| HS Code | 843611 |
| Chemical Formula | NaOH |
| Cas Number | 1310-73-2 |
| Appearance | White Flakes |
| Purity | 99% |
| Molecular Weight | 40.00 g/mol |
| Melting Point | 318°C (604°F) |
| Boiling Point | 1388°C (2530°F) |
| Density | 2.13 g/cm³ |
| Solubility In Water | Easily soluble, exothermic |
| Hs Code | 28151100 |
As an accredited Caustic Soda Flakes | China Top Caustic Soda Flakes Manufacturer & Factory factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaging: 25kg PP woven bags with PE inner liner, palletized and stretch-wrapped for safe export shipment. |
| Container Loading (20′ FCL) | Caustic soda flakes packed in 20' FCL containers, moisture-proof and palletized, ensuring safe, efficient transport from China. |
| Shipping | Our caustic soda flakes are shipped in secure, moisture-proof packaging to prevent caking and contamination. As a top Chinese manufacturer, we ensure prompt container loading, reliable documentation, and efficient global logistics. Trust our export experience for safe, timely delivery worldwide. |
| Storage | Store caustic soda flakes in a dry, cool, well-ventilated area inside sealed, moisture-proof containers. Keep away from water, acids, and incompatible chemicals. Use corrosion-resistant flooring and ensure proper labeling. Protect containers from physical damage and maintain controlled humidity to prevent caking and degradation. Always follow safety data guidelines. |
| Shelf Life | Shelf life: 2 years if stored in sealed, moisture-proof packaging. Keep away from humidity and air for best quality. |
Within Bayer circuits processing high-silica bauxite, caustic soda flakes are dissolved in carbon steel or nickel-lined tanks to a 50 wt% NaOH stock solution before injection into spent liquor; the dissolution station is equipped with external recirculation and cooling because heat of dilution can raise bulk temperature above 95 °C at flake addition rates above 3 t/h in a 20 m³ batch tank. Liquor preparation is covered by GB/T 209-2018 for solid sodium hydroxide, with NaOH assay ≥ 99.0 wt%, Na₂CO₃ ≤ 0.5 wt%, NaCl ≤ 0.05 wt%, and Fe ≤ 0.003 wt% specified to reduce digester heater scale and hydrogen-induced cracking. For monohydrate bauxite digestion, the Na₂O:Al₂O₃ molar ratio of the digestion liquor is maintained between 1.45:1 and 1.65:1, corresponding to caustic concentrations of 180–250 g/L Na₂O; soda loss to red mud typically falls between 75 kg and 150 kg caustic soda per tonne of alumina, depending on reactive silica content. The liquor is heated through live-steam shell-and-tube slurry heaters and digested in agitated autoclaves at 140–280 °C depending on gibbsite, boehmite, or diaspore feed. Red mud is separated in high-compression thickeners with flocculant dose 30–60 g/t dry mud; clarified aluminate solution is cooled in multi-stage flash tanks to 65–75 °C and seeded with fine gibbsite seed at 100–500 g/L in precipitation vessels. Gibbsite agglomeration is controlled by the liquor sodium oxide-to-alumina ratio 1.5:1 to 1.8:1 and cooling rate. Rotary calcination at 1,000–1,100 °C produces smelter-grade alumina with Al₂O₃ ≥ 98.5 wt%; chemical-grade alumina hydrate with BET surface area 40–80 m²/g is also produced for zeolite, catalyst, and flame retardant applications. Direct flake addition into hot spent liquor is avoided because localized pH above 14 causes caustic embrittlement in carbon steel.
Kraft digesters operating with softwood furnish at 150–170 °C and 600–800 kPa consume sodium hydroxide for white liquor sulfidity control, oxygen-delignification alkali charge, and bleach extraction stages. White liquor prepared from flake caustic is analyzed under TAPPI T 624 cm-21 for active alkali, effective alkali, and sulfidity; spent liquor kappa number is determined using ISO 302:2004. Effective alkali charge on oven-dry wood ranges from 14 wt% to 20 wt% for softwood and 12 wt% to 16 wt% for hardwood; flake caustic is introduced as a 50 wt% solution into the cold-blow dilution section rather than directly into the digester to avoid localized fiber degradation. Continuous Kamyr digesters and batch systems with hydraulic compression zones require white liquor NaOH concentration stabilized to ±2 g/L Na₂O for uniform chip penetration. In oxygen delignification, addition of 18–22 kg NaOH/t pulp at 85–100 °C and 600–800 kPa oxygen partial pressure reduces Kappa number by 40–50%; the subsequent Eop extraction stage receives 8–12 kg NaOH/t pulp. Bleach-stage filtrate piping uses 316L stainless steel because residual peroxide and caustic can trigger chloride stress-corrosion cracking in 304 stainless. Terminal outputs include bleached softwood Kraft pulp with ISO brightness 88–90% and alpha-cellulose 86–90%, and dissolving pulp for viscose with alpha-cellulose ≥ 92%. Direct flake addition to brownstock washers is avoided because undissolved particles create local pH excursions above 13.5 and accelerate cellulose chain scission.
