| HS Code | 347437 |
| Chemical Formula | Na2SeO3 |
| Molecular Weight | 172.94 g/mol |
| Cas Number | 10102-18-8 |
| Purity | 98% |
| Appearance | white crystalline powder |
| Density | 3.1 g/cm3 at 20°C |
| Melting Point | 350°C (decomposes) |
| Solubility In Water | soluble in water |
| Hazard Classification | toxic if swallowed; dangerous for the environment |
| Storage Conditions | store in a cool, dry place in a tightly sealed container, protected from moisture and light |
As an accredited Sodium Selenite Anhydrous 98% factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Sodium Selenite Anhydrous 98%: 25 kg net in double polyethylene bags inside sealed fiber drums with clear labeling. |
| Container Loading (20′ FCL) | 20′ FCL: one 20-foot container loaded with Sodium Selenite Anhydrous 98%, packed in sealed drums, secured and labeled for safe transport. |
| Shipping | Sodium Selenite Anhydrous 98% ships as a toxic hazardous substance under UN2630, Class 6.1. It is packed in sealed, UN-approved containers with hazard labels and dry, moisture-resistant packaging. Transport requires authorized carriers and proper documentation. Keep cool and dry, away from incompatible materials. Air and sea shipments follow strict regulatory controls. |
| Storage | Store Sodium Selenite Anhydrous 98% in a tightly sealed container in a cool, dry, well-ventilated area. Protect from moisture, heat, and direct sunlight. Keep away from acids, strong oxidizers, reducing agents, and foodstuffs. Ensure the container is clearly labeled and segregated from incompatible materials to prevent accidental exposure or reaction. |
| Shelf Life | Shelf life is typically 2 years when stored tightly sealed in a cool, dry place away from light and moisture. |
In container glass furnaces, the green transmission minimum caused by ferrous iron in the batch is corrected by adding a selenium component that introduces a complementary pink absorption band. Sodium selenite anhydrous 98% serves as the weighed selenium carrier; the assay floor translates to a selenium metal equivalent of not less than 44.7% by mass, calculated from the selenium atomic mass of 78.96 g/mol against the formula mass of 172.94 g/mol. The absence of crystalline water compared with the pentahydrate reduces energy consumed in the melter and avoids batch water that would otherwise be evaporated at the cold top.
Batch logs from soda-lime container glass operations frequently record addition rates of 10 g to 80 g of sodium selenite anhydrous per metric ton of batch, with the actual set point depending on Fe₂O₃ content between 0.02% and 0.15%, cullet ratio, and target L*a*b* coordinates. The addition is pre-blended with dry silica sand at a 1:20 mass ratio before introduction to the main mixer; this reduces segregation in horizontal ploughshare mixers. The redox state of the furnace atmosphere controls selenium retention. Under oxidative air-fuel firing, selenium can be volatilised as SeO₂; under reducing conditions, selenium is retained more effectively but can interact with iron to shift the compensating pink colour toward a reddish cast. Furnace temperatures in commercial soda-lime glass operation run between 1450 °C and 1550 °C, with pull-sample spectrochemical verification reduced to CIE L*a*b* coordinates under ASTM E308-18. Plant-specific colour control limits rather than universal selenium dosage values are used because fibre, container and tableware furnaces differ in atmosphere and residence time.
Sodium selenite is incorporated into feed premixes as a high-assay selenium source. Because the anhydrous 98% material contains no crystalline water, it can reduce the moisture-mediated caking that occurs when pentahydrate is stored in multi-ingredient premixes. In production, the crystalline solid is first diluted into a 1% preblend using calcium carbonate or wheat middlings; the preblend is then introduced into a twin-shaft or ribbon mixer at the main micro-ingredient stage. Uniformity is assessed by collecting 10 sampling points across the batch and measuring selenium concentration by ICP-MS after microwave digestion according to EN 17053:2018. A coefficient of variation below 5% is the commonly accepted release criterion for micro-ingredient premix uniformity.
