| HS Code | 520765 |
| Product Name | Caustic Soda Flakes 25KG NaOH 99% Supply |
| Chemical Name | Sodium Hydroxide |
| Chemical Formula | NaOH |
| Cas Number | 1310-73-2 |
| Molecular Weight | 40.00 g/mol |
| Purity | 99% min |
| Appearance | White flakes |
| Physical Form | Solid flakes |
| Packaging | 25 kg bag |
| Solubility In Water | 109 g/100 mL at 20°C |
| Melting Point | 318°C |
| Boiling Point | 1,388°C |
| Ph 1 Solution | Approximately 13-14 |
| Bulk Density | Approximately 0.8-1.2 g/cm³ |
| Hs Code | 2815.11 |
As an accredited Caustic Soda Flakes 25KG NaOH 99% Supply factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 25kg net in double-layer PP woven bags with inner PE liner, sealed and moisture-proof for safe transport. |
| Container Loading (20′ FCL) | Loading 20ft FCL: 25kg bags of NaOH 99% caustic soda flakes palletized, shrink-wrapped, dry, ventilated, securely braced. |
| Shipping | Shipping available worldwide via sea freight, air freight, or courier. Packed in 25kg PP woven bags with PE inner lining, palletized and wrapped. Ensure handling per hazardous goods regulations, keep dry, avoid moisture. Lead time and freight costs vary by destination. |
| Storage | Store in a cool, dry, well-ventilated area away from moisture, heat, and direct sunlight. Keep containers tightly sealed and elevated on pallets to prevent water contact. Separate from acids, metals, and incompatible chemicals. Use corrosion-resistant shelving, ensure spill containment, and handle with appropriate PPE to prevent chemical burns. |
| Shelf Life | Shelf life is approximately 2 years when stored sealed in a cool, dry area, protected from moisture and air. |
Caustic soda flakes supplied at 99% NaOH in 25 kg bags enter distinct industrial routes where compliance anchors, addition rate, downstream processing, and terminal product specifications diverge. Incoming assay is checked against ASTM E291-18; the substance falls under REACH (EC) No 1907/2006 Annex VI with Skin Corr. 1A H314, and U.S. occupational handling follows 29 CFR 1910.1000 Table Z-1 with a 2 mg/m³ 8-hour TWA PEL. The flake form complicates automated charging: above 60% relative humidity, surface hydration creates hopper bridging, so transfer lines require dry-air blankets or dehumidified enclosed screw conveyors. The following technical scenarios isolate application-specific thresholds without repeating cross-sector mixing generalities.
In Bayer plants treating diasporic bauxite, caustic soda flakes are first dissolved with recycled process condensate in steam-jacketed dissolvers to a liquor containing 200–260 g/L Na2O caustic and 20–40 g/L Na2CO3 before blending into the digestion circuit. The make-up NaOH demand in published plant data ranges from 80 to 180 kg NaOH per metric ton of calcined alumina, with reactive silica consuming approximately 1.0–1.3 kg NaOH per kg SiO2 through desilication products such as sodalite and cancrinite. Digestion temperatures are mineralogy-dependent: gibbsitic feeds are held at 140–160 °C and 0.3–0.6 MPa, while diasporic feeds require 240–265 °C and 3.5–5.0 MPa in multi-pass tubular digesters with live steam injection. Residence time ranges from 20 to 45 minutes in single-stream units, after which the slurry is pressure-fed to high-rate thickeners and countercurrent washing trains; residual caustic in red mud cake is controlled to ≤5 g/L Na2O before dry stacking to prevent soluble alkalinity leaching. Pregnant liquor is filtered, cooled through flash evaporators, and seeded with fine alumina trihydrate for precipitation; the resulting crystals are classified, washed, and calcined at 950–1,100 °C to smelter-grade alumina. Equipment compliance includes ASME Section VIII Div. 1 for digesters and flash vessels, PED 2014/68/EU for European installations, and ASTM E291-18 for incoming caustic assay. Terminal product types include smelter-grade alumina for Hall-Héroult reduction, chemical-grade alumina for zeolite and catalyst synthesis, and fine alumina trihydrate used as flame-retardant filler.
