| HS Code | 834740 |
| Chemical Name | Sodium Hydroxide |
| Chemical Formula | NaOH |
| Cas Number | 1310-73-2 |
| Molecular Weight | 40.00 g/mol |
| Appearance | White solid flakes or pearls |
| Purity | ≥99% (industrial grade) |
| Form | Solid flakes/prills |
| Packaging | 50 kg bag (woven polypropylene with inner PE liner) |
| Density | 2.13 g/cm³ at 25°C |
| Melting Point | 318 °C (604 °F) |
| Boiling Point | 1,388 °C (2,530 °F) |
| Solubility In Water | 111 g/100 mL at 20°C |
| Ph 1 Aqueous Solution | Approximately 13 |
| Hygroscopic | Yes, absorbs moisture from air |
As an accredited Caustic Soda 50kg factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Caustic soda 50 kg is packed in sturdy, moisture-proof woven plastic bags, 40 bags per pallet, protecting the chemical during transport and storage. |
| Container Loading (20′ FCL) | Loading 50kg bags of Caustic Soda into a 20-foot FCL, ensuring secure palletization and proper ventilation for safe transport. |
| Shipping | Caustic soda, 50 kg bags, shipped as UN1823 Sodium hydroxide, solid, Class 8, Packing Group II. Ensure sealed, dry, corrosive-labeled packaging, palletized and secured. Store away from acids and moisture. Use ventilated containers; handlers require PPE and spill containment. |
| Storage | Store Caustic Soda 50kg in a cool, dry, well-ventilated area, away from moisture, acids, and incompatible chemicals. Keep bags tightly sealed and elevated on pallets to prevent water contact. Use corrosion-resistant containers and ensure no leakage. Limit access to trained personnel, post warning signs, and have emergency eyewash and neutralization supplies nearby. |
| Shelf Life | Shelf life is indefinite when stored sealed, dry, and uncontaminated. Avoid moisture and air exposure to maintain quality. |
In alumina refineries processing diasporic bauxite, 50 kg caustic soda bags are discharged through a bag dump hopper with wet-dust suppression into a heated make-down tank using clarified wash water; the dissolution exotherm is controlled to keep liquor below boiling, producing digestion liquor with 220–260 g/L Na₂O caustic before injection into single-stream autoclaves rated at 3.5–6.0 MPa and operated at 240–270 °C. Caustic soda does not merely supply free alkalinity; it dissolves aluminium trihydroxide into pregnant sodium aluminate liquor while reactive silica is converted into sodalite-type desilication products that irreversibly bind sodium oxide. Refinery mass balances commonly report caustic consumption of 100–150 kg NaOH per metric ton of smelter-grade alumina for diasporic ore, with the lower interval achieved only when lime is dosed before digestion and when red mud washing recovers free soda from residue. Batch-to-batch variance in bagged caustic soda active content can shift liquor molar ratios by approximately ±0.5%, making online titrators on high-pressure injection lines necessary for stable digestion. Alumina quality compliance is anchored to ISO 2927:2005 for smelter-grade alumina, and REACH registration covers the unloading of bagged sodium hydroxide, liquor preparation, and workplace exposure. Downstream processing comprises sand removal, red mud settling with flocculants, security filtration, seeded precipitation of aluminium trihydroxide, and calcination at 950–1,050 °C. Terminal product types include calcined smelter-grade alumina for Hall-Héroult reduction cells, fine alumina hydrate for flame retardants, and alumina trihydrate for catalyst supports.
