| HS Code | 273801 |
| Product Name | Caustic Soda 25KG |
| Chemical Name | Sodium Hydroxide |
| Chemical Formula | NaOH |
| Cas Number | 1310-73-2 |
| Molecular Weight | 40.00 g/mol |
| Appearance | White solid flakes, pellets, or beads |
| Purity | 98-99% |
| Packaging | 25 kg bag |
| Density | 2.13 g/cm³ at 25°C |
| Melting Point | 318 °C |
| Boiling Point | 1,388 °C |
| Solubility In Water | Soluble, exothermic; 111 g/100 mL at 20°C |
| Ph 1 Percent Solution | ~13 |
| Hazard Class | Corrosive; UN 1823 |
As an accredited Caustic Soda 25KG factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Supplied in 25 kg quantities: sealed polypropylene woven bags with PE inner liner for moisture resistance and safe transport. |
| Container Loading (20′ FCL) | 20′ FCL loading: caustic soda in 25kg bags, palletized, shrink-wrapped, and secured for safe, efficient transport. |
| Shipping | Caustic Soda 25KG is shipped in UN-approved, moisture-resistant bags or drums. It must be labeled as corrosive, Class 8 hazardous material. Transport complies with ADR/IMDG regulations, with proper segregation from acids and reactive metals. Handling requires protective gear to prevent skin and eye contact. Ensure dry, ventilated conditions to avoid damage. |
| Storage | Store Caustic Soda 25KG in a cool, dry, well-ventilated area, away from moisture, acids, and incompatible metals. Keep containers tightly sealed and elevated on pallets to prevent contact with damp floors. Use original packaging or compatible plastic drums, and ensure spill containment measures are available. Always wear appropriate PPE when handling. |
| Shelf Life | Shelf life is approximately 5 years when stored sealed in a cool, dry place, protected from moisture and air contamination. |
Bayer process digestion consumes solid sodium hydroxide continuously as bauxite dissolves in hot pregnant liquor. A 25 kg bag charge is commonly discharged into a 316L stainless steel dissolution vessel containing spent liquor at 80–90°C. The dissolution exotherm of 44.5 kJ/mol is removed by jacket cooling before the makeup stream enters the mill caustic header. Digestion of gibbsitic bauxite operates at 140–150°C, whereas boehmitic feed demands 240–260°C. Caustic concentration in the circulating liquor is maintained at 180–240 g/L Na₂O. Reactive silica consumes caustic through desilication precipitation. Bauxite with reactive silica above 6 wt% typically raises caustic demand to 100–150 kg NaOH per 1,000 kg smelter-grade alumina. Red mud washing circuits recover entrained caustic, but sodalite-bound sodium loss remains irreversible. Centrifugal pumps with hard iron wetted parts are standard on red mud transfer. The caustic makeup stream itself is handled in 316L or lined carbon steel because unlined carbon steel is not selected for continuous high-caustic slurry service at digestion temperature. The resulting smelter-grade alumina is tested by ISO 2926:2013 for particle size distribution and ISO 806:2004 for loss on ignition before reduction cell delivery.
Bauxite batch-to-batch variation in reactive silica can shift caustic demand by 15–20%. The mill laboratory adjusts daily charge according to X-ray fluorescence analysis of the ground bauxite. Desilication before digestion is run at 95–105°C for 6–10 h when reactive silica is high. Lime addition in the digester at 2–4 wt% of dry bauxite precipitates calcium silicate and recovers part of the caustic from desilication products. Lime overdosing, however, raises red mud solids and reduces alumina extraction through sodalite formation. A direct addition of solid NaOH from 25 kg bags into the bauxite slurry is avoided because local caustic concentration peaks can gelatinise fine bauxite particles and lower digestion yield. The dissolved caustic stream is instead fed under density control into the pregnant liquor loop at a point downstream of slurry preheating. This keeps the digestion charge stable and avoids unintended precipitation in pipes when spent liquor temperature falls below 60°C.