| Bauxite mineralogy | Digestion temperature | Digestion pressure | Published make-up caustic window |
|---|---|---|---|
| Gibbsite | 140–160 °C | 0.3–0.6 MPa | 60–120 kg NaOH/t alumina |
| Boehmite | 200–240 °C | 2.5–3.5 MPa | 100–160 kg NaOH/t alumina |
| Diaspore | 240–265 °C | 3.5–5.0 MPa | 130–180 kg NaOH/t alumina |
Medium-consistency oxygen delignification lines meter NaOH 99% flake as a 10–15 wt% stock solution into the pre-retention screw, targeting a final pH of 10.5–11.5 at 80–110 °C and 400–800 kPa oxygen partial pressure. In elemental chlorine-free sequencing, the oxygen-stage caustic charge is typically 1.5–3.0 wt% NaOH on oven-dry kraft pulp, while subsequent peroxide-reinforced extraction stages use 1.0–2.5 wt% NaOH on oven-dry pulp to solubilize oxidized lignin fragments and hexenuronic acid degradation products. The dissolution step is process-critical: flakes are charged to a stainless steel batch dissolver with an external plate heat exchanger, and undissolved fines are removed through a 250–500 µm basket filter before the metering pump, because larger particles create localized pH spikes in medium-consistency mixers. Direct steam sparging is avoided where bicarbonate-hard water is used, since calcium carbonate scale on oxygen reactor internals reduces heat transfer and forces premature boil-out. Kappa number reduction to bleachable grade is verified under ISO 302:2015, with mill laboratories cross-checking Kappa factor using TAPPI T 236 cm-13. Terminal product types include bleached softwood kraft for tissue and packaging grades, bleached hardwood kraft for printing and writing paper, and dissolving pulp for viscose and acetate conversion.
Continuous soap noodle plants running palm oil and coconut oil feedstocks adjust free alkali within a narrow band because residual NaOH above 0.15 wt% initiates oxidative rancidity and colour reversion, while values below 0.03 wt% produce soft, sticky noodles that block vacuum plodders. The theoretical NaOH demand is calculated from the feedstock saponification value: kg NaOH per kg oil = SV (mg KOH/g) × 0.000713. Refined vegetable oils with an SV of 190–205 require 0.135–0.146 kg NaOH per kg oil, and 99% flake is fed as a 30–35 wt% solution through a mass-flow meter into a high-shear recycle loop before entering the saponification reactor at 100–120 °C. Glycerine is split and concentrated to 80–88 wt% in the by-product circuit, while the soap phase is vacuum-flash cooled, dried to 12–14% moisture, and extruded through 3–6 mm die plates to form noodles. Free caustic alkalinity in finished noodles is tested under ISO 684:1974; the specification for toilet soap base commonly reads 0.05–0.10 wt% NaOH, with total fatty matter 80–82 wt% and chloride below 0.3 wt%. Terminal product types include toilet soap noodles, translucent laundry soap chips, hard soap bases for multipurpose cleaning, and glycerine-rich semi-boiled soap for industrial cleaners.
Holding 18–25 wt% NaOH mercerizing liquor at 15–20 °C requires a continuous caustic recovery loop, because bath temperature drift above 25 °C shifts equilibrium swelling from intra-crystalline to intercrystalline regions and lowers fibre tenacity. The wetting agent dosage in the padding trough is held at 2–5 g/L of a sulfated fatty alcohol, and liquor pick-up is controlled to 80–100% on dry fabric weight. Cotton yarn or open-width fabric enters a mercerizing range at 25–60 m/min, passes through a dwell section of 30–90 s, and is then stretched under tension while being washed in a countercurrent recuperator; the first wash outlet is collected at 6–10 wt% NaOH and routed to evaporation for re-concentration. If recovered caustic alkalinity falls below 5 wt%, make-up from 99% flake is dissolved in soft water to 20–25 °Bé before returning to the saturator. Dimensional stability is assessed by AATCC 89-2012, alkali release from finished fabric is verified by aqueous extract pH according to ISO 3071:2020, and ZDHC MRSL 3.1 conformance covers restricted auxiliaries. Terminal product types include mercerized cotton yarn for sewing thread, glossy woven shirting and poplin, stabilized cotton knitwear, low-shrinkage open-end denim, and mercerized towels with increased dye uptake.
Reactive silica dissolution in agitated autoclaves follows a temperature-dependent hydroxide consumption curve where NaOH 99% flake is charged at 1.5–2.0 mol NaOH per mol SiO2 for sodium silicate ratios of 2.2–3.0:1 SiO2:Na2O. The process is run at 160–180 °C and 0.6–1.2 MPa in steam-heated carbon steel autoclaves with turbine agitation, because lower temperatures leave a quartz residue that increases filtration load while higher temperatures accelerate caustic embrittlement in weld zones. Flake is pre-dissolved to 20–30 wt% NaOH and blended with silica sand ground to D50 < 75 µm; the slurry is held for 2–4 h until residual undissolved silica falls below 0.3 wt%, after which the liquor is flashed to atmospheric pressure and filtered through a plate-and-frame press coated with diatomaceous earth. The resulting sodium silicate is adjusted to commercial gravity of 40–42 °Bé at 20 °C. Compliance testing uses ASTM D537-85 analytical methods for total silica and Na2O ratio, and welding procedures for the autoclave follow ASME Section VIII Div. 1 with post-weld heat treatment where service is above 150 °C. Terminal product types include liquid water glass for detergent builders, silicate-based foundry binders, precipitated silica for rubber reinforcement, silica gel desiccants, and zeolite A precursors for phosphate-free detergents.