| Bauxite mineralogy | Liquor Na₂O caustic | Digestion temperature | Digestion pressure | Caustic consumption |
|---|---|---|---|---|
| Gibbsitic | 140–160 g/L | 125–145 °C | 0.3–0.5 MPa | 60–90 kg NaOH/t Al₂O₃ |
| Boehmitic | 180–220 g/L | 200–240 °C | 2.0–3.5 MPa | 80–120 kg NaOH/t Al₂O₃ |
| Diasporic | 220–260 g/L | 240–270 °C | 3.5–6.0 MPa | 100–150 kg NaOH/t Al₂O₃ |
Continuous kraft digesters receiving softwood chips with a kappa target of 26–30 mL/g are operated with an effective alkali charge of 16–20% Na₂O on oven-dry wood and sulfidity of 30–35%; the make-down of 50 kg caustic soda bags into white liquor involves controlled dissolution in water at 60–70 °C before mixing with recovered smelt to avoid localized boiling. In oxygen delignification and Eop extraction, sodium hydroxide is dosed at 1.0–1.5 wt% on oven-dry pulp, with the Eop tower maintained at 75–85 °C and 0.4–0.6 MPa oxygen partial pressure. The process sequence includes chip steaming, impregnation, co-current and counter-current cooking zones, blow tank dilution, screening, oxygen delignification, Eop treatment, and multi-stage wash presses with countercurrent washing to recover residual alkali for black liquor evaporators. Residual effective alkali in washed brownstock is maintained at 8–12 g/L Na₂O to prevent lignin precipitation during washing; a charge below 16% effective alkali increases rejects and raises kappa deviation, while a charge above 20% accelerates carbohydrate degradation and reduces pulp yield. Compliance for bleached chemical pulp production is governed by the EU BAT conclusions under Commission Implementing Decision 2014/687/EU, with AOX discharge testing carried out according to ISO 9562:2004 and kappa testing according to ISO 302:2015. Terminal products include bleached softwood kraft pulp for tissue, sack kraft, and bleached hardwood market pulp for coated printing paper.
In municipal disinfection systems, 50 kg caustic soda bags are dissolved with softened water to a 25% NaOH working solution and metered into the recirculation loop of a chlorine absorption tower; the reaction of chlorine gas with sodium hydroxide to form sodium hypochlorite requires 0.564 t NaOH per metric ton of Cl₂ on a stoichometric basis. Commercial sodium hypochlorite generation is controlled to a final excess alkalinity of 0.2–0.5 wt% NaOH and a pH above 12.5 to suppress chlorate formation and maintain available chlorine stability. The downstream process typically includes a vacuum chlorinator, caustic scrubber, heat exchanger to keep liquor below 30 °C, and fiberglass-reinforced plastic storage tanks with PVC piping. For direct potable water pH adjustment, caustic soda is metered at 1–5 mg/L as 25% NaOH to maintain a Langelier Saturation Index of +0.2 to +0.5. Dissolution into hard water without softening precipitates calcium carbonate and reduces scrubber packing efficiency. Potable water treatment chemicals in this application are required to conform to NSF/ANSI/CAN 60 and AWWA B501-19 for sodium hydroxide, while disinfection byproducts are managed under WHO Guidelines for Drinking-water Quality. Terminal product types include 12.5–15 wt% trade-strength sodium hypochlorite for drinking water disinfection, cooling water biocide feeds, and wastewater effluent chlorination-dechlorination skids.
When coconut oil or palm kernel oil with a saponification value of 250–264 mg KOH/g is charged to a jacketed saponification kettle, the stoichometric sodium hydroxide requirement is 140–185 kg NaOH per metric ton of refined oil after accounting for 98% active content and a controlled excess. Caustic soda from 50 kg bags is dissolved to 32–38% NaOH and fed into the kettle at 70–90 °C with an anchor agitator; completion is determined by titration of free caustic alkali against ISO 684:1974. The process sequence includes saponification, glycerine liquor separation, neat soap washing, vacuum drying, and extrusion into noodles; glycerine recovery uses ion exchange and evaporation to reach 99.5% refined glycerine. Excess free alkali above 0.5% in neat soap causes darkening and rancidity in unsaturated oil systems. EU Detergent Regulation 648/2004 governs the finished detergent surfactant content and labelling, while REACH covers the industrial handling of sodium hydroxide in soap plants. Terminal product types are high-titre soap noodles, laundry soap bars, and low-salt toilet soap base with free alkali held at 0.4–0.5% NaOH and moisture below 12%.