White liquor is prepared by dissolving solid NaOH from 25 kg bags into demineralised water at 40–50°C and mixing with recovered smelt-derived Na₂S. The effective alkali charge is reported as Na₂O on oven-dry wood. Typical hardwood cooks run at 14–18% Na₂O, while softwood cooks run at 18–22% Na₂O. Sulfidity is held at 25–35%. Digestion proceeds at 165–170°C with a liquor-to-wood ratio of 3.5:1–4.5:1. A 25 kg bag charge is not added directly to the digester. It is dissolved in a makeup tank and injected into the white liquor header under conductivity and density control. High effective alkali accelerates endwise cellulose degradation and lowers pulp viscosity below the ISO 5351:2010 limit of 800 mL/g in cupri-ethylenediamine. Low effective alkali leaves kappa number above 18 and increases rejects at the pressure screen. The cook is controlled by targeting h-factor rather than simple temperature-time measurement.
| Furnish | Effective alkali, % Na₂O | Sulfidity, % | H-factor | Kappa target |
|---|---|---|---|---|
| Softwood | 18–22 | 25–35 | 1,500–2,000 | 25–30 |
| Hardwood | 14–18 | 25–35 | 800–1,200 | 14–18 |
Subsequent oxygen delignification stages use an NaOH charge of 2.0–3.5% on oven-dry pulp at 90–100°C, oxygen pressure of 400–600 kPa, and stock consistency of 10–12%. Insufficient extraction-stage NaOH leaves dark shives and raises hydrogen peroxide demand in the following bleach stage. Excess NaOH lowers pulp viscosity below 700 mL/g by ISO 5351:2010. After the digester blow tank, the unbleached pulp is washed on a vacuum drum washer to reduce carryover black liquor. Residual alkali in the washer filtrate is recirculated to weak liquor storage. Makeup NaOH compensates for sodium losses in dregs, grits, and pulp washing rather than entering the recovery boiler smelt directly. The terminal bleached hardwood kraft pulp is controlled to kappa number <1 by ISO 302:2015 and brightness above 88% by ISO 2470-1:2016.
On cotton knit mercerisation lines, solid NaOH from 25 kg bags is dissolved to a 22% w/v solution in a jacketed mixing tank and held at 15–20°C. A padded application with dwell of 45–60 s under controlled weft tension is typical. Below 14% NaOH at 20°C, swelling is insufficient for full mercerisation. Above 24%, bath viscosity and caustic carryover increase the wash load. Hot water rinsing at 80°C removes alkali from the fibre. Neutralisation with 1–2 g/L acetic acid completes the restoration of the fabric surface pH. Mercerised cotton poplin is tested by AATCC TM 89-2017 for barium activity number, with typical values above 115. Open-width mercerisation on a stenter frame prevents cross-direction shrinkage. The applied tension raises fibre orientation and tensile strength. Residual NaOH is reduced to below pH 8.0 before reactive dyeing to avoid dye hydrolysis.
Caustic soda is metered into the oil phase as a 30–35% w/w aqueous solution prepared from 25 kg bags in a separate dissolving tank. The required NaOH mass is calculated from saponification value. A 1,000 kg charge of palm oil with SV 198 mg KOH/g demands 141.2 kg NaOH theoretical, based on 198 × 40 / 56.1. A process excess of 0.3–0.5% NaOH drives the reaction to completion. Free alkali in finished soap noodles is controlled to 0.05–0.10% w/w by ASTM D460-91(2014). Batch kettle saponification operates at 80–85°C for 6–10 h under slow sweep agitation. Continuous saponification lines run at 120–130°C under 2–3 bar back pressure and reduce reaction time to 1–2 min. Solid caustic must not be added directly to hot oil. Local over-concentration forms soap curds with high free alkali pockets. The resulting soap noodles carry moisture at 12–14% and total fatty matter above 76%. They are used as feedstock for bar soap extrusion. Equipment for caustic dissolution and soap processing is stainless steel or nickel alloy; zinc, aluminium, and galvanised surfaces are not used at 80°C.