At line speeds of 40–60 m/min, open-width mercerizing ranges processing 100% cotton fabric apply 18–24 wt% NaOH maintained at 15–25 °C; low temperature prevents localized alkaline dissolution and ensures uniform crystal lattice conversion from cellulose I to cellulose II. Caustic soda flakes are dissolved and diluted from a 700–760 g/L NaOH stock solution in 316L stainless steel dissolution stations with chilled water at 5–10 °C to avoid flash boiling. Dimensional stability is audited by AATCC Test Method 89-2017; residual alkali on fabric is determined by titration to a phenolphthalein endpoint, with washwater conductivity continuously monitored to maintain recovery efficiency. The working concentration is controlled by Baumé density: 20–24 °Bé for open-width tension mercerization, 28–30 °Bé for slack knit mercerization, corresponding approximately to 160–240 g/L NaOH. Impregnation takes place in a two-bowl padder with dwell time 30–60 s and stenter width control; hot water stabilization at 80–90 °C fixes the swollen structure before counterflow washing and vapor-compression evaporation recover residual caustic. Terminal products include mercerized cotton yarns for sewing thread, chino twill, poplin, and high-luster cotton sateen. If NaOH concentration exceeds 30 wt% and temperature rises above 30 °C, cotton cellulose begins to dissolve and washwater BOD increases.
In epichlorohydrin trains relying on propylene-derived or glycerol-derived dichloropropanol, dehydrochlorination uses 50 wt% NaOH generated from flakes; the alkali is fed to a continuous stirred-tank reactor maintained at 60–90 °C with a molar ratio NaOH:dichloropropanol between 1.05:1 and 1.15:1. Caustic soda flakes for this route are specified with total chloride below 0.05 wt% to limit co-product sodium chloride and with carbonate below 0.5 wt% to minimize CO₂ release in the reactor overhead. The process operates within REACH 1907/2006/EC registration for sodium hydroxide as an intermediate; effluent sodium chloride brine is monitored for adsorbable organic halides by ISO 9562:2004. Reactors and distillation columns use nickel alloys such as Hastelloy C276 because simultaneous caustic and chlorinated hydrocarbon exposure accelerates chloride stress-corrosion cracking in standard austenitic stainless steels. Epichlorohydrin is stripped and purified in two-stage distillation at 115–120 °C; byproduct sodium chloride is crystallized in forced-circulation evaporators and returned to the downstream chlor-alkali balance. Terminal products include epichlorohydrin with purity ≥ 99.9 wt%, which is further converted to bisphenol-A diglycidyl ether epoxy resin precursors and synthetic glycerol. Local overfeed of caustic into dichloropropanol with inadequate agitation causes premature hydrolysis to glycerol monochlorohydrin and reduces ECH yield below 85%; caustic feed tank level control and static mixer placement are critical.
| Application | Standard / code | Parameter | Typical acceptance range / condition |
|---|---|---|---|
| Alumina refining | GB/T 209-2018 | NaOH assay, Type I solid | ≥ 99.0 wt% |
| Alumina refining | GB/T 209-2018 | Sodium carbonate | ≤ 0.5 wt% |
| Kraft pulping | TAPPI T 624 cm-21 | Effective alkali, white liquor | 12–20 wt% Na₂O on OD wood |
| Kraft pulping | ISO 302:2004 | Kappa number after cooking | Process-specific |
| Textile mercerization | AATCC 89-2017 | Dimensional stability | Process-specific |
| Soap | ISO 684:2008 | Free caustic alkali | ≤ 0.10 wt% |
| Water treatment | AWWA B501-19, NSF/ANSI/CAN 60 | Product purity | Standard-type tables |
| Food processing | 21 CFR 172.104 | Sodium hydroxide food additive | GMP |
In sodium soap production, batch saponification kettles charging bleached palm stearin at 5,000 kg per batch add flake caustic as a 25 wt% solution over 45–60 min under agitator torque control to prevent false graining. Finished soap noodles are tested under ISO 684:2008 for total fatty matter and free caustic alkali; free NaOH is limited to 0.05–0.10 wt% to meet skin safety requirements. The NaOH charge is calculated from the saponification value of the oil charge: for a saponification value of 200 mg KOH/g, a 5,000 kg oil charge requires approximately 713 kg 100% NaOH, equivalent to about 720 kg flake caustic at 99.0 wt% assay. Caustic solution is delivered through a mass flow meter with dosing accuracy ±0.5% at 70–90 °C. After saponification, soap is salted out with dry NaCl at 1–2 wt% of oil charge and settled for 6–8 h; vacuum spray drying in a single-stage tower at air inlet temperature 180–200 °C converts neat soap into noodles. Terminal outputs include sodium soap noodles with TFM 78–82 wt%, laundry bars, and cosmetic sodium soap bases. Excess free NaOH above 0.15 wt% causes darkening and rancidity during storage; carbonate contamination above 0.5 wt% leads to grainy texture in finished bars.
