Caustic Soda Prills Price Per Ton

Caustic Soda Prills Price Per Ton is the commercial specification value for solid sodium hydroxide supplied as white spherical micropearls under CAS 1310-73-2, UN 1823, and EC 215-185-5. The product is procured on a dry NaOH basis, with a typical assay of not less than 99.0 wt% determined by ASTM E291-18 acid-base titration. Representative bulk properties include a particle-size band of 0.5 mm to 1.2 mm, pour bulk density between 1.10 g/cm³ and 1.28 g/cm³, and a heat of solution of approximately −44.5 kJ/mol at infinite dilution. The material is packed in 25 kg woven bags, 50 kg drums, or 1000 kg flexible intermediate bulk containers, and the price per ton is quoted as FOB production site, CIF destination port, or delivered to works with freight and packaging shown as separately invoiced line items. A representative grade designation such as CSP-99/0.5-0.1 identifies 99.0 wt% NaOH, 0.5 wt% maximum Na₂CO₃, and 0.1 wt% maximum NaCl.

Low-iron grades with Fe₂O₃ ≤ 0.002 wt% are specified in rayon spin-bath make-up and synthetic detergent granulation where transition-metal contamination triggers oxidative degradation or discoloration. Sodium carbonate at or below 0.5 wt% prevents excess buffering of mercerizing solutions; chloride above 0.1 wt% may promote pitting corrosion on 316L stainless steel transfer piping when residual caustic films are wetted by condensation under insulation. The assay and impurity profile therefore segment the product price independently of freight, because lower carbonate and chloride limits require membrane-cell caustic feedstock and additional evaporation or purification control.

Why Does Sodium Hydroxide Prill Price Per Ton Deviate From 50% Liquor Contract Indices?

Solid prill pricing is rarely a single bulk value. A purchaser buying 99.0 wt% solid is paying for 0.99 tonne of NaOH per tonne of product, whereas 50.0 wt% membrane-grade liquor contains 0.50 tonne of NaOH per tonne of product. The dry-NaOH unit price is obtained by dividing the delivered product price by the NaOH mass fraction. The freight burden for water in 50% liquor is approximately 49.5 kg of water per 100 kg of dry NaOH equivalent, which must be offset by lower raw-material cost or terminal proximity. Conversely, solid prills avoid shipping liquid water but require bagging or polypropylene liners, palletisation, and climate-controlled warehouses to prevent deliquescence. A delivered price per ton therefore contains the mill netback, the solidification premium, the packaging differential, and destination freight. Price quotations that appear inexpensive on a product-weight basis may be uneconomical when evaluated on a dry-NaOH basis with discharge, storage, and melting labour included.

In alumina refineries, caustic soda prills are fed to the Bayer circuit as a high-assay solid for inventory trim when evaporator capacity or white liquor make-up is constrained. Bauxite digestion consumes NaOH through gibbsite dissolution and boehmite attack, and the soda-lime circuit regenerates NaOH by causticizing sodium carbonate with slaked lime. Dosing prills directly into causticized green liquor can create localized exotherms if addition outpaces recirculation mixing. Standard practice is to pre-dissolve prills in a dedicated dissolving tank with forced agitation at 55 °C to 70 °C before transfer to the Bayer stream. Pre-dissolution also reduces transient aluminium hydroxide nucleation on undissolved prill surfaces, which can otherwise contribute to scale in the liquor flash tanks.

Hygroscopicity, Caking, and Pneumatic Conveying Requirements

Because sodium hydroxide prills are deliquescent, storage and transfer define usable shelf life. At relative humidity above approximately 50%, surface moisture absorption increases sharply, and atmospheric CO₂ converts a thin film of NaOH to Na₂CO₃. The resulting surface carbonate forms crusts on hopper walls and reduces flow through rotary feeders. A dry-air purge of 0.5 m³/h to 2.0 m³/h per storage silo is typically used when ambient dew point exceeds 10 °C. Pneumatic transfer is preferred over screw conveying because the prills are hard but brittle; dense-phase systems with conveying velocities of 4 m/s to 8 m/s reduce pellet fracture and dust generation compared with dilute-phase systems. Fracture and attrition below 0.15 mm increase dust loading in charging hoppers, and sodium hydroxide dust is corrosive to carbon steel aspiration ducting, requiring either 316L stainless steel or humidity-controlled baghouse internals.

In textile mercerization, the prills are dissolved to a caustic concentration of 20 °Bé to 30 °Bé, corresponding to approximately 180 g/L to 300 g/L NaOH. Carbonate in the dissolving water and recirculated bath is controlled below 1.0 wt% Na₂CO₃ because carbonate softens the mercerizing action and precipitates as white deposits on tension rollers. Continuous bath reconstitution from solid prills permits tighter caustic mass-balance control than direct purchase of 50% liquor, provided the dissolution system includes a plate heat exchanger capable of removing the −44.5 kJ/mol heat of solution. If the chiller undersizes the exotherm, the bath temperature rises above the 20 °C target and reduces the swelling-induced crystallinity change in cotton.

When Mercury-Cell Derived Caustic Is Compared Against Membrane-Grade Prills

Mercury-cell caustic historically supplied high-purity 50% liquor with low chloride and low chlorate, but residual mercury content may make it unsuitable for applications where wastewater limits or food-processing cleaning systems apply. Membrane-cell caustic prills typically avoid mercury contamination and can be supplied with sodium chloride below 0.1 wt% and sodium chlorate below 10 mg/kg when the product is evaporated from high-purity membrane liquor. Sodium chlorate is not a neutral impurity in acid-gas scrubbing: it can oxidize reduced sulfur compounds and produce unwanted sulfate sludges. Buyers comparing sources should specify the mercury, nickel, and chlorate ceilings in the purchase order, not merely the NaOH assay, because standard 99.0 wt% industrial prills may carry trace levels that are incompatible with rayon, pharmaceutical, or food-contact cleaning use.

Caustic soda prills differ from flakes primarily in geometry, dusting, and flow. Flakes are irregularly shaped, thin, and break into angular fragments during mechanical feeding; prills are dense spheres with a lower surface-area-to-volume ratio for a given screen cut. The spherical geometry produces less interparticle friction and fewer fines during air conveying, but it also reduces the initial dissolution surface area relative to flakes of equivalent mass. In stirred dissolving tanks, this difference is compensated by maintaining vortex depth above half the tank diameter and by avoiding addition directly into the vortex, which can entrain air and form floating rafts of partially hydrated prills. A dissolution tank with a top-entering turbine impeller operating at a tip speed of 3.0 m/s to 4.5 m/s provides sufficient shear for the prill size range while limiting dust carryover.

In kraft pulp mills, prills are used for make-up alkali to the white liquor circuit, where NaOH is required to maintain effective alkali charge when oxidised white liquor or causticized liquor is weak. The prills are dissolved into weak wash or filtered water at 40 °C to 60 °C and then metered into the white liquor tank. Because kraft white liquor contains sodium sulfide, direct addition of solid NaOH raises the sodium-to-sulfur ratio and may temporarily shift the cooking selectivity; therefore the addition rate is matched to the digester charging schedule and verified by a 30-minute residual effective alkali test. Localized addition to the suction side of the white liquor transfer pump is avoided because the resulting exotherm can exceed 90 °C at the pump casing and cause cavitation when the impeller eye reaches the vapor pressure of water. Published data for this specific configuration is limited, so mill-specific pump suction-temperature measurements are required before switching from liquid caustic to prill make-up.