For cotton yarn entering a chain mercerizer at 15–20 °C, caustic soda solution is maintained at 18–24°Bé, equivalent to 195–275 g/L NaOH, with a low-foam wetting agent dosed at 3–5 g/L to ensure uniform penetration. Tension mercerization under tenter-frame control converts cellulose I to cellulose II and raises yarn tenacity by 15–25%, while countercurrent wash recovery reduces alkali consumption per tonne of fabric. The downstream process includes impregnation at 45–60 s dwell time, a controlled hot-water washing cascade, acid neutralization with acetic acid, and final extraction to residual alkali below 0.05% on fabric as measured by aqueous extract pH per ISO 3071:2005. Inadequate caustic recovery below 90% raises salt loading in wastewater and increases neutralization acid demand. Compliance for textile auxiliaries and residues aligns with ZDHC MRSL 3.1 and OEKO-TEX Standard 100. Terminal products are mercerized cotton yarn, high-luster woven sheeting, and uniform-dyeing cotton knitwear.
At reactor temperatures of 90–110 °C, aluminium trihydrate is digested with 50 kg bagged caustic soda solution to produce liquid sodium aluminate for phosphorus precipitation in wastewater. The stoichometric caustic demand is 513 kg NaOH per metric ton of Al(OH)₃, based on the reaction Al(OH)₃ + NaOH → NaAlO₂ + 2H₂O; commercial batching maintains free NaOH at 5–15 g/L to prevent gelation and ensure filterability. The downstream production process uses a jacketed stainless-steel reactor with turbine agitation for 1–2 h, followed by dilution with softened water to 26–45% sodium aluminate solids, cooling, and transfer to HDPE storage. Phosphorus precipitation dose is typically 1.5–2.5 mol Al per mol total phosphorus at pH 6.5–7.5, with simultaneous addition of polymer for floc settling. Overdosing free NaOH above 15 g/L can cause post-precipitation of aluminium hydroxide at lower pH. Compliance with drinking water treatment coagulant specifications is governed by ANSI/AWWA B405-16 for sodium aluminate, while REACH registration covers the alkaline reaction mass. Terminal product types include liquid sodium aluminate for phosphate abatement in municipal wastewater, sulfide control in collection systems, and coagulation aid for low-alkalinity surface water.
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Caustic Soda 50kg is a packaged anhydrous form of sodium hydroxide, supplied as white deliquescent flakes or pearls with a nominal net mass of 50 kg per laminated high-density polyethylene/woven polypropylene bag. The commercial model code is supplier-assigned and commonly identifies form, grade, and package mass; this document uses the functional designation Caustic Soda 50kg for the 99.0% solid bagged product. The substance is identified by formula NaOH, molar mass 40.00 g/mol, CAS 1310-73-2, EC 215-185-5, UN 1823, hazard class 8, packing group II. The package is used in alumina refining, kraft pulp processing, saponification, water treatment, textile mercerizing, and industrial neutralization. The solid format contains no vapor pressure and does not require heat-traced storage such as that used for 50% liquid sodium hydroxide, but it introduces controlled dust exposure, moisture uptake, and exothermic dissolution as the primary process boundaries. The product differs from smaller bags principally in unit-load handling and changeover frequency, while remaining chemically identical to other solid NaOH grades of the same assay.
A 50 kg solid package delivers approximately 49.5 kg of NaOH equivalent per bag at 99.0% assay, while 50 kg of a 50% liquid stream delivers 25 kg NaOH and 25 kg water. The solid therefore reduces freight mass for the same alkali duty by roughly 50%, but it transfers the cost and control burden from tanker unloading and heated storage to dry bag slitting, screw conveying, and dust extraction. Relative to 25 kg bags, the 50 kg pack reduces the number of bag lifts per tonne from 40 to 20; however, the peak manual-handling mass increases, and repetitive lift controls such as those described in ISO 11228-1:2021 must be applied in manual charging rooms. Table 1 compares the solid 50 kg pack with liquid 50% and the smaller solid bag.