The finished feed selenium ceiling is set by jurisdiction-specific regulations, not by the premix manufacturer. Under United States rules, selenium supplementation is limited to 0.3 mg/kg complete feed for chickens, turkeys, swine, sheep and cattle under 21 CFR 573.920. In the European Union, sodium selenite is authorised as a nutritional feed additive under Regulation (EC) No 1831/2003, and the maximum total selenium in complete feed is 0.5 mg/kg at a feed moisture content of 12%. These maxima are upper limits; commercial formulations frequently target 0.1 mg/kg to 0.3 mg/kg supplemental selenium depending on basal diet selenium and species sensitivity.
| Jurisdiction | Species scope | Maximum total selenium in complete feed | Reference |
|---|---|---|---|
| United States | Chickens, turkeys, swine, sheep, cattle | 0.3 mg/kg | 21 CFR 573.920 |
| European Union | All animal species | 0.5 mg/kg at 12% moisture | Regulation (EC) No 1831/2003 |
The Se(IV) centre is oxidative. Dry blending with unprotected ascorbic acid or ferrous sulphate can reduce selenite to elemental selenium, producing a pink-gray residue in blender dead zones and causing assay drift. The anhydrous material is therefore segregated from reducing micro-ingredients or moved through dedicated loss-in-weight feeders. Storage below 40% relative humidity and use of vented waste dust collection lines prevent agglomeration and dust accumulation in bucket elevators.
Acidification of anhydrous sodium selenite in aqueous media is used to generate selenious acid without the additional water burden of the pentahydrate. A glass-lined reactor is charged with demineralised water, and the solid is added under cooling at 20 °C–30 °C; the solution exotherm is controlled before stoichiometric sulphuric acid is metered. The high assay simplifies mass balance because the salt provides a selenium concentration determined by the anhydrous molecular weight, 172.94 g/mol, rather than by an uncertain hydration state. Oxidation to sodium selenate is run with hydrogen peroxide at pH 8.5–9.5 under redox potential control, with the endpoint checked by iodometric titration after peroxide quenching. SO₂ reduction of an acidified selenious acid stream precipitates red selenium metal; a vent gas scrubber is required for excess SO₂. Published preparative yield data for specific organoselenium derivatives from sodium selenite are limited because most organic routes require reduction to selenium or diselenide intermediates before carbon-selenium bond formation.
Where an electrodeposition bath requires a Se(IV) additive but chloride and sulphate carryover are restricted, sodium selenite anhydrous 98% is dissolved separately in high-purity water and metered into the working electrolyte after filtration through a 0.45 µm capsule filter. For selenite conversion-coating and alloy deposition trials, the bath pH is held at 2.0–3.0 with nitric acid, and the temperature is maintained at 25 °C±2 °C. Published data for specific selenite-containing alloy deposition current densities and throwing power values remain limited, so Hull cell panels and voltammetric scans should be used to establish the working window for each bath matrix.
Sodium selenite is spiked into chemically defined basal media as a trace element supplement for mammalian cell expansion. A separate stock solution is made at 0.1 g/L, sterile-filtered through a 0.22 µm polyethersulfone membrane, and diluted into the cooled basal medium to a final selenium concentration below 1 µmol/L for most serum-free systems. The final concentration is set by cell-line-specific factorial screening rather than by a universal medium formula. Selenite must be kept away from cysteine and glutathione during preparation because thiol reduction converts Se(IV) to elemental selenium, forming a red precipitate and reducing the bioavailable selenium content. The complete medium is visually checked after 4 h at 2 °C–8 °C; any turbidity indicates selenite-thiol reaction and requires discard of the batch.
In cadmium sulfoselenide pigment manufacture, sodium selenite is pre-dissolved and reduced in alkaline slurry before co-precipitation with cadmium sulfide precursors. The selenite solution is adjusted to pH 9.0–9.5, charged to a baffled reactor at 50 °C, and reduced under controlled redox conditions until the filtrate conductivity stabilises. The washed precipitate is calcined at 400 °C–600 °C under nitrogen or argon; the final red hue is governed by the CdS/CdSe molar ratio, not by selenium assay alone. Colour is measured on pressed powder plaques under ISO 11664-4:2008 after dispersing 100 g pigment in a standard linseed oil vehicle. The 98% anhydrous grade is used because residual crystalline water from the pentahydrate would perturb the solid-state calcination stoichiometry and reduce batch-to-batch hue repeatability.
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Sodium selenite anhydrous 98% is an inorganic selenium compound supplied as a white to off-white crystalline powder with the empirical formula Na2SeO3, CAS registry number 10102-18-8, and a molecular weight of 172.94 g/mol. The product model designation in procurement documentation is commonly sodium selenite anhydrous 98%, technical or feed grade, where the 98% assay is expressed on an anhydrous basis. The theoretical selenium concentration is 45.66% by weight, compared with 30.00% for sodium selenite pentahydrate; this difference reduces the mass of selenium-bearing salt required in a premix and lowers the hydration load introduced into moisture-critical dry blends. The anhydrous solid dissolves in water at approximately 85 g/100 mL at 20 °C, producing an alkaline solution with a pH typically between 8.0 and 9.5 at 20% solids. In acidified systems, the selenite ion acts as an oxidizing agent and releases selenium dioxide, which is the basis for several synthesis and glass-melting applications. The material is hygroscopic and may convert to the pentahydrate when exposed to ambient relative humidity above 60%; therefore, moisture-tight packaging, desiccant placement, and short transfer time are required to maintain assay mass balance in bulk handling operations.
