is transported under UN 2630 as an inorganic selenite. Incompatibilities include strong reducing agents, strong acids, and oxidizable organic materials; exposure to acid generates toxic selenium vapors. The US OSHA permissible exposure limit for selenium compounds as Se is 0.2 mg/m3; current safety data sheets should be consulted for local occupational exposure limits and personal protective equipment requirements. If the package is left open in low-humidity environments, the pentahydrate may effloresce, shifting the water content and changing the apparent assay; assay-based correction is required before any precise selenium formulation.