| Parameter | 50 kg solid NaOH | 50% liquid NaOH | 25 kg solid NaOH |
|---|---|---|---|
| NaOH mass per 100 kg product | ≥ 99.0 kg | 50.0 kg | ≥ 99.0 kg |
| Water content | ≤ 0.5% | 50% | ≤ 0.5% |
| Freezing point | Solid; no freeze point | Approximately 12°C | Solid; no freeze point |
| Delivery equipment | Bag slitter, hopper, screw feeder | Tanker or IBC, metering pump, heat tracing | Manual bag charging |
| Bag lifts per tonne | 20 | 0 | 40 |
| Heat of solution at infinite dilution | -44.5 kJ/mol | Dilution exotherm | -44.5 kJ/mol |
| Storage dependency | Dry, ≤ 50% RH | Heat-traced tank below 15°C | Dry, ≤ 50% RH |
The replacement of liquid with solid is most justified where winter ambient temperatures fall below 15°C and liquid 50% lines would require continuous heat tracing. In contrast, liquid remains preferable where the dissolver is already designed for pump transfer and where operators are not available for bag handling at the required dosing cadence. The solid product is not equivalent to flake or pearl material sourced from different electrolytic cells because trace chloride and iron can vary; the package size itself does not alter the NaOH assay, but it changes the exposure profile during charging.
The 50 kg solid pack differs from a 25 kg pack primarily in unit-load handling and exposure time, not in assay. For the same bag opening frequency, a 50 kg bag exposes twice the product mass when opened; therefore the charging station should be sized to consume a full bag within one shift at high humidity. Compared with 1,000 kg flexible intermediate bulk containers, the 50 kg bag has higher labour demand but allows more precise lot control and smaller warehousing increments, and the FIBC is usually reserved for continuous plants with dedicated hoist and central dust collection.
In alumina refining, the Bayer process digests bauxite in a sodium aluminate liquor where free NaOH is maintained in the range 180–250 g/L Na2O equivalent; the 50 kg solid is dissolved in weak wash water and injected into side-stream caustic make-up circuits. In kraft pulp cooking, the solid is combined with sodium sulfide to form white liquor, and effective alkali is controlled at 15–25 g/L NaOH equivalent for typical softwood kappa targets. Solid addition to a slaker or dissolver is sequenced so that the localized exotherm does not create boiling at the solid-liquid interface; water-to-caustic mass ratio is normally maintained above 1.2:1. Published data for specific Bayer digestion or delignification yield differences between solid and liquid make-up is limited, but the solution-phase species is identical once dissolution is complete.
The merchant specification for 50 kg solid caustic soda is controlled by alkalimetric titration and photometric methods. The product is frequently supplied against GB/T 209-2018 for solid industrial sodium hydroxide, and the analytical methods are aligned with ASTM E291-18. Sodium carbonate is the principal surface contaminant because atmospheric carbon dioxide reacts with exposed NaOH; carbonate contributes to scaling in dissolver jackets and reduces the yield of saponification batches. Chloride and iron are critical in pulp and rayon operations where iron can stain cellulose or catalyze peroxide decomposition. Table 2 lists representative limits for a 99% solid grade.
| Parameter | Limit | Test method |
|---|---|---|
| Sodium hydroxide (NaOH) | ≥ 99.0% by mass | ASTM E291-18 |
| Sodium carbonate (Na2CO3) | ≤ 0.8% by mass | ASTM E291-18 |
| Sodium chloride (NaCl) | ≤ 0.05% by mass | ASTM E291-18 |
| Iron as Fe2O3 | ≤ 0.005% by mass | ASTM E291-18 / GB/T 209-2018 |
| Sodium sulfate as Na2SO4 | ≤ 0.03% by mass | ASTM E291-18 |
| Water | ≤ 0.5% by mass | Gravimetric, ASTM E291-18 |
When the product is supplied as pearls, the same analytical limits apply, but the lower surface area per unit mass reduces the rate of carbon dioxide uptake compared with flakes. Solid sodium hydroxide produced by diaphragm cell, membrane cell, or mercury cell routes can exhibit different trace chloride profiles; membrane-cell grade often reports lower NaCl than diaphragm-cell grade. The certificate of analysis should be reviewed against the specific standard named on the product datasheet, and sampling should follow the producer’s documented procedure. Where a validated internal specification requires tighter iron control, a separate lot qualification is necessary.
Conversion to 50 kg bags on a semi-automated dosing line requires verification of bag-cutting equipment, hopper geometry, and feed-screw torque. Loss-in-weight feeders with vertical agitators and flexible polyurethane hoppers are commonly specified because the solid’s angle of repose and compaction behavior differ by flake versus pearl morphology. A 50 kg bag increases the mass per bag-change event, so the dosing skid must be designed for fewer but heavier bag placements; mechanical lift assists are used when bag-change frequency creates manual-handling strain. The dust generated during bag slitting is controlled by a local exhaust ventilation hood at the sack tip, because sodium hydroxide dust is corrosive to unprotected conduit and bearings.