Representative acceptance limits cross-referenced to the current FCC monograph for sodium selenite include assay 98.0–101.0% on the anhydrous basis, loss on drying ≤0.5%, selenium content 44.8–46.0%, arsenic ≤3 mg/kg, heavy metals as lead ≤5 mg/kg, chloride ≤0.02%, and sulfate ≤0.05%. Each lot should be released against a certificate of analysis containing the actual titration result, the selenium assay determined by hydride generation atomic absorption or ICP-MS, and the moisture content determined by Karl Fischer method if the material has been stored at relative humidity above 45%. For feed applications, the final dietary selenium level in complete feed is controlled under FDA 21 CFR 573.920; the premises and mixer records must document the batch number of the sodium selenite source and the calculated total selenium from all ingredients.
| Parameter | Sodium Selenite Anhydrous 98% | Sodium Selenite Pentahydrate |
|---|---|---|
| Chemical formula | Na2SeO3 | Na2SeO3·5H2O |
| CAS registry number | 10102-18-8 | 26970-82-1 |
| Molecular weight | 172.94 g/mol | 262.99 g/mol |
| Theoretical selenium content | 45.66% | 30.00% |
| Assay basis | 98.0–101.0% Na2SeO3 | 98.0–102.0% Na2SeO3·5H2O |
| Loss on drying | ≤0.5% | not applied; hydrate water release on heating |
| Typical commercial form | white crystalline powder | white crystalline solid |
Because sodium selenite is dosed at milligram-per-kilogram levels in animal feed, analytical recovery across different matrix dilutions is a critical release parameter. Method validation under AOAC 996.16 should include matrix spikes at 0.1 mg/kg, 0.3 mg/kg, and 0.6 mg/kg selenium; recovery outside 85–115% indicates interference from high iron phosphate, calcium carbonate, or organic acid carriers. When the anhydrous 98% material is specified, the certificate of analysis should report not only assay but also particle-size distribution, because the dry additive must pass through a 600 µm screen to avoid discrete visible particles in the final premix. A sieve residue above 0.5% on a 600 µm sieve is a batch rejection criterion in many premix plants even if the assay remains within specification.
In a 1,000 kg horizontal ribbon mixer operating at 12–15 rpm, the anhydrous grade is added as a pre-diluted premix rather than as neat powder. Direct addition of neat anhydrous powder below 50 g per batch may produce selenium-rich pockets at the end plates and under the shaft seal because the fine particle fraction segregates during the final 3 min of mixing. A controlled procedure disperses 50 g of the anhydrous product into 2.0 kg of ground limestone or rice hull carrier through a 600 µm screen, then adds this mixture to the main mixer after 70% of the carrier has been charged. Mixing continues for 6–8 min after premix addition; blend uniformity is tested by collecting 10 samples from defined zones per batch and assaying selenium by AOAC 996.16. The acceptance criterion is a coefficient of variation ≤5.0% with no individual sample outside ±10% of the target concentration. Batches exceeding the limit are re-mixed for 2 min increments and re-sampled; three consecutive failed re-mixes indicate wet bridging at the feeder or crystal size segregation requiring sieve rework.
When the anhydrous material replaces pentahydrate in an existing premix formula, the salt mass must be recalculated by selenium contribution rather than by direct weight substitution. A formula containing 10.0 g of pure pentahydrate per 100 kg carrier supplies 3.00 g of selenium. The equivalent selenium contribution from anhydrous 98% material is 6.70 g per 100 kg when compensating for both the 45.66% theoretical selenium content and the 98% assay. Failure to recalculate on selenium equivalence produces under-supplementation and may place the final feed outside the FDA 21 CFR 573.920 concentration requirement.
Cross-contamination failures often originate at the mixer discharge rather than the weighing station. In a twin-shaft paddle mixer with a nominal capacity of 1,000 kg and a discharge gate opening of 200 mm × 200 mm, residual premix accumulates on the gate frame and in the flexible connector to the bucket conveyor. If the next batch is a selenium-free dairy mineral, carryover above 0.15 mg/kg may be detected by a single composite sample collected after 1 min of discharge. The corrective action is to sequence selenium-supplemented batches consecutively, followed by a 50 kg purge of ground limestone that is separately collected and handled as selenium-containing product, and then to verify the next batch by selenium assay before release.
