Caustic Soda Powder Price 1 KG

Alkalinity in the Bayer circuit is maintained with caustic soda powder as a controlled process variable, not a generic neutralizer, and the digestion profile is governed by bauxite mineralogy. Digestion liquor is held at a total alkali concentration of 120–260 g/L Na₂O equivalent, with gibbsitic ores processed in pipe digesters at 140–170°C and boehmitic or diasporic ores processed through multi-stage autoclaves at 220–280°C. The recirculated pregnant liquor is held at an Al₂O₃/Na₂O ratio of 0.60–0.70; drift above 0.75 in high-temperature circuits is associated with scale deposition on preheater tube surfaces and reduced throughput across the flash train. Caustic powder additions are introduced into the weak liquor stream after the red mud washing circuit before it re-enters the digestion heat recovery train, because adding dry solid directly to high-aluminate pregnant liquor can trigger localized sodium aluminate gelation and create flow restrictions in interstage piping. The powder must meet alumina-grade specifications such as GB/T 209-2018 or IS 252:2013, with sodium carbonate limited to 0.8 wt% maximum, because CO₂ absorbed during storage raises the dead-load Na₂CO₃ concentration and lowers effective hydroxide availability. Powder feed is delivered through loss-in-weight screw feeders with 316L stainless steel contact surfaces and nitrogen-purged storage hoppers to suppress carbon dioxide ingress; a gravimetric feed deviation of more than ±1% causes a swing in the caustic ratio and downstream gibbsite precipitation variability. The filtered aluminate liquor is cooled in vacuum flash tanks to 75–85°C before precipitation, and the cooling rate is made deliberately slow to limit fine gibbsite nucleation. Published data for small 1 kg powder additions in industrial Bayer circuits is limited, and laboratory solubility tests are not transferable to continuous autoclave trains with extended residence time.

Why Is Effective Alkali Held Between 75 g/L and 120 g/L in Kraft White Liquor?

Caustic soda powder enters the kraft cycle as direct alkali make-up and as the causticizing reagent in the recausticizing island. Effective alkali in white liquor is held at 75–120 g/L as Na₂O with 25–35% sulfidity, while the active alkali charge on softwood chips ranges from 16–20 wt% on oven-dry wood and the digester operates at 150–170°C for 60–120 min depending on H-factor and target kappa number. At the low end of the effective alkali range, delignification slows and shive content rises in the blowline stock; at the high end, cellulose viscosity loss accelerates, detected as a fall in intrinsic viscosity measured by TAPPI T 230 from above 1,200 cm³/g to below 900 cm³/g in bleachable grades. Causticizing of the green liquor is carried out with slaked lime in continuous causticizer trains at 90–100°C, where sodium carbonate is converted to sodium hydroxide and calcium carbonate mud is separated on a vacuum precoat filter. The lime-mud filter is run at a vacuum of 40–60 kPa gauge; carryover of fine lime particles above 0.1 wt% into white liquor induces scale in digester heat exchangers and reduces liquor clarity below the recommended 80–90% transmittance. The recausticized white liquor is polished through pressure leaf filters before entering the digester, and residual calcium carbonate above 0.02 wt% shortens the cleaning interval of the digester heating surface. A 1 kg powder charge is used in laboratory autoclave digestions to verify caustic charge ratios before changing wood species or chip thickness, but it is not representative of continuous mill consumption.

Mercerisation Caustic Strength, Fabric Tension, and Temperature Window

At 18–24 wt% NaOH and 15–18°C, a mercerising saturator delivers uniform cellulosic swelling only when the fabric is held under width control and longitudinal tension for 25–60 s. A drop below 16 wt% NaOH produces uneven cellulosic swelling and barre defects after reactive dyeing, while residual alkali carried out of the saturator above 1.5 wt% on weight of fiber increases rinse-water caustic load and requires neutralization with acetic acid to pH 6.5–7.0 before drying. The caustic powder is dissolved, settled for 24 h, and filtered through a 10 µm bag filter before entering the saturator; undissolved carbonate and iron particles otherwise deposit on squeeze rolls and create liquor-streak defects. The temperature window is critical: above 20°C, the improvement in dye uptake from alkali-induced fiber circularity is reduced, and below 12°C the liquor viscosity rises enough to lower uniform pickup across wide-format fabric. Tension control across the chain frame is monitored at 2–5 N/cm for lightweight shirting, while heavy twill requires higher longitudinal tension to prevent fiber shrinkage during the dwell section. Caustic recovery from the first rinse is performed by evaporation to 70–75 wt% NaOH, then re-dilution to process strength; batch-to-batch variance in the evaporated caustic stream is tested by acid titration of a 25 mL sample against 1 N HCl. For laboratory trials, 1 kg caustic powder is sufficient to prepare approximately 4 L of 20 wt% mercerizing liquor, but the prepared solution must be chilled below 18°C before cotton hanks are immersed.