A 5–10 wt% NaOH solution prepared from flake and demineralized water is injected into two-stage packed towers where cracked LPG and light naphtha are contacted countercurrently to strip hydrogen sulfide and methyl/ethyl mercaptans. Fresh caustic addition is set by feed sulfur load so that the spent prewash purge retains 3–12 wt% Na2S and 1–5 wt% free NaOH; lower free caustic causes mercaptan reversion, while higher values increase emulsification and sodium sulfide carryover into the coalescer. The second-stage caustic is regenerated in a mercaptan oxidation unit, where dissolved mercaptides are catalytically oxidized to disulfide oil at 60–80 °C with compressed air and a phthalocyanine catalyst, then separated by gravity. Spent caustic from the prewash is routed to wet air oxidation at 150–200 °C and 2–10 MPa, reducing sulfide to sulfate and lowering disposal COD. Corrosion control in the scrubber circuit requires stress-relieved carbon steel to limit caustic stress corrosion cracking, and piping is designed under ASME B31.3. Product quality is released by ASTM D2420-13 for H2S in LPG and ASTM D1838-16 copper strip corrosion for LPG and motor fuel components. Terminal product types include sweetened LPG after caustic and amine treating, light straight-run naphtha for gasoline blending, kerosene and jet fuel after Merox treating, and elemental sulfur recovered from downstream Claus units.
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Caustic Soda Flakes 25KG NaOH 99% Supply is a solid alkali packaged in 25 kg PE-film-lined woven polypropylene bags, designated as flake grade CS-25-99, with CAS registry number 1310-73-2. The material is classified as UN 1823, transport hazard Class 8, Packing Group II, and is supplied as white deliquescent flakes with a sodium hydroxide assay of 99.0% w/w minimum. A representative certificate of analysis aligns with GB/T 209-2018 for industrial solid sodium hydroxide: sodium carbonate ≤0.5%, sodium chloride ≤0.03%, and iron as Fe₂O₃ ≤0.001%. The loose bulk density of flake product typically falls within 0.9–1.1 kg/L, and the specific gravity of the solid is 2.13 g/cm³ at 20 °C. When dissolved, the product releases approximately 44.5 kJ/mol NaOH; uncontrolled addition to water can generate localized boiling, so dilution is performed by adding flakes to a stirred tank containing water, never water onto static flakes, with temperature monitored at addition ports. Storage in unsealed bags above 60% relative humidity leads to rapid caking and surface carbonation.
| Parameter | Method or Reference | Specification |
|---|---|---|
| Sodium hydroxide, NaOH | GB/T 209-2018, ASTM E291-18 | 99.0% w/w min |
| Sodium carbonate, Na₂CO₃ | GB/T 209-2018 | 0.5% w/w max |
| Sodium chloride, NaCl | ASTM E291-18 | 0.03% w/w max |
| Iron as Fe₂O₃ | GB/T 209-2018 | 0.001% w/w max |
Flake caustic is formed by chilling molten cell liquor on a flaking drum; the product fractures into irregular platelets with higher external surface area than cast block but lower fines content than mechanically ground powder. Pearl or prill grades are produced via sprayed cooling or granulation and generally exhibit better free-flow behaviour in automatic dosing screws, whereas flake grade is used where lower dusting during manual bag addition is an operational requirement. The 99.0% NaOH threshold is not unique to flake; equivalent assay can be supplied in pearls, but the flake delivery format in 25 kg bags removes the need for heated storage unlike 50% membrane-cell liquor, which has a crystallization onset near 12 °C. The carbonate and chloride ceilings of this product—≤0.5% Na₂CO₃ and ≤0.03% NaCl—are the critical discrimination points against commodity 96% or 98% grades used for lower-purity neutralization. For polymer-grade dissolutions, elevated carbonate can raise turbidity in downstream alkaline baths and increase scaling on heat exchangers.