At relative humidity above 60%, the anhydrous powder forms a hard surface crust as it hydrates to the pentahydrate, and this crust interferes with loss-on-drying determination and with screw feeder accuracy. Transfer of bulk material should occur through flexible screw conveyors with polished stainless steel contact surfaces; carbon steel components are unsuitable because selenite dust combined with condensation can initiate pitting corrosion at welded joints. Operators should verify the seal integrity of intermediate bulk containers and use dry-air sweeping or nitrogen padding in silo day bins when ambient dew point exceeds 15 °C. Dust extraction on bag dump stations must be designed for toxic metal compounds, with prefilters and HEPA filtration. Wastewater from equipment cleaning is classified as selenium-bearing; it must be diverted to permitted treatment rather than floor drains. In areas with high humidity, the powder should be pre-dried at 70–80 °C for 2 h before use only if the process cannot tolerate the water of hydration formed during storage.
Moisture uptake is reversible at low hydration levels, but the resulting surface hydration changes flowability and bulk density, leading to feeder calibration drift. A gravimetric twin-screw feeder set for 250 g/min may lose 4–6% of effective selenium output after 8 h in an unconditioned room if the discharge hopper is not sealed and the product has formed agglomerates on the screw. The agglomerates bridge the feed hopper, producing intermittent feed and introducing selenium variability into the final premix. Operators should use hopper agitation or screw features appropriate for cohesive powders, and verify feeder output by catch-weight tests every 30 min for the first 2 h of a production run.
Acidification of sodium selenite with hydrochloric acid precipitates selenium dioxide after intermediate selenious acid formation. The anhydrous grade reduces water introduced into the reaction vessel by 34.2% relative to pentahydrate on a molar basis, which is significant when process solvent capacity is fixed. In a glass-lined reactor, a 20% solution of sodium selenite anhydrous can be acidified to pH 2.0 with 32% hydrochloric acid, yielding crystalline SeO2 that is recovered by filtration. The mother liquor retains sodium chloride and unreacted selenium species; the selenium content of the mother liquor is measured before discharge to comply with aqueous emissions limits. Published data for this specific configuration is limited at smaller scale; pilot development should establish the exact addition rate, cooling capacity, and filterability of the precipitate.
The lower water content also influences the thermal profile of the reaction. Hydrate water from pentahydrate can absorb some heat of dissolution, masking the exotherm of acidification; the anhydrous form causes a sharper temperature rise when concentrated acid is added. A cooling jacket with brine at −10 °C or controlled dosing of 32% HCl at 2.0 L/min per 100 L batch maintains the reaction temperature below 40 °C and prevents premature decomposition of selenious acid to selenium dioxide fumes. Oxidation-reduction potential is monitored at the end of acidification; the endpoint is accepted when the redox potential remains stable for 5 min, indicating complete precipitation of the selenium dioxide fraction.
Compared with sodium selenate, sodium selenite carries selenium in the +4 oxidation state and exhibits different redox behavior in glass melting, where the selenite ion is reduced to the elemental state to produce pink-to-red color in selenium ruby glasses. Sodium selenate requires a stronger reducing environment and higher addition rates for the same chromatic effect. In feed formulations, the selenite form is widely authorized as an inorganic selenium source under FDA 21 CFR 573.920; sodium selenate may be authorized in other jurisdictions but is less commonly used in dry premixtures because of its higher solubility and different particle-surface behavior. Organic selenium sources such as selenomethionine and selenized yeast differ in metabolic pathway and tissue accretion; they are not direct substitutes in mineral premix calculations, and their activity is expressed in standardized feeding trials rather than as sodium selenite equivalents. Selenium dioxide is a volatile acidic oxide with a higher inhalation risk and is not suitable for direct feed supplementation; the anhydrous sodium salt provides a non-volatile solid form that can be handled in open-mouth packaging with dust extraction.
Glassmakers using sodium selenite anhydrous 98% for decolorizing or selenium ruby glass employ batch addition rates in the range of 0.01–0.1% by sand mass, with the exact rate determined by redox state, cullet ratio, and iron or chromium content. The anhydrous material is selected because it does not introduce five moles of water per mole of selenium, which can shift furnace humidity and batch free moisture. In continuous furnaces operated above 1,350 °C, selenium volatilization is controlled by reducing agents and tracked through baghouse dust analyses using EPA SW-846 Method 7742 or equivalent selenium speciation methods. Published data for specific furnace configurations is limited because glass color formulations are proprietary; therefore, pilot melt trials with the exact cullet ratio are required before full production use.