Across sodium hypochlorite manufacture, a cold sodium hydroxide solution absorbs chlorine gas at a maintained excess alkalinity. A 25 kg bag is dissolved in chilled demineralised water to 15% w/w NaOH and fed through a plate heat exchanger into a counter-current chlorination column. Chlorine is metered at 1.128 kg NaOH per 1 kg Cl₂ stoichiometrically. The actual line holds final excess NaOH at 0.2–1.0% w/w to stabilise the resulting sodium hypochlorite at pH 12.5–13.0. Reactor temperature is kept at 15–20°C; above 30°C chlorate formation increases. The column is fabricated from titanium or PTFE-lined FRP because hypochlorous acid attacks stainless steel at low pH. Terminal bleach with 12–15% available chlorine is tested under EN 901:2013 for chlorate content and alkali reserve. Acid addition to the finished hypochlorite is avoided because chlorine gas evolution occurs rapidly below pH 11.0.
Neutralisation of spent hydrochloric acid is designed on 0.9125 kg HCl consumed per 1 kg NaOH. For sulphuric acid the ratio is 1.225 kg H₂SO₄ per 1 kg NaOH. A 25 kg bag is diluted to 5–10% w/w in a polypropylene day tank and injected by a positive displacement metering pump into a flash mixing chamber. pH control with dead band ±0.1 pH units ramps dosing before the neutralised stream enters a retention tank sized for 15–30 min residence time. For potable water pH adjustment the solid caustic meets EN 896:2022 and NSF/ANSI/CAN 60. Terminal effluent is released after pH is confirmed at 6–9 and settled solids are removed.
Lye peeling of tomatoes and root vegetables uses 1–5% w/w NaOH at 60–80°C with contact of 30–120 s, followed by high-pressure water sprays to detach skin and wash residual alkali. Pretzel dipping immerses dough pieces in 1–2% NaOH at 85–95°C for 10–20 s, gelatinising surface starch before baking. Use in food is limited to current good manufacturing practice under FDA 21 CFR 184.1763. A 25 kg bag of food-grade flake must be dissolved in a closed stainless steel vessel and filtered before the peel bath. Residual peel solution is neutralised before discharge, and final food surfaces are washed to neutral pH before further processing.
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Caustic Soda 25KG is an anhydrous sodium hydroxide material supplied as white flakes or pearl granules in sealed 25 kg woven polypropylene bags with internal polyethylene liners. The material is identified by CAS 1310-73-2 and EC 231-659-4, with transport classification UN1823, packing group II. The standard industrial grade carries a minimum sodium hydroxide mass fraction of 99.0% and is manufactured to GB/T 209-2018 for solid industrial sodium hydroxide. Model designations on the bag label are batch-specific and may include grade identifiers such as IS-I, IS-II, or IS-III; the 25KG reference identifies the packaged mass rather than a distinct chemical grade. The packaging format is intended for point-of-use dissolution in batch tanks, manual or semi-automatic feed hoppers, and reformulation work where full bulk liquid handling infrastructure is not present. Because the material is highly hygroscopic and deliquescent, the bag liner must remain sealed until dosing; moisture ingress produces surface caking and alters the free-flowing character of the flake.