Downstream of demineralizer trains, boiler feedwater pH trim systems operating under phosphate-pH control accept 5–20 wt% sodium hydroxide solution prepared from flakes in fiberglass-reinforced plastic tanks with CO₂ exclusion; the solution is metered by diaphragm pumps into static mixers with 30–60 s contact time. The chemical is supplied under AWWA B501-19 and certified to NSF/ANSI/CAN 60 for drinking water treatment; maximum impurity limits for arsenic, lead, and mercury follow the standard's product-type tables, though site-specific dose rates require jar testing because published universal alkali demand is limited. Caustic dose is determined by online conductivity and pH; distribution system corrosion control setpoints are typically 8.0–8.5, while cation-exchange regeneration uses 4–8 wt% NaOH at 40–60 °C and 6–8 L/min per cubic meter of resin. Treated output includes potable distribution water, demineralized water for pharmaceutical operations, and high-purity boiler feedwater with cation conductivity ≤ 0.1 µS/cm. Direct flake dosing into softened water is avoided because localized high pH induces calcium carbonate precipitation and downstream cartridge filter fouling.
For clingstone peach and tomato lye peeling, 1.5–2.5 wt% NaOH solution at 60–70 °C prepared from flake caustic is applied in stainless steel contact troughs for 30–90 s depending on fruit maturity. The material meets 21 CFR 172.104 for sodium hydroxide as a food additive and is used under GMP; residual caustic after rinsing is neutralized with citric acid to pH 3.5–4.0. In cocoa alkalization, flake caustic is added at 1–3 wt% of nib weight as a 10 wt% solution; clean-in-place operations in dairy evaporators use 1–2 wt% NaOH at 75–82 °C circulated for 15–20 min. Lye peeling is followed by high-pressure water sprays at 2–4 bar and an acid dip; cocoa liquor is alkalized at 85–100 °C and dried to 2–5% moisture. Terminal outputs include peeled canned peaches, tomato dice, alkalized cocoa powder with pH 6.8–7.8, and cleaned dairy evaporator surfaces. Excess caustic in lye peeling causes surface saponification of fruit skin and flavor degradation; final rinse caustic residual is controlled below 0.5 mg/L.
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Caustic soda flakes supplied from China-based manufacturer and factory operations are white deliquescent flakes composed primarily of sodium hydroxide, CAS 1310-73-2, EINECS 215-185-5, with a typical NaOH content of 99.0–99.5 wt% for membrane-cell grade and 96.0–98.0 wt% for diaphragm-cell grade. Pure sodium hydroxide has a solid density of approximately 2.13 g/cm³ at 20 °C; the flake bulk density is lower, typically 900–1,100 kg/m³, because of interparticle voidage. The material melts at 318 °C and boils at approximately 1388 °C at atmospheric pressure. The solid product is obtained by concentrating filtered sodium hydroxide liquor in a multi-effect evaporation train, followed by solidification on a water-cooled drum flaker. Flake thickness is controlled between 1.0 mm and 2.5 mm through drum speed and coolant temperature; this dimension influences both dissolution rate and dust generation during sack tipping. Procurement specifications should reference GB/T 209-2018 for industrial solid sodium hydroxide and analytical methods such as ASTM E291-20 where cross-border conformity is required. Where a model designation is required in purchase documents, the material is identified by grade code and production route rather than a mechanical model number; membrane-cell flake may be ordered as Grade 99% or as IS-I in Chinese domestic classification, while diaphragm-cell material is commonly ordered as Grade 96%. The absence of a unified model code reflects that caustic soda is a standardized chemical product rather than an equipment item.