| Form | NaOH Assay | Typical Package | Handling Profile | Thermal Storage |
|---|---|---|---|---|
| Flake | 99.0% min | 25 kg bag | Moderate dust; plate bridging possible if humid | No freeze point; humidity caking |
| Pearl / prill | 98.5–99.0% | 25 kg bag, bulk sack | Lower dust; free-flowing | No freeze point; humidity caking |
| Liquid 50% | 50.0% w/w | Tanker, IBC | None | Crystallizes near 12 °C |
For acid waste neutralization, 99.0% NaOH flake yields 24.75 equivalents of alkalinity per kilogram of product. In steel pickling wastewater, 1 kg of this flake neutralizes approximately 903 g of hydrogen chloride gas or 1214 g of sulfuric acid when the reaction proceeds to sodium chloride or sodium sulfate at stoichiometric endpoint. For the mineral acid portion alone of 10% w/v HCl spent rinse water, approximately 116 g of flake per litre is required; dissolved ferrous and ferric cations consume additional alkali before hydroxide precipitation. The exotherm can raise batch temperature by more than 30 °C in un-cooled tanks, and pH overshoot above 9.0 complicates metal hydroxide settling. Dosing is therefore conducted with a 20–25% w/w stock solution prepared in high-density polyethylene or lined carbon steel with bottom-out discharge to prevent undissolved flake accumulation. In-line pH probes with proportional-integral control are used where discharge compliance is regulated, and sampling after 15 min of recirculation reduces carbonate-scaled sensor drift.
Bayer process circuits for gibbsitic bauxite typically digest at temperatures between 145 °C and 180 °C, while boehmitic and diasporic bauxites can require 220–265 °C and higher free-caustic concentrations. Solid flake caustic is used as make-up after evaporator losses because its 99.0% NaOH content reduces water introduction relative to 50% liquid. In closed-loop liquor, sodium chloride accumulates and contributes to stress-corrosion cracking of digestor shell welds under high-temperature steam heating. A flake grade with chloride ceiling ≤0.03% reduces the incremental chloride load per tonne of alumina when compared with technical grades carrying 0.1–0.3% chloride. Sodium carbonate content ≤0.5% lowers the carbonate load that must be purged via causticizing or oxalate removal. The addition rate is governed by free-caustic titration rather than fixed bag addition because spent liquor composition varies with bauxite reactive silica and organic carbon. Published corrosion-rate data for every possible digestor tube alloy under variable chloride and temperature combinations are limited; plant-specific corrosion coupon programs supersede general comparisons.
In peroxide brightening of thermomechanical pulp, sodium hydroxide is metered to control the equilibrium between hydrogen peroxide and perhydroxyl anion. A high-consistency bleach tower typically requires pH 10.5–11.5 at 25–30% consistency, with total alkali charge of 0.8–2.0 kg NaOH per oven-dry tonne depending on wood species and transition metal load. Over-alkalization above pH 11.8 accelerates peroxide decomposition and reduces brightness gain, while under-alkalization below pH 9.5 limits stain removal; the narrow operating window requires in-line alkali metering rather than manual bag addition. The low iron specification of ≤0.001% Fe₂O₃ reduces the risk of Fenton-type peroxide decomposition in the bleach liquor. In kraft pulping, the same flake grade is used for white liquor strength correction and bleach extraction-stage alkali, where excess carbonate would impose additional load on the lime slaker.
In textile wet processing, flake caustic is dissolved to 18–24% w/w for mercerizing cotton under controlled tension. The alkali penetrates the secondary cell wall and converts cellulose I to cellulose II after tensioned extraction, increasing dye uptake; the process is temperature-sensitive, with 15–25 °C baths and wetting agents required because high viscosity and slow penetration above 30% w/w create uneven luster. The product’s low chloride content limits salt deposition on pantograph clips, whereas higher sodium chloride in lower-grade caustic can precipitate at pinch points. After impregnation, fabric is washed in a counterflow range, with residual alkali titration kept at 5–8% NaOH on fabric weight before souring to avoid hydrolysis damage during storage.
Fats and oils with saponification values between 190 mg KOH/g and 205 mg KOH/g require 135–146 g NaOH per kilogram of lipid for complete saponification. In batch soap manufacture, flake caustic is pre-dissolved to 25–30% w/w and metered into the oil phase under high-shear mixing; the initial water content and temperature determine gel phase formation, with typical kettle temperatures held at 70–85 °C. Sodium chloride ≤0.03% assists electrolyte balance and soap graining, while carbonate ≤0.5% limits free alkalinity drift from sodium carbonate buffering. The product is not used in direct neutralization of fatty acid distillates unless the resulting soap is intended for technical or liquid formulations; food-contact and cosmetic use requires separate pharmacopoeial verification.
Contact with aluminum, zinc, magnesium, or galvanized surfaces must be prevented because hydrogen evolution from these metals creates explosion hazards in enclosed dosing systems. Continuous dosing lines require fluoropolymer, polypropylene, or lined steel wetted parts because hot caustic can embrittle ABS and PVC. Pressure relief and venting are provided when dissolving in closed tanks.
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