| Parameter | Specification | Reference basis |
|---|---|---|
| Sodium hydroxide, NaOH | ≥99.0% w/w | GB/T 209-2018, solid industrial grade |
| Sodium carbonate, Na₂CO₃ | ≤0.5% w/w | GB/T 209-2018 |
| Sodium chloride, NaCl | ≤0.03% w/w | titrimetric/ICP-OES routine |
| Iron as Fe₂O₃ | ≤0.005% w/w | colorimetric/ICP-OES routine |
| Water-insoluble matter | ≤0.05% w/w | gravimetric |
| Heavy metals as Pb | ≤0.001% w/w | GB/T 209-2018 trace limits |
Dissolution of the solid material into water is strongly exothermic. The heat of solution for anhydrous NaOH is approximately −44.5 kJ/mol at infinite dilution. In agitated stainless steel tanks, the addition sequence should be caustic to water, not water to caustic, to avoid localized boiling and splatter. A 50% w/w stock solution has a density of about 1.53 g/cm³ at 20°C and a viscosity below 2.5 mPa·s at 20°C. Published data for the heat-transfer coefficient of the specific bag-empty hopper configuration is limited. Production-scale blending rooms typically install bag slitting stations with local dust extraction and maintain storage relative humidity below 60% to limit caking. In many manufacturing lines, a rotary screw feeder with variable frequency drive transfers the flake into a high-shear eductor; residual carbonate content below 0.5% w/w reduces scaling on the eductor nozzle after repeated batches. The bulk density of the flake product is generally in the range of 0.9–1.2 g/cm³, which must be considered when sizing silo or hopper load cells.
The primary distinction is transport and inventory form rather than active alkalinity after dilution. A 50% membrane-grade liquid eliminates dissolution exotherm at the use point but carries approximately 0.5 t of water per tonne of product, increasing freight and storage volume. The solid 25 kg format stores at roughly 0.9–1.2 g/cm³ bulk density and allows fresh dissolution strength to be set per batch. Liquid systems allow magnetically coupled metering pumps to deliver exact stoichiometry to continuous processes, while dry systems require batch dissolution or a fully enclosed screw feeder. For continuous dosing loops, the dry solid is less convenient than liquid; for intermittent or remote pH correction, the packaged solid avoids heated storage tanks and recirculation lines. The dry material is not a direct substitute where alkalinity must be added without increasing tank volume.
| Attribute | Caustic Soda 25KG | 50% liquid membrane-grade caustic soda |
|---|---|---|
| NaOH content | ≥99.0% w/w | 50% w/w |
| Water transport mass | ≤0.5% w/w | 50% w/w |
| Feed equipment | rotary screw feeder, eductor, batch dissolve | PTFE diaphragm or peristaltic metering pump |
| Freezing point risk | not applicable | heated tanks required below 12°C |
| Transport class | UN1823, PG II | UN1824, PG II |
In alumina refining, anhydrous sodium hydroxide is dissolved into process condensate to maintain the Bayer digestion liquor caustic concentration. The dosing target is commonly expressed as 200–280 g/L Na₂O(caustic) in mill liquors, with digestion temperatures from 140°C to 260°C depending on bauxite type. Carbonate introduced with solid NaOH participates in sodium aluminium carbonate scale formation on heat-transfer tubes; therefore a sodium carbonate limit of ≤0.5% w/w is process-critical for low-temperature digestion units. In high-temperature tube digesters, scale control also relies on continuous causticisation with lime. No single product specification eliminates scale entirely; operational boundaries include maintaining free alkali to alumina ratio within the range 1.2–1.8 mol/mol and limiting residence time to prevent nonproductive desilication product formation.
In kraft pulping, the solid caustic is used as make-up alkali in white liquor systems. The material is added to dissolving tanks equipped with high-torque agitators, and the resulting alkaline solution is pumped into green liquor lines. Carbonate content in make-up caustic below 0.5% w/w reduces recausticizing load and calcium carbonate sludge generation in the slaker. Chloride accumulates in the liquor loop if make-up alkali chloride content exceeds 0.03% w/w; that threshold is a standard batch acceptance criterion for mills operating high-solids recovery boilers. Published data for specific carry-out of chloride into the recovery boiler with this package configuration is limited.