| Parameter | Specification | Reference method |
|---|---|---|
| Sodium hydroxide as NaOH | ≥99.0 wt% | GB/T 209-2018, ASTM E291-20 |
| Sodium carbonate as Na2CO3 | ≤0.5 wt% | GB/T 209-2018 |
| Sodium chloride as NaCl | ≤0.03 wt% | GB/T 209-2018 |
| Iron as Fe2O3 | ≤0.001 wt% | GB/T 209-2018 |
| Sodium chlorate as NaClO3 | ≤0.002 wt% | GB/T 209-2018, ASTM E291-20 |
| Sodium sulfate as Na2SO4 | ≤0.005 wt% | GB/T 209-2018 |
| Water-insoluble matter | ≤0.01 wt% | GB/T 209-2018 |
Representative values are not a contractual guarantee; certificates of analysis vary by brine feed quality, cell technology, and evaporator fouling. For diaphragm-cell material, sodium chloride content is generally higher and is reported separately in the certificate of analysis.
Membrane electrolysis physically separates the anode and cathode compartments with a selective ion-exchange membrane. This design limits chloride transport into the catholyte, so membrane-cell caustic soda flakes after evaporation and drum solidification typically contain NaCl below 0.03 wt% and NaClO3 below 0.002 wt%. Diaphragm-cell caustic soda is produced from a moving cathode diaphragm that permits partial mixing of brine and catholyte; the resulting solid grade can contain NaCl in the range 0.5–2.0 wt% and NaClO3 in the range 0.05–0.5 wt%. This chloride differential is material in catalytic processing, nickel electroplating, fine chemical synthesis, and chlorate-sensitive polymer treatments. Rayon-grade material adds a separate low-iron requirement because soluble iron catalyzes oxidative degradation in viscose dope and destabilizes spin-bath clarity. For procurement, meeting a 99.0 wt% NaOH minimum does not automatically guarantee rayon-grade performance unless Fe2O3 is held at or below 0.001 wt% and chlorate is separately bounded. In China-based production, membrane-cell flakes are therefore the default choice for low-chloride applications, while diaphragm-cell flakes are used where chloride tolerance is higher and alkali value per tonne is the primary economic driver.
Dissolution of solid sodium hydroxide in water is strongly exothermic, with an integral heat of solution of approximately 44.5 kJ/mol at infinite dilution. In batch preparation tanks, rapid flake addition without sufficient circulation can create a high-density lower layer at the tank bottom, where local temperatures may exceed 80 °C when final concentration is above 25 wt%. The dissolution rate is controlled by particle thickness, bulk liquid turbulence, and the local film temperature; flakes with a mean thickness of 1.0–2.5 mm dissolve slower than micropearls under equal agitation but generate less airborne respirable dust than powdered caustic. For water treatment and neutralization skids, the preferred dilution sequence is metered flake addition into a stirred tank containing water at 20–40 °C, with a circulating loop flow velocity above 1.0 m/s to prevent dead zones. This operation reduces the risk of localized boiling at the flake surface and limits sodium carbonate formation from atmospheric CO2 absorption.
Sodium hydroxide liquid at 50 wt% begins to freeze at approximately 12 °C; therefore, storage tanks, transfer pipes, and unloading stations in northern Chinese industrial parks require steam tracing or electric heat tracing during winter operation. Solid flakes at 99 wt% remove the freezing constraint and reduce the mass of water shipped per tonne of NaOH, which offers a logistics advantage for alumina refineries and pulp mills located inland. The countervailing constraints are hygroscopic caking, dust generation during sack opening, and slower make-down compared with liquid. Bulk handling systems for flakes use low-humidity conveying air, steep hopper liners, and lump-breaking devices at bag dumps because flakes can bridge when surface moisture exceeds 0.5 wt% or when storage temperature rises above 30 °C in humid air. A production-scale drum flaker discharges flakes at 70–90 °C before cooling; packaging warm flake directly into polyethylene-lined sacks can cause condensation inside the liner and later caking. Cooling the flake to below 40 °C prior to bagging is therefore a standard batch-end control point. In liquid systems, pump and valve materials that are satisfactory at 50 wt% and ambient temperature may require upgrading when heat tracing raises the surface skin temperature above 60 °C; this is less of a concern with ambient solid flake storage.