The heat of solution of anhydrous NaOH in water at infinite dilution is approximately -44.5 kJ/mol. For a final concentration of 25% NaOH, the adiabatic temperature rise from a 20°C initial water charge is sufficient to exceed 60°C; therefore continuous dissolvers are specified with external cooling or controlled addition to maintain a maximum bulk temperature of 80°C. Localized boiling at the solid-liquid interface is prevented by adding the solid below the liquid surface and maintaining a minimum impeller tip speed of 1.0–1.5 m/s. The dissolution vessel and transfer piping should exclude aluminium, zinc, tin, galvanized steel, and brass; carbon steel is acceptable for dry handling at ≤ 40% relative humidity and ambient temperature, while 304 stainless steel or EPDM-lined carbon steel is preferred for continuous wet service.
In boiler water treatment and municipal pH adjustment, the solid is dissolved to a 5–10% stock solution and injected into clarified water or boiler feedwater. The alkalinity contribution is based on one hydroxide equivalent per mole of NaOH, but practical dose depends on raw-water bicarbonate buffering; jar testing with the actual influent is required because published standard doses apply only to defined alkalinity values. For anion exchange regeneration, a 4–6% NaOH solution is drawn through the resin bed at 2–4 bed volumes per hour, and insoluble iron must be kept low to avoid resin fouling. The solid product used in potable or boiler applications is often supplied against ANSI/AWWA B501. The 50 kg pack reduces bag-change frequency in water treatment plants, but smaller packages may be preferred where chemical feed rooms have limited clear height or where dust extraction is not available.
Sodium hydroxide solid is strongly hygroscopic and reacts with atmospheric carbon dioxide to form sodium carbonate. Unopened 50 kg bags retain assay for 2–3 years when stored at ≤ 40°C and ≤ 50% relative humidity in sealed manufacturer packaging; opened bags should be reclosed and consumed within 24–48 hours if ambient humidity exceeds 60%. Bags are stored on pallets in a dry, covered area with no direct contact with concrete floors. Incompatible storage includes strong acids such as sulfuric or hydrochloric acid, ammonium salts, aluminum fines, and chlorinated solvents; contact with acids releases heat, while contact with ammonium salts can release ammonia. The product is non-combustible but corrosive to skin and eyes; PPE includes ANSI/ISEA Z87.1 eye protection, chemical-resistant gloves, and face shield.
For saponification of triglycerides, the solid is dissolved and metered into a jacketed reactor; the stoichiometric requirement is calculated from the oil’s saponification value. A fat charge with saponification value 190–200 mg KOH/g requires approximately 0.14–0.15 kg NaOH per kg oil, and the 50 kg bag supports batch records where dry caustic is dispensed from a closed sack tip. Residual free alkali is controlled to ≤ 0.05% in neat soap to limit skin irritation. Caustic soda is not interchangeable with caustic potash on a mass basis because KOH has molar mass 56.11 g/mol and supplies fewer hydroxide equivalents per kilogram; 1 kg NaOH supplies approximately 25.0 mol hydroxide, while 1 kg KOH supplies 17.8 mol. Relative to soda ash, 1 kg NaOH provides hydroxide alkalinity equivalent to approximately 1.325 kg Na2CO3 on an acid-neutralizing equivalent basis.
In cotton mercerizing, the 50 kg solid is dissolved to a caustic concentration of 19–23% NaOH by mass, and the yarn or fabric is treated under controlled tension. The solid grade should have low chloride and iron content to avoid fabric yellowing and uneven dye uptake. In linear alkylbenzene sulfonate production and methyl ester sulfonation, the solid is used as a stoichiometric neutralization agent; sulfonic acid neutralization is fast and exothermic, and the neutralization vessel is specified with a maximum skin temperature of 70°C. The 50 kg package permits direct charging through an enclosed sack tip with dust extraction, which is not feasible with bulk liquid deliveries and reduces bag-change operations compared with 25 kg manual charging in continuous neutralization lines.
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