Mercerisation baths are prepared by dissolving dry caustic to 18–28% w/w NaOH. The solution density at 20°C ranges from approximately 1.19 g/cm³ at 18% to 1.31 g/cm³ at 28% w/w. Uniform fibre swelling depends on temperature control below 20°C and on low levels of carbonate and chloride that otherwise create localised ionic strength differences. In continuous ranges, the caustic bath is fitted with circulation pumps and plate coolers to remove both dilution heat and the exothermic heat of cellulose swelling. High-purity solid product permits the same bath to be reused for multiple runs, with carbonate build-up from atmospheric CO₂ absorption requiring periodic purge. Sodium carbonate in the bath buffers caustic activity and produces differential swelling if the concentration gradient across the fabric web exceeds ±2°Bé. Residual iron above 0.005% w/w as Fe₂O₃ can deposit as iron hydroxide in oxygen-rich baths, causing pale-yellow fibre staining and reduced dye uptake in subsequent reactive dyeing.
On-site sodium hypochlorite generation uses the 25 kg solid to prepare a 10–15% w/w NaOH solution for chlorine absorption. The absorption column is typically a packed tower with countercurrent scrubbing, where chlorine gas reacts to form sodium hypochlorite and sodium chloride. The reactor temperature must remain below 25°C to suppress sodium chlorate formation. Excess alkalinity is maintained at 0.1–0.5% w/w NaOH in the product liquor, measured by titration after recirculation through a heat exchanger. In continuous bleach plants, the dry material is dissolved in a day tank equipped with PTFE-lined impellers; titanium or Hastelloy C-276 wetted parts are used downstream because hypochlorite solutions can promote pitting of 316L stainless steel.
In petroleum refining, caustic is dissolved to 5–15% w/w and injected into crude or distillate streams to neutralise naphthenic acids. The treated stream then passes through a desalter or separator. Fresh caustic must meet chloride specifications because chlorides entering the crude unit can hydrolyse to hydrochloric acid in the presence of water and promote overhead corrosion. A chloride limit of ≤0.03% w/w in the dry product translates to low salt accumulation in the desalter brine. Inline static mixers contact the alkali with the hydrocarbon, and injection rate is controlled by online sodium and pH analysers downstream of the coalescer. Spent caustic contains sodium naphthenates and sulphides and is not compatible with direct biological treatment at high load. Published data for this specific package configuration in spent caustic oxidation is limited.
Liquid potassium hydroxide is often used to produce potassium soaps and certain fatty acid salts. When the 25 kg dry sodium hydroxide is selected as an alternative, the stoichiometry changes because the saponification equivalent is 40.0 g NaOH per mole fatty acid versus 56.1 g KOH per mole. The resulting sodium soap has a higher Krafft point and lower water solubility at ambient temperature, which affects the formulation of liquid hand soaps and cutting fluids. The reaction is carried out at 70–90°C with agitation sufficient to maintain emulsion contact. Residual alkalinity after saponification is controlled by acid number and pH targeting, not by excess caustic addition. Slow addition of dry solid through a screw feeder into heated oil avoids gel formation that occurs if the entire alkali charge is added at once. Published data for the exact effect on soap crystal habit at this package size is limited.
In municipal water treatment, the product is dissolved to 5–10% w/w for pH adjustment and hardness precipitation. Dosing is regulated to maintain effluent pH within discharge permit boundaries, commonly 6.0–9.0. Compared with sodium carbonate, the product provides a stronger alkalinity swing per unit mass but has no buffering capacity, which requires tighter feedback control. In clean-in-place operations, dry caustic is mixed to 2–4% w/w at 60–80°C and circulated through plate heat exchangers. The low chloride grade avoids stress corrosion cracking of 316L stainless steel surfaces when the cleaning cycle exceeds 80°C; standard operational boundaries recommend chloride below 0.03% w/w in the diluted bath. The caustic solution is not compatible with aluminium parts, zinc coatings, or glass-lined vessels when the temperature exceeds 50°C.
The product liberates heat on contact with water and reacts violently with strong acids, aluminium metal in moist conditions, and halogenated solvents under specific temperature and pressure excursions. Storage must be isolated from ammonium salts and organic peroxides. In the event of bag rupture, vacuum recovery with HEPA-filtered equipment is preferred over water flushing inside occupied areas because the resulting alkaline film poses a secondary slip and corrosion hazard.
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