Drinking-water pH correction in the EU is governed by EN 896:2012, and in North America by ANSI/AWWA B501. On a municipal skid, caustic soda powder is dissolved to a 20–25 wt% stock solution in HDPE tanks with low-shear axial-flow mixers; the enthalpy of solution from 1 kg NaOH in 10 L water can raise the liquid temperature by more than 25°C if the powder is added as a single charge. Dosing pumps with PTFE diaphragm heads deliver the solution into raw water after flash mixing, maintaining clarified-water pH at 6.8–7.4 prior to chlorine contact. Alkalinity is monitored by titration to pH 4.5 following ISO 9963-1, and the target residual alkalinity is set at 20–40 mg/L CaCO₃ to buffer the corrosion-index change. Caustic soda is deliberately not injected ahead of alum coagulation in surface plants because local pH excursion above 8.5 at the injection point can hydrolyze aluminum sulfate, forming low-density floc that carries over to sand filters. When carbonate content in the stored caustic stock rises to 0.8 wt%, the pH titration slope changes and the proportional dosing loop must increase stroke frequency by 15–25% to hold the same set point. The same stock solution is used for acid-neutralization of membrane cleaning waste and for pH adjustment in ion-exchange regenerant neutralization pits.

When a Batch Kettle Saponification Run Is Controlled by SAP Value and Caustic Dosing Rate

The saponification value of the fat charge fixes the caustic soda mass before dosing begins, and the calculation uses ISO 3657. A fat blend with a saponification value of 195 mg KOH/g requires approximately 0.139 kg NaOH per kg fat; for a 5,000 kg charge, this is 695 kg NaOH as 100% basis, equating to 702 kg of 99 wt% powder. The powder is pre-dissolved to 38–45 wt% NaOH and dosed into a jacketed crutcher at 80–95°C over 45–60 min with continuous agitation from a scraped-surface paddle mixer operating at 30–40 rpm. If the dosing rate exceeds roughly 10 kg NaOH/min per 5,000 kg batch, the local soap curd formation can gel the crutcher contents and reduce heat transfer at the jacket walls; this is a recognized batch defect in open kettles. At the end of saponification, free caustic is titrated and held below 0.1 wt% as NaOH per ISO 456, while excess unsaponified fat is kept at 0.2–0.5 wt% to prevent high-alkali bars. The salt content of the caustic powder is critical: NaCl above 0.5 wt% shifts the soap neat phase boundary and increases the viscosity of the neat soap in the crutcher, leading to longer drop times. A 1 kg caustic powder charge is used for each small laboratory saponification batch of 7.2 kg oil when the saponification value is 195 mg KOH/g, but the same calculation must be validated by a laboratory glycerine recovery check.

Post-consumer PET hot-wash lines use caustic soda powder in a 2–3 wt% NaOH solution at 80–90°C inside a continuous friction washer, where the alkaline bath hydrolyzes paper label fibers and casein-based adhesives and allows them to detach from perforated PET flake under mechanical shear. A minimum 2 wt% NaOH concentration is required because below that threshold, hot-melt adhesive residues remain cohesive and redeposit on the flake surface in the subsequent rinse. For depolymerization to terephthalic acid, post-consumer PET flake is charged into a jacketed reactor with 4–10 wt% NaOH at 100–130°C for 2–6 h under atmospheric reflux; the sodium terephthalate liquor is then neutralized with sulfuric acid to pH 3–4 to precipitate crude terephthalic acid. The hydrolysis rate is strongly influenced by flake particle size; flakes below 8 mm are preferred for reactor feed because flakes above 12 mm can retain unreacted crystalline PET cores under polarized light after 6 h. Low-chloride caustic is specified for this route because sodium chloride contamination above 0.01 wt% reduces the purity of recovered terephthalic acid and raises the ash content after drying. A 1 kg caustic powder charge prepares 8–10 L of 10 wt% hydrolysis liquor for laboratory screening of flake size and catalyst effects, but published data for continuous pilot-scale hydrolysis of post-consumer flake with small powder additions is limited.

CIP Recirculation Is Governed by Conductivity Rather Than Alkalinity Alone

Cleaning performance in a dairy CIP circuit is controlled by return-line conductivity, typically 20–35 mS/cm, not by a fixed batch time, because proteinaceous soil neutralizes caustic and reduces the free NaOH signal. The caustic soda powder is prepared as a 2–3 wt% solution and recirculated through plate heat exchangers, spray balls, and recovery tanks at 70–80°C for 15–20 min per circuit. If the caustic solution falls below 1.5 wt% NaOH, the saponification of fat residues slows and the cleaning performance for dried whey or cream soils becomes erratic between production cycles. The CIP caustic is returned to a storage tank and reused; total suspended solids are removed by centrifugal clarification or decanting, and the caustic bath is discharged when carbonate content reaches 1.0–1.2 wt% NaOH equivalent. The powder used in food-plant caustic systems must meet food chemical specifications; sodium hydroxide is regulated under 21 CFR 184.1763 when used as a pH control agent for food contact, and the final equipment rinse is verified to neutral pH 6.5–7.5 with conductivity below 100 µS/cm. Batch tanks are not insulated above 85°C because local boiling at the heating surface accelerates stress-corrosion cracking of stainless steel injection lances. Published temperature and concentration data for 1 kg powder batches are useful only for start-up calibration of the chemical dosing pump; plant-scale CIP performance depends on spray-ball coverage, impingement pressure, and soil type.