At open-storage transfer points, atmospheric CO2 reacts with the surface film of solid caustic soda to form sodium carbonate. The reaction can increase the measured Na2CO3 content of exposed material from 0.3 wt% to 1.0 wt% or more depending on exposure time and relative humidity. Therefore, storage bays should be closed, air-conditioned, and equipped with dehumidification when relative humidity exceeds 40%. Carbon steel is compatible with dry solid NaOH at ambient temperature; however, concentrated caustic service at elevated temperatures can cause stress corrosion cracking of austenitic stainless steels such as 304L and 316L, especially above 60 °C. Nickel alloys, including UNS N02201 and UNS N06002, are used for high-temperature strong caustic circuits. Contact with aluminum, magnesium, zinc, tin, and their alloys generates hydrogen and must be prevented. Under CLP Regulation 1272/2008, sodium hydroxide flakes are classified as Skin Corr. 1A, hazard statement H314; transport classification is UN 1823, Class 8, Packing Group II. The ACGIH occupational exposure limit for sodium hydroxide is a ceiling of 2 mg/m³. Packaging for industrial distribution includes 25 kg and 50 kg woven polypropylene sacks with polyethylene inner liners and 1,000 kg flexible intermediate bulk containers. Sacks should be resealed immediately after sampling to prevent moisture uptake and caking.
Alumina refineries use solid caustic soda for Bayer-liquor makeup, particularly where weak wash streams are insufficient and lime-based causticization covers only a fraction of the sodium oxide inventory. The digestion step maintains an Na2O-to-Al2O3 molar ratio typically in the range 1.4–1.7 depending on bauxite mineralogy; low-iron flake feed reduces the accidental introduction of iron into precipitation circuits, where iron can co-precipitate and lower smelter-grade alumina brightness. In cotton mercerization, caustic soda flakes are dissolved to a working concentration of 18–25 wt% NaOH, which swells cellulose and converts cellulose I to cellulose II, increasing fiber tenacity and dye uptake. Control of carbonate in mercerization liquor is necessary because sodium carbonate can buffer alkali activity and reduce mercerizing efficiency; membrane-grade flakes with Na2CO3 below 0.5 wt% minimize this variance. In saponification, the stoichiometric caustic requirement is derived from the saponification value of the fat or oil; industrial soap manufacture runs a slight free-alkali excess and relies on the low chloride content of membrane-grade flakes to avoid salt imbalance in the grained-out soap mass. The same low-iron requirement applies to detergent processing where iron can darken the finished powder or catalyze oxidative rancidity in fatty acid chains.
Kraft pulp bleaching and caustic extraction stages use caustic soda to solubilize chlorinated lignin fragments, with partial substitution of caustic by kraft white liquor. The flake product is dissolved in treated condensate to 10–20 wt% before injection into the extraction tower. Sodium chloride content should be limited because chloride contributes to corrosion in the bleach plant and increases the load on the recovery boiler. In a membrane-cell flake specification, the 0.03 wt% NaCl ceiling is below the level at which chloride-induced corrosion acceleration is usually observed in 316L extraction-stage piping under acid bleach filtrate recycle. Published data for this specific configuration is limited and must be evaluated against the actual bleach filtrate chemistry.
One tonne of NaOH flake neutralizes approximately 0.91 tonnes of hydrogen chloride gas on a stoichiometric basis, assuming complete reaction to sodium chloride and water. The design allowance in industrial scrubbers is typically higher because of mass-transfer inefficiency and variable acid gas load. In continuous flue-gas neutralization systems, the solid feed is first dissolved to 10–20 wt% NaOH and metered through a ring-lobe pump into a Venturi scrubber loop. Published data for a specific scrubber configuration may be required to establish the minimum liquid-to-gas ratio and circulation rate. For batch acid neutralization, endpoint control is normally carried out with pH electrodes; the control band is often between 6.5 and 8.5 in treated industrial wastewater.
Caustic soda flakes differ from caustic potash flakes in hydroxide equivalents and solubility behavior. Sodium hydroxide has a molar mass of 40.00 g/mol, while potassium hydroxide has a molar mass of 56.11 g/mol; as a result, 1 kg of NaOH delivers 25.0 mol of hydroxide, whereas 1 kg of KOH delivers 17.8 mol. This difference may reduce the formulation mass required for neutralization and saponification when sodium hydroxide can be used. Compared with soda ash, caustic soda flakes provide a higher endpoint pH and a stronger alkalinity reserve but require more careful materials selection because of their corrosive action on amphoteric metals. The choice among these alkali sources is therefore made from the stoichiometric neutralization requirement, the tolerated residual chloride and iron levels, and the logistics